Contribution of ionotropic glutamate receptors and voltage-dependent calcium channels to the potentiation phenomenon induced by transient pentylenetetrazol in the CA1 region of rat hippocampal slices (original) (raw)
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Experimental Brain Research, 2020
Herein field recordings were utilized to test the effects of a transient period of pentylenetetrazol (PTZ) treatment on thetaburst long-term potentiation (LTP) at the Schaffer collateral-CA1 synapses as well as RT-PCR was used to investigate the effects of the combination of the pharmacological treatment and the theta-burst LTP induction on the expression of NMDA subunit mRNA in hippocampal slices. The slope of field excitatory postsynaptic potential (fEPSP) was unaffected while the population spike amplitude and area were increased by a transient period of PTZ treatment (3 mM, 10 min). After a theta burst, a brief PTZ exposure can lead to an enhancement of LTP as documented by fEPSP recording. The effect can be blocked by a selective NMDA receptor antagonist DL-AP5. An increase in the expression of GluN2B and GluN2A subunit mRNAs was also shown due to the combined treatment. The results indicate that the combined treatment increases the degree of NMDA-dependent LTP and are in accord with literature data on the subunit alterations of the hippocampal NMDA receptors. Moreover, our experimental paradigm can be used as a new approach to study the relevance of LTP-like phenomena and epileptic mechanisms.
PLoS ONE, 2013
Epileptic activity is generally induced in experimental models by local application of epileptogenic drugs, including pentylenetetrazol (PTZ), widely used on both vertebrate and invertebrate neurons. Despite the high prevalence of this neurological disorder and the extensive research on it, the cellular and molecular mechanisms underlying epileptogenesis still remain unclear. In this work, we examined PTZ-induced neuronal changes in Helix monosynaptic circuits formed in vitro, as a simpler experimental model to investigate the effects of epileptiform activity on both basal release and post-tetanic potentiation (PTP), a form of short-term plasticity. We observed a significant enhancement of basal synaptic strength, with kinetics resembling those of previously described use-dependent forms of plasticity, determined by changes in estimated quantal parameters, such as the readily releasable pool and the release probability. Moreover, these neurons exhibited a strong reduction in PTP expression and in its decay time constant, suggesting an impairment in the dynamic reorganization of synaptic vesicle pools following prolonged stimulation of synaptic transmission. In order to explain this imbalance, we determined whether epileptic activity is related to the phosphorylation level of synapsin, which is known to modulate synaptic plasticity. Using western blot and immunocytochemical staining we found a PTZ-dependent increase in synapsin phosphorylation at both PKA/CaMKI/IV and MAPK/Erk sites, both of which are important for modulating synaptic plasticity. Taken together, our findings suggest that prolonged epileptiform activity leads to an increase in the synapsin phosphorylation status, thereby contributing to an alteration of synaptic strength in both basal condition and tetanusinduced potentiation.
Journal of Neuroscience Research, 2014
Alterations in inhibitory and excitatory neurotransmission play a central role in the etiology of epilepsy, with overstimulation of glutamate receptors influencing epileptic activity and corresponding neuronal damage. N-methyl-D-aspartate (NMDA) receptors, which belong to a class of ionotropic glutamate receptors, play a primary role in this process. This study compared the anticonvulsant properties of two NMDA receptor channel blockers, memantine and 1-phenylcyclohexylamine (IEM-1921), in a pentylenetetrazole (PTZ) model of seizures in rats and investigated their potencies in preventing PTZ-induced morphological changes in the brain. The anticonvulsant properties of IEM-1921 (5 mg/kg) were more pronounced than those of memantine at the same dose. IEM-1921 and memantine decreased the duration of convulsions by 82% and 37%, respectively. Both compounds were relatively effective at preventing the tonic component of seizures but not myoclonic seizures. Memantine significantly reduced the lethality caused by PTZ-induced seizures from 42% to 11%, and all animals pretreated with IEM-1921 survived. Morphological examination of the rat brain 24 hr after administration of PTZ revealed alterations in the morphology of 20-25% of neurons in the neocortex and the hippocampus, potentially induced by excessive glutamate. The expression of the excitatory amino acid transporter 1 protein was increased in the hippocampus of the PTZ-treated rats. However, dark neurons did not express caspase-3 and were immunopositive for the neuronal nuclear antigen protein, indicating that these neurons were alive. Both NMDA antagonists prevented neuronal abnormalities in the brain. These results suggest that NMDA receptor channel blockers might be considered possible neuroprotective agents for prolonged seizures or status epilepticus leading to neuronal damage.
2010
Segal, Michael M. and Andrea F. Douglas. Late sodium channel rons has become increasingly apparent (Taylor 1993). Three openings underlying epileptiform activity are preferentially diminlines of evidence, taken together, suggest that persistent soished by the anticonvulsant phenytoin. J. Neurophysiol. 77: 3021dium currents may be important in the treatment of convul-3034, 1997. Late openings of sodium channels were observed in sions and are a possible site of abnormalities producing conoutside-out patch recordings from hippocampal neurons in culture. vulsive seizures. In previous studies of such neurons, a persistent sodium current 1) The sodium current is a well-characterized pharmacologiappeared to underlie the ictal epileptiform activity. All the channel cal target for controlling seizures. Most clinically useful anticurrents were blocked by tetrodotoxin. In addition to the transient convulsants with known mechanisms of action reduce sodium openings of sodium channels making up the peak sodium current, currents (Rogawski and Porter 1990). Among the best studied there were two types of late channel openings: brief late and burst openings. These late channel openings occurred throughout voltage of these drugs are phenytoin (Kuo and Bean 1994; Matsuki at pulses that lasted 750 ms, producing a persistent sodium current. al. 1984; Willow et al. 1985), carbamazepine (Willow et al. At 030 mV, this current was 0.4% of the peak current. The late 1985), and lamotrigine (Lang et al. 1993). channel openings occurred throughout the physiological range of 2) The persistent sodium current may be a particularly trans-membrane voltages. The anticonvulsant phenytoin reduced important component of the sodium current involved in seithe late channel openings more than the peak currents. The effect zures because the hallmark of the ''ictal'' epileptiform activon the persistent current was greatest at more depolarized voltages, ity is a persistent depolarization of the neuronal voltage lastwhereas the effect on peak currents was not substantially voltage ing seconds to minutes (Kandel and Spencer 1961; Matsudependent. In the presence of 60 mM phenytoin, peak sodium curmoto and Ajmone Marsan 1964). Evidence from a simplified rents at 030 mV were 40-41% of control, as calculated using culture system displaying epileptiform activity suggests that different methods of analysis. Late currents were 22-24% of control. Phenytoin primarily decreased the number of channel open-a persistent sodium current may be an important component ings, with less effect on the duration of channel openings and no of this sustained depolarization (Segal 1994). In that simplieffect on open channel current. This set of findings is consistent fied system, neurons with the ictal sustained depolarizations with models in which phenytoin binds to the inactivated state of also have endogenous bursts of action potentials and depolarthe channel. The preferential effect of phenytoin on the persistent ization even when synaptic transmission is blocked, which sodium current suggests that an important pharmacological mechais evidence for a nontransmitter persistent inward current. nism for a sodium channel anticonvulsant is to reduce late openings
Effects of Potassium Channel Openers on Pentylenetetrazole-Induced Seizures in Mice
Pharmacology & Toxicology, 1990
Potassium conductances are involved in the control of neuronal excitability and cell firing. Inhibitors of these conductances, such as the aminopyridines, guanidine and the neurotoxin MCD (mast cell degranulating peptide), increase neuronal excitability (Matthews & Wickelgren 1977) and induce convulsions in vitro (Baranyi & Fehkr 1979; Galvan et ul. 1982) and in vivo (Gandolfo et ul. I989 a & b). The opposite effects would be expected by drugs which enhance potassium currents. In fact, the potassium channel opener cromakalim has been shown to inhibit neuronal excitability and convulsive discharges induced by several stimuli in vitro (Alzheimer & ten Bruggencate 1988); however, the possible anticonvulsant effects of potassium channel openers in vivo are not well characterized. In this study we evaluated the effects of two potassium channel openers, cromakalim and pinacidil, on pentylenetetrazole-induced seizures in vivo. In addition, we attemped to reverse the effects of these drugs with the potassium channel blocker Caminopyridine, in order to clarify the possible involvement of potassium channels in the responses observed.
Toxicology and Applied Pharmacology, 2001
The actions of trimethylolpropane phosphate (TMPP), an ethyl bicyclophosphate convulsant produced during the partial pyrolysis of some phosphate ester-based lubricants, were tested on CA1 neurons of rat hippocampal slices using intracellular recording techniques. Bath application of TMPP (0.1-100 M) induced spontaneous paroxysmal depolarizing shifts and the associated spontaneous epileptiform bursts followed by after-hyperpolarizations in 63% of neurons tested. The TMPP-induced epileptiform bursts were blocked by muscimol, a ␥-aminobutyric acid A (GABA A ) receptor agonist, diazepam (DZP), a GABA A -benzodiazepine ionophore complex agonist, or baclofen, a GABA B receptor agonist. While bath application of muscimol, DZP, or baclofen suppressed spontaneous activity in CA1 neurons not previously exposed to TMPP, subsequent application of TMPP (10 M) reversed the actions of muscimol and diazepam, but not baclofen. TMPP (0.1-100 M) also induced membrane hyperpolarization associated with an increase in peak input resistance and inward rectification in 33% of neurons tested or membrane depolarization associated with an increase in input resistance in 17% of neurons tested. In summary, TMPP induced epileptiform activities in hippocampal CA1 neurons. The epileptogenic effects of TMPP are consistent with its interaction with GABA A -benzodiazepine receptors.
NeuroMolecular Medicine, 2013
Glutamate over-activation and the consequent neuronal excitotoxicity have been identified as crucial players in brain dysfunctions such as status epilepticus (SE). Owing to the central function of 2-amino-3-(hydroxyl-5-methylisoxazole-4-yl) propionic acid receptors (AMPARs) in fast excitatory neurotransmission, these receptors have been recognized to play a prominent role in the development and generation of epileptic seizure. This study was undertaken to investigate both the early changes that affect glutamatergic neurons in the rat cerebral cortex and hippocampus and the level and channel properties of AMPARs in response to SE. The results obtained after 3 h of pilocarpine (PILO)-induced SE showed a disorganization of glutamatergic neurons in the CA3 and a thinner neuronal cell layer in the dentate gyrus (DG) region as compared with controls. A significant increase in AMPAR GluA2 protein expression, a decrease in GluA1, GluA3, and GluA4 expression, and a reduction in the phosphorylation of Ser831-GluA1 and Ser880-GluA2 were also observed. In addition, we report a downregulation of R/G editing levels and of Flip splicing isoforms, with a prominent effect on the hippocampus of PILO-treated rats. Our results suggest the presence of an attenuation of AMPARs' post-synaptic excitatory response to glutamate after PILO treatment, thus conferring neuronal protection from the excitotoxic conditions observed in the SE. This study suggests a role for AMPARs in alterations of the glutamatergic pathway during the onset and early progression of epilepsy, thus indicating additional targets for potential therapeutic interventions.
Brain Research Bulletin, 2013
The Na + /Ca 2+ exchanger (NCX) is thought to play an important role in the pathogenesis of pentylenetetrazole (PTZ)-induced tonic flexion in mice. Here, I investigated the expression of PTZ-induced generalized clonic and tonic-clonic seizures in rats, using two potent NCX reverse mode inhibitors, KB-R7943 and SN-6 for NCX subtypes 3 (NCX3) and 1 (NCX1), respectively. Pretreatment with KB-R7943 (3, 10, and 30 mg/kg; p.o.) significantly reduced the expression of PTZ-induced generalized seizures with clonic and tonic-clonic components in 12-62% and 25-62% of the treated animals, respectively. In the remaining animals that exhibited seizures, KB-R7943 (3 mg/kg; p.o.) pretreatment significantly delayed the onset of the first seizure episode and reduced the seizure severity. Following pretreatment with SN-6 (0.3, 1, 3, 10, and 30 mg/kg; p.o.), clonic and tonic-clonic PTZ-induced generalized seizures were reduced in 25-50% and 38-63% of treated animals, respectively. SN-6 (0.3, 1, and 3 mg/kg; p.o.) also significantly reduced PTZ-induced seizure severity scores, but did not alter seizure latencies. KB-R7943 (3 and 30 mg/kg; p.o.) or SN-6 (3 and 30 mg/kg; p.o.) administration potentiated the sub-anticonvulsant dose of diazepam (2.5 mg/kg; i.p.) that suppresses clonic and tonic-clonic PTZ-induced seizures. These findings suggested that Ca 2+ influx via the NCX in reverse mode contributes to a neuronal hyperexcitability that leads to clonic and tonic-clonic generalized seizures and that the NCX1 and NCX3 isoforms may serve as novel molecular targets for seizure suppression.
Suppression of drug-induced epileptiform discharges by cyclic AMP in rat hippocampus
Molecular and Chemical Neuropathology, 1997
The effect of cyclic adenosine Y,5'-monophosphate (cAMP) on epileptiform activity in rat hippocampal slices was investigated. Bathapplied cAMP reversibly decreased the frequency of extracellularly recorded discharges in the CA3 subfield induced by bethanechol-or theophylline-containing solutions. Because cAMP was presumed to be relatively membrane impermeant, we developed and tested the hypothesis that this cAMP-mediated effect occurred extracellularly through the catabolic conversion of cAMP to 5'-AMP and, in turn, to adenosine, a known inhibitory neuromodulator. Three predictions *Opinions or assertions contained herein are the private views of the authors and are not to be construed as official or as reflecting the views of the US Army or the Department of Defense. *Research was conducted in compliance with the Animal Welfare Act and other Federal statutes and regulations relating to animals and experiments involving animals and adheres to principles stated in the Guide for the Care and Use of Laboratory Animals, NIH Publication 85-23, 1985.