5-HT3Receptors Mediate Serotonergic Fast Synaptic Excitation of Neocortical Vasoactive Intestinal Peptide/Cholecystokinin Interneurons (original) (raw)
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Neocortical neurons expressing the serotonin 5-HT 3 receptor (5-HT 3 R) were characterized in rat acute slices by using patchclamp recordings combined with single-cell RT-PCR and histochemical labeling. The 5-HT 3A receptor subunit was expressed selectively in a subset of GABAergic interneurons coexpressing cholecystokinin (CCK) and vasoactive intestinal peptide (VIP). The 5-HT 3B subunit was never detected, indicating that 5-HT 3 Rs expressed by neocortical interneurons did not contain this subunit. In 5-HT 3A -expressing VIP/CCK interneurons, serotonin induced fast membrane potential depolarizations by activating an inward current that was blocked by the selective 5-HT 3 R antagonist tropisetron. Furthermore, we observed close appositions between serotonergic fibers and the dendrites and somata of 5-HT 3 R-expressing neurons, suggestive of possible synaptic contacts. Indeed, in interneurons exhibit-ing rapid excitation by serotonin, local electrical stimulations evoked fast EPSCs of large amplitude that were blocked by tropisetron. Finally, 5-HT 3 R-expressing neurons were also excited by a nicotinic agonist, indicating that serotonergic and cholinergic fast synaptic transmission could converge onto VIP/CCK interneurons. Our results establish a clear correlation between the presence of the 5-HT 3A receptor subunit in neocortical VIP/CCK GABAergic interneurons, its functional expression, and its synaptic activation by serotonergic afferent fibers from the brainstem raphe nuclei.
Frontiers in Cellular Neuroscience, 2015
The 5-HT7 receptor is one of the several serotonin (5-HT) receptor subtypes that are expressed in the dorsal raphe nucleus (DRN). Some earlier findings suggested that 5-HT7 receptors in the DRN were localized on GABAergic interneurons modulating the activity of 5-HT projection neurons. The aim of the present study was to find out how the 5-HT7 receptor modulates the GABAergic synaptic input to putative 5-HT DRN neurons, and whether blockade of the 5-HT7 receptor would affect the release of 5-HT in the target structure. Male Wistar rats with microdialysis probes implanted in the prefrontal cortex (PFC) received injections of the 5-HT7 receptor antagonist (2R)-1-[(3-hydroxyphenyl)sulfonyl]-2-[2-(4-methyl-1piperidinyl)ethyl]pyrrolidine hydrochloride (SB 269970), which induced an increase in the levels of 5-HT and its metabolite, 5-hydroxyindoleacetic acid (5-HIAA) in the PFC. In another set of experiments whole-cell recordings from presumed projection neurons were carried out using DRN slices. SB 269970 application resulted in depolarization and in an increase in the firing frequency of the cells. In order to activate 5-HT7 receptors, 5-carboxamidotryptamine (5-CT) was applied in the presence of N-[2-[4-(2-methoxyphenyl)-1piperazinyl]ethyl]-N-2-pyridinylcyclohexanecarboxamide (WAY100635). Hyperpolarization of cells and a decrease in the firing frequency were observed after activation of the 5-HT7 receptor. Blockade of 5-HT7 receptors caused a decrease in the mean frequency of spontaneous inhibitory postsynaptic currents (sIPSCs), while its activation induced an increase. The mechanism of these effects appears to involve tonically-active 5-HT7 receptors modulating firing and/or GABA release from inhibitory interneurons which regulate the activity of DRN serotonergic projection neurons. Keywords: brain slices, HPLC , m icrodialysis, prefrontal cortex, w h o le -c ell recording Abbreviations: 5-C T , 5-carboxam idotryptam ine; 5-H IA A , 5-hydroxyindoleacetic acid; 5-H T , 5-hydroxytryptamine, serotonin; A C SF, artificial cerebrospinal fluid; D RN , dorsal raphe nucleus; SB 269970, (2R)-1-[(3-hydroxyphenyl)sulfonyl]-2-[2-(4-m ethyl-1-piperidinyl)ethyl] pyrrolidine hydrochloride; sIPSC, spontaneous inhibitory postsynaptic current; W AY 100635, N -[2-[4-(2-m ethoxyphenyl)-1piperazinyl]ethyl]-N -2-pyridinylcyclohexanecarboxam ide. Frontiers in Cellular Neuroscience | www.frontiersin.org August 2015 | Volume 9 | Article 324 Kusek et al. 5 -HT7 receptor in the dorsal raphe
Correspondence between 5HT2 receptors and serotonergic axons in rat neocortex
Brain Research, 1988
The anatomic relationship between serotonergic (5-HT) axons and 5-HT 2 receptors in the rat forebrain was determined by a combined analysis of transmitter irnmunocytochemistry and receptor autoradiography. High densities of 5-HT 2 receptors, localized by the ligand Nl-methyl-2J25I-LSD (125I-MIL), are found in neocortex and striatum; these regions also receive a dense serotonergic innervation. Regional variations in the density of 5-HT 2 receptors and 5-HT axons correspond closely in most, but not all, areas of the forebrain. In somatosensory cortex (SI), the laminar distribution of 5-HT 2 receptors closely matches that of 5-HT axons: in particular, a dense band of 5-HT 2 receptors in layer V~ of SI is in precise register with a dense plexus of fine 5-HT axons. We have also observed a close spatial relationship between 5-HT 2 receptors and fine axons in other areas of the forebrain, suggesting that 5-HT 2 receptors may be selectively linked to a particular type of 5-HT axon terminal. Since fine axons of this type have been reported to arise from the dorsal raphe nucleus, it appears likely that 5-HT 2 receptors may mediate the effects of dorsal but not median raphe projections.
1997
The type 3 serotonin receptor (5-HT 3 R) is a ligand-gated ion channel whose presence in the CNS has been established by radioligand binding, in situ hybridization, and immunohistochemical analysis. To analyze further the role of the 5-HT 3 R in the CNS, we used in situ hybridization and immunocytochemistry to determine that 5-HT 3 R-expressing neurons are mainly GABA-containing cells in the rat telencephalon. We determined that 5-HT 3 R/GABA-containing neurons do not exhibit somatostatin immunoreactivity but often contain cholecystokinin (CCK) immunoreactivity. 5-HT 3 R-expressing cells with CCK immunoreactivity were observed in the neocortex, olfactory cortex, hippocampus, and amygdala. The 5-HT 3 R/CCK interneurons represent between 35 and 66% of the total population of CCK-containing cells in the neocortex.
In vivo excitation of GABA interneurons in the medial prefrontal cortex through 5-HT3 receptors
Serotonin (5-hydroxytryptamine, 5-HT) controls pyramidal cell activity in prefrontal cortex (PFC) through various receptors, in particular, 5-HT1A and 5-HT2A receptors. Here we report that the physiological stimulation of the raphe nuclei excites local, putatively GABAergic neurons in the prelimbic and cingulate areas of the rat PFC in vivo. These excitations had a latency of 36 +/- 4 ms and a duration of 69 +/- 9 ms and were blocked by the i.v. administration of the 5-HT3 receptor antagonists ondansetron and tropisetron. The latency and duration were shorter than those elicited through 5-HT2A receptors in pyramidal neurons of the same areas. Double in situ hybridization histochemistry showed the presence of GABAergic neurons expressing 5-HT3 receptor mRNA in PFC. These cells were more abundant in the cingulate, prelimbic and infralimbic areas, particularly in superficial layers. The percentages of GAD mRNA-positive neurons expressing 5-HT3 receptor mRNA in prelimbic cortex were 40, 18, 6 and 8% in layers I, II-III, V and VI, respectively, a distribution complementary to that of cells expressing 5-HT2A receptors. Overall, these results support an important role of 5-HT in the control of the excitability of apical dendrites of pyramidal neurons in the medial PFC through the activation of 5-HT3 receptors in GABAergic interneurons.
Neuroscience, 2007
The amygdalar basolateral nuclear complex (BLC) has very high levels of the type 3 serotonin receptor (5-HT 3 R). Previous studies have reported that 5-HT 3 R protein in the BLC is expressed in interneurons and that 5-HT 3 R mRNA is coexpressed with GABA and certain neuropeptides or calcium-binding proteins in these cells. However, there have been no detailed descriptions of the distribution of 5-HT 3 R+ neurons in the amygdala, and no quantitative studies of overlap of neurons expressing 5-HT 3 R protein with distinct interneuronal subpopulations in the BLC. The present investigation employed dual-labeling immunohistochemistry using antibodies to the 5-HT-3A receptor subunit (5-HT 3A R) and specific interneuronal markers to address these questions. These studies revealed that there was a moderate density of nonpyramidal 5-HT 3A R+ neurons in the BLC at all levels of the amygdala. In addition, immunostained cells were also seen in anterior portions of the cortical and medial nuclei. Although virtually all 5-HT 3A R+ neurons in the BLC were GABA+, very few expressed neuropeptide or calcium-binding protein markers for individual subpopulations. The main interneuronal marker expressed by 5-HT 3A R+ neurons was cholecystokinin (CCK), but only 8-16% of 5-HT 3 R+ neurons in the BLC, depending on the nucleus, were CCK+. Most of these CCK+/5-HT 3A R+ double-labeled neurons appeared to belong to the subpopulation of large type L CCK+ interneurons. Very few 5-HT 3A R+ neurons expressed calretinin, vasoactive intestinal peptide, or parvalbumin, and none expressed somatostatin or calbindin. Thus, the great majority of neurons expressing 5-HT 3A R protein appear to constitute a previously unrecognized subpopulation of GABAergic interneurons in the BLC.
Expression of serotonin 5-HT2C receptors in GABAergic cells of the anterior raphe nuclei
Journal of Chemical Neuroanatomy, 2005
We have used double in situ hybridization to examine the cellular localization of 5-HT 2C receptor mRNA in relation to serotonergic and GABAergic neurons in the anterior raphe nuclei of the rat. In the dorsal and median raphe nuclei 5-HT 2C receptor mRNA was not detected in serotonergic cells identified as those expressing serotonin (5-HT) transporter mRNA. In contrast, 5-HT 2C receptor mRNA was found in most GABAergic cells, recognized by the presence of glutamic acid decarboxylase mRNA. Such 5-HT 2C receptor-positive GABAergic neurons were mainly located in the intermediolateral and lateral portions of the dorsal raphe and lateral part of the median raphe. The present data give anatomical support to a previous hypothesis that proposed a negative-feedback loop involving reciprocal connections between GABAergic interneurons bearing 5-HT 2A/2C receptors and 5-HT neurons in the dorsal raphe and surrounding areas. According to this model, the excitation of GABAergic interneurons through these 5-HT 2C (and also 5-HT 2A ) receptors would result in the suppression of 5-HT cell firing. #
Serotonin 5-HT3 receptors in the central nervous system
Cell and Tissue Research, 2006
The 5-HT 3 receptor is a ligand-gated ion channel activated by serotonin (5-HT). Although originally identified in the peripheral nervous system, the 5-HT 3 receptor is also ubiquitously expressed in the central nervous system. Sites of expression include several brain stem nuclei and higher cortical areas such as the amygdala, hippocampus, and cortex. On the subcellular level, both presynaptic and postsynaptic 5-HT 3 receptors can be found. Presynaptic 5-HT 3 receptors are involved in mediating or modulating neurotransmitter release. Postsynaptic 5-HT 3 receptors are preferentially expressed on interneurons. In view of this specific expression pattern and of the well-established role of 5-HT as a neurotransmitter shaping development, we speculate that 5-HT 3 receptors play a role in the formation and function of cortical circuits.
European Journal of Neuroscience, 1990
Physiological, pharmacological and radioautographic binding studies have suggested the presence of the 5-HT1A autoreceptors on midbrain serotoninergic neurons. The recent production of specific anti-rat 5-HT1A receptor antibodies in rabbits injected with a synthetic peptide has provided a tool to examine this problem directly. Using the immunoperoxidase method to localize the receptor protein, neurons of all the sizes and forms characterizing the neuronal populations in the dorsal and median raphe nuclei were stained. Reaction product was distributed along the neuronal surface, outlining the contours of perikarya and dendrites in a continuous but uneven manner. Intracellular staining was scarce and confined to the perinuclear region. Double immunohistochemical staining using the anti-5-HT1A receptor antibodies and an anti-serotonin (5-HT) antiserum showed that all the 5-HT1A receptor immunoreactive neurons in the dorsal raphe, and the vast majority of them in the median raphe, are serotoninergic neurons. These data provide the first direct demonstration of the existence of 5-HT1A autoreceptors on the perikarya and dendrites of serotoninergic neurons in the anterior raphe nuclei.
Synapse, 1991
As a prerequisite to pharmacological analysis of the excitatory effects of serotonin (5-HT) on piriform pyramidal cells and interneurons, this study first examined the physiological characteristics of these two cell types. Intracellular recordings confirmed that the subpopulation of 5-HT-activated cells located at the border of layers II and III are indeed interneurons. Voltage clamp recordings in pyramidal cells showed that the increase in excitability produced by 5-HT in these cells was the result of voltage- and Ca(2+)-dependent outward currents with the characteristics of IM and IAHP. Pharmacological studies were designed to discriminate 5-HT2 from 5-HT1C responses in interneurons and pyramidal cells of piriform cortex. The 5-HT antagonist spiperone, which has a much higher affinity for 5-HT2 receptors than for 5-HT1C receptors, blocked the excitatory effect of 5-HT at lower concentrations in interneurons (IC50 = 31 nM) than in pyramidal cells (IC50 = 2.1 microM). Similarly, ritanserin, a drug which also has a higher affinity for 5-HT2 than 5-HT1C receptors, blocked the effect of 5-HT at lower concentrations in interneurons (IC50 = 400 nM) than in pyramidal cells (IC50 = 8.1 microM). In contrast, LY 53857, an antagonist with higher affinity for 5-HT1C than for 5-HT2 receptors, blocked the effect of 5-HT at lower concentrations in pyramidal cells (IC50 = 26 nM) than in interneurons (IC50 = 364 nM). The 5-HT1C partial agonist/5-HT2 antagonist mCPP produced agonist-like effects in only 66% of pyramidal cells tested indicating that not all pyramidal cells may express 5-HT1C receptors. In that both spiperone and ritanserin have higher affinity for 5-HT2 receptors than for 5-HT1C receptors and LY 53857 has a higher affinity for 5-HT1C receptors than for 5-HT2 receptors, these data suggest that in piriform cortex excitatory effects of 5-HT are mediated by 5-HT1C receptors in pyramidal cells an by 5-HT2 receptors in interneurons.