Protein kinase C inhibitors enhance the 5-HT2A receptor-mediated excitatory effects of serotonin on interneurons in rat piriform cortex

Previously it has been shown that excitatory effects of 5-hydroxytryptamine (5-HT) upon interneurons in the rat piriform cortex are mediated by 5-HT_2A receptors. This receptor is linked to phosphoinositide turnover, and one consequence of stimulating this receptor is the activation of protein kinase C (PKC). In the present study, the effect of PKC inhibitors on the 5-HT excitation of piriform cortical interneurons was examined by extracellular recording in a rat brain slice preparation. Bath application of the selective PKC inhibitors, bisindolylmalemide and chelerythrine, and the nonselective protein kinase inhibitor, H-7, all enhanced the excitatory effects of 5-HT. Two other nonselective protein kinase inhibitors, H-8 and HA 1004, which are 2.5-fold and 6.7- fold less potent than H-7 at inhibiting PKC, produced a slight or no enhancement, respectively, of the excitatory effect of 5-HT. Bisindolylmalemide, chelerythrine, and H-7 did not enhance the excitatory effects of norepinephrine or carbachol on the same interneurons. The PKC activator phorboll2,13-diacetate (PDA) decreased the excitatory effect of 5-HT this decrease was rapidly reversed by H-7. As inhibitors of PKC selectively enhanced rather than blocked the excitation by 5-HT mediated by 5-HT_2A receptors, we conclude that activation of PKC does not mediate the excitation by 5-HT of piriform cortical interneurons. Instead, we propose that PKC may have a negative feedback role in modulating the excitation by 5-HT of piriform cortical interneurons. © 1995 Wiley-Liss, Inc.     

5-HT(1A) receptor-mediated inhibition and 5-HT(2) as well as 5-HT(3) receptor-mediated excitation in different subdivisions of the rat amygdala

The techniques of extracellular single cell recording and microiontophoresis were used to study the effects of serotonin (5-HT) and of 5-HT(1A), 5-HT(2A/2C) and 5-HT(3) receptor agonists on the spontaneous activity of amygdaloid neurons in rats anesthetized with urethane. The background discharge rate was modified by 5-HT as well as by 5-HT agonists in about two-thirds of neurons tested in different nuclei of the amygdaloid complex. Whereas the 5-HT(2) and 5-HT(3) agonists significantly increased the neuronal discharge rate in nearly all subdivisions of the amygdala, the 5-HT(1A) agonist significantly inhibited the firing rate. Co-administration of bicuculline and 5-HT receptor agonists prevented the 8-OH-DPAT-induced increases in the firing rate in most cases tested, as well as the inhibitory effects of DOI or 2-methyl-5HT. Therefore, GABAergic interneurons seem to be involved in the mediation of serotonergic effects. The action of 5-HT agonists on the neuronal discharge rate was blocked by different receptor-specific antagonists. The results support the hypothesis that 5-HT exerts control throughout the amygdala by acting at least on 5-HT(1A), 5-HT(2A/2C) and 5-HT(3) receptors seemingly located both on projection and interneurons.     

Cellular and subcellular distribution of the serotonin 5-HT2A receptor in the central nervous system of adult rat.

Light and electron microscope immunocytochemistry with a monoclonal antibody against the N-terminal domain of the human protein was used to determine the cellular and subcellular localization of serotonin 5-HT2A receptors in the central nervous system of adult rat. Following immunoperoxidase or silver-intensified immunogold labeling, neuronal, somatodendritic, and/or axonal immunoreactivity was detected in numerous brain regions, including all those in which ligand binding sites and 5-HT2A mRNA had previously been reported. The distribution of 5-HT2A-immunolabeled soma/dendrites was characterized in cerebral cortex, olfactory system, septum, hippocampal formation, basal ganglia, amygdala, diencephalon, cerebellum, brainstem, and spinal cord. Labeled axons were visible in every myelinated tract known to arise from immunoreactive cell body groups. In immunopositive soma/dendrites as well as axons, the 5-HT2A receptor appeared mainly cytoplasmic rather than membrane bound. Even though the dendritic labeling was generally stronger than the somatic, it did not extend to dendritic spines in such regions as the cerebral and piriform cortex, the neostriatum, or the molecular layer of the cerebellum. Similarly, there were no labeled axon terminals in numerous regions known to be strongly innervated by the immunoreactive somata and their axons (e.g., molecular layer of piriform cortex). It was concluded that the 5-HT2A receptor is mostly intracellular and transported in dendrites and axons, but does not reach into dendritic spines or axon terminals. Because it has previously been shown that this serotonin receptor is transported retrogradely as well as anterogradely, activates intracellular transduction pathways and intervenes in the regulation of the expression of many genes, it is suggested that one of its main functions is to participate in retrograde signaling systems activated by serotonin.     

Colocalization of serotonin receptor subtypes 5-HT2A, 5-HT2C,and 5-HT6 with neuropeptides in rat striatum

There are two primary output pathways from the striatum: a projection to the globus pallidus, and a projection to the substantia nigra. Certain striatally expressed neuropeptides are differentially distributed between these two pathways. Specifically, enkephalin is expressed in striatopallidal neurons, whereas substance P and dynorphin are expressed in striatonigral neurons. Several serotonin receptors are also prominently expressed in the striatum, but little is known about how they fit into the molecular neuroanatomy described above. We used double-label in situ hybridization to determine the striatal distribution of the mRNAs of the serotonin2A (5-HT2A), serotonin2C (5-HT2C), and serotonin6 (5-HT6) receptors in relation to enkephalin, substance P, and dynorphin expressing output neurons. Rat brain sections were simultaneously hybridized with an ³⁵S riboprobe for one of the serotonin receptors and a digoxygenin labeled riboprobe for one of the neuropeptides. Sections were examined by using brightfield microscopy, and the degree of colocalization of the two mRNAs determined. All the serotonin receptors colocalized extensively with all three of the neuropeptides examined. None of the serotonin receptors showed preferential colocalization in striatopallidal (enkephalin containing), or striatonigral (substance P or dynorphin containing) cells. The 5-HT2A and 5-HT2C mRNAs displayed a differential distribution with regard to the scattered islands of strongly dynorphin mRNA positive cells, which are thought to reside in the striatal patch compartment. Within these islands, 5-HT2C mRNA expression was much higher than in surrounding areas. 5-HT2A mRNA showed the opposite pattern with decreased expression over dynorphin rich cell clusters. © 1996 Wiley-Liss, Inc.     

Effects of selected serotonin 5-HT(1) and 5-HT(2) receptor agonists on feeding behavior: possible mechanisms of action

Serotonin (5-HT) receptor agonists with high affinity for the different subtypes (i.e. 5-HT(1A-1F), 5-HT(2A-2C)) of the 5-HT(1)- and 5-HT(2) receptor families have been shown to affect ingestive behavior. It has been assumed that: (1) stimulation of hypothalamic 5-HT(2C) or 5-HT(1B) receptors leads to a behaviorally specific hypophagic effect by accelerating satiety processes; (2) stimulation of 5-HT(2A) receptors leads to a disruption of the feeding cascade; and (3) stimulation of 5-HT(1A) and 5-HT(2B) receptors leads to a hyperphagic effect. The present paper reviews studies performed with the relatively selective receptor agonists ipsapirone (5-HT(1A)), CP-94,253 (5-HT(1B)), BW 723C86 (5-HT(2B)) and ORG 37684 (5-HT(2C)), as well as the nonselective receptor agonists TFMPP (5-HT(1B/2C)), m-CPP (5-HT(2C/1B)) and DOI (5-HT(2A/2C)) in a variety of feeding paradigms in rats, both after systemic and local injection. These studies support a role for other neuroanatomical regions (i.e. brain stem) and behavioral mechanisms (i.e. appetitive processes) in the hypophagic effects of these compounds, possibly as a function of the administered dose. Studies with 5-HT receptor antagonists indicate that the proposed role of particular 5-HT(1/2) receptor subtypes in the hypophagic effects of these 5-HT receptor agonists may be more complicated than originally thought. Further characterization of the role of 5-HT(1/2) receptor subtypes in the control of ingestive behavior will require extensive pharmacological and behavioral studies, using more selective receptor agonists and antagonists and different behavioral procedures, as well as verification in transgenic animals.     

Segregation of serotonin 5-HT2A and 5-HT3 receptors in inhibitory circuits of the primate cerebral cortex

An emerging concept of cortical network organization is that distinct segments of the pyramidal neuron tree are controlled by functionally diverse inhibitory microcircuits. We compared the expression of two serotonin receptor subtypes, the G-protein-coupled 5-hydroxytryptamine2A receptors and the ion-channel gating 5-HT3 receptors, in cortical neuron types, which control these microcircuits. Here we show, using light and electron microscopic immunocytochemical techniques, that 5-HT2A receptors are segregated from 5-HT3 receptors in the macaque cerebral cortex. 5-HT2A receptor immunolabel was found in pyramidal cells and also in GABAergic interneurons known to specialize in the perisomatic inhibition of pyramidal cells: large and medium-size parvalbumin- and calbindin-containing interneurons. In contrast, 5-HT3 label was only present in small GABA-, substance P receptor-, and calbindin-containing neurons and in medium-size calretinin-containing neurons: interneurons known to preferentially target the dendrites of pyramidal cells. This cellular segregation indicates a serotonin-receptor-specific segmentation of the GABAergic inhibitory actions along the pyramidal neuron tree.     

The therapeutic role of 5-HT1A and 5-HT2A receptors in depression

The selective serotonin reuptake inhibitors (SSRIs) are the most frequently prescribed antidepressant drugs, because they are well tolerated and have no severe side effects. They rapidly block serotonin (5-HT) reuptake, yet the onset of their therapeutic action requires weeks of treatment. This delay is the result of presynaptic and postsynaptic adaptive mechanisms secondary to reuptake inhibition. The prevention of a negative feedback mechanism operating at the 5-HT autoreceptor level enhances the neurochemical and clinical effects of SSRIs. The blockade of 5-HT2A receptors also seems to improve the clinical effects of SSRIs. These receptors are located postsynaptically to 5-HT axons, mainly in the neocortex. Pyramidal neurons in the prefrontal cortex are particularly enriched in 5-HT2A receptors. Their blockade may affect the function of prefrontal-subcortical circuits, an effect that probably underlies the beneficial effects of the addition of atypical antipsychotic drugs, which are 5-HT2A receptor antagonists, to SSRIs in treatment-resistant patients.     

In vivo evidence for serotonin 5-HT2C receptor-mediated long-lasting excitability of lumbar spinal reflex and its functional interaction with 5-HT1A receptor in the mammalian spinal cord

The purpose of the present study was to investigate the 5-HT(2C) receptor-mediated effects on the spinal monosynaptic mass reflex activities and also its functional interactions with 5-HT(1A) receptors in anesthetized, acutely spinalized mammalian adult spinal cord in vivo. Intravenous administration of (+/-)-2,5-dimethoxy-4-iodoamphetamine hydrochloride (DOI) (0.1 mg/kg), an agonist of 5-HT(2A/2C) receptors, significantly increased the excitability of spinal motoneurons as reflected by an increase in the spinal monosynaptic mass reflex amplitude to 150-200% of the control. 5-HT(2A/2C) receptor-induced motoneuron excitability was slow, persistent and long-lasting for more than 2h that was significantly inhibited by 5-HT(2C) receptor specific antagonist SB 242084 administered 10 min prior to DOI. Simultaneous administration of DOI (0.1 mg/kg, i.v.) along with (+/-)-8-hydroxy dipropylaminotetraline hydrobromide (8-OH-DPAT) (0.1 mg/kg, i.v.) completely inhibited DOI-induced spinal monosynaptic mass reflex facilitation. In another separate study, administration of 8-OH-DPAT (0.1 mg/kg, i.v.) at the maximum response of DOI also inhibited the motoneuron's excitability; however, the inhibition lasted only for a period of 40-60 min after administration of 8-OH-DPAT, after which the spinal monosynaptic mass reflex amplitude reached its maximum level. These findings suggest that the 5-HT(2C) receptor is primarily involved in the mediation of the long-lasting excitability of spinal motoneurons and possibly interacts with its functional counterpart, 5-HT(1A) receptors in the mammalian adult spinal cord.     

Combined treatment with citalopram and buspirone: effects on serotonin 5-HT2A and 5-HT2C receptors in the rat brain

INTRODUCTION: We wanted to elucidate whether the proposed advantages of citalopram-buspirone combination treatment are related to changes in 5-HT(2A/C) receptor-mediated neurotransmission. METHODS: The affinity of buspirone to 5-HT2A and 5-HT2C receptors was measured in vitro, and the influence of buspirone on 5-HT2C receptor-mediated phosphoinositide hydrolysis was estimated. Four groups of rats received citalopram (10 mg/kg), buspirone (6 mg/kg), citalopram-buspirone combination, or saline once a day s.c. for 14 days. Treatment effects on 5-HT2A and 5-HT2C receptors were investigated by receptor autoradiography with antagonist and agonist radioligands. RESULTS: Buspirone was found to be a weak 5-HT2C receptor antagonist, with a low affinity for 5-HT2A and 5-HT2C receptors. Repeated buspirone-citalopram combination treatment markedly decreased [3H]ketanserin and [125I]DOI binding to 5-HT2A receptors. Repeated administration of buspirone and buspirone-citalopram combination increased the affinity of [3H]mesulergine toward 5-HT2C receptors, and buspirone-citalopram combination also decreased [125I]DOI binding to 5-HT2C receptors. DISCUSSION: We suggest that downregulation of brain 5-HT2A receptors and possibly of 5-HT2C receptor agonist sites is involved in the beneficial clinical effects of buspirone-SSRI augmentation treatment. Furthermore, a conversion of brain 5-HT2C receptors from high- to low-affinity state may provide an additional mechanism for the anti-anxiety effects of buspirone.     

Distribution of serotonin 5-HT2A and 5-HT7 receptors in the Onuf''s nucleus of the rat spinal cord

BACKGROUND: Motoneurons from the Onuf's nucleus of the spinal cord, which innervate the striated muscle of the pelvic floor, play an important role in erection, ejaculation, and urine control. Serotonin (5-hydroxytryptamine, 5-HT) regulates motoneuron activity from the Onuf's nucleus of the spinal cord.However, few studies exist that describe 5-HT receptor distribution in the Onuf's nucleus. In addition, the nature of the effects of 5-HT receptor on the innervating striated muscle of the pelvic floor is controversial.OBJECTIVE: To investigate the distribution of serotonin 5-HT2A and 5-HT7 receptors in motoneurons of Onuf's nucleus in the spinal cord of male rats, and to analyze the relationship of 5-HT2A and 5-H7 receptors to central modulation of urogenital function.DESIGN, TIME AND SETTING: The neural morphology experiment was performed at the Ultramicrostructure Laboratory of Reproductive Medicine, Basic Medical College, Chongqing Medical University, China from April to December 2007.MATERIALS: Ten adult, Sprague Dawley rats (eight males and two females) were randomly divided into a gender control group (n = 4,50% male and 50% female) and a retrograde tracing group (n = 6, 100% male).Recombinant pseudorabies virus (PRV-152) was provided by Professor LW Enquist from Princeton University, USA. Rabbit anti-5-HT2A and 5-HT7 receptor antibodies were purchased from Diasorin, France.METHODS: In the gender control group, the spinal L5-6segments were harvested, sliced, and then incubated antibodies specific against 5-HT2A or 5-HT7 receptors for immunohistochemical staining. In the retrograde tracing group, PRV-152 was separately injected into the right ischiocavernosus (ischiocavernosus subgroup,n = 3) and the fight external urethral sphincter (external urethral sphincter subgroup, n = 3). Four days after injection, L5-6 segments were harvested, sliced, and incubated with antibodies specific against 5-HT2A or 5-HT7 receptors for double-labeling immunofluoresccnce staining.MAIN OUTCOME MEASURES: Distribution analysis of 5-HT2A and 5-Ht7 receptors in Onuf's nucleus utilizing optical or laser confocal microscopy.RESULTS: 5-HT2A receptor immunoreactivity was revealed primarily in the medial region of the dorsolateral nucleus of Onuf's nucleus. 5-HT7 receptor expression was observed in the lateral part of the dorsolateral nucleus. 5-HT2A and 5-HT7 receptor expressions in the Onuf's nucleus were significantly greater in male rats, compared to female rats. Double-labeling immunofluorescence demonstrated that 5-HT2A receptors were distributed primarily in the surrounding motoneurons innervating the ischiocavernosus, and 5-HT7 receptors were primarily expressed in motoneurons innervating the external urethral sphincter.CONCLUSION: Motoneurons innervating the ischiocavernosus and external urethral sphincter are located primarily in the medial and lateral region of the dorsolateral nucleus of L5-6 segments. The 5-HT2A receptor-innervating ischincavernosus may be preferentially involved in the regulation of sexual reflex, and the 5-HT7 receptor-innervating external urethral sphincter may mainly join in regulating micturition reflex.     

Developmentally regulated serotonin 5-HT2B receptors.

Serotonin (5-hydroxytryptamine, 5-HT) binds to numerous cognate receptors to initiate its biological effects. In this review, we have focused on the 5-HT2B receptor to address how signaling and expression of this receptor is specifically implicated in embryonic development and adult health and disease. Transduction of the 5-HT2B signaling is complex, including phospholipase C and A2 stimulation, cGMP production and a mitogenic signal that integrates the tyrosine kinase-signaling pathway. Furthermore, 5-HT, through the 5-HT2B receptors, has the ability to control serotonergic differentiation of committed neuron-like cells. In addition, 5-HT2B receptors are actively involved in the transient action of 5-HT during embryonic morphogenesis. Our recent data presented the first genetic evidence that 5-HT via 5-HT2B receptors regulates cardiac embryonic development and adult functions and suggested that this receptor subtype may be involved in other physiopathological situations. In particular, 5-HT-dependent molecular mechanisms may be involved in embryonic development and postnatal maturation of the enteric nervous system. Also, the involvement of the 5-HT2B receptor in the vascular growth often observed in hypertension is likely. These probably result from reactivation of developmentally regulated receptors in pathological situations. Finally, embryonic functions of 5-HT2 receptors observed in Drosophila gastrulation suggest evolutionary conserved mechanisms.     

Involvement of the 5-HT1A and 5-HT2A/2C serotonin receptors in the anxious behavior of prenatally stressed ovariectomized rats

We compared the effects of an antagonist of 5-HT_1A receptors, NAN-190 (0.1 mg/kg intraperitoneally), and an antagonist of 5-HT_2A/2C receptors, ketanserin (0.1 mg/kg intraperitoneally), which were chronically injected for 14 days, on the anxiety level in prenatally stressed female rats with an ovariectomyinduced experimental deficiency of estrogens. Chronic administration of ketanserin to ovariectomized prenatally stressed females had an anxiolytic effect and corrected disturbed levels of follitropin, lutropin, and estradiol. Administration of NAN-190 to ovariectomized prenatally stressed rats increased the anxiety level and decreased the ratio between the levels of tropic and peripheral sex hormones.     

5-HT2A receptor antagonist M100907 reduces serotonin synthesis: an autoradiographic study

The effects of the administration of the serotonin (5-HT)_2A antagonist, M100907, on 5-HT synthesis rates, were evaluated using the α-[¹⁴C]methyl-l-tryptophan (α-MTrp) autoradiographic method. In the treatment study, M100907 (10 mg/kg) was injected intraperitoneally 30 min before the α-MTrp injection (30 μCi over 2 min). A single dose of M100907 caused a significant decrease in the synthesis in the anterior olfactory nucleus, accumbens nucleus, frontal cortex, sensory-motor cortex, cingulate cortex, medial caudate-putamen, dorsal thalamus, substantia nigra, inferior collicus, raphe magnus nucleus, superior olive, and raphe pallidus nucleus.These data suggest that the terminal 5-HT_2A receptors are involved in the regulation of 5-HT synthesis in the entire brain. Further, 5-HT synthesis is likely regulated by the 5-HT_2A antagonistic property of M100907 in the cortices, anterior olfactory nucleus, caudate putamen, and nucleus accumbens.     

Distribution of serotonin 5-HT2A and 5-HT7 receptors in the Onuf’s nucleus of the rat spinal cord*★

BACKGROUND：Motoneurons from the Onuf’s nucleus of the spinal cord, which innervate the striated muscle of the pelvic floor, play an important role in erection, ejaculation, and urine control. Serotonin （5-hydroxytryptamine, 5-HT） regulates motoneuron activity from the Onuf’s nucleus of the spinal cord. However, few studies exist that describe 5-HT receptor distribution in the Onuf’s nucleus. In addition, the nature of the effects of 5-HT receptor on the innervating striated muscle of the pelvic floor is controversial. OBJECTIVE： To investigate the distribution of serotonin 5-HT2A and 5-HT7 receptors in motoneurons of Onuf’s nucleus in the spinal cord of male rats, and to analyze the relationship of 5-HT2A and 5-HT7 receptor to central modulation of urogenital function. DESIGN, TIME AND SETTING： The neural morphology experiment was performed at the Ultramicro-structure Laboratory of Reproductive Medicine, Basic Medical College, Chongqing Medical University, China from April to December 2007. MATERIALS： Ten adult, Sprague Dawley rats （eight males and two females） were randomly divided into gender control group （n = 4, 50% male and 50% female） and a retrograde tracing group （n = 6, 100% male） Recombinant pseudorabies virus （PRV-152） was provided by Professor LW Enquist from Princeton University, USA. Rabbit anti-5-HT2A and 5-HT7 receptor antibodies were purchased from Diasorin, France. METHODS： In the gender control group, the spinal L5-6 segments were harvested, sliced, and then incubate antibodies specific against 5-HT2A or 5-HT7 receptors for immunohistochemical staining. In the retrograde tracing group, PRV-152 was separately injected into the right ischiocavernosus （ischiocavernosus subgroup, n = 3） and the right external urethral sphincter （external urethral sphincter subgroup, n = 3）. Four days after injection, L5-6 segments were harvested, sliced, and incubated with antibodies specific against 5-HT2A or 5-HT7 receptors for double-labeling immunofluorescence stain     

Behavioral mechanisms for the anorectic action of the serotonin (5-HT) uptake inhibitor sertraline in rats: Comparison with directly acting 5-HT agonists

The 5-HT uptake inhibitor, sertraline (5-40 mumol/kg, IP) reduced the volume of milk consumed by food-deprived rats during a 30-min test (ID50 = 12 mumol/kg). Observations using a time-sampling method revealed that sertraline shortened meal duration (ID50 = 14 mumol/kg) by decreasing feeding and increasing resting without altering nonfeeding activity or the overall sequence of behavior that characterizes normal satiety. In separate experiments, analysis of videotapes demonstrated that sertraline (10 mumol/kg) decreased not only the time that rats fed but also their actual rate of intake. In comparison, doses of the direct 5-HT agonists, mCPP (1-[3-chlorophenyl]piperazine), RU 24969 (5-methoxy-3-[1,2,3,6-tetrahydropyridin-4-yl]-1H-indole), and DOI (1-[2,5-dimethoxy-4-iodophenyl]-2-amino-propane) that produced similar anorectic effects altered either feeding time or rate but not both. DOI also disrupted the continuity of feeding and the 5-HT agonist, 8-OH-DPAT (8-hydroxy-di-N-propylamino tetralin) produced marked stereotypy at anorectic doses. Together, these results imply that stimulating a number of different serotonergic mechanisms can reduce food intake in rats. Sertraline appears to accelerate the onset of normal satiety, presumably by enhancing physiological actions of endogenous 5-HT.     

Association study of serotonin 2A receptor (5-HT2A) and serotonin transporter (5-HTT) gene polymorphisms with schizophrenia

OBJECTIVE: To investigate (i) the association between four serotonergic polymorphisms (A-1438G and T102C of the 5-HT2A receptor gene, and 5-HTT VNTR and 5-HTTLPR of the 5-HT transporter gene) and schizophrenia and (ii) the potential interaction of those polymorphisms in the development of schizophrenia. SUBJECTS AND METHODS: 227 outpatients with schizophrenia (DSM-IV criteria) and 420 unrelated healthy controls from Asturias (Northern Spain) were genotyped using standard methods. RESULTS: Both groups showed Hardy-Weinberg equilibrium for the analyzed genetic variability. A-1438G and T102C polymorphisms are in complete linkage disequilibrium in our population. There was an apparent difference in the distribution of genotypes for the A-1438G (or T102C) polymorphisms (p=0.018, not significant after a Bonferroni correction). The 5-HT2A -1438A (or 102T) allele was significantly more frequent in patients than controls (0.53 and 0.45, respectively; corrected p=0.028, OR=1.39 (95% CI=1.11-1.75)). Genotype and allele distributions for 5-HTT polymorphisms were similar in both groups. However, assessment of the combined influence of 5-HT2A A-1438G and 5-HTTLPR polymorphisms demonstrated a significant effect (chi(2) (3)=11.51, p=0.009), whereby the combination of -1438A and 5-HTTLPR S alleles was associated with schizophrenia. CONCLUSIONS: Our findings support a possible synergistic effect of genetic factors influencing serotonergic neurotransmission on susceptibility to schizophrenia.     

Serotonin and learned helplessness: a regional study of 5-HT1A, 5-HT2A receptors and the serotonin transport site in rat brain

Serotonin (5-HT) plays a central role in the neurochemistry of the learned helplessness animal model of depression. Using quantitative autoradiography, we measured the density of 5-HT1A and 5-HT2A receptors and of 5-HT transport sites in medial prefrontal cortex, dorsal hippocampus, septum, hypothalamus, and amygdala in learned helpless rats, and in rats that were nonhelpless after inescapable stress, as well as in shuttlebox-tested and nonhandled controls. We found no changes in 5-HT1A receptor density among the groups in any region studied. In dorsal hippocampus, 5-HT2A receptor density was decreased in nonhelpless rats, while in amygdala 5-HT2A receptor density was decreased in both groups of stressed rats, whether helpless or nonhelpless. In the hypothalamus 5-HT2A receptor density, was decreased in helpless rats as compared to controls. In medial prefrontal cortex, the serotonin transport sites showed decreased density in helpless rats as compared to controls but not to nonhelpless rats. These findings further highlight the complexity of regional 5-HT effects in the learned helplessness animal model.     

Structure of the mouse 5-HT1C, 5-HT2 and stomach fundus serotonin receptor genes.

By analysis of the mouse 5-HT1C receptor gene we found that its coding region contains three introns. We next isolated cDNA and genomic clones for the closely related 5-HT2 receptor using a probe derived from the 5-HT1C receptor sequence. This probe also hybridized to an additional gene, called SRL (Serotonin Receptor Like). We have evidence demonstrating that it encodes the stomach fundus 5-HT receptor. Two introns are present within the coding regions of the mouse 5-HT2 receptor gene and the SRL gene at positions which correspond to those of introns in the 5-HT1C receptor gene. This intron distribution is unique and distinguishes these receptors from other members of the family of receptors coupled to G-proteins.     

Selective genotyping for the role of 5-HT2A, 5-HT2C, and GABA alpha 6 receptors and the serotonin transporter in the level of response to alcohol: a pilot study.

BACKGROUND: The vulnerability to alcohol dependence appears to be genetically influenced through a variety of mechanisms. One potentially genetically mediated channel may be a low level of response (LR) to alcohol, which has been seen in children of alcoholics and noted to predict future alcohol abuse and dependence. This pilot study uses a case and control genetic association approach to evaluate the possible role of five genotypes in both LR and alcoholism in informative subgroups of men with high and low LR scores documented 15 years earlier. METHODS: As part of a larger study, 41 men, about 39 years old, were selected from among the first 113, completed 15-year follow-ups in a prospective study. The 17 subjects whose LRs at age 20 were in the lower third were compared on five polymorphisms of four genes with 24 men whose reactions to alcohol had been above the median. RESULTS: The 14 men with the LL genotype of the serotonin transporter (5-HTT) polymorphism and the seven with the Pro/Ser genotype of the GABAA alpha 6 polymorphism had demonstrated lower LR scores at about age 20, and had significantly higher proportions of alcoholics than the other genotypes for those loci. All four subjects with combined LL and Pro/Ser genotypes had developed alcoholism and demonstrated the lowest LR scores overall. There was no evidence that two polymorphisms of the 5-HT2A receptor gene and one of the 5-HT2C receptor gene were related to LR or alcoholism in this sample. CONCLUSIONS: These results are consistent with animal and human studies suggesting a possible role for genetic variation in the GABAA alpha 6 and the serotonin transporter in the reaction to alcohol and the alcoholism risk.