Clemens Allgaier - Academia.edu (original) (raw)
Papers by Clemens Allgaier
Neuroscience, 2001
öAstrocytes express a variety of neurotransmitter receptors which render them capable of respondi... more öAstrocytes express a variety of neurotransmitter receptors which render them capable of responding to extracellular stimuli, like ATP. Release of ATP, e.g. after brain injury, may initiate reactive gliosis via stimulation of purinergic P2X and P2Y receptors. In the present study, the expression and cellular localization of P2X receptor subtypes on astrocytes in the nucleus accumbens of rats under normal physiological conditions and after stab wound were investigated. Reverse transcription-polymerase chain reaction (RT-PCR) with speci¢c P2X 1À7 primers, and double immuno-£uorescence with antibodies to glial ¢brillary acidic protein (GFAP, a speci¢c marker of ¢brous astrocytes) and to di¡erent P2X receptor subtypes (P2X 1À4 , P2X 7) were used. The RT-PCR of tissue extracts of the nucleus accumbens of untreated rats revealed the presence of all seven currently known P2X receptor subtype mRNAs indicating the presence of these receptors in this region. A double immuno£uorescence approach with confocal laser scanning microscopy showed the localization of P2X 2À4 receptor subtypes on GFAP-labelled astrocytes in untreated rats. Labelling for P2X 1 and P2X 7 receptor subtypes was not found. After mechanical damage all P2X receptor subtypes studied (P2X 1À4 , P2X 7) were observed on the GFAP-labelled reactive astrocytes. A characteristic distribution of the P2X receptors on astrocytic processes and cell bodies as well as an up-regulation of the P2X-immuno£uorescence was found. In conclusion, the data show the presence of P2X receptors on rat nucleus accumbens astrocytes and suggest that astrogliosis in vivo is associated with an up-regulation of distinct P2X receptor subtypes.
European Journal of Pharmacology, 1990
Modulation of Synaptic Transmission and Plasticity in Nervous Systems, 1988
1.) Regulatory G-proteins participate in the inhibition of noradrenaline (NA) and acetylcholine (... more 1.) Regulatory G-proteins participate in the inhibition of noradrenaline (NA) and acetylcholine (ACh) release following activation of the respective autoreceptors (α2, M2). Isletactivating protein (IAP) and N-ethylmaleimide (NEM) increased the electrically evoked release of [3 H]NA and [3 H]ACh from hippocampal slices and reduced inhibition of release by the autoreceptor agonists clonidine and carbachol as well as its facilitation by the antagonists yohimbine and atropine. In synaptosomes prepared from rabbit hippocampus two polypeptides with molecular weights corresponding to those of Gi α and Go α a were [32P]ADP-ribosylated by IAP in the presence of [3 2P]NAD+. Pretreatment of synaptosomes with NEM reduced the subsequent [3 2P]ADP-ribosylation by IAP in a concentration-dependent manner.
Neurochemistry International, 2001
Activation of adenosine A 1 receptors by endogenous adenosine plays a neuroprotective role under ... more Activation of adenosine A 1 receptors by endogenous adenosine plays a neuroprotective role under various pathophysiological conditions including hypoxia. Intracellular recordings were made in rat pyramidal cells of the somatosensory cortex. Hypoxia (5 min) induced a membrane depolarization and a decrease of input resistance. The A 1 receptor agonist N 6-cyclopentyladenosine (CPA, 100 mM) reversibly inhibited the hypoxic depolarization. The inhibition was also present after blockade of the A 2A , A 2B and A 3 receptor subtypes by selective antagonists. CPA had no effect on the hypoxic decrease of input resistance. 1,3-Dipropyl-8cyclopentylxanthine (DPCPX), a selective A 1 receptor antagonist, which did not alter hypoxic depolarization when given alone abolished the inhibitory effect of CPA. Neither CPA nor DPCPX influenced membrane potential or apparent input resistance under normoxic conditions. The novel pyrimidoindole (R)-9-(1-methylbenzyl)-2-(4%-pyridyl)-9H-pyrimido[4,5-b]indole-4-amine (APPPI, 1 and 10 mM) reversibly diminished hypoxic depolarization but had no significant effect on input resistance. The effect of APPPI at a concentration of 1 mM, but not at 10 mM, was blocked by DPCPX (0.1 mM). CPA (100 mM) inhibited [ 3 H]-noradrenaline ([ 3 H]-NA) release from rat hippocampal brain slices significantly only in the presence of rauwolscine (0.1 mM), an a 2-adrenoceptor antagonist. APPPI (1 and 10 mM) exhibited an inhibitory effect similar to that observed with CPA. The effects of both CPA and APPPI were antagonized by DPCPX (0.1 mM). The present data suggest that mainly presynaptic mechanisms prevent neurons from hypoxic changes by an inhibition of transmitter release. However, in contrast to CPA, APPPI exhibited additional effects, which require further investigation.
Presynaptic Receptors and Neuronal Transporters, 1991
In rabbit hippocampus [ 3 H]noradrenaline ([ 3 H]NA) release evoked by electrical field stimulati... more In rabbit hippocampus [ 3 H]noradrenaline ([ 3 H]NA) release evoked by electrical field stimulation with 3 6 pulses/3 Hz was strongly facilitated by the α 2 -adrenoceptor antagonist yohimbine, indicating autoinhibition by NA released into the synaptic cleft upon membrane depolarization. Under these conditions, the preferential A 1 -adenosine receptor agonist R-PIA (10 μM) caused a maximum inhibition of approximately 60%. When autoinhibition was almost completely avoided by stimulating the tissue with 4 pulses/100 Hz (POP), the A 1 -receptor-mediated inhibition was significantly increased to 85%. In POP experiments the α 2 -adrenoceptor agonist clonidine, 30 nM, significantly diminished the A 1 -mediated inhibition of release, whereas 6 nM were ineffective. These results show that the interaction between the α 2 and the A 1 mechanism largely depended upon the extent of receptor activation. The highly selective A 1 -adenosine receptor antagonist 1,3-dipropyl-8-cyclopentylxanthine (DPCPX) increased [ 3 H]NA release to a significantly higher extent in the absence than in the presence of autoinhibition. Release evoked by POP or 3 6 pulses/3 Hz in the presence of yohimbine was similarly enhanced by the antagonist by approximately 4 0%, indicating that the local endogenous adenosine concentration surrounding the A 1 receptor was constant before and during electrical stimulation, using the p A 2 value of DPCPX (9.25) in conjunction with the DPCPX-induced increase of NA release in POP experiments, the local concentration of adenosine was calculated to be 1.07 μM.
The Journal of pharmacology and experimental therapeutics, 1991
The question was studied whether there is a direct link between protein kinase C and presynaptic ... more The question was studied whether there is a direct link between protein kinase C and presynaptic alpha-2 adrenoceptors regulating depolarization-induced norepinephrine (NE) release. Effects of the protein kinase C activator 4 beta-phorbol 12,13-dibutyrate (4 beta-PDB) on electrically evoked [3H]NE release were investigated in rabbit and rat hippocampus. Release evoked with 4 pulses/100 Hz (POP stimulation; i.e. under conditions virtually free of autoinhibition), was increased by 4 beta-PDB in a comparable manner in both species. Conversely, the alpha-2 adrenoceptor agonist clonidine diminished POP-induced [3H]NE release in a concentration-dependent manner. The net effects of clonidine were of a similar magnitude up to near maximal concentrations, irrespective of whether or not the 4 beta-PDB was present. Correspondingly, the net effect of 4 beta-PDB remained unchanged under these conditions. An impairment of the net effect of 4 beta-PDB was only seen at higher concentrations of clon...
Allgemeine und spezielle Pharmakologie und Toxikologie, 2013
The pharmacological treatment of neurodegenerative disorders such as Alzheimer's disease, Parkins... more The pharmacological treatment of neurodegenerative disorders such as Alzheimer's disease, Parkinson's disease and amyotrophic lateral sclerosis (ALS) currently represents a major medical challenge. The mechanisms involved in the apoptotic neuronal cell death, associated with such disorders, are still not clear, but recent data suggest that cyclindependent kinases (CDKs) play a prominent role (Liu et al., 2003). Canonical CDKs such as CDK2 and CDK4/CDK6 are enzymes associated with cyclin regulatory subunits that control cell cycle progression. The evidence that neurons in postmortem brain tissue from patients with neurodegenerative diseases express CDKs, supports to the hypothesis that re-entry into the cell cycle could be an apoptotic pathway involved in the neurodegenerative process. Several authors suggest that the transcription factor E2F-1 function as a link between the cell cycle and apoptosis in neurons. Additionally the expression of CDK5 has been demonstrated in postmortem brain tissue from patients with neurodegenerative diseases. CDK5 is an atypical CDK, that does not require association with a cyclin and is not implicated in the cell cycle progression. Instead, it is associated with the neuronal co-activators p35 and p39, and is required for neuronal development, axonal outgrowth, learning and memory. Recent evidence also points to a leading role for CDK5/p25 in apoptosis and neurodegeneration. CDK inhibitors such as flavopiridol and roscovitine are being developed and tested in clinical trials as novel antineoplasic agents. Thus, due to the implication of CDKs in neuronal apoptosis, a new application of these drugs in the treatment of neurodegenerative diseases is suggested.
Neuroscience, 2005
Although numerous studies have demonstrated a neuroprotective and anti-apoptotic role of lithium ... more Although numerous studies have demonstrated a neuroprotective and anti-apoptotic role of lithium in neuronal cell cultures, the precise mechanism by which this occurs, remains to be elucidated. In this study, we evaluated the lithium-mediated neuroprotection against colchicine-induced apoptosis in cultured cerebellar granule neurons. Previously, it has been demonstrated that colchicine mediates apoptosis in cerebellar granule neurons through cytoskeletal alteration and activation of an intrinsic pro-apoptotic pathway. Recently we also demonstrated a potential role of cyclin-dependent kinase 5 (cdk5) in this pathway. Here we report that colchicine induces dephosphorylation in Ser-9 and phosphorylation in Tyr-216, and thus activation, of glycogen synthase kinase-3beta in cerebellar granule neurons, and that this modification is inhibited by the presence of 5 mM lithium. However, the selective glycogen synthase kinase-3beta inhibitors SB-415286 and SB-216763 were unable to prevent colchicine-induced apoptosis in these cells, suggesting that the anti-apoptotic activity of lithium is not mediated by glycogen synthase kinase-3beta under these conditions. On the other hand, 5 mM lithium prevented the colchicine-induced increase in cdk5 expression and breakdown of cdk5/p35 to cdk5/p25. In addition, we show that up-regulation of cdk5/p25 is unrelated to inhibition of the activity of myocyte enhancer factor 2, a pro-survival transcription factor. These data suggest a previously undescribed neuroprotective mechanism of lithium associated with the modulation of cdk5/p35 or cdk5/p25 expression.
Neurochemistry International, 1992
Acetylcholine (ACh) release in rat striatum is regulated by D-2 receptors as well as muscarinic a... more Acetylcholine (ACh) release in rat striatum is regulated by D-2 receptors as well as muscarinic autoreceptors. In the present study, we collected evidence for the coupling of D-2 receptors, mediating the inhibition of ACh release from rat striil tissue, to K'channels as well as to Ca"-mobilizaton. Both transduction mechanisms operate independent from CAMP formation. Concerning homologous receptor regulation, we found that sustained activation of the D-2 receptor did not lead to any desensitization of this receptor. Concerning heterologous receptor regulation, we found that stimulation of the muscarinic autoreceptor considerably attenuated the effect on ACh release upon stimulation of the D-2 receptor and vice versa. This phenomenon could be explained by the finding that also the muscarinic autoreceptor exerts its inhibitory control of ACh release to a large extent through the opening of K'channels. lt was concluded that the interaction between the two receptor types occurs through competition for the same pool of "signal transduction molecules".
Neurochemical Research, 1988
The involvement of G proteins in receptor mediated astroglial cAMP formation was studied. Isoprot... more The involvement of G proteins in receptor mediated astroglial cAMP formation was studied. Isoproterenol or prostaglandin E2 stimulated adenylate cyclase of primary astroglial cells was inhibited by somatostatin. Preincubation, of cells with increasing concentrations of islet activating protein (IAP) diminished somatostatin inhibition of adenylate cyclase. At an IAP concentration of 50 ng/ml somatostatin inhibition was completely abolished. Studies on IAP
Naunyn-Schmiedeberg's Archives of Pharmacology, 1991
SummaryThe aim of the present study was to obtain a more detailed understanding of the interactio... more SummaryThe aim of the present study was to obtain a more detailed understanding of the interaction between presynaptic α2-adrenoceptors and A1 adenosine receptors mediating inhibition of noradrenaline release in the central nervous system. Slices of rabbit hippocampus, prelabelled with [3H]noradrenaline, were superfused in the presence of the re-uptake inhibitor (+)-oxaprotiline and electrically stimulated during superfusion. During stimulation with 36 pulses at 3 Hz the α2-adrenoceptor antagonist yohimbine induced a five-fold increase of noradrenaline release indicating a pronounced autoinhibition of approximately 80%. In these experiments the inhibition of release caused by R-PIA, a preferential A1 agonist, as well as its facilitation caused by DPCPX, a selective A1 antagonist, were smaller in comparison to the effects of these compounds on release virtually free of autoinhibition (i. e. by stimulating the tissue with 4 pulses at 100 Hz (POP-stimulation) or with 36 pulses at 3 Hz in presence of yohimbine). Clonidine, an α2-adrenoceptor agonist, was used to impose a distinct α2-adrenoceptor-mediated inhibition of release elicited by POP-stimulation. Only, however, in the presence of 30 nmol/l clonidine, causing maximum inhibition of approximately 80% of 3H-overflow, but not in the presence of 6 nmol/l clonidine, causing approximately 50% inhibition, a significant diminution of the inhibitory effect of R-PIA was seen. Similarly, the α2-adrenoceptor mechanism was affected only by 10 μmol/l R-PIA causing maximum inhibition of approximately 80%, but remained unchanged in the presence of 30 nmol/l R-PIA diminishing release by 50%. In addition, the α2-adrenoceptor-mediated inhibition remained unaffected in the presence of DPCPX, indicating that the concentration of endogenous adenosine attained was not sufficient to influence the α2-adrenoceptor mechanism. In conclusion, the present results suggest that activation of the presynaptic α2 and A1 receptors inhibits depolarization-induced noradrenaline release in an additive manner. Only extensive (near maximal or maximal) activation of one receptor mechanism impairs the inhibition due to activation of the other.
Naunyn-Schmiedeberg's Archives of Pharmacology, 1989
The effects ofprostaglandin E2 (PGE2) on electrically evoked noradrenaline release in rat brain c... more The effects ofprostaglandin E2 (PGE2) on electrically evoked noradrenaline release in rat brain cortex were studied under conditions under which autoinhibition of release was avoided. When stimulation was carried out with 36 pulses at 3 Hz, 1 ~tmol/1 pGE2, produced about 50% inhibition of release. In the presence of the e2-adrenoceptor antagonist yohimbine (1 gmol/1) the effect of PGE2 was markedly increased. When release was elicited by 3 pulses/ 100 Hz the period of stimulation was too short to permit development of autoinhibition by released noradrenaline. Then the concentration-response-curve for PGE2 was very similar to that obtained under the above conditions (36 pulses/3 Hz, in the presence of yohimbine). These data suggest that both the e2-adrenoceptor and the PGE2-receptor are linked to a common pathway. Since indometacin (10 gmol/1) did not enhance evoked transmitter release, an influence of endogenous PG's on in vitro release of noradrenaline from rat brain cortex slices can be excluded.
Naunyn-Schmiedeberg's Archives of Pharmacology, 1993
concentration-response curve (estimated as slope parameter c) did not correspond to that of a con... more concentration-response curve (estimated as slope parameter c) did not correspond to that of a concentration-binding curve. In conclusion, mathematical modelling by nonlinear regression analysis of the autoinhibitory circuit of noradrenaline release allows the estimation of a parameter c of this feedback regulation which supports or rejects the assumption of direct proportionality between receptor occupation and functional response. When the given requirement of direct proportionality is shown to hold, this analysis allows the feedback circuit to be described quantitatively in terms of the affinity of noradrenaline for, and of the biophase concentration of noradrenaline at, the presynaptic a2-adrenoceptors.
![Research paper thumbnail of A role for protein kinase C in the electrically evoked release of [3H]?-aminobutyric acid in rabbit caudate nucleus](https://attachments.academia-assets.com/113591185/thumbnails/1.jpg)
](Naunyn-Schmiedeberg's Archives of Pharmacology, 1989
A possible participation of protein kinase C (PKC) in depolarization-induced release of 7-aminobu... more A possible participation of protein kinase C (PKC) in depolarization-induced release of 7-aminobutyric acid (GABA) in rabbit caudate nucleus was examined by means ofphorbol esters and staurosporine. Slices of caudate nucleus were loaded with [3H]GABA, then superfused and stimulated electrically (3 ms, 5 Hz, 24 mA, 5 V/cm) for 2 min. Aminooxyacetic acid and the uptake inhibitor nipecotic acid were present throughout. The PKC activator 4 fl-phorbol 12,13-dibutyrate (4 fi-PDB) markedly enhanced the evoked [3H]GABA release. In contrast, its biologically inactive isomer, 4e-PDB, did not facilitate transmitter release. Staurosporine, an inhibitor of PKC, diminished [3H]GABA release and counteracted the effects caused by 4fl-PDB. The above results suggest a participation of PKC in depolarization-induced GABA release in rabbit caudate nucleus. The mechanism underlying the modulation of GABA release by PKC seems to be independent of presynaptic GABA, dopamine and 5-hydroxytryptamine receptors.
Naunyn-Schmiedeberg's Archives of Pharmacology, 1995
The present study investigates the pharmacological profile of P2-purinoceptors modulating noradre... more The present study investigates the pharmacological profile of P2-purinoceptors modulating noradrenaline release from cultured chick sympathetic neurons. ATP (30 gM-3 mM) and 2-methylthio-ATP (3-100gM), but not c03-methylene-ATP (up to 100 gM), caused a significant facilitation of electrically evoked [3Hl-noradrenaline release when added 2 rain before depolarization. The facilitation declined with time of exposure suggesting receptor desensitization. The facilitatory effect was markedly diminished by the P2-purinoceptor antagonists reactive blue 2 (3 gM) and suramin (300 gM), but not changed by mecamylamine (10 gM), a nicotinic receptor antagonist. At 1 mM and higher concentrations, ATP added for 12 min, inhibited noradrenaline release; release was virtually abolished by 6 mM ATP. The inhibitory effect of ATP was slightly diminished by suramin but not affected by reactive blue 2. Electrically evoked [3H]-noradrenaline release remained unaffected in the presence of the adenosine (P1)-receptor agonists R(-)N6-(2-phenylisopropyl)adenosine (R-PIA), 2-[p-(2-carboxyethyl)phenylethylamino]-5'-N-ethylcarboxamidoadenosine (CGS-21680), 5'-Nethylcarboxamidoadenosine (NECA), and N6-2-(4-aminophenyl)ethyladenosine (APNEA), used up to 1 gM. The present results confirm the existence of two P2-purinoceptors affecting noradrenaline release: 1) a facilitatory receptor which is activated by 2-methylthio-ATP as well as ATP, and blocked by suramin as well as reactive blue 2, and 2) an inhibitory receptor which is activated by ATP, only slightly affected by suramin but not at all by reactive blue 2 and does not belong to the established P2-purinoceptor subtypes.
Naunyn-Schmiedeberg's Archives of Pharmacology, 1992
The possible involvement of dopamine D~ receptors in the regulation of acetylcholine release in t... more The possible involvement of dopamine D~ receptors in the regulation of acetylcholine release in the rabbit caudate nucleus was investigated. Caudate slices, preincubated with [3H]choline, were superfused continuously and subjected to electrical field stimulation with only a single pulse. In agreement with the view that the release of acetylcholine evoked by a single electrical pulse is not influenced by endogenous transmitters, atropine and domperidone failed to icnrease the evoked release of [3H]acetylcholine, whereas oxotremorine and quinpirole caused a concentration-dependent inhibition of transmitter release. Neither the dopamine D1 receptor antagonist SCH 23390 nor the D~ agonist SKF 38393 in a concentration range of 0.01-1 gmol/1 changed the evoked [3H]acetylcholine release. The inhibitory effect of the dopamine D 2 receptor agonist quinpirole was virtually abolished in the presence of 0.1 gmol/l domperidone and diminished in the presence of 1 ~mol/1 SCH 23390. It remained unchanged in the presence of 1 gmol/1 SKF 38393. It is concluded that the inhibition of acetylcholine release by dopamine is mediated exclusively via presynaptic dopamine D a receptors and that the antagonistic effect of SCH 23390 on the inhibition of acetylcholine release by quinpirole is due to its interaction with dopamine D 2 rather than D 1 receptors located on cholinergic nerve terminals.
Journal of Physiology-Paris, 1994
The purpose of the present investigation was to characterize regulation of noradrenaline (NA) rel... more The purpose of the present investigation was to characterize regulation of noradrenaline (NA) release from sympathetic neurons. Seven days old dissociated cell cultures of chick embryonic paravertebral ganglia, loaded with [3H]-NA (0.05/JM), were subjected to electrical field stimulation (36 pulses/3 Hz) during superfusion in the presence of (+)-oxaprotiline, an inhibitor of NA reuptake. [3H]-NA release was Ca2+-dependent and sensitive to tetrodotoxin (TTX). ~.-Conotoxin (,,-CTX; 100 nmol/I) abolished [3H]-NA release indicating the dominant role of N-type voltage sensitive Ca2+ channels (VSCCs) in transmitter release. 1,4-dihydro-2,6-dimethyl-5-nitro-4-[2-(trifluoromethyl)phenyl]-3-pyridine carboxylic acid methyl ester ((+)Bay K 8644) and (+)4-(4benzofurazanyl)-1,4-dihydro-2,6-dimethyl-3-nitro-5-pyridinecarboxylic acid isopropyl ester ((+)-202-791), agonists at L-type VSCCs, increased NA release and induced, in addition, an overflow of tritium which was Ca2+-dependent and prevented by the presence of TTX. The L-type VSCC antagonists (-)-202-791 and (+)-4-(4-benzofurazanyl)-l,4-dihydro-2,6-dimethyl-3,5-pyridinedicarboxylic acid methyl, isopropyl ester) ((+)-PN 200-110) diminished [3H]-NA release. These data suggest that L-type VSCCs, probably located on the cell body of the neuron, play an additional role in modulation of release. The full ~t2adrenoceptor agonists 5-bromo-6-(2-imidazolin-2-ylamino)-quinoxaline (UK-14,304) and NA significantly inhibited NA release, whereas clonidine, a partial (z2-agonist, produced only a slight inhibition even at 10/drool/I, indicating that NA release from chick sympathetic neurons is regulated by an ct2adrenoceptor which needs further subtype characterization. In addition to the c~2-adrenoceptors, inhibitory I*,-adrenoceptors, opioid ~< and {' receptors, and P2-purinoceptors as well as facilitatory prostaglandin (PG) E receptors and P2Y-like purinoceptors were detected. The electrically induced increase in free [Ca2+]i measured in the processes of sympathetic neurons showed similar properties: it was completely Ca2+ dependent and TTX-sensitive, only slightly affected by L-type VSCC antagonists, but distinctly counteracted by .~-CTX, In conclusion, these data show that cultured chick sympathetic neurons are an.appropriate model for investigating the mechanisms bringing about receptor-coupled modulation of NA release.
Journal of Neurochemistry, 2004
Excitatory ATP responses in rat cultured thoracolumbar sympathetic neurones are mediated by somat... more Excitatory ATP responses in rat cultured thoracolumbar sympathetic neurones are mediated by somatic P2X 2 receptors. The present study investigated a possible role of axonal P2X 2 as well as P2X 7 receptors on the same preparation. Confocal laser scanning microscopy demonstrated P2X 2 and P2X 7 immunoreactivity along the axons as well as P2X 7 immunoreactivity surrounding the cell nuclei. P2X 7 mRNA expression was detected in individual neurones using a single-cell RT-PCR approach. Adenosine triphosphate (ATP) caused a significant increase in axonal Ca 2+ concentration which was dependent on external Ca 2+ but insensitive to depletion of the cellular Ca 2+ pools by cyclopiazonic acid. Pyridoxal-phosphate-6-azophenyl-2¢,4¢-disulfonate (PPADS; 30 lM) virtually abolished the ATP response, whereas brilliant blue G (0.1 lM), a selective P2X 7 receptor antagonist, had no effect. Dibenzoyl-ATP (BzATP; 100 lM) induced a much smaller increase in axonal [Ca 2+ ] concentration than ATP at equimolar concentrations. The response to BzATP was distinctly reduced by PPADS but not by brilliant blue G. The overall pharmacological profile of the axonal P2X receptors resembled closely that of the somatic P2X 2 receptors. In conclusion, the present data suggest the occurrence of axonal excitatory P2X 2 receptors in thoracolumbar sympathetic neurones. However, the functional significance of axonal and (peri)-nuclear P2X 7 receptors has still to be proven.
European Journal of Pharmacology, 1994
ATP (1 mM) inhibited, whereas 2-methylthio-ATP (30 microM), a P2Y-selective purinoceptor agonist,... more ATP (1 mM) inhibited, whereas 2-methylthio-ATP (30 microM), a P2Y-selective purinoceptor agonist, increased electrically evoked release of [3H]noradrenaline from chick sympathetic neurons. The P2X-selective purinoceptor agonist alpha,beta-methylene-ATP (30 microM) had no effect. The ATP-induced inhibition of release as well as the facilitation caused by 2-methylthio-ATP was not affected by the selective adenosine (P1) receptor antagonist 8-(p-sulfophenyl)-theophylline (8-PST; 100 microM), but completely prevented by the non-selective P2 antagonist suramin (300 microM). The present data reveal a dual regulation of noradrenaline release from sympathetic neurons. Facilitation seems to be mediated by a P2Y purinoceptor, whereas inhibition is caused by a P2 purinoceptor which needs further subtype characterization.
Neuroscience, 2001
öAstrocytes express a variety of neurotransmitter receptors which render them capable of respondi... more öAstrocytes express a variety of neurotransmitter receptors which render them capable of responding to extracellular stimuli, like ATP. Release of ATP, e.g. after brain injury, may initiate reactive gliosis via stimulation of purinergic P2X and P2Y receptors. In the present study, the expression and cellular localization of P2X receptor subtypes on astrocytes in the nucleus accumbens of rats under normal physiological conditions and after stab wound were investigated. Reverse transcription-polymerase chain reaction (RT-PCR) with speci¢c P2X 1À7 primers, and double immuno-£uorescence with antibodies to glial ¢brillary acidic protein (GFAP, a speci¢c marker of ¢brous astrocytes) and to di¡erent P2X receptor subtypes (P2X 1À4 , P2X 7) were used. The RT-PCR of tissue extracts of the nucleus accumbens of untreated rats revealed the presence of all seven currently known P2X receptor subtype mRNAs indicating the presence of these receptors in this region. A double immuno£uorescence approach with confocal laser scanning microscopy showed the localization of P2X 2À4 receptor subtypes on GFAP-labelled astrocytes in untreated rats. Labelling for P2X 1 and P2X 7 receptor subtypes was not found. After mechanical damage all P2X receptor subtypes studied (P2X 1À4 , P2X 7) were observed on the GFAP-labelled reactive astrocytes. A characteristic distribution of the P2X receptors on astrocytic processes and cell bodies as well as an up-regulation of the P2X-immuno£uorescence was found. In conclusion, the data show the presence of P2X receptors on rat nucleus accumbens astrocytes and suggest that astrogliosis in vivo is associated with an up-regulation of distinct P2X receptor subtypes.
European Journal of Pharmacology, 1990
Modulation of Synaptic Transmission and Plasticity in Nervous Systems, 1988
1.) Regulatory G-proteins participate in the inhibition of noradrenaline (NA) and acetylcholine (... more 1.) Regulatory G-proteins participate in the inhibition of noradrenaline (NA) and acetylcholine (ACh) release following activation of the respective autoreceptors (α2, M2). Isletactivating protein (IAP) and N-ethylmaleimide (NEM) increased the electrically evoked release of [3 H]NA and [3 H]ACh from hippocampal slices and reduced inhibition of release by the autoreceptor agonists clonidine and carbachol as well as its facilitation by the antagonists yohimbine and atropine. In synaptosomes prepared from rabbit hippocampus two polypeptides with molecular weights corresponding to those of Gi α and Go α a were [32P]ADP-ribosylated by IAP in the presence of [3 2P]NAD+. Pretreatment of synaptosomes with NEM reduced the subsequent [3 2P]ADP-ribosylation by IAP in a concentration-dependent manner.
Neurochemistry International, 2001
Activation of adenosine A 1 receptors by endogenous adenosine plays a neuroprotective role under ... more Activation of adenosine A 1 receptors by endogenous adenosine plays a neuroprotective role under various pathophysiological conditions including hypoxia. Intracellular recordings were made in rat pyramidal cells of the somatosensory cortex. Hypoxia (5 min) induced a membrane depolarization and a decrease of input resistance. The A 1 receptor agonist N 6-cyclopentyladenosine (CPA, 100 mM) reversibly inhibited the hypoxic depolarization. The inhibition was also present after blockade of the A 2A , A 2B and A 3 receptor subtypes by selective antagonists. CPA had no effect on the hypoxic decrease of input resistance. 1,3-Dipropyl-8cyclopentylxanthine (DPCPX), a selective A 1 receptor antagonist, which did not alter hypoxic depolarization when given alone abolished the inhibitory effect of CPA. Neither CPA nor DPCPX influenced membrane potential or apparent input resistance under normoxic conditions. The novel pyrimidoindole (R)-9-(1-methylbenzyl)-2-(4%-pyridyl)-9H-pyrimido[4,5-b]indole-4-amine (APPPI, 1 and 10 mM) reversibly diminished hypoxic depolarization but had no significant effect on input resistance. The effect of APPPI at a concentration of 1 mM, but not at 10 mM, was blocked by DPCPX (0.1 mM). CPA (100 mM) inhibited [ 3 H]-noradrenaline ([ 3 H]-NA) release from rat hippocampal brain slices significantly only in the presence of rauwolscine (0.1 mM), an a 2-adrenoceptor antagonist. APPPI (1 and 10 mM) exhibited an inhibitory effect similar to that observed with CPA. The effects of both CPA and APPPI were antagonized by DPCPX (0.1 mM). The present data suggest that mainly presynaptic mechanisms prevent neurons from hypoxic changes by an inhibition of transmitter release. However, in contrast to CPA, APPPI exhibited additional effects, which require further investigation.
Presynaptic Receptors and Neuronal Transporters, 1991
In rabbit hippocampus [ 3 H]noradrenaline ([ 3 H]NA) release evoked by electrical field stimulati... more In rabbit hippocampus [ 3 H]noradrenaline ([ 3 H]NA) release evoked by electrical field stimulation with 3 6 pulses/3 Hz was strongly facilitated by the α 2 -adrenoceptor antagonist yohimbine, indicating autoinhibition by NA released into the synaptic cleft upon membrane depolarization. Under these conditions, the preferential A 1 -adenosine receptor agonist R-PIA (10 μM) caused a maximum inhibition of approximately 60%. When autoinhibition was almost completely avoided by stimulating the tissue with 4 pulses/100 Hz (POP), the A 1 -receptor-mediated inhibition was significantly increased to 85%. In POP experiments the α 2 -adrenoceptor agonist clonidine, 30 nM, significantly diminished the A 1 -mediated inhibition of release, whereas 6 nM were ineffective. These results show that the interaction between the α 2 and the A 1 mechanism largely depended upon the extent of receptor activation. The highly selective A 1 -adenosine receptor antagonist 1,3-dipropyl-8-cyclopentylxanthine (DPCPX) increased [ 3 H]NA release to a significantly higher extent in the absence than in the presence of autoinhibition. Release evoked by POP or 3 6 pulses/3 Hz in the presence of yohimbine was similarly enhanced by the antagonist by approximately 4 0%, indicating that the local endogenous adenosine concentration surrounding the A 1 receptor was constant before and during electrical stimulation, using the p A 2 value of DPCPX (9.25) in conjunction with the DPCPX-induced increase of NA release in POP experiments, the local concentration of adenosine was calculated to be 1.07 μM.
The Journal of pharmacology and experimental therapeutics, 1991
The question was studied whether there is a direct link between protein kinase C and presynaptic ... more The question was studied whether there is a direct link between protein kinase C and presynaptic alpha-2 adrenoceptors regulating depolarization-induced norepinephrine (NE) release. Effects of the protein kinase C activator 4 beta-phorbol 12,13-dibutyrate (4 beta-PDB) on electrically evoked [3H]NE release were investigated in rabbit and rat hippocampus. Release evoked with 4 pulses/100 Hz (POP stimulation; i.e. under conditions virtually free of autoinhibition), was increased by 4 beta-PDB in a comparable manner in both species. Conversely, the alpha-2 adrenoceptor agonist clonidine diminished POP-induced [3H]NE release in a concentration-dependent manner. The net effects of clonidine were of a similar magnitude up to near maximal concentrations, irrespective of whether or not the 4 beta-PDB was present. Correspondingly, the net effect of 4 beta-PDB remained unchanged under these conditions. An impairment of the net effect of 4 beta-PDB was only seen at higher concentrations of clon...
Allgemeine und spezielle Pharmakologie und Toxikologie, 2013
The pharmacological treatment of neurodegenerative disorders such as Alzheimer's disease, Parkins... more The pharmacological treatment of neurodegenerative disorders such as Alzheimer's disease, Parkinson's disease and amyotrophic lateral sclerosis (ALS) currently represents a major medical challenge. The mechanisms involved in the apoptotic neuronal cell death, associated with such disorders, are still not clear, but recent data suggest that cyclindependent kinases (CDKs) play a prominent role (Liu et al., 2003). Canonical CDKs such as CDK2 and CDK4/CDK6 are enzymes associated with cyclin regulatory subunits that control cell cycle progression. The evidence that neurons in postmortem brain tissue from patients with neurodegenerative diseases express CDKs, supports to the hypothesis that re-entry into the cell cycle could be an apoptotic pathway involved in the neurodegenerative process. Several authors suggest that the transcription factor E2F-1 function as a link between the cell cycle and apoptosis in neurons. Additionally the expression of CDK5 has been demonstrated in postmortem brain tissue from patients with neurodegenerative diseases. CDK5 is an atypical CDK, that does not require association with a cyclin and is not implicated in the cell cycle progression. Instead, it is associated with the neuronal co-activators p35 and p39, and is required for neuronal development, axonal outgrowth, learning and memory. Recent evidence also points to a leading role for CDK5/p25 in apoptosis and neurodegeneration. CDK inhibitors such as flavopiridol and roscovitine are being developed and tested in clinical trials as novel antineoplasic agents. Thus, due to the implication of CDKs in neuronal apoptosis, a new application of these drugs in the treatment of neurodegenerative diseases is suggested.
Neuroscience, 2005
Although numerous studies have demonstrated a neuroprotective and anti-apoptotic role of lithium ... more Although numerous studies have demonstrated a neuroprotective and anti-apoptotic role of lithium in neuronal cell cultures, the precise mechanism by which this occurs, remains to be elucidated. In this study, we evaluated the lithium-mediated neuroprotection against colchicine-induced apoptosis in cultured cerebellar granule neurons. Previously, it has been demonstrated that colchicine mediates apoptosis in cerebellar granule neurons through cytoskeletal alteration and activation of an intrinsic pro-apoptotic pathway. Recently we also demonstrated a potential role of cyclin-dependent kinase 5 (cdk5) in this pathway. Here we report that colchicine induces dephosphorylation in Ser-9 and phosphorylation in Tyr-216, and thus activation, of glycogen synthase kinase-3beta in cerebellar granule neurons, and that this modification is inhibited by the presence of 5 mM lithium. However, the selective glycogen synthase kinase-3beta inhibitors SB-415286 and SB-216763 were unable to prevent colchicine-induced apoptosis in these cells, suggesting that the anti-apoptotic activity of lithium is not mediated by glycogen synthase kinase-3beta under these conditions. On the other hand, 5 mM lithium prevented the colchicine-induced increase in cdk5 expression and breakdown of cdk5/p35 to cdk5/p25. In addition, we show that up-regulation of cdk5/p25 is unrelated to inhibition of the activity of myocyte enhancer factor 2, a pro-survival transcription factor. These data suggest a previously undescribed neuroprotective mechanism of lithium associated with the modulation of cdk5/p35 or cdk5/p25 expression.
Neurochemistry International, 1992
Acetylcholine (ACh) release in rat striatum is regulated by D-2 receptors as well as muscarinic a... more Acetylcholine (ACh) release in rat striatum is regulated by D-2 receptors as well as muscarinic autoreceptors. In the present study, we collected evidence for the coupling of D-2 receptors, mediating the inhibition of ACh release from rat striil tissue, to K'channels as well as to Ca"-mobilizaton. Both transduction mechanisms operate independent from CAMP formation. Concerning homologous receptor regulation, we found that sustained activation of the D-2 receptor did not lead to any desensitization of this receptor. Concerning heterologous receptor regulation, we found that stimulation of the muscarinic autoreceptor considerably attenuated the effect on ACh release upon stimulation of the D-2 receptor and vice versa. This phenomenon could be explained by the finding that also the muscarinic autoreceptor exerts its inhibitory control of ACh release to a large extent through the opening of K'channels. lt was concluded that the interaction between the two receptor types occurs through competition for the same pool of "signal transduction molecules".
Neurochemical Research, 1988
The involvement of G proteins in receptor mediated astroglial cAMP formation was studied. Isoprot... more The involvement of G proteins in receptor mediated astroglial cAMP formation was studied. Isoproterenol or prostaglandin E2 stimulated adenylate cyclase of primary astroglial cells was inhibited by somatostatin. Preincubation, of cells with increasing concentrations of islet activating protein (IAP) diminished somatostatin inhibition of adenylate cyclase. At an IAP concentration of 50 ng/ml somatostatin inhibition was completely abolished. Studies on IAP
Naunyn-Schmiedeberg's Archives of Pharmacology, 1991
SummaryThe aim of the present study was to obtain a more detailed understanding of the interactio... more SummaryThe aim of the present study was to obtain a more detailed understanding of the interaction between presynaptic α2-adrenoceptors and A1 adenosine receptors mediating inhibition of noradrenaline release in the central nervous system. Slices of rabbit hippocampus, prelabelled with [3H]noradrenaline, were superfused in the presence of the re-uptake inhibitor (+)-oxaprotiline and electrically stimulated during superfusion. During stimulation with 36 pulses at 3 Hz the α2-adrenoceptor antagonist yohimbine induced a five-fold increase of noradrenaline release indicating a pronounced autoinhibition of approximately 80%. In these experiments the inhibition of release caused by R-PIA, a preferential A1 agonist, as well as its facilitation caused by DPCPX, a selective A1 antagonist, were smaller in comparison to the effects of these compounds on release virtually free of autoinhibition (i. e. by stimulating the tissue with 4 pulses at 100 Hz (POP-stimulation) or with 36 pulses at 3 Hz in presence of yohimbine). Clonidine, an α2-adrenoceptor agonist, was used to impose a distinct α2-adrenoceptor-mediated inhibition of release elicited by POP-stimulation. Only, however, in the presence of 30 nmol/l clonidine, causing maximum inhibition of approximately 80% of 3H-overflow, but not in the presence of 6 nmol/l clonidine, causing approximately 50% inhibition, a significant diminution of the inhibitory effect of R-PIA was seen. Similarly, the α2-adrenoceptor mechanism was affected only by 10 μmol/l R-PIA causing maximum inhibition of approximately 80%, but remained unchanged in the presence of 30 nmol/l R-PIA diminishing release by 50%. In addition, the α2-adrenoceptor-mediated inhibition remained unaffected in the presence of DPCPX, indicating that the concentration of endogenous adenosine attained was not sufficient to influence the α2-adrenoceptor mechanism. In conclusion, the present results suggest that activation of the presynaptic α2 and A1 receptors inhibits depolarization-induced noradrenaline release in an additive manner. Only extensive (near maximal or maximal) activation of one receptor mechanism impairs the inhibition due to activation of the other.
Naunyn-Schmiedeberg's Archives of Pharmacology, 1989
The effects ofprostaglandin E2 (PGE2) on electrically evoked noradrenaline release in rat brain c... more The effects ofprostaglandin E2 (PGE2) on electrically evoked noradrenaline release in rat brain cortex were studied under conditions under which autoinhibition of release was avoided. When stimulation was carried out with 36 pulses at 3 Hz, 1 ~tmol/1 pGE2, produced about 50% inhibition of release. In the presence of the e2-adrenoceptor antagonist yohimbine (1 gmol/1) the effect of PGE2 was markedly increased. When release was elicited by 3 pulses/ 100 Hz the period of stimulation was too short to permit development of autoinhibition by released noradrenaline. Then the concentration-response-curve for PGE2 was very similar to that obtained under the above conditions (36 pulses/3 Hz, in the presence of yohimbine). These data suggest that both the e2-adrenoceptor and the PGE2-receptor are linked to a common pathway. Since indometacin (10 gmol/1) did not enhance evoked transmitter release, an influence of endogenous PG's on in vitro release of noradrenaline from rat brain cortex slices can be excluded.
Naunyn-Schmiedeberg's Archives of Pharmacology, 1993
concentration-response curve (estimated as slope parameter c) did not correspond to that of a con... more concentration-response curve (estimated as slope parameter c) did not correspond to that of a concentration-binding curve. In conclusion, mathematical modelling by nonlinear regression analysis of the autoinhibitory circuit of noradrenaline release allows the estimation of a parameter c of this feedback regulation which supports or rejects the assumption of direct proportionality between receptor occupation and functional response. When the given requirement of direct proportionality is shown to hold, this analysis allows the feedback circuit to be described quantitatively in terms of the affinity of noradrenaline for, and of the biophase concentration of noradrenaline at, the presynaptic a2-adrenoceptors.
Naunyn-Schmiedeberg's Archives of Pharmacology, 1989
A possible participation of protein kinase C (PKC) in depolarization-induced release of 7-aminobu... more A possible participation of protein kinase C (PKC) in depolarization-induced release of 7-aminobutyric acid (GABA) in rabbit caudate nucleus was examined by means ofphorbol esters and staurosporine. Slices of caudate nucleus were loaded with [3H]GABA, then superfused and stimulated electrically (3 ms, 5 Hz, 24 mA, 5 V/cm) for 2 min. Aminooxyacetic acid and the uptake inhibitor nipecotic acid were present throughout. The PKC activator 4 fl-phorbol 12,13-dibutyrate (4 fi-PDB) markedly enhanced the evoked [3H]GABA release. In contrast, its biologically inactive isomer, 4e-PDB, did not facilitate transmitter release. Staurosporine, an inhibitor of PKC, diminished [3H]GABA release and counteracted the effects caused by 4fl-PDB. The above results suggest a participation of PKC in depolarization-induced GABA release in rabbit caudate nucleus. The mechanism underlying the modulation of GABA release by PKC seems to be independent of presynaptic GABA, dopamine and 5-hydroxytryptamine receptors.
Naunyn-Schmiedeberg's Archives of Pharmacology, 1995
The present study investigates the pharmacological profile of P2-purinoceptors modulating noradre... more The present study investigates the pharmacological profile of P2-purinoceptors modulating noradrenaline release from cultured chick sympathetic neurons. ATP (30 gM-3 mM) and 2-methylthio-ATP (3-100gM), but not c03-methylene-ATP (up to 100 gM), caused a significant facilitation of electrically evoked [3Hl-noradrenaline release when added 2 rain before depolarization. The facilitation declined with time of exposure suggesting receptor desensitization. The facilitatory effect was markedly diminished by the P2-purinoceptor antagonists reactive blue 2 (3 gM) and suramin (300 gM), but not changed by mecamylamine (10 gM), a nicotinic receptor antagonist. At 1 mM and higher concentrations, ATP added for 12 min, inhibited noradrenaline release; release was virtually abolished by 6 mM ATP. The inhibitory effect of ATP was slightly diminished by suramin but not affected by reactive blue 2. Electrically evoked [3H]-noradrenaline release remained unaffected in the presence of the adenosine (P1)-receptor agonists R(-)N6-(2-phenylisopropyl)adenosine (R-PIA), 2-[p-(2-carboxyethyl)phenylethylamino]-5'-N-ethylcarboxamidoadenosine (CGS-21680), 5'-Nethylcarboxamidoadenosine (NECA), and N6-2-(4-aminophenyl)ethyladenosine (APNEA), used up to 1 gM. The present results confirm the existence of two P2-purinoceptors affecting noradrenaline release: 1) a facilitatory receptor which is activated by 2-methylthio-ATP as well as ATP, and blocked by suramin as well as reactive blue 2, and 2) an inhibitory receptor which is activated by ATP, only slightly affected by suramin but not at all by reactive blue 2 and does not belong to the established P2-purinoceptor subtypes.
Naunyn-Schmiedeberg's Archives of Pharmacology, 1992
The possible involvement of dopamine D~ receptors in the regulation of acetylcholine release in t... more The possible involvement of dopamine D~ receptors in the regulation of acetylcholine release in the rabbit caudate nucleus was investigated. Caudate slices, preincubated with [3H]choline, were superfused continuously and subjected to electrical field stimulation with only a single pulse. In agreement with the view that the release of acetylcholine evoked by a single electrical pulse is not influenced by endogenous transmitters, atropine and domperidone failed to icnrease the evoked release of [3H]acetylcholine, whereas oxotremorine and quinpirole caused a concentration-dependent inhibition of transmitter release. Neither the dopamine D1 receptor antagonist SCH 23390 nor the D~ agonist SKF 38393 in a concentration range of 0.01-1 gmol/1 changed the evoked [3H]acetylcholine release. The inhibitory effect of the dopamine D 2 receptor agonist quinpirole was virtually abolished in the presence of 0.1 gmol/l domperidone and diminished in the presence of 1 ~mol/1 SCH 23390. It remained unchanged in the presence of 1 gmol/1 SKF 38393. It is concluded that the inhibition of acetylcholine release by dopamine is mediated exclusively via presynaptic dopamine D a receptors and that the antagonistic effect of SCH 23390 on the inhibition of acetylcholine release by quinpirole is due to its interaction with dopamine D 2 rather than D 1 receptors located on cholinergic nerve terminals.
Journal of Physiology-Paris, 1994
The purpose of the present investigation was to characterize regulation of noradrenaline (NA) rel... more The purpose of the present investigation was to characterize regulation of noradrenaline (NA) release from sympathetic neurons. Seven days old dissociated cell cultures of chick embryonic paravertebral ganglia, loaded with [3H]-NA (0.05/JM), were subjected to electrical field stimulation (36 pulses/3 Hz) during superfusion in the presence of (+)-oxaprotiline, an inhibitor of NA reuptake. [3H]-NA release was Ca2+-dependent and sensitive to tetrodotoxin (TTX). ~.-Conotoxin (,,-CTX; 100 nmol/I) abolished [3H]-NA release indicating the dominant role of N-type voltage sensitive Ca2+ channels (VSCCs) in transmitter release. 1,4-dihydro-2,6-dimethyl-5-nitro-4-[2-(trifluoromethyl)phenyl]-3-pyridine carboxylic acid methyl ester ((+)Bay K 8644) and (+)4-(4benzofurazanyl)-1,4-dihydro-2,6-dimethyl-3-nitro-5-pyridinecarboxylic acid isopropyl ester ((+)-202-791), agonists at L-type VSCCs, increased NA release and induced, in addition, an overflow of tritium which was Ca2+-dependent and prevented by the presence of TTX. The L-type VSCC antagonists (-)-202-791 and (+)-4-(4-benzofurazanyl)-l,4-dihydro-2,6-dimethyl-3,5-pyridinedicarboxylic acid methyl, isopropyl ester) ((+)-PN 200-110) diminished [3H]-NA release. These data suggest that L-type VSCCs, probably located on the cell body of the neuron, play an additional role in modulation of release. The full ~t2adrenoceptor agonists 5-bromo-6-(2-imidazolin-2-ylamino)-quinoxaline (UK-14,304) and NA significantly inhibited NA release, whereas clonidine, a partial (z2-agonist, produced only a slight inhibition even at 10/drool/I, indicating that NA release from chick sympathetic neurons is regulated by an ct2adrenoceptor which needs further subtype characterization. In addition to the c~2-adrenoceptors, inhibitory I*,-adrenoceptors, opioid ~< and {' receptors, and P2-purinoceptors as well as facilitatory prostaglandin (PG) E receptors and P2Y-like purinoceptors were detected. The electrically induced increase in free [Ca2+]i measured in the processes of sympathetic neurons showed similar properties: it was completely Ca2+ dependent and TTX-sensitive, only slightly affected by L-type VSCC antagonists, but distinctly counteracted by .~-CTX, In conclusion, these data show that cultured chick sympathetic neurons are an.appropriate model for investigating the mechanisms bringing about receptor-coupled modulation of NA release.
Journal of Neurochemistry, 2004
Excitatory ATP responses in rat cultured thoracolumbar sympathetic neurones are mediated by somat... more Excitatory ATP responses in rat cultured thoracolumbar sympathetic neurones are mediated by somatic P2X 2 receptors. The present study investigated a possible role of axonal P2X 2 as well as P2X 7 receptors on the same preparation. Confocal laser scanning microscopy demonstrated P2X 2 and P2X 7 immunoreactivity along the axons as well as P2X 7 immunoreactivity surrounding the cell nuclei. P2X 7 mRNA expression was detected in individual neurones using a single-cell RT-PCR approach. Adenosine triphosphate (ATP) caused a significant increase in axonal Ca 2+ concentration which was dependent on external Ca 2+ but insensitive to depletion of the cellular Ca 2+ pools by cyclopiazonic acid. Pyridoxal-phosphate-6-azophenyl-2¢,4¢-disulfonate (PPADS; 30 lM) virtually abolished the ATP response, whereas brilliant blue G (0.1 lM), a selective P2X 7 receptor antagonist, had no effect. Dibenzoyl-ATP (BzATP; 100 lM) induced a much smaller increase in axonal [Ca 2+ ] concentration than ATP at equimolar concentrations. The response to BzATP was distinctly reduced by PPADS but not by brilliant blue G. The overall pharmacological profile of the axonal P2X receptors resembled closely that of the somatic P2X 2 receptors. In conclusion, the present data suggest the occurrence of axonal excitatory P2X 2 receptors in thoracolumbar sympathetic neurones. However, the functional significance of axonal and (peri)-nuclear P2X 7 receptors has still to be proven.
European Journal of Pharmacology, 1994
ATP (1 mM) inhibited, whereas 2-methylthio-ATP (30 microM), a P2Y-selective purinoceptor agonist,... more ATP (1 mM) inhibited, whereas 2-methylthio-ATP (30 microM), a P2Y-selective purinoceptor agonist, increased electrically evoked release of [3H]noradrenaline from chick sympathetic neurons. The P2X-selective purinoceptor agonist alpha,beta-methylene-ATP (30 microM) had no effect. The ATP-induced inhibition of release as well as the facilitation caused by 2-methylthio-ATP was not affected by the selective adenosine (P1) receptor antagonist 8-(p-sulfophenyl)-theophylline (8-PST; 100 microM), but completely prevented by the non-selective P2 antagonist suramin (300 microM). The present data reveal a dual regulation of noradrenaline release from sympathetic neurons. Facilitation seems to be mediated by a P2Y purinoceptor, whereas inhibition is caused by a P2 purinoceptor which needs further subtype characterization.