5-HT1 receptors in rats with amnesia

5-HT1 receptors of the amygdala, midbrain's central gray substance, hippocampus and frontal cortex of the rats were investigated during the memory trace retrieval, using the model of "psychogenic" amnesia. It was found that specific binding of 3H 5-HT in amygdala and central gray substance was decreased in the rats with passive avoidance retention. 3H 5-HT binding in the amnesic rats didn't differ from the control animals. Absence of decrease of 5-HT1 receptors number could be considered as one of the possible mechanisms of the memory trace non-retrieval due to amnesia or its consequence.     

5-HT receptors on identified Lymnaea neurones in culture. Pharmacological characterization of 5-HT1A receptors

The ability of the selective 5-HT_1A receptor agonist R(+)-8-hydroxydipropylaminotetralin hydrobromide (8-OH-DPAT) to bind with 5-HT receptor(s) on cultured, identified neurones in Lymnaea stagnalis was examined. The identified neurones studied were from the buccal ganglia and the serotonin-containing cerebral giant cells (CGCs). 5-HT and its agonists were applied from puffer pipettes, whilst 5-HT antagonists were applied in the bathing medium. At 10⁻³ M, the 5-HT_1A agonist, always produced paroxysmal depolarizing shifts (PDS) while at a lower concentration (10⁻⁴ M), it always mimicked the effects of 10⁻³ M 5-HT. 8-OH-DPAT (10⁻⁴ M) and 5-HT 10⁻³ M produced dose-dependent increases in the responses they evoked. At 10⁻⁴ M, the 5-HT₃ receptor agonist 1-(m-chlorophenyl)-biguanide hydrochloride (m-CPBG), failed to hyperpolarize most of the neurones hyperpolarized by 5-HT. At 10⁻⁴ M, the antagonists ketanserin (5-HT₂), MDL 72222 (5-HT₃), and pindobind-5-HT_1A (5-HT_1A) consistently abolished spike generation ii spontaneously active neurones. Both ketanserin and MDL 72222 failed to block the actions of 8-OH-DPAT and only partially blocked those of 5-HT, but pindobind-5-HT_1A completely, but reversibly,blocked the 8-OH-DPAT effects while greatly reducing those of 5-HT. These results suggest that 5-HT_1A receptor subtypes might be involved in the hyperpolarizing responses of the CGCs and their follower motor neurones in the buccal ganglia of Lymnaea stagnalis to 5-HT. The presence of 5-HT_1A receptors on these neurones can be considered to correspond with those found in mammals because their pharmacological responses resemble those of mammalian 5-HT_1A receptors.     

The role of putative 5-HT1A and 5-HT1B receptors in the control of feeding in rats

8-hydroxy-2(di-n-propylamino)tetraline (8-OH-DPAT) and 5-methoxy-3(1,2,3,6-tetrahydro-4-pyridinyl)1H indole succinate (RU 24969), two agonists on the putative serotonin 1A and serotonin 1B receptors, were used for exploring the role of these sites in the inhibitory effect of serotonin (5-HT) on feeding. In free-feeding rats, 2.5-5 mg/kg RU 24969 significantly reduced food intake while doses of 8-OH-DPAT ranging from 0.125 to 0.5 mg/kg increased eating. The effects of the highest doses were associated with hyperlocomotion and hyperreactivity for RU 24969 and a typical motor syndrome (flat body posture and forepaw treading) for 8-OH-DPAT. The motor syndrome caused by 0.5 mg/kg 8-OH-DPAT was much more obvious in food-deprived rats in which food intake was also markedly reduced. RU 24969 1.25 and 5 mg/kg reduced food intake by food-deprived rats and caused hyperlocomotion not different from that in free-feeding animals. Pretreatment with metergoline (2 mg/kg i.p.) prevented the effect of 5 mg/kg RU 24969 on food intake by food-deprived rats but had no effect on the reduction of eating caused by 0.5 mg/kg 8-OH-DPAT. The motor syndrome caused by 8-OH-DPAT was not changed by metergoline but the hyperlocomotion caused by RU 24969 was potentiated. Haloperidol (0.1 mg/kg i.p.) completely blocked the hyperlocomotion but did not change the reduction of food intake caused by RU 24969 in food-deprived rats. It is suggested that the putative serotonin 1B receptors specifically mediate the inhibitory effect of 5-HT on feeding whereas serotonin 1A sites act by enhancing eating only in free-feeding animals.     

Presynaptic 5-HT1A receptors in immunomodulation

It is shown that a selective agonist of 5-HT1A receptors 8-OH-DPAT in a low dose (0.1 mg/kg), which is known to affect mainly the presynaptic 5-HT1A receptors increased the immune response at the peak of reactions (the forth or fifth day after immunization with sheep red blood cells - SRBC) in CBA mice and Wistar rats. Treatment of the animals with the drug 15 min prior to antigen injection raised the number of plaque-forming cells (lgM-PFC) and rosette-forming cells (RFC) in the spleen. The preliminary blockade of 5-HT1A receptor with a selective antagonist of 5-HT1A receptors WAY-100635 (0.1 mg/kg) prevented the immunostimulating effect of 5-HT 1A receptors agonist 8-OH-DPAT, whereas WAY-100635 administration alone in the same dose didn't change the immune response. Activation of 5-HT1A receptors under conditions of electrical lesion of 5-HTergic neurons of the nucleus raphe was unable to enhance the immune reactions, as it did in sham-operated rats. The data obtained indicate that the somatodendric 5-HT1A autoreceptors are involved in immunomodulation.     

Activation of 5-HT(1A) receptors attenuates tachycardia induced by restraint stress in rats

To better understand the central mechanisms that mediate increases in heart rate (HR) during psychological stress, we examined the effects of systemic and intramedullary (raphe region) administration of the serotonin-1A (5-HT(1A)) receptor agonist 8-hydroxy-2-(di-n-propylamino)tetraline (8-OH-DPAT) on cardiac changes elicited by restraint in hooded Wistar rats with preimplanted ECG telemetric transmitters. 8-OH-DPAT reduced basal HR from 356 +/- 12 to 284 +/- 12 beats/min, predominantly via a nonadrenergic, noncholinergic mechanism. Restraint stress caused tachycardia (an initial transient increase from 318 +/- 3 to 492 +/- 21 beats/min with a sustained component of 379 +/- 12 beats/min). beta-Adrenoreceptor blockade with atenolol suppressed the sustained component, whereas muscarinic blockade with methylscopolamine (50 microg/kg) abolished the initial transient increase, indicating that sympathetic activation and vagal withdrawal were responsible for the tachycardia. Systemic administration of 8-OH-DPAT (10, 30, and 100 microg/kg) attenuated stress-induced tachycardia in a dose-dependent manner, and this effect was suppressed by the 5-HT(1A) antagonist WAY-100635 (100 microg/kg). Given alone, the antagonist had no effect. Systemically injected 8-OH-DPAT (100 microg/kg) attenuated the sympathetically mediated sustained component (from +85 +/- 19 to +32 +/- 9 beats/min) and the vagally mediated transient (from +62 +/- 5 to +25 +/- 3 beats/min). Activation of 5-HT(1A) receptors in the medullary raphe by microinjection of 8-OH-DPAT mimicked the antitachycardic effect of the systemically administered drug but did not affect basal HR. We conclude that tachycardia induced by restraint stress is due to a sustained increase in cardiac sympathetic activity associated with a transient vagal withdrawal. Activation of central 5-HT(1A) receptors attenuates this tachycardia by suppressing autonomic effects. At least some of the relevant receptors are located in the medullary raphe-parapyramidal area.     

GABA(B) receptors in 5-HT transporter- and 5-HT1A receptor-knock-out mice: further evidence of a transduction pathway shared with 5-HT1A receptors

The functional properties of GABA(B) receptors were examined in the dorsal raphe nucleus (DRN) and the hippocampus of knock-out mice devoid of the 5-HT transporter (5-HTT-/-) or the 5-HT(1A) receptor (5-HT(1A)-/-). Electrophysiological recordings in brain slices showed that the GABA(B) receptor agonist baclofen caused a lower hyperpolarization and neuronal firing inhibition of DRN 5-HT cells in 5-HTT-/- versus 5-HTT+/+ mice. In addition, [(35)S]GTP-gamma-S binding induced by GABA(B) receptor stimulation in the DRN was approximately 40% less in these mutants compared with wild-type mice. In contrast, GABA(B) receptors appeared functionally intact in the hippocampus of 5-HTT-/-, and in both this area and the DRN of 5-HT(1A)-knock-out mice. The unique functional changes of DRN GABA(B) receptors closely resembled those of 5-HT(1A) autoreceptors in 5-HTT-/- mice, further supporting the idea that both receptor types are coupled to a common pool of G-proteins in serotoninergic neurons.     

Hypothalamic 5-HT functional regulation through 5-HT1A and 5-HT2C receptors during pancreatic regeneration

5-HT receptors are predominantly located in the brain and are involved in pancreatic function and cell proliferation through sympathetic nervous system. The objective of this study was to investigate the role of hypothalamic 5-HT, 5-HT1A and 5-HT2C receptor binding and gene expression in rat model of pancreatic regeneration using 60% pancreatectomy. The pancreatic regeneration was evaluated by 5-HT content, 5-HT1A and 5-HT2C receptor gene expression in the hypothalamus of sham operated, 72 h and 7 days pancreatectomised rats. 5-HT content was quantified by HPLC. 5-HT1A receptor assay was done by using specific agonist [3H]8-OH DPAT. 5-HT2C receptor assay was done by using specific antagonist [3H]mesulergine. The expression of 5-HT1A and 5-HT2C receptor gene was analyzed by RT-PCR. 5-HT content was higher in the hypothalamus of 72 h pancreatectomised rats. 5-HT1A and 5-HT2C receptors were down-regulated in the hypothalamus. RT-PCR analysis revealed decreased 5-HT1A and 5-HT2C receptor mRNA expression. The 5-HT1A and 5-HT2C receptors gene expression in the 7 days pancreatectomised rats reversed to near sham level. This study is the first to identify 5-HT1A and 5-HT2C receptor gene expression in the hypothalamus during pancreatic regeneration in rats. Our results suggest the hypothalamic serotonergic receptor functional regulation during pancreatic regeneration.     

大鼠杏仁核5—HT3受体参与免疫调制

实验通过大鼠侧脑室和杏仁核给予5－HT3受体激动剂1－phenylbiguanide(PBG),用3H－TdR掺入法测定脾细胞丝裂原（concanavalin A,Con A和lipopolysaccharide,LPS)刺激增殖效应,用活化脾细胞增殖法测定IL－2生成,MTT法测定自然杀伤（natural killer,NK)细胞活性和用放射免疫测定血浆皮质酮水平,以探讨大鼠杏仁核5－HT3受体在免疫调控中的作用。结果表明：5－HT3受体拮抗剂granisetron(GNT,0.1-0.4mg/kg ip)剂量依赖地增强Con A和LPS刺激的脾细胞增殖,作用在连续给药5d最明显,双侧脑室给予PBG（5ug/side)可增强ConA和LPS刺激的脾细胞增殖效应,作用在连续给药3d最明显,双侧和单侧中共杏仁核给予PBG0．5ug均增强ConA刺激的脾细胞增殖和IL－2生成,底内侧杏仁核给予同剂量PBG仅增强LPS刺激的脾细胞增殖效应,不影响ConA刺激的脾细胞增殖和IL－2生成,中央杏仁核给予PBG升高血浆皮质酮的作用较底侧杏仁核给予等量PBG引起的升高血浆皮质酮作用明显（P＜0．01）,侧脑室,中央杏仁核和底内杏仁核给予PBG对丝裂原刺激的脾细胞增殖效应影响不同,但均被同时同部位给予GNT所拮抗,提示杏仁核中央核和底内侧核的5－HT3受体可能以不同方式参与ConA或LPS刺激的脾细胞增殖效应的调制。     

Involvement of 5-HT1A receptors in passive avoidance learning in intact and ovariectomized female rats

The influence of chronic administration of 5-HT1A receptor agonist 8-OH-DPAT (0.05 mg/kg, s.c.) and 5-HT1A receptor antagonist NAN-190 (0.1 mg/kg, i.p.) injected for 14 days alone or in combination with 17beta-estradiol (0.5 microg i.m./rat/day) was studied on passive avoidance performance (PAR) and on behavior in the open field test in adult intact and ovariectomized (OVX) female rats. Administration of 5-HT1A receptor antagonist NAN-190 alone significantly improved PAR (p<0.05) in intact females with proestrus and estrus and in OVX females. Administration of 5-HT1A receptor agonist 8-OH-DPAT alone or in combination with 17beta-estradiol significantly (p<0.05) improved PAR in OVX rats and failed to normalize PAR in intact rats with proestrus and estrus. Results of the work specify the involvement of 5-HT1A receptors in the mechanisms of passive avoidance learning in OVX female rats.     

Sensitization of adenylate cyclase by short-term activation of 5-HT1A receptors

Long-term (18 h) activation of 5-HT1A receptors alters 5-HT1A receptor-G protein coupling and leads to heterologous sensitization of adenylate cyclase. In contrast, the effects of short-term (2 h) 5-HT1A receptor activation on subsequent adenylate cyclase activity have not been determined. The present study examined and characterized 5-HT1A receptor-induced heterologous sensitization following short-term activation in CHO-5-HT1A cells. Short-term activation of 5-HT1A receptors with full agonists, as well as the partial agonist, buspirone, markedly enhanced subsequent forskolin-stimulated cyclic AMP accumulation. This heterologous sensitization was evident after 30 min treatment with 5HT and appeared to be near maximal following 2 h agonist treatment. Sensitization was characterized by a dose-dependent increase in forskolin-stimulated cyclic AMP accumulation and was prevented by WAY 100635 or by pertussis toxin treatment. The ability of the 5-HT1A agonists to induce heterologous sensitization was not significantly altered by agents shown previously to modulate 5-HT1A-mediated inhibition of cyclic AMP accumulation.     

CB1 knockout mice display impaired functionality of 5-HT1A and 5-HT2A/C receptors

Interaction between brain endocannabinoid (EC) and serotonin (5-HT) systems was investigated by examining 5-HT-dependent behavioral and biochemical responses in CB₁ receptor knockout mice. CB₁ knockout animals exhibited a significant reduction in the induction of head twitches and paw tremor by the 5-HT_2A/C receptor selective agonist (±) DOI, as well as a reduced hypothermic response following administration of the 5-HT_1A receptor agonist (±)-8-OH-DPAT. Additionally, exposure to the tail suspension test induced enhanced despair responses in CB₁ knockout mice. However, the tricyclic antidepressant imipramine and the 5-HT selective reuptake inhibitor fluoxetine induced similar decreases in the time of immobility in the tail suspension test in CB₁ receptor knockout and wild-type mice. No differences were found between both genotypes with regard to 5-HT_2A receptor and 5-HT_1A receptors levels, measured by autoradiography in different brain areas. However, a significant decrease in the ability of both, the 5-HT_1A receptor agonist (±)-8-OH-DPAT and the 5-HT_2A/C receptor agonist (−)DOI, to stimulate [³⁵S]GTPγS binding was detected in the hippocampal CA₁ area and fronto-parietal cortex of CB₁ receptor knockout mice, respectively. This study provides evidence that CB₁ receptors are involved in the regulation of serotonergic responses mediated by 5-HT_2A/C and 5-HT_1A receptors, and suggests that a reduced coupling of 5-HT_1A and 5-HT_2A receptors to G proteins might be involved in these effects.     

5-HT activates ERK MAP kinase in cultured-human peripheral blood mononuclear cells via 5-HT1A receptors

In the present work, we tested the hypothesis that serotonin (5-hydroxytryptamine = 5-HT) might activate the extracellular signal-regulated kinase (ERK) pathway in human peripheral blood mononuclear cells (PBMC). PBMC were maintained in culture for 72 hrs at 37 degrees C prior to the addition of 5-HT. Our results showed an increase in ERK activation by 5-HT with a peak effect at 30 min and maximal stimulation with 5-HT at 1microM. This activation of ERK did not occur in adherent monocytes suggesting that the effect was on lymphocytes. In addition, p38 MAP kinase was not activated under these conditions. The effect of 5-HT on ERK activation appeared to be mediated through the activation of 5-HT1A receptors since similar results were obtained with R-+-8-hydroxy-DPAT, a selective 5-HT1A receptor agonist and WAY100635, a selective 5-HT1A receptor antagonist, reversed the 5-HT and the R-+-8-hydroxy-DPAT effects. Results from Western blot analysis confirmed the presence of 5-HT1A receptors on the PBMC. A 5-HT2A antagonist, ketanserin, and a 5-HT transport inhibitor, fluoxetine, both failed to block the activation of ERK by 5-HT. Our results indicate that 5-HT activates ERK, but not p38, MAP kinase of human PBMC via a 5-HT1A receptor.     

Evidence that reciprocal hindlimb scratching elicited in mice by intrathecal administration of muscarinic agonists is mediated through M1 type receptors

Intrathecal (IT) administration of pilocarpine to mice produces a vigorous and dose-related reciprocal hindlimb scratching (RHS) response (ED50 = 0.6 microgram) that is potently blocked by simultaneous IT administration of atropine (ID50 = 0.002 microgram). We now report that RHS is (1) also elicited by the more selective M1 agonist McN-A-343-11 (ED50 = 11.6 micrograms), (2) blocked by the selective M1 antagonist pirenzepine (ID50 = 0.001 microgram), and (3) is not blocked by the selective M2 antagonist AF-DX 116 BS at a dose up to 100 times the ID50 dose of pirenzepine. These results extend our earlier findings and suggest that the RHS elicited in mice by IT injection of muscarinic agonists is mediated through pirenzepine-sensitive (presumably M1) receptors and that RHS may be a convenient in vivo centrally mediated M1 endpoint.     

Molecular dynamics of buspirone analogues interacting with the 5-HT1A and 5-HT2A serotonin receptors

Three-dimensional (3-D) models of the human serotonin 5-HT1A and 5-HT2A receptors were constructed, energy refined, and used to study the interactions with a series of buspirone analogues. For both receptors, the calculations showed that the main interactions of the ligand imide moieties were with amino acids in transmembrane helix (TMH) 2 and 7, while the main interactions of the ligand aromatic moieties were with amino acids in TMH5, 6 and 7. Differences in binding site architecture in the region of highly conserved serine and tyrosine residues in TMH7 gave slightly different binding modes of the buspirone analogues at the 5-HT1A and 5-HT2A receptors. Molecular dynamics simulations of receptor-ligand interactions indicated that the buspirone analogues did not alter the interhelical hydrogen bonding patterns upon binding to the 5-HT2A receptor, while interhelical hydrogen bonds were broken and others were formed upon ligand binding to the 5-HT1A receptor. The ligand-induced changes in interhelical hydrogen bonding patterns of the 5-HT1A receptor were followed by rigid body movements of TMH2, 4 and 6 relative to each other and to the other TMHs, which may reflect the structural conversion into an active receptor structure.     

Novel 5-HT(1A/1B/1D) receptors antagonists with potent 5-HT reuptake inhibitory activity

Novel 2-methyl-5-quinolinyl-1-piperazinylalkyl-3,4-dihydro-2H-1,4-benzoxazin-3-ones showing high affinities for the 5-HT(1A/1B/1D) receptors coupled with potent 5-HT reuptake inhibitory activity have been discovered. This is the first report describing docking of the lead compound 6-{2-[4-(2-methyl-5-quinolinyl)-1-piperazinyl]ethyl}-2H-1,4-benzoxazin-3(4H)-one 1, into a model of the 5-HT transporter and the 5-HT(1A) receptor model.     

Effect of long-term cold adaptation on the mRNA expression of serotonin 5-HT1A and 5-HT2A receptors

The mRNA expression of serotonin receptors 5-HT1A and 5-HT2A was investigated by the quantitative method RT-PCR in rats adapted to cold (5 weeks at +4 -(+6) degrees C) and in control (5 weeks at +20-22 degrees C). Four brain regions were examined: frontal cortex, hypothalamus, hippocampus, and midbrain. The influence of cold adaptation on the mRNA expression of 5-HT15 receptor was not found to be absent. The mRNA expression of 5-HT2A receptor changed under long-term cold exposure. These changes in different brain regions were various: in hypothalamus, there was an increase of the 5-HT2A receptor mRNA expression; in the cortex, a decrease; in the hippocampus and midbrain, significant changes of the mRNA expression were absent. The findings appear bo te adaptive and, according to their localization in the central nervous system, regulatory. They also suggest involvement of brain serotoninergic system in mechanism of adaptive reorganization of temperature regulation.     

Target size analysis of serotonin 5-HT1 and 5-HT2 receptors in bovine brain membranes

Freeze-dried crude synaptic membranes prepared from bovine cerebral cortex and striatum were exposed to high energy gamma ray from the source of 60Co. The size of serotonin 5-HT1 receptors labeled by [3H]serotonin and that of 5-HT2 receptors labeled by [3H]spiperone or [3H]ketanserin was determined by target size analyses. The values were 57,000 daltons, 145,000 daltons and 152,000 daltons for the cerebral cortex and 56,000 daltons, 141,000 daltons and 150,000 daltons for the striatum, respectively. The estimated sizes were deduced by reference to enzyme standards with known molecular masses and which were irradiated in parallel. Our results demonstrate that the molecular entities in situ for 5-HT1 receptors are distinct from those for 5-HT2 receptors, thus supporting data on the existence of two distinct populations of serotonin receptors, hitherto evidenced physiopharmacologically.     

gamma-Carbolines: binding at 5-HT5A serotonin receptors

Screening of various agents resulted in the identification of 5-methyl-1,2,3,4-tetrahydro-gamma-carboline (1; K(i)=5,300 nM) as a compound with modest affinity for mouse 5-HT(5A) receptors. Structure-affinity studies were conducted resulting in 5-methyl-2-[3-(4-fluorophenoxy)propyl]-1,2,3,4-tetrahydro-gamma-carboline (17; K(i)=13 nM). Although 17 also binds at 5-HT(2) receptors, it serves as a novel lead for the further development of 5-HT(5A) ligands.     

Blockade of striatal 5-HT2 receptors produces retrograde amnesia in rats

We have recently reported that intrastriatal administration of the serotonin (5-HT) releasing drug p-chloroamphetamine, and of 5-HT itself, produces a significant retention deficit of inhibitory avoidance. It is not known which of the 5-HT receptors are involved in the amnesic effect of serotonin. The present experiment was aimed at determining whether 5-HT2 receptors within the striatum are involved in memory consolidation. Ketanserine (0.5, 1.0, 2.0, or 4.0 ng) was infused bilaterally into the striatum of Wistar rats immediately after training of inhibitory avoidance, and retention of the task was measured 24 h later. A dose-dependent retention deficit was found. Together with the results from appropriate control groups, the results strongly suggest that striatal 5-HT2 receptors participate in memory consolidation of this aversive task.     

Sympathoinhibition from ventrolateral periaqueductal gray mediated by 5-HT(1A) receptors in the RVLM

The role of 5-hydroxytryptamine 1A (5-HT(1A)) receptors located in the rostral ventrolateral medulla (RVLM) in the mediation of a sympathoinhibitory and depressor response elicited from the ventrolateral periaqueductal gray (vlPAG) matter of the midbrain was examined in pentobarbital sodium-anesthetized rats. Activation of neurons in the vlPAG evoked a decrease in renal and lumbar sympathetic nerve activities and a decrease in arterial blood pressure. After microinjection of the specific 5-HT(1A)-receptor antagonist WAY-100635 into the pressor area of the RVLM, the vlPAG-evoked sympathoinhibition and hypotension was attenuated to control levels (7 of 15 animals) or converted into a sympathoexcitation and pressor response (8 of 15 animals). Baroreflex inhibition of sympathetic nerve activity was not impaired by microinjection of WAY into the sympathoexcitatory region of the RVLM. These data suggest that sympathoinhibition and hypotension elicited by activation of neurons in the vlPAG are mediated by 5-HT(1A) receptors in the RVLM.