The effects of 5-HT1A and 5-HT2C receptor agonists on behavioral satiety sequence in rats

The present study examined the effects of 5-HT1A and 5-HT2C receptor agonists on behavioral satiety sequence (BSS) in rats. The 5-HT1A receptor agonist, 8-OH-DPAT (0.5 microg), and the 5-HT2C receptor agonist, Ro-60-0175 (3.0 microg), were injected into the paraventricular nucleus (PVN) of rats. The animals were maintained on an ad libitum feeding paradigm with access to water and individual sources of protein, carbohydrate, and fat. Intra-PVN administration of each agonist was associated with decreased carbohydrate consumption. The effect was enhanced by the administration of both agonists together. Behavioral analysis indicated that co-administration of 8-OH-DPAT and Ro-60-0175 interrupted the natural BSS with an increase in non-feeding behavior, whereas the 8-OH-DPAT alone promoted early development of the natural BSS. In conclusion, the 5-HT receptor agonists affected serotonergic modulation of feeding behavior in a functionally selective way.     

5-HT1A receptor activation counteracted the effect of acute immobilization of noradrenergic neurons in the rat locus coeruleus

The aim of our study was to evaluate the effect of acute stress and the 5-HT(1A) receptor involvement in both, the hippocampus noradrenaline (NA) tissue levels and the c-Fos immunoreactivity (c-Fos-IR) in the catecholaminergic neurons of the locus coeruleus (LC). Double immunocytochemical staining of tyrosine hydroxilase (TH) and c-Fos protein combined with stereological techniques were used to study the specific cell activation in the LC neurons in five experimental groups (control group, immobilization (1h) group, 8-OH-DPAT group (8-OH-DPAT 0.3mg/kg, s.c.), DPAT+IMMO group (8-OH-DPAT 0.3mg/kg, s.c., 30' prior acute immobilization) and WAY+DPAT+IMMO group (WAY-100635 0.3mg/kg, s.c. and 8-OH-DPAT 0.3mg/kg, s.c., 45'and 30', respectively, before immobilization). The results showed that hippocampal NA tissue levels and c-Fos-IR in the TH positive neurons of the LC were significantly increased immediately and after 90', respectively, after the immobilization period. Pre-treatment with 8-OH-DPAT counteracted the effects induced by immobilization, but pre-treatment with WAY-100635 did not block the effects induced by 8-OH-DPAT. These results suggest that noradrenaline system is associated in a significant way with immobilization stress. The role of 5-HT(1A) receptor activation in this stress response is also discussed.     

The Effects of Hypothyroidism on 5-HT1A and 5-HT2A Receptors and the Serotonin Transporter Protein in the Rat Brain

The effects of hypothyroidism on 5-HT_1A and 5-HT_2A receptors and the serotonin transporter protein were studied in thyroidectomized male Wistar rats in two experimental groups: 1) animals kept on an iodine-free diet (hypothyroid rats) and 2) animals kept on thyroxine (15 g/kg) for 21 days (giving normal thyroid hormone levels, euthyroid animals). Sham-operated rats served as controls. Binding of [³H]8-OH-DPAT with 5-HT_1A receptors and [³H]citalopram with the transporter protein in the hippocampus and midbrain showed no changes in hypothyroid rats as compared with controls. Conversely, there were significant decreases in [³H]ketanserin binding to 5-HT_2A receptors in the frontal cortex in hypothyroid rats as compared with controls; this decrease was reversed by thyroxine treatment. Thus, losses of cortical 5-HT_2A receptors appears to be the main consequence of hypothyroidism at the level of the serotonin system of the brain.     

5-HT1A receptor activation counteracts c-Fos immunoreactivity induced in serotonin neurons of the raphe nuclei after immobilization stress in the male rat

The serotoninergic system and the 5-HT_1A receptors have been involved in the brain response to acute stress. The aim of our study was evaluate the role of the 5-HT_1A receptors in serotoninergic cells of rostral and caudal raphe nuclei under acute immobilization in rats. Double immunocytochemical staining of 5-hydroxy-tryptamine and c-Fos protein and stereology techniques were used to study the specific cell activation in the raphe nuclei neurons in five groups (control group, immobilization group (immobilization lasting 1 h), DPAT group (8-OH-DPAT 0.3 mg/kg, s.c.), DPAT + IMMO group (8-OH-DPAT 0.3 mg/kg, s.c., 30′ prior acute immobilization) and WAY + DPAT + IMMO group (WAY-100635 0.3 mg/kg, s.c. and 8-OH-DPAT 0.3 mg/kg, s.c., 45′ and 30′, respectively, before immobilization). Our results showed an increase in the number of c-Fos immunoreactive nuclei in serotoninergic cells in both dorsal and median raphe nuclei in the immobilized group. The 8-OH-DPAT pretreatment counteracted the excitatory effects of the acute immobilization in these brain regions. In addition, WAY-100635 administration reduced the effect of 8-OH-DPAT injection, suggesting a selective 5-HT_1A receptor role. Raphe pallidus and raphe obscurus did not show any differences among experimental groups. We suggest that somatodendritic 5-HT_1A receptors in rostral raphe nuclei may play a crucial role in both mediating the consequences of uncontrollable stress and the possible beneficial effects of treatment with 5-HT_1A receptor agonists.     

Chronic thyroxine treatment activates the 5-HT2A serotonin receptor in the mouse brain

Chronic thyroxine administration (2.0 mg/l, 60 days) significantly increases the 5-HT2A serotonin receptor gene mRNA level in the frontal cortex and augments the frequency of head twitches induced by the receptor agonist DOI (1.0 mg/kg, i.p.) in AKR mice. The result indicates thyroid hormones involvement in 5-HT2A receptor regulation in adult brain.     

Changes in 5-HT2A-mediated behavior and 5-HT2A- and 5-HT1A receptor binding and expression in conditional brain-derived neurotrophic factor knock-out mice

Changes in brain-derived neurotrophic factor (BDNF) expression have been implicated in the etiology of psychiatric disorders. To investigate pathological mechanisms elicited by perturbed BDNF signaling, we examined mutant mice with central depletion of BDNF (BDNF^2L/2LCk-cre). A severe impairment specific for the serotonin 2A receptor (5-HT_2AR) in prefrontal cortex was described previously in these mice. This is of much interest, as 5-HT_2ARs have been linked to neuropsychiatric disorders and anxiety-related behavior. Here we further characterized the serotonin receptor alterations triggered by BDNF depletion. 5-HT_2A ([³H]-MDL100907) and 5-HT_1A ([³H]-WAY100635) receptor autoradiography revealed site-specific alterations in BDNF mutant mice. They exhibited lower 5-HT_2A receptor binding in frontal cortex but increased binding in hippocampus. Additionally, 5-HT_1A receptor binding was decreased in hippocampus of BDNF mutants, but unchanged in frontal cortex. Molecular analysis indicated corresponding changes in 5-HT_2A and 5-HT_1A mRNA expression but normal 5-HT_2C content in these brain regions in BDNF^2L/2LCk-cre mice. We investigated whether the reduction in frontal 5-HT_2AR binding was reflected in reduced functional output in two 5-HT_2A-receptor mediated behavioral tests, the head-twitch response (HTR) and the ear-scratch response (ESR). BDNF^2L/2LCk-cre mutants treated with the 5-HT_2A receptor agonist (±)-2,5-dimethoxy-4-iodoamphetamine (DOI) showed a clearly diminished ESR but no differences in HTR compared to wildtypes. These findings illustrate the context-dependent effects of deficient BDNF signaling on the 5-HT receptor system and 5-HT_2A-receptor functional output.     

Selective decline of 5-HT1A receptor binding sites in rat cortex, hippocampus and cholinergic basal forebrain nuclei during aging

The effect of aging on 5-HT_1A receptor binding in several forebrain areas associated with the basal forebrain cholinergic system was investigated in rats of 3-, 24- and 30-months-old by receptor autoradiography and biochemical binding assay using [³H]8-OH-DPAT as a ligand. Autoradiographic measurements demonstrated a marked region-specific decline of ligand binding in: (i) regions of the basal forebrain cholinergic cell groups, i.e. the medial septum, diagonal band nuclei and magnocellular nucleus basalis, (ii) the frontal and parietal neocortex and (iii) the dentate gyrus of the hippocampus. No change or only a slight decrease of the 5-HT_1A receptor density was found in other areas investigated: the CA1 and CA3 sectors of hippocampus, the cingular and perirhinal cerebral cortex and the lateral septum. The autoradiographic findings were substantiated by the biochemical binding assay, which revealed a comparable loss of 5-HT_1A receptor in the hippocampus and neocortex at the age of 30 months. The results clearly show that with increasing age the decrement of 5-HT_1A receptor binding in the rat forebrain is remarkably region-selective and particularly affects the cholinergic cell groups that innervate cortex and hippocampus. This phenomenon appears to be especially significant in relation to the neuronal substrates underlying the age-related alterations of mood and cognition.     

免疫源性的ACTH受体及5-HT1A受体表达研究

目的:通过检测ACTHR、5HT1AR蛋白及其mRNA在人淋巴组织中的表达情况,寻求神经免疫内分泌网络之间功能双向调节的形态学依据。方法:应用免疫组织化学及核酸分子原位杂交方法检测ACTHR、5HT1AR蛋白及其mRNA在人100例淋巴结、脾脏及肠道淋巴组织中的表达。结果:免疫组织化学显示ACTHR、5HT1AR在各种淋巴组织中表达的阳性率为82.5%和86.3%,与原位杂交(阳性率为70%和75%)之间无统计学差异(χ2=1.907、0.570,均P>0.05)。结论:人的免疫活性细胞不但可以表达ACTHR、5HT1AR蛋白,还可以合成其mRNA,ACTH、5HT都可以通过免疫细胞膜上的ACTHR、5HT1AR发挥对免疫系统的调节作用。     

The firing activity of pyramidal neurons in medial prefrontal cortex and their response to 5-hydroxytryptamine-1A receptor stimulation in a rat model of Parkinson's disease

The changes in the firing rate and firing pattern of pyramidal neurons in medial prefrontal cortex (mPFC) and the effects of selective 5-hydroxytryptamine-_1A (5-HT_1A) receptor agonist (R)-(+)-8-hydroxy-2-(dipropylamino)tetralin hydrobromide (8-OH-DPAT) and antagonist N-(2-(4-(2-methoxyphenyl)-1-piperazinyl)ethyl)-N-2-pyridylcyclohexane carboxamide maleate salt (WAY-100635) on the firing activity of the neurons were studied in sham-lesioned rats and rats with 6-hydroxydopamine lesions of the substantia nigra pars compacta (SNc). The lesion of the SNc increased the firing rate of pyramidal neurons significantly compared to sham-lesioned rats, and the firing pattern of these neurons also changed significantly towards a more burst-firing. The systemic administration of 8-OH-DPAT at doses in the range of 0.5–128 μg/kg showed an excitatory-inhibitory effect on the firing rate of pyramidal neurons in mPFC of sham-lesioned rats. At lower doses, 0.5–32 μg/kg, it evoked excitation of the neurons, and at a high dose, i.e. 128 μg/kg, inhibited the activity of the neurons. In contrast to sham-lesioned rats, 8-OH-DPAT, at the same doses, showed no excitatory effect in the lesioned rats although the inhibitory phase of the effect of 8-OH-DPAT on the firing rate of pyramidal neurons in mPFC was still present. Furthermore, the local application of 8-OH-DPAT, 5 μg, in mPFC inhibited the firing rate of pyramidal neurons in sham-lesioned rats, while having no effect on firing rate in the lesioned rats. The excitatory or inhibitory effects of 8-OH-DPAT were reversed by WAY-100635, indicating that these effects are mediated by 5-HT_1A receptor. Altogether, these results indicate that the lesion of the SNc leads to hyperactivity of pyramidal neurons in mPFC and the abnormality of response of these neurons to 5-HT_1A receptor stimulation, suggesting that mPFC may be involved in the pathophysiology of the psychiatric disturbance of Parkinson's disease.     

Excitability of small-diameter trigeminal ganglion neurons by 5-HT is mediated by enhancement of the tetrodotoxin-resistant sodium current due to the activation of 5-HT(4) receptors and/or by the inhibition of the transient potassium current

The aims of the present study were to investigate whether the activation of the 5-HT receptor subtypes (5-HT(4) and 5-HT(3)) acted significantly on the modification of the tetrodotoxin-resistant sodium current (I(NaR)) in small-sized rat trigeminal ganglion (TG) neurons and whether the inhibition of the transient K(+) current (I(A)) contributed to the excitability in those neurons. 5-HT applications in at concentrations ranging from 0.01-10 microM significantly increased the peak I(NaR). One micromolar 5-HT application caused the greatest increase in the peak I(NaR) amplitude accompanied by a hyperpolarizing shift in the activation curve. A similar modification of I(NaR) properties was also obtained via the application of the 5-HT(4) receptor agonist, RS 67333, in concentrations ranging from 0.001-1 microM. The largest effects of 5-HT (1 microM) and RS 67333 (0.1 microM) on the modification of I(NaR) were abolished by pretreatment with ICS 205-930 (a 5-HT(3/4) receptor antagonist, 10 microM), which showed no significant effect on the baseline I(NaR). However, ICS 205-930 application at 30 microM caused a significant decrease in the baseline I(NaR). Phenylbiguanide (a 5-HT(3) receptor agonist) did not significantly alter I(NaR) properties when applied in concentrations ranging from 1 to 100 microM. The application of 0.1 microM RS 67333 decreased the transient K(+) current (I(A)) by approximately 31%. The threshold for action potential generation was significantly lower after the application of 0.1 microM RS 67333. Furthermore, 0.1 microM RS 67333 application increased the number of action potentials and the resting membrane potential got more positive, but it decreased the duration of depolarization phase of action potential. In addition, neither the additional application of 1 microM 5-HT in the presence of 10 microM forskolin, a stimulator of adenylyl cyclase, nor the opposite applications of 5-HT and forskolin caused the enhancement of increased I(NaR), which indicates the presence of an 'occluding effect.' These results suggest that the 5-HT-induced modification of I(NaR) is mediated by the activation of 5-HT(4) receptors, involving a cAMP-dependent signaling pathway, and that the inhibition of I(A) following the application of a 5-HT(4) receptor agonist also contributes to the increased number of action potentials.     

Unilateral lesion of the nigrostriatal pathway induces an increase of neuronal firing of the midbrain raphe nuclei 5-HT neurons and a decrease of their response to 5-HT1A receptor stimulation in the rat

Several studies have shown that the 5-hydroxytryptamine (serotonin, 5-HT) system is severely affected after degeneration of nigrostriatal dopaminergic neurons. In the present study, we examined the changes in the firing rate and firing pattern of the dorsal and median raphe nuclei (DRN and MRN) 5-HT neurons, and the effect of the selective 5-HT_1A receptor agonist (R)-(+)-8-hydroxy-2-(dipropylamino)tetralin hydrobromide (8-OH-DPAT) and antagonist (N-(2-(4-(2-methoxyphenyl)-1-piperazinyl)ethyl)-N-2-pyridylcyclohexane carboxamide maleate salt (WAY-100635) on the neuronal firing in rats with 6-hydroxydopamine (6-OHDA) lesions of the substantia nigra pars compacta by using extracellular recording. The unilateral lesion of the nigrostriatal pathway significantly increased the mean firing rate of DRN and MRN 5-HT neurons compared with normal rats, and the firing pattern of these neurons also changed significantly towards a more bursty one. The lower dose of 8-OH-DPAT, 4 μg/kg (cumulative doses, i.v.), completely inhibited the firing activity of all DRN and MRN 5-HT neurons examined in normal and sham rats. In contrast to normal and sham rats, only the higher doses of 8-OH-DPAT, 128 and 64 μg/kg, completely inhibited the firing rate of DRN and MRN 5-HT neurons in 6-OHDA-lesioned rats, respectively. Furthermore, the local application of 8-OH-DPAT, 1.5 μg, in the DRN completely inhibited the firing rate of 5-HT neurons in normal and sham rats, while having no effect on firing rate in the lesioned rats. Altogether, these results indicate that lesion of the nigrostriatal pathway leads to hyperactivity of DRN and MRN 5-HT neurons, suggesting the implication of the DRN and MRN in the pathophysiology of Parkinson's disease, and the decreased response of these 5-HT neurons to 5-HT_1A receptor stimulation, reflecting 5-HT_1A receptor dysfunction in 6-OHDA-lesioned rats.     

Central 5-HT3 receptor-induced hypothermia in mice: Interstrain differences and comparison with hypothermia mediated via 5-HT1A receptor

The selective agonist of serotonin 5-HT₃ receptor 1-(3-chlorophenyl)biguanide hydrochloride (m-CPBG) administered intracerebroventricularly (40, 80 or 160 nmol) produced long-lasting dose-dependent hypothermic response in AKR/2J mice. m-CPBG (160 nmol i.c.v.) induced profound hypothermia (delta t = −4 °C) that lasted up to 7 h. m-CPBG (40 nmol i.c.v.)-induced hypothermia was attenuated by 5-HT₃ receptor antagonist ondansetron pretreatment. At the same time, intraperitoneal administration of m-CPBG in a wide range of doses (0.5, 1.0, 5.0 or 10.0 mg/kg) did not affect the body temperature. These findings indicate: (1) the implication of central, rather than peripheral 5-HT₃ receptor in the thermoregulation; (2) the inability of m-CPBG to cross blood–brain barrier in mice. The comparison of brain 5-HT₃-induced hypothermic reaction in six inbred mouse strains (DBA/2J, CBA/Lac, C57BL/6, BALB/c, ICR, AKR/J) was performed and two highly sensitive to m-CPBG strains (CBA/Lac and C57BL/6) were found. In the same six mouse strains the functional activity of 5-HT_1A receptor was studied. The comparison of hypothermic reactions produced by 5-HT_1A receptor agonist 8-OH-DPAT (1.0 mg/kg i.p.) and m-CPBG revealed significant correlation between 5-HT₃ and 5-HT_1A-induced hypothermia in five out of six investigated mouse strains. 5-HT_1A receptor antagonist p-MPPI pretreatment (1 mg/kg i.p.) diminished hypothermia produced by centrally administered m-CPBG (40 nmol i.c.v.). The data suggest the cross-talk between 5-HT_1A and 5-HT₃ receptors in the mechanism of 5-HT-related hypothermia.     

Differential role of the 5-HT1A receptor in aggressive and non-aggressive mice: an across-strain comparison

Differential role of the 5-HT(1A) receptor in aggressive and non-aggressive mice: an across-strain comparison. PHYSIOL BEHAV 00(0) 000-000, 2006. According to the serotonin (5-HT)-deficiency hypothesis of aggression, highly aggressive individuals are characterized by low brain 5-HT neurotransmission. Key regulatory mechanisms acting on the serotonergic neuron involve the activation of the somatodendritic inhibitory 5-HT(1A) autoreceptor (short feedback loop) and/or the activation of postsynaptic 5-HT(1A) receptors expressed on neurons in cortico-limbic areas (long feedback loop). In this study, we examined whether low serotonin neurotransmission is associated with enhanced 5-HT(1A) (auto)receptor activity in highly aggressive animals. Male mice (SAL-LAL, TA-TNA, NC900-NC100) obtained through different artificial-selection breeding programs for aggression were observed in a resident-intruder test. The prefrontal cortex level of 5-HT and its metabolite 5-HIAA were determined by means of HPLC. The activity of the 5-HT(1A) receptors was assessed by means of the hypothermic response to the selective 5-HT(1A) agonists S-15535 (preferential autoreceptor agonist) and 8-OHDPAT (full pre- and postsynaptic receptor agonist). Highly aggressive mice had lower serotonin levels in the prefrontal cortex and two out of three aggressive strains had higher 5-HT(1A) (auto)receptor sensitivity. The results strengthen the validity of the serotonin-deficiency hypothesis of aggression and suggest that chronic exaggerated activity of the 5-HT(1A) receptor may be a causative link in the neural cascade of events leading to 5-HT hypofunction in aggressive individuals.     

Differential distribution of MAP1A isoforms in the adult mouse barrel cortex and comparison with the serotonin 5-HT2A receptor

Microtubule-associated protein 1A (MAP1A) is essential during the late differentiation phase of neuronal development. Here, we demonstrated the presence of two MAP1A isoforms with a differential spatial distribution in the adult mouse barrel cortex. Antibody A stained MAP1A in pyramidal and stellate cells, including dendrites that crossed layer IV in the septa between barrels. The other antibody, BW6 recognized a MAP1A isoform that was mainly confined to the barrel hollow and identified smaller caliber dendrites. Previously, an interaction of MAP1A and the serotonin 5-hydroxytryptamine 2A (5-HT(2A)) receptor was shown in the rat cortex. Here, we identified, by double-immunofluorescent labeling, MAP1A isoform and serotonin 5-HT(2A) receptor distribution. MAP1A co-localized mainly with 5-HT(2A) receptor in larger apical dendrites situated in septa. This differential staining of MAP1A and a serotonin receptor in defined barrel compartments may be due to changes in the expression or processing of MAP1A during dendritic transport as a consequence of functional differences in processing of whisker-related sensory input.     

Effect of chronic activation of 5-HT3 receptors on 5-HT3, 5-HT1A and 5-HT2A receptors functional activity and expression of key genes of the brain serotonin system

Among serotonin (5-HT) receptors, the 5-HT₃ receptor is the only ligand-gated ion-channel. Little is known about the interaction between the 5-HT₃ receptor and other 5-HT receptors and influence of 5-HT₃ chronic activation on other 5-HT receptors and the expression of key genes of 5-HT system. Chronic activation of 5-HT₃ receptor with intracerebroventricularly administrated selective agonist 1-(3-chlorophenyl)biguanide hydrochloride (m-CPBG) (14 days, 40 nmol, i.c.v.) produced significant desensitization of 5-HT₃ and 5-HT_1A receptors. The hypothermic responses produced by acute administration of selective agonist of 5-HT₃ receptor (m-CPBG, 40 nmol, i.c.v.) or selective agonist of 5-HT_1A receptor (8-hydroxy-2-(di-n-propylamino)tetralin) (8-OH-DPAT, 1 mg/kg, i.p.) was significantly lower in m-CPBG treated mice compared with the mice of control groups. Chronic m-CPBG administration failed to induce any significant change in the 5-HT_2A receptor functional activity and in the expression of the gene encoding 5-HT_2A receptor. Chronic activation of 5-HT₃ receptor produced no considerable effect on the expression on 5-HT₃, 5-HT_1A, and 5-HT transporter (5-HTT) and tryptophan hydroxylase-2 (TPH-2) genes – the key genes of brain 5-HT system, in the midbrain, frontal cortex and hippocampus. In conclusion, chronic activation of ionotropic 5-HT₃ receptor produced significant desensitization of 5-HT₃ and postsynaptic 5-HT_1A receptors but caused no considerable changes in the expression of key genes of the brain 5-HT system.     

Effects of the 5-HT4 receptor agonist RS67333 and paroxetine on hippocampal extracellular 5-HT levels

The 5-HT₄ receptor modulates activity of serotonergic neurons and is a new potential target for antidepressant treatment. This microdialysis study evaluated the effect of the 5-HT₄ receptor agonist, RS67333, on extracellular serotonin (5-hydroxytryptamine, 5-HT) and 5-HIAA levels in rat ventral hippocampus during chloral hydrate anaesthesia, and explored the ability of RS67333 to augment the effect of the selective serotonin reuptake inhibitor paroxetine. The effect of RS67333 was examined after acute and subchronic (3 days) administration. Acute RS67333 (1.5 mg/kg i.v.) had no effect on extracellular 5-HT or 5-HIAA levels, while acute paroxetine (0.5 mg/kg i.v.) increased 5-HT levels by 299 ± 16% and decreased 5-HIAA levels by 25 ± 4%. Administration of RS67333 80 min after paroxetine caused an additional transient increase in 5-HT levels (to 398 ± 52% of baseline). Subchronic RS67333 administration (1.5 mg/kg i.p.) increased basal 5-HT levels by 73 ± 15% and decreased 5-HIAA levels by 27 ± 13%. In conclusion, the 5-HT₄ receptor agonist RS67333 augmented the acute effect of paroxetine on extracellular 5-HT levels in the ventral hippocampus, and after 3 days increased basal hippocampal 5-HT levels.     

ASSOCIATION ANALYSIS OF 5-HTTLPRVARIANTS, 5-HT2ARECEPTOR GENE 102T/CPOLYMORPHISM AND MIGRAINE

It is well known that migraine has a strong genetic component, although the type and number of genes involved is not yet clear. There is evidence to suggest that serotonin-related genes participate in the pathogenesis of migraine. Previous studies have shown that gender differences influence the serotonergic neurotransmission and, in addition, the migraine prevalence is higher in females than males. Therefore, we investigated the functional polymorphism in the upstream regulatory region of the serotonin transporter gene (5-HTTLPR) and the 102T/Cpolymorphism of the 5-HT_2Areceptor gene in the Hungarian female population. These genes were analysed in 126 migraine sufferers (with or without aura)and 101 unrelated healthy controls using case control design. A borderline association (χ²=3.84, df=1, p=0.049; OR=1.45, 95% CI=1.00–2.12) between 5-HTTLPRshort (S) allele and migraine was found. No significant difference between migraine sufferers and controls was observed for the 102T/Cpolymorphism of 5-HT_2Areceptor gene. Furthermore, there was no significant interaction between5-HTTLPRand 102T/Cpolymorphisms in our study population. In conclusion, our results support that the genetic susceptibility of migraine may be associated with a locus at or near the 5-HT transporter gene.     

Localization of 5-HT2A, 5-HT3, 5-HT5A and 5-HT7 receptor-like immunoreactivity in the rat cerebellum

Although serotonin (5-hydroxytryptamine, 5-HT) is known to exert a modulatory action on cerebellar function, our current knowledge of the nature of receptor subtypes mediating serotonergic activity in this part of the brain remains fragmentary. In this study, we report the presence and distribution of 5-HT3, 5-HT5A and 5-HT7 receptor-like immunoreactivity in the rat cerebellum using immunofluorescence histochemistry. 5-HT3 immunoreactivity was found in fibers sparsely distributed throughout the cerebellum. Most of them were seen in the cerebellar cortex as fine varicose 5-HT3-positive axonal processes. 5-HT5A immunoreactivity, on the other hand, was observed in neuronal somata of the cerebellar cortex and deep cerebellar nuclei. Based upon cell morphology and the use of cell-specific markers, Purkinje cells, molecular layer interneurons and Golgi cells were found to be 5-HT5A immunopositive. In addition, the use of cell-specific markers allowed us to identify previously reported large 5-HT2A-positive cells in the granular layer as being Golgi cells. Finally, 5-HT7 immunoreactivity was observed only in Purkinje cells. Corroborating previous radioligand-binding, in situ hybridization and immunohistochemical studies, our data relate serotonin receptor subtypes to specific cerebellar cell types and may consequently contribute to the elucidation of serotonergic actions in the cerebellum.     

Enhancement of agonist binding to 5-HT1A receptors in rat brain membranes by millimolar Mn

Manganese in millimolar concentration caused increase in specific binding of [³H]8-OH-DPAT to rat hippocampal membranes up to 44% in comparison with experiments in the presence of Mg²⁺, while no significant differences were found in rat cortical membranes. Similar increase in high-affinity agonist binding sites by Mn²⁺ was found in displacement curves of 8-OH-DPAT, where antagonist [³H]WAY100635 was used as reporter ligand. The removal of bivalent ions with EDTA caused full loss of high-affinity binding of agonists, but not for antagonists. Therefore it was hypothesized, that the effect of Mn²⁺- and Mg²⁺-ions was modulated through their action on different G-proteins. Results showed that efficient coupling of G-protein and 5-HT_1A receptors is crucial to modify Mg²⁺ and Mn²⁺ effects, whereas Mn²⁺ is more potent stabilizer of agonist high-affinity binding, especially when GTPγS is present. Using Sf9 cells as model system, we have shown that G_i1 proteins are required to modulate Mn²⁺-dependent high-affinity agonist binding to 5-HT_1A receptors, but further studies are necessary to find the cofacors of Mn²⁺ modulation to signal transduction.     

Regulation of cortical and striatal 5-HT1A receptors in the MPTP-lesioned macaque

Serotonergic 1A (5-HT_1A) receptor agonists reduce L-3,4-dihydroxyphenylalanine (L-DOPA)-induced dyskinesia in Parkinson's disease (PD), though the mechanism(s) and site(s) of action remain unclear. We employed [³H]-WAY 100,635 autoradiographic receptor binding to measure 5-HT_1A receptor levels in 4 groups of macaques: normal (vehicle-vehicle); 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned, without exposure to L-DOPA, i.e., untreated parkinsonian (MPTP-vehicle); MPTP-lesioned, receiving a single administration of L-DOPA to alleviate parkinsonism (MPTP-L-DOPA-acute); and MPTP-lesioned, chronically treated with L-DOPA, parkinsonism alleviated but exhibiting dyskinesia (MPTP-L-DOPA-chronic). We demonstrate that 5-HT_1A receptor binding decreases (by 10%-20%, p < 0.05) in the external layers, but increases (by 80%-100%, p < 0.05) in the middle layers, of the premotor and motor cortex of all MPTP-lesioned macaques. In the striosomes of the caudate nucleus, 5-HT_1A receptor binding increases in MPTP-vehicle macaques (by 50%, p < 0.05), compared with normal macaques. While 5-HT_1A receptor binding is low in the matrix of the caudate nucleus in normal macaques, it increases (by 200%, p < 0.05) in MPTP-L-DOPA-chronic macaques. These data suggest that 5-HT_1A receptors are involved in the pathophysiology of both parkinsonism and complications of L-DOPA therapy.