5-HT2受体介导大鼠DRG神经元膜GABA-激活电流的增强作用

目的探讨5-HT对大鼠DRG神经元膜GABA-激活电流的调节作用及其机制。方法在新鲜分离的大鼠DRG神经元标本上，以全细胞膜片钳技术记录膜电流，用排管快速换液装置行胞外给药，以胞内透析技术分析信号转导途径。结果给予GABA可使多数受检细胞产生浓度依赖性内向电流(I_GABA)。预加5-HT，可使I_GABA增加。此效应可被5-HT₂受体特异性激动剂α-methyl-5-HT(1×10^-6 mol·L^-1)所模拟，被5-HT₂受体选择性拮抗剂cyproheptadine所阻断。在部分细胞，5-HT本身可引起由5-HT₃受体介导的快速内向电流，但并未发现该电流与5-HT对I_GABA的增强作用有必然的联系。从GABA激活电流的量效曲线可见，预加5-HT后和对照曲线相比，阈浓度不变、EC₅₀值相近，I_GABA最大值增加33.6%。胞内透析GDP-β-S或H-7可取消5-HT增强I_GABA的效应，而透析H-9无效。结论5-HT可增强GABA-激活电流，其机制为5-HT₂受体激活后通过PKC引起GABA_A受体胞内磷酸化所致。     

Anxiolytic-like effect of a serotonergic ligand with high affinity for 5-HT1A, 5-HT2A and 5-HT3 receptors

S-(-)-2-[[4-(napht-1-yl)piperazin-1-yl]methyl]-1,4-dioxoperhydropyrrolo[1,2-alpha]-pyrazine (CSP-2503) is a serotonin (5-HT) receptor ligand with selectivity and high affinity for 5-HT1A, 5-HT2A and 5-HT3 receptors. CSP-2503 reduced rectal temperature and 5-HT neuronal hypothalamic activity in mice, decreased electrical activity of raphe nuclei cells in rats and blocked the enhancement of adenylate cyclase activity induced by forskolin in HeLa cells transfected with the human 5-HT1A receptor. This compound also blocked head-twitches induced by the 5-HT(2A/2C) receptor agonist 2,5-dimethoxy-4-iodoamphetamine (DOI). Contractions of guinea pig ileum induced by the 5-HT3 receptor agonist 2-methyl-5-HT were prevented by CSP-2503. Moreover, it reduced the bradycardia reflex induced by 2-methyl-5-HT in anaesthetized rats. In the light/dark box and social interaction tests, CSP-2503 presented anxiolytic activity, an action shared by 5-HT1 agonists and 5-HT3 antagonists. Taken together, these results suggest that CSP-2503 is a new 5-HT1 receptor agonist with 5-HT2A and 5-HT3)receptor antagonist activities that might be useful in a number of conditions associated with anxiety.     

5-HT2受体介导大鼠DRG神经元膜GABA-激活电流的增强作用

目的　探讨 5 HT对大鼠DRG神经元膜GABA 激活电流的调节作用及其机制。方法　在新鲜分离的大鼠DRG神经元标本上,以全细胞膜片钳技术记录膜电流,用排管快速换液装置行胞外给药,以胞内透析技术分析信号转导途径。结果　给予GABA可使多数受检细胞产生浓度依赖性内向电流 (IGABA)。预加 5 HT,可使IGABA增加。此效应可被 5 HT2受体特异性激动剂α methyl 5 HT( 1×10-6mol·L-1 )所模拟,被 5 HT2受体选择性拮抗剂cyproheptadine所阻断。在部分细胞, 5 HT本身可引起由 5 HT3受体介导的快速内向电流,但并未发现该电流与 5 HT对IGABA的增强作用有必然的联系。从GABA激活电流的量效曲线可见,预加 5 HT后和对照曲线相比,阈浓度不变、EC50值相近,IGABA最大值增加 33. 6%。胞内透析GDP β S或H 7可取消 5 HT增强IGABA的效应,而透析H 9无效。结论　5 HT可增强GABA 激活电流,其机制为 5 HT2受体激活后通过PKC引起GABAA受体胞内磷酸化所致。     

mCPP-induced hyperactivity in 5-HT2C receptor mutant mice is mediated by activation of multiple 5-HT receptor subtypes

The serotonin receptor agonist mCPP induces hyperlocomotion in 5-HT2C receptor knockout (KO) mice or in the presence of a 5-HT2C receptor antagonist. In the present group of experiments, we evaluate the role of 5-HT1A, 5-HT1B and 5-HT2A receptors in mCPP-induced hyperactivity in 5-HT2C KO mice. We also assess the ability of agonists at these receptors to induce hyperactivity in wildtype (WT) mice pre-treated with a selective 5-HT2C receptor antagonist. As previously reported, mCPP (3 mg/kg) induced hyperactivity in 5-HT2C KO mice. A combination of the 5-HT1B receptor agonist CP-94,253 (20 mg/kg) and the 5-HT1A receptor agonist 8-OH-DPAT (0.5 mg/kg) induced marked hyperactivity in WT but not in 5-HT2C KO mice, nor in mice treated with the selective 5-HT2C receptor antagonist, SB 242084 (1.5 mg/kg). Neither CP-94,253 nor 8-OH-DPAT had any intrinsic effect on locomotion in WTs. mCPP-induced hyperactivity was attenuated in 5-HT2C KO mice by the 5-HT1B receptor antagonist SB 224289 (2.5 mg/kg), and the 5-HT2A receptor antagonists ketanserin (0.3 mg/kg) and M100907 (0.01 mg/kg) but not by the 5-HT1A receptor antagonist WAY 100635 (1 mg/kg). The 5-HT(2A/2B/2C) receptor agonist, Ro 60-0175 (3 mg/kg), induced a modest increase in locomotor activity in WT mice pre-treated with SB 242084. However, the combination of Ro 60-0175 with CP-94,253 induced a substantial increase in activity in 5-HT2C KO mice, an effect comparable to mCPP-induced hyperactivity. Thus, joint activation of 5-HT1A and 5-HT1B receptors stimulates locomotion in WT mice but this response is dependent on a functional 5-HT2C receptor population and hence is absent in 5-HT2C KO mice. By contrast, mCPP-induced hyperactivity depends on the inactivation of a separate 5-HT2C receptor population and is mediated by 5-HT2A and 5-HT1B receptor activation.     

Competitive antagonism by recognised 5-HT2 receptor antagonists at 5-HT1C receptors in pig choroid plexus

Summary The effects of several antagonists, known to interact with 5-HT₂ receptors (ritanserin, LY 53857, ICI 169,369, methysergide, mesulergine and ketanserin), were tested against 5-HT-stimulated production of inositol phosphate in pig choroid plexus, a 5-HT_1C receptor model. These antagonists produced dextral shifts of the concentration response curve to 5-HT in a parallel manner, without depressing significantly the maximal response. The following pA₂ values (in parentheses) were obtained: mesulergine (8.88), methysergide (8.85), LY 53857 (8.69), ritanserin (8.69), ICI 169,369 (7.86), and ketanserin (6.57). These pA₂ values were in good agreement with the pK_D values determined in radioligand binding studies performed in pig choroid plexus with [³H]mesulergine. The present data demonstrate that several drugs described as 5-HT₂ receptor selective antagonists (e.g. ritanserin, LY 53857 and ICI 169,369) are also potent, competitive and surmountable antagonists at 5-HT_1C receptors. Thus, the results provide further evidence for the pharmacological similarity of 5-HT_1C and 5-HT₂ receptors. However, in contrast to the situation described with methysergide, ritanserin and LY 53857 in several 5-HT₂ receptor models, none of these antagonists acted in a non-competitive or unsurmountable fashion at 5-HT_1C receptors. These results suggest, but do not firmly rule out, that at least in the presence of the drugs tested in the present study, 5-HT_1C receptors in the choroid plexus do not undergo an allosteric modulation; these findings are apparently in contrast to a model proposed previously for 5-HT₂ receptors (Kaumann and Frenken 1985, Naunyn-Schmiedeberg's Arch Pharmacol 328: 295–300) Send offprint requests to P. Schoeffter at the above address     

5-HT7, but not 5-HT2B, receptors mediate hypotension in vagosympathectomized rats

This study evaluated the possible involvement of 5-HT(2B) receptors in long-lasting hypotension to 5-hydroxytryptamine (5-HT), which is predominantly mediated by 5-HT7 receptors, in anaesthetised vagosympathectomized rats. Intravenous injections of 5-HT and 5-carboxamidotryptamine (5-CT) elicited a dose-dependent hypotension that was dose-dependently antagonised by (R)-1-[(3-hydroxyphenyl)sulfonyl]-2-[2-(4-methyl-1-piperidinyl) ethyl] pyrrolidine (SB-269970; a selective 5-HT7 receptor antagonist), but not by saline. Interestingly, alpha-methyl-5-(2-thienylmethoxy)-1H-indole-3-ethanamine (BW723C86; a 5-HT(2B) receptor agonist) produced vasopressor responses without affecting hypotension to 5-HT. These results suggest that hypotension to 5-HT and 5-CT is mainly mediated by 5-HT7 receptors, whilst the role of 5-HT(2B) receptors seems unlikely.     

Lithium decreases 5-HT1A and 5-HT2 receptor and α2-adrenoreceptor mediated function in mice

Lithium administration (LiCl, 10 mmol/kg, SC on day 1, followed by 3 mmol/kg twice daily subsequently) for 14 days to mice produced attenuation of the hypothermic response to injection of 8-hydroxy-2-(di-n-propyla-mino)tetralin (8-OH-DPAT, 0.5 mg/kg SC). Head twitch responses to the 5-HT-receptor agonist 5-methoxy-N,N-dimethyltryptamine (2.5 mg/kg IP) and to precursor loading with carbidopa (25 mg/kg, IP) and 5-hydroxytryptophan (100 mg/kg IP) were similarly attenuated. By contrast with this reduction of 5-hydroxytryptamine (5-HT) function mediated by the 5-HT_1A and 5-HT₂ receptor sub-types, repeated lithium administration had no effect on the motor response to a putative 5-HT_1B receptor agonist 5-methoxy-3(1,2,3,6-tetrahydropyridin-4-yl)1H indole (RU 24969, 3 mg/kg IP). Alpha₂ adrenoceptor function, assessed by the sedation response to clonidine (0.25 mg/kg, IP), was also attenuated by repeated lithium administration. It is proposed that these actions may explain the emergence of lithium as an adjunct to the treatment of refractory depressive illness.     

Molecular structural basis of ligand selectivity for 5-HT2 versus 5-HT1C cortical receptors

Summary A molecular structural criterion of ligand selectivity for the 5-HT₂ versus 5-HT_1C receptor was hypothesized on the basis of radioligand binding data. Despite the large number of compounds which have been tested at both receptors, analysis of published data led to the identification of only five agents which are greater than 10-fold selective for the 5-HT₂ versus the 5-HT_1C receptor. Comparison of the two-dimensional structures revealed that, although these five compounds represent three distinct structural classes, they share a common structural feature located in the region hypothesized to be involved in receptor binding: a carbonyl or carboxyl oxygen interposed spatially between an aromatic ring and nitrogen atom. This structural feature was used to predict the relative selectivity of compounds that had not previously been analyzed at both the 5-HT₂ and 5-HT_1C receptors.All six drugs tested which contain the identified reactive carbonyl or carboxyl group were found to be selective for the 5-HT₂ versus the 5-HT_1C receptor with selectivity ratios ranging from 26 to 380. By contrast, three agents which are structurally similar but do not contain the reactive carbonyl or carboxyl group displayed equally high affinity for both receptor binding sites. Since the physiological roles of the 5-HT₂ and 5-HT_1C receptor are markedly different, it would be of potential clinical and scientific value to utilize this molecular structural feature to further identify chemical compounds which would selectively interact with only one of the two receptors. Send offprint requests to S. J. Peroutka at the current address     

Potentiation of the effects of raclopride on sucrose consumption by the 5-HT2 antagonist ritanserin

We examined the effects on sucrose consumption of a dopamine (DA) D₂/D₃ antagonist (raclopride, 0–0.3 mg/kg), a serotonin 5-HT_2/2c antagonist (ritanserin, 0–0.4 mg/kg), and raclopride (0.15 mg/kg) combined with ritanserin (0–0.4 mg/kg). Three different concentrations of sucrose solution (0.7%, 7.0% and 34%) were tested. The concentration-intake function in drug-free rats was an inverted-U, with 7.0% sucrose supporting the highest intake. Raclopride (0.3 mg/kg) inhibited intake of 7.0% sucrose, but its effect on 0.7% sucrose fell short of significance (P<0.06) and intake of 34% sucrose was unchanged. Ritanserin did not affect sucrose intake when given on its own, but synergized with a previously ineffective dose of raclopride (0.15 mg/kg) so as to cause a significant inhibition of 7.0% sucrose intake and increase in 34% sucrose intake. These data indicate that 5-HT₂ antagonism potentiated the behavioural effects of raclopride and we speculate that this interaction might contribute to the efficacy of atypical neuroleptic drugs.     

An examination of the behavioural specificity of hypophagia induced by 5-HT1B, 5-HT1C and 5-HT2 receptor agonists using the post-prandial satiety sequence in rats

Previous studies have shown that administration of 5-HT_1B, 5-HT_1C or 5-HT₂ agonists decreases food intake in rats. However, it has not been established whether these drugs induce satiety or decrease feeding by a non-specific mechanism. In the present study the post-prandial satiety sequence was used to characterise the actions of the 5-HT₂ receptor agonist, 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI), the 5-HT_1B/5-HT_1C receptor agonists, 1-(3-chorophenyl) piperazine (mCPP) and 1-[3-(trifluoromethyl)phenyl] piperazine (TFMPP), and the 5-HT_1B agonist, 5-methoxy-3-(1,2,3,6-tetrahydro-4-pyridinyl)H-indole (RU 24969), on feeding in rats. All four compounds reduced food intake in rats that had been food deprived overnight. The 5-HT_1B/5-HT_1C agonists, TFMPP (at a dose of 1.0 mg/kg) and mCPP (at a dose of 3.0 mg/kg), appeared to produce satiety as their effects on the satiety sequence were similar to those induced by a food pre-load. In contrast, the 5-HT_1B agonist RU 24969 and the 5-HT₂ agonist DOI did not produce behavioural profiles that resembled satiety. Thus, RU 24969 elevated active behaviours and did not accelerate resting whereas DOI appeared to induce hypophagia by a non-specific fragmentation of behaviour. The results suggest that simultaneous activation of 5-HT_1B and 5-HT_1C receptors may be sufficient to elicit behaviourally specific satiety in the rat. In contrast, selective activation of 5-HT₂ receptors does not induce satiety but elicits active behaviours and decreases feeding by response competition.     

Bradykinin potentiates 5-HT3 receptor-mediated current in rat trigeminal ganglion neurons

AIM: To explore the modulatory effect of bradykinin (BK) on 5-HT(3 )receptor-mediated current in trigeminal ganglion (TG) neurons in rats. METHODS: The whole-cell patch-clamp technique was used to record 5-HT-activated currents (I(5-HT)) in neurons freshly dissociated from rat TG. Drugs were applied by rapid solution exchange. RESULTS: The majority of the neurons examined responded to 5-HT applied externally with an inward current (76.3%, 74/97) that could be blocked by the 5-HT(3 )receptor antagonist, ICS-205,930 (10(-6) mol/L). In 66 of the 74 cells sensitive to 5-HT (89.2%), pretreatment for 30 s with BK (10(-6)-10(-10) mol/L) could potentiate I(5-HT) with the maximal modulatory effect occurring at 10(-7) mol/L BK (71.6%+/-4.9%). BK shifted the 5-HT concentration-response curve upwards with an increase of 68.9%+/-7.2% in the maximal current response, but with no significant change in the EC(50) value (19.1+/-3.2 mumol/L vs 20.9+/-3.5 micromol/L; t-test, P>0.05; n=8). BK potentiated I(5-HT) in a holding potential-independent manner and did not alter the reverse potential of I(5-HT). This BK-induced potentiation of I(5-HT) was almost completely blocked by Hoe 140 (5*10(-7) mol/L), a selective B2 BK receptor antagonist, and was removed after intracellular dialysis of GF-109203X (2 micromol/L), a selective protein kinase C (PKC) inhibitor, with the re-patch clamp. CONCLUSION: Pre-application of BK exerts an enhancing effect on I(5-HT) via a PKC-dependent pathway in rat TG neurons, which may explain the peripheral mechanism of pain and hyperalgesia caused by, for example, tissue damage and inflammation.     

Effect of 5-HT3 receptor antagonists on the discriminative stimulus properties of morphine in rats

5-HT₃ receptor antagonists, e.g. MDL72222, ondansetron and ICS205-930, have been previously reported to block a morphine (1.5 mg/kg)-induced conditioned place preference in rats. This finding suggests that these drugs may modify the morphine discriminative stimulus which underlies place conditioning. To study this further we have examined the effects of MDL72222, ondansetron and ICS205-930 against a morphine discriminative stimulus using a two-choice, food reinforced, operant paradigm. In an attempt to provide consistency with previous place conditioning studies, a morphine training dose of 1.5 mg/kg was used in addition to a higher 3 mg/kg dose which was studied in separate animals. Stimulus control of behaviour was attained at both morphine training doses, the characteristics of each being consistent with an effect at the mu opioid receptor. Ondansetron (0.001–1 mg/kg), MDL72222 (0.1–3 mg/kg), and ICS205-930 (0.001–1 mg/kg) all failed to consistently antagonise the morphine cue at both training doses, although a mild attenuation was seen in the 1.5 mg/kg group following pretreatment with an intermediate dose of ondansetron and ICS205-930 (both 0.01 mg/kg). The present results therefore suggest hat 5-HT₃ antagonists do not block a morphine discriminative state, at least in rats.     

Effects of blockade of 5-HT2 receptors and activation of 5-HT1A receptors on the exploratory activity of rats in the elevated plus-maze

Acute administration of gepirone, a 5-HT_1A agonist, caused a dose dependent (1–10 mg/kg, IP) reduction in the locomotor activity (open and closed arms) of rats tested in the elevated plus-maze. However, rats housed in individual cages and submitted to chronic treatment with gepirone (10 mg/kg PO) showed a marked increase in the percentages of number and time spent in the open arms as compared to controls. These results are compatible with the idea that the antiaversive effect due to long-term treatment with 5-HT_1A agonists is the result of a progressive desensitization of the somatodendritic 5-HT autoreceptor with the consequent recovery of firing rate of 5-HT neurons along with an activation of normosensitive postsynaptic 5-HT neurons. Ketanserin caused a biphasic effects on the exploratory behavior of rats in the plus-maze. The lower dose (0.5 mg/kg) decreased the aversion to the open arms and the higher dose (1.0 mg/kg) caused an unspecific decrease in the overall activity of the animals. Ketanserin is supposed to have antagonistic action on 5-HT₂ and on -adrenergic receptors. As prazosin (0.5–1.0 mg/kg), an -adrenergic receptor blocker, did not present any significant effect in the present work it is suggested that the effects of the lower dose of ketanserin was due to its high antagonistic action on 5-HT₂ receptors.     

Calcium modulation of 5-HT3 receptor binding and function

Calcium modulates the 5-HT₃ receptor response by reducing peak current amplitude and increasing rates of activation, deactivation and desensitisation, but the binding site(s) and mechanism(s) of this modulation are unknown. Here we study residues that may be involved in calcium binding in two partially overlapping regions of the extracellular domain (E213-E215-E218 and D204-E218-V219). The modulatory effects of calcium were assessed by radioligand binding and whole-cell patch-clamp. Comparisons of [³H]granisetron binding showed an increase in K_d in 10 mM calcium that was abolished by the substitutions E213Q, E215Q, D204N and V219L. E218Q mutant receptors displayed no specific binding or function, and immunofluorescence showed that they did not reach the cell surface. E213Q increased inherent rates of desensitisation, but the relative effects of calcium on these rates, and on the reduction in current amplitude, were similar to wild type receptors. Current responses and calcium-mediated effects at E215Q mutant receptors were indistinguishable from wild type. D204N and V219L mutants were non-functional. A calcium impermeable mutant (E277A/S297R) revealed no changes in peak amplitude or kinetics with increased calcium. Our results are consistent with residues D204, E218 and V219 participating in receptor assembly, structure and/or trafficking to the plasma membrane, and we speculate that this might rely upon the stabilising effect of bound calcium. E213, E215, D204 and V219 may contribute to a calcium binding site that is responsible for the calcium-mediated effects on ligand binding. However, the major site for calcium-dependent modulation of the 5-HT₃ current is located within the ion channel or cell interior.     

5-Hydroxytryptamine potentiates neurogenic contractions of rat isolated urinary bladder through both 5-HT(7) and 5-HT(2C) receptors

Serotonin (5-HT) enhances the neurogenic contractile response induced by electrical field stimulation (EFS) in the rat isolated urinary bladder. The aim of this study was to functionally characterize the receptors involved in this effect by using a range of 5-HT receptor subtype selective agonists and antagonists. 5-HT produced a concentration-dependent potentiation of contractile responses to EFS with a pEC₅₀ value of 6.86 ± 0.24. SB-269970 (0.01, 0.1 and 1 μM), a selective 5-HT₇ receptor antagonist, caused a concentration-dependent rightward shift of the 5-HT-induced response. The pA₂ value was 8.16 with a slope of 0.46 ± 0.08. Neither ketanserine nor SB-204741, 5-HT_2A and 5-HT_2B receptors antagonists, respectively, affected the concentration–response curve to 5-HT. However, 5-HT response was antagonized by the selective 5-HT_2C receptor antagonist SB-242084 (0.1 and 1 μM). In the presence of 1 μM of both antagonists SB-269970 and SB-242084, 5-HT response was almost fully inhibited. 5-CT, a 5-HT₇ receptor agonist, induced a biphasic concentration-dependent potentiation of neurogenic contractions. SB-269970 concentration-dependently antagonized the first phase of 5-CT response with a pA₂ value of 8.77 and a slope not significantly different from unity (0.91 ± 0.11) that suggests a competitive antagonism. WAY-161503, a 5-HT_2C receptor agonist (0.01–10 μM), induced a concentration-dependent potentiation of contractile response to EFS while DOI (a selective 5-HT_2A agonist) had no effect. SB-242084 (0.1 and 1 μM) antagonized the effect of WAY-161503 in a concentration-dependent manner. The current results demonstrate that 5-HT potentiates neurogenic contractions of rat isolated detrusor muscle through both 5-HT₇ and 5-HT_2c receptors.     

Modulation by 5-HT3 and 5-HT4 receptors of the release of 5-hydroxytryptamine from the guinea-pig small intestine

Summary The effects of agonists and antagonists of 5-hydroxytryptamine (5-HT) receptors on the release of endogenous 5-HT from enterochromaffin cells were studied in the vascularly perfused isolated guinea-pig small intestine. The experiments were done in the presence of tetrodotoxin in order to exclude a neuronally mediated influence on 5-HT release.The 5-HT₃ receptor agonist 2-methyl-5-HT increased 5-HT release, and this effect was antagonized by 1 nmol/l tropisetron. Nanomolar concentrations of tropisetron, MDL 72 222 and granisetron decreased 5-HT release. Ondansetron (0.1 and 1 mol/1) did not modify 5-HT release.5-Methoxytryptamine, BIMU8 and cisapride concentration-dependently inhibited 5-HT release. BIMU8 was more potent than 5-methoxytryptamine. Micromolar concentrations of tropisetron (1 and 10 mol/1) enhanced the release, whilst methiothepine (0.1 mol/l) did not affect the release of 5-HT.The results suggest that enterochromaffin cells of the guinea-pig ileum do not contain 5-HT₁ and 5-HT₂ receptors, but are endowed with 5-HT₃ and 5-HT₄ autoreceptors. Activation of the 5-HT₃ receptors triggers a positive feedback mechanism leading to an increase of 5-HT release. The 5-HT₃ receptors on the enterochromaffin cell differ from neuronal 5-HT3 receptors on guinea-pig myenteric plexus by their high affinity for tropisetron and MDL 72 222, and their very low affinity for ondansetron. Stimulation of 5-HT₄ receptors causes inhibition of release; the inhibitory 5-HT₄ receptor mechanism appears to predominate.Correspondence to H. Kilbinger at the above address     

On the role of brain 5-HT7 receptor in the mechanism of hypothermia: comparison with hypothermia mediated via 5-HT1A and 5-HT3 receptor

Intracerebroventricular administration of selective agonist of serotonin 5-HT₇ receptor LP44 (4-[2-(methylthio)phenyl]-N-(1,2,3,4-tetrahydro-1-naphthalenyl)-1-pyperasinehexanamide hydrochloride; 10.3, 20.5 or 41.0 nmol) produced considerable hypothermic response in CBA/Lac mice. LP44-induced (20.5 nmol) hypothermia was significantly attenuated by the selective 5-HT₇ receptor antagonist SB 269970 (16.1 fmol, i.c.v.) pretreatment. At the same time, intraperitoneal administration of LP44 in a wide range of doses 1.0, 2.0 or 10.0 mg/kg (2.0, 4.0, 20.0 μmol/kg) did not cause considerable hypothermic response. These findings indicate the implication of central, rather than peripheral 5-HT₇ receptors in the regulation of hypothermia. The comparison of LP44-induced (20.5 nmol) hypothermic reaction in eight inbred mouse strains (DBA/2J, CBA/Lac, C57BL/6, BALB/c, ICR, AKR/J, C3H and Asn) was performed and a significant effect of genotype was found.In the same eight mouse strains, functional activity of 5-HT_1A and 5-HT₃ receptors was studied. The comparison of hypothermic responses produced by 5-HT₇ receptor agonist LP44 (20.5 nmol, i.c.v.) and 5-HT_1A receptor agonist 8-OH-DPAT 1.0 mg/kg, i.p. (3.0 μmol/kg), 5-HT₃ receptor agonist m-CPBG (40.0 nmol, i.c.v.) did not reveal considerable interstrain correlations between 5-HT₇ and 5-HT_1A or 5-HT₃ receptor-induced hypothermia. The selective 5-HT₇ receptor antagonist SB 269970 (16.1 fmol, i.c.v.) failed to attenuate the hypothermic effect of 8-OH-DPAT 1.0 mg/kg, i.p. (3.0 μmol/kg) and m-CPBG (40.0 nmol, i.c.v.) indicating that the brain 5-HT₇ receptor is not involved in the hypothermic effects of 8-OH-DPAT or m-CPBG. The obtained results suggest that the central 5-HT₇ receptor plays an essential role in the mediation of thermoregulation independent of 5-HT_1A and 5-HT₃ receptors.     

Inhibition by 5-HT3 receptor antagonists of release of cholecystokinin-like immunoreactivity from the frontal cortex of freely moving rats

Summary Effects of the 5-HT₃ receptor antagonists, ondansetron and tropisetron, on the release of cholecystokipin-like immunoreactivity (CCK-LI) in rat frontal cortex were investigated in conscious, unrestrained rats using intracerebral microdialysis. The release of CCK-LI was augmented by perfusion with 100 g/ml veratrine and was fully Ca²⁺-dependent and tetrodotoxin-sensitive. Ondansetron and tropisetron, each at 0.1–1 mol/l, decreased concentration-dependently the veratrine-evoked efflux of CCK-LI. The reduction of CCK-LI output was approximately 30%u when the antagonists were infused at 0.1 mol/l.The data suggest that 5-HT₃ receptor antagonists prevent the release of CCK evoked by endogenous 5-hydroxytryptamine. These drugs may thus represent a novel therapeutic approach in disease states, like anxiety, in which an inappropriately high release of brain CCK or 5-hydroxytryptamine seems to be involved.Correspondence to M. Raiteri at the above address