Differential Sensitivity to 8‐Hydroxy‐2‐(di‐n‐propylamino)tetralin‐Induced Corticosterone Secretion and Hypothermia between Sprague‐Dawley Rats from Different Breeding Colonies

Abstract: The sensitivity of Sprague‐Dawley rats from 4 different breeding colonies (ALAB, M&B, B&K, Charles River) and one breeding colony of Wistar rat (M&B) to the 5‐hydroxytryptamine_1A (5‐HT_1A) receptor stimulatory effect of 8‐hydroxy‐2‐(di‐n‐propylamino)tetralin hydrobromide (8‐OH‐DPAT) resulting in corticosterone secretion and hypothermia was compared. The dose‐response curves of the increase in plasma corticosterone showed that ALAB and M&B rats were 3.5 times more sensitive to 8‐OH‐DPAT than B&K and Charles River rats, the Wistar rats being in between. The attenuation of the corticosterone response 24 hr after a single injection of 1 mg/kg 8‐OH‐DPAT was greater for the ALAB and M&B rats than for B&K, Charles River and Wistar rats. The comparison of the 8‐OH‐DPAT‐induced hypothermia in the various rat colonies showed a similar pattern: the sensitivity of ALAB rats was about twice that of M&B, B&K and Wistar rats, Charles River rats being 9 times less sensitive. The attenuation of the response 24 hr after 1 mg/kg 8‐OH‐DPAT measured as the shift in dose‐response showed similar shift factors (4.1 to 6.7) for all rat colonies except for the B&K rats (3.0). The hypothermic response at 0.1 mg/kg 8‐OH‐DPAT was significantly lower for the Charles River and B&K rats than for the ALAB rats. Similarly was the maximal attenuation of the hypothermic effect in these rats less than half of that of the ALAB rats. The possible cause of the observed differences in the response to 8‐OH‐DPAT between these rat colonies is discussed in terms of receptor reserves and the involvement of other transmitter systems in the responses.     

Counteraction of the rapid tolerance to 8-hydroxy-2-(di-n-propylamino)tetralin-induced hypothermia in rats by activation of the GABAA receptor-chloride channel complex

The effects of compounds that open the GABAA receptor-chloride channel complex on the rapidly developed tolerance to the 8-hydroxy-2-(di-n-propylamino)tetralin hydrobromide(8-OH-DPAT)-induced hypothermia in rats were examined. The test compound was injected 15 min. before 1 mg/kg subcutaneous 8-OH-DPAT or saline and 24 hr later a challenge dose of 0.1 mg/kg subcutaneous 8-OH-DPAT was given. The rectal temperature was measured before the challenge dose and 30, 60, 90 and 120 min. thereafter. The hypothermic effect was calculated as the area under the curve. It was found that all the GABAergic compounds examined significantly counteracted the 8-OH-DPAT-induced tolerance to the hypothermic response: muscimol at 3 mg/kg subcutaneous, diazepam at 1 - 3 mg/kg subcutaneous, pentobarbitone sodium at 20 mg/kg subcutaneous, and chlormethiazole at 40 mg/kg subcutaneous. Combined treatment of the rats with the GABAA receptor antagonist, bicucculine, or the GABAA receptor-chloride channel blocker, picrotoxin and diazepam, pentoparbitone sodium or chlormethiazole significantly antagonised this counteraction of the 8-OH-DPAT-induced tolerance. Depletion of 5-HT by pretreatment of the rats with the tryptophan hydroxylase inhibitor p-chlorophenylalanine did not counteract the 8-OH-DPAT-induced tolerance to the hypothermic response. Pretreatment of the rats with dexamethazone did not change the development of the tolerance to 8-OH-DPAT-induced hypothermic effect which seems to exclude the involvement of the hypothalamo-pituitary-adrenocortical axis in the tolerance development. It is concluded that the results support the hypothesis that GABA neurones beyond the 5-HT neurones are involved in the mechanism causing tolerance to the 5-HT1A receptor-mediated hypothermia in rats.     

Characterization of the dopamine D3 receptor agonist R(+)‐7‐hydroxy‐N,N‐di‐n‐propyl‐2‐aminotetralin‐induced hypo‐ and hypermotility in mice

The present study was designed to characterize the dopamine D₃ receptor agonist R(+)‐7‐hydroxy‐N,N‐di‐n‐propyl‐2‐aminotetralin (R(+)‐7‐OH‐DPAT)‐induced changes in locomotor activity in mice. Although R(+)‐7‐OH‐DPAT (0·01–10 mg/kg) produced a significant decrease in horizontal and vertical motility within 15 min after the start of behavioural measurements, the dopamine D₁ receptor antagonist R(+)‐SCH23390 (0·05 mg/kg) and the dopamine D₃ receptor antagonist (+)‐UH232 (10 mg/kg) had no antagonistic effects on the R(+)‐7‐OH‐DPAT (3 mg/kg)‐induced hypomotility, while the dopamine D₂ receptor antagonist S(−)‐sulpiride (20 mg/kg) augmented it. Although R(+)‐7‐OH‐DPAT (0·01–1 mg/kg) had no marked effects on horizontal or vertical motility, higher doses (3 and 10 mg/kg) of the drug produced a significant increase in horizontal or vertical motility from 30 to 90 min after the start of the behavioural measurements. S(−)‐sulpiride (20 mg/kg) and (+)‐UH232 (10 mg/kg) almost completely inhibited the R(+)‐7‐OH‐DPAT (3 mg/kg)‐induced hypermotility, whereas the antagonistic effects of R(+)‐SCH23390 (0·05 mg/kg) were partial. These results suggest that the R(+)‐7‐OH‐DPAT‐induced hypermotility is mediated principally via dopamine D₂ and D₃ receptors, whereas it is unlikely that the hypomotility results from the activation of presynaptic dopamine D₂ or D₃ receptors. Copyright © 1999 John Wiley & Sons, Ltd.     

Augmentative effect of spinosin on pentobarbital-induced loss of righting reflex in mice associated with presynaptic 5-HT1A receptor

Objectives This study investigated whether spinosin potentiates pentobarbital‐induced loss of righting reflex (LORR) in mice via 5‐HT_1A receptors. Methods Our primary endpoint for sedation was LORR. In addition, the basal rectal temperature was measured. Key findings The results demonstrated that the 5‐HT_1A agonist 8‐OH‐DPAT (s.c.) induced reductions in duration of LORR at 0.1, 0.5 and 1.0 mg/kg (P < 0.01), and prolongation of LORR latency at 0.5 and 1.0 mg/kg (s.c., P < 0.01) in pentobarbital (45 mg/kg, i.p.)‐treated mice. This effect of 8‐OH‐DPAT was antagonized either by 5‐HT_1A antagonist p‐MPPI (5 mg/kg, i.p.) or by spinosin (15 mg/kg, i.g.) with significance, respectively. Co‐administration of spinosin and p‐MPPI both at ineffective doses (spinosin at 5.0 mg/kg, i.g. and p‐MPPI at 1.0 mg/kg, i.p.) showed significant augmentative effects in reducing latency to LORR, and increasing LORR duration (P < 0.01) in pentobarbital‐treated mice. On the other hand, spinosin inhibited 8‐OH‐DPAT‐induced hypothermia, which has been generally attributed to the activation of somatodendritic 5‐HT_1A autoreceptors in mice. Conclusions Based on our previous results and the present data, it should be presumed that presynaptic 5‐HT_1A autoreceptor mechanisms may be involved in the inhibitory effect of spinosin on 8‐OH‐DPAT‐induced hypothermia and also in the potentiating effect of spinosin on pentobarbital‐induced LORR in mice.     

Synthesis and Evaluation of a Series of 3,4,5‐Trimethoxycinnamic Acid Derivatives as Potential Antinarcotic Agents

A series of 3,4,5‐trimethoxycinnamic acid derivatives was prepared and evaluated for antinarcotic effects on morphine dependence in mice and binding affinities on serotonergic receptors. The key synthetic strategies involve generation of ketones 6–7 , esters 9–12 through condensation reaction, and amides 13–19 via coupling reaction using 1‐hydroxybenzotriazole/ethyl(dimethylaminopropryl)carbodiimide system in high yield. We found that the naloxone‐induced morphine withdrawal syndrome was significantly suppressed by new synthetic 3,4,5‐trimethoxycinnamic acid derivatives (20 mg/kg/day). Most of 3,4,5‐trimethoxycinnamic acid derivatives were found to have high affinity to 5‐HT_1A receptor. The naloxone‐induced morphine withdrawal syndrome was attenuated by (+)8‐OH‐DPAT (0.1 mg/kg/day, i.p.), a 5‐HT_1A receptor agonist. In cortical neuronal cells, (+)8‐OH‐DPAT (1 μm ) produced an elevation of the pERK 1/2 expression, and the elevated pERK levels were inhibited by WAY 100635, a 5‐HT_1A receptor‐specific antagonist. Interestingly, the pERK levels were increased by the 3,4,5‐trimethoxycinnamic acid derivatives and the derivatives‐mediated changes in pERK levels were blocked by the WAY 100635. These results suggested that new synthetic 3,4,5‐trimethoxycinnamic acid derivatives have a potential antinarcotic effect through acting as a 5‐HT_1A receptor agonist in mice.     

Biochemical profile of anseculin (KA‐672) at different brain receptors

Anseculin (KA‐672) is a multifunctional antidementia agent under development that may be of therapeutic value in the treatment of progressive neuronal and cognitive decline, which are common in Alzheimer disease. In vitro and ex vivo experiments have characterized anseculin as a potent functional antagonist of central α₁‐adrenoceptors. In comparison to prazosin, the in vitro potency of anseculin for α₁‐adrenoceptors is about 8 times less. Like prazosin, anseculin shows an inhibition of phenylephrine‐ (norepinephrine‐) induced accumulation of inositol phosphates. Oral treatment with 1 mg/kg anseculin or 1 mg/kg prazosin show similar effects on α₁‐adrenergic receptor binding ex vivo, indicating a greater ex vivo potency of anseculin on central α₁‐adrenergic receptors. Anseculin has only weak affinity for central muscarinic cholinergic receptors. Anseculin inhibited adenylate cyclase and reduced intracelluar cAMP levels of about 30%, similar to the 5‐HT_1A agonist, 8‐OH‐DPAT. Together with its high affinity for 5‐HT_1A receptors (IC₅₀ for ³H‐8‐OH‐DPAT binding is about 8 nM), these data suggest that anseculin also exhibits 5‐HT_1A agonistic properties. Drug Dev. Res. 55:187–196, 2002. © 2002 Wiley‐Liss, Inc.     

Discriminative stimulus properties of idazoxan: mediation by both α2 adrenoceptor antagonism and 5‐HT1A receptor agonism

Idazoxan is reference α₂ adrenoceptor antagonist and has been extensively used preclinically to support the “α₂/D₂ receptor hypothesis” for atypical antipsychotic effects. However, previous studies have shown that the anticataleptic and discriminative stimulus properties of idazoxan may be mediated by 5‐HT_1A receptor agonism. The present study was conducted to further assess the role of α₂ adrenoceptor antagonism and 5‐HT_1A receptor agonism in the discriminative stimulus properties of idazoxan using a 5.0‐mg/kg training dose in rats. Idazoxan produced full‐stimulus generalization to itself, the α₂ adrenoceptor antagonist yohimbine, and the 5‐HT_1A receptor partial agonist, 8‐OH‐DPAT. Both the α₂ adrenoceptor agonists clonidine and guanfacine, and the 5‐HT_1A receptor antagonist WAY100635, partially blocked the discriminative stimulus effects of idazoxan. Finally, partial stimulus generalization occurred to the atypical antipsychotic drug clozapine. On the basis of these findings, both α₂ adrenoceptor antagonism and 5‐HT_1A receptor agonism appear to contribute to the discriminative stimulus effects of idazoxan. Thus, the role of 5‐HT_1A receptor agonism should be considered when evaluating the behavioral effects of idazoxan. Drug Dev Res 71: 261–267, 2010. © 2010 Wiley‐Liss, Inc.     

Lack of generalisation between the GABA<Subscript>A</Subscript> receptor agonist,gaboxadol, and allosteric modulators of the benzodiazepine binding site in the rat drug discrimination procedure

Introduction The binding sites for γ-aminobutyric acid (GABA) and GABA_A receptor agonists are located differently from the binding sites for benzodiazepine receptor agonists. Furthermore, the major pharmacological effects of benzodiazepine receptor agonists and the GABA_A receptor agonist gaboxadol (4,5,6,7-tetrahydrroisoxazolo(5,4-c)pyridin-3-ol, THIP) are mediated by different GABA_A receptor subunit compositions; that is, gaboxadol may interact primarily with extra-synaptically located α₄β_2/3δ-containing receptors and benzodiazepines with the synaptically located α₁β_2/3γ₂-containing receptors. Objectives The aim of the present study was to address if this different receptor subtype selectivity was reflected in vivo. Materials and methods A two-lever liquid reinforced operant discrimination procedure was conducted. Three groups of rats were trained to discriminate gaboxadol, diazepam and zolpidem 5.5, 1.5 and 0.7 mg/kg i.p., respectively, from vehicle. Results Substitution tests showed that gaboxadol-trained animals failed to recognize diazepam (0.75–1.5 mg/kg), zolpidem (0.4–0.7 mg/kg), zopiclone (2.5 mg/kg), zaleplon (1.0–1.5 mg/kg) or indiplon (0.31 mg/kg). In contrast, all benzodiazepine receptor agonists, but not gaboxadol (4.5–5.5 mg/kg), generalised to the discriminative stimulus in diazepam- and zolpidem-trained animals. Discussion In agreement with these data, the competitive benzodiazepine receptor antagonist flumazenil (10 mg/kg s.c.) antagonised the discriminative stimulus of zolpidem but not of gaboxadol. Interaction tests showed no synergistic interaction of concomitant administration of gaboxadol and zolpidem or diazepam. Conclusion Previous studies have shown that gaboxadol and benzodiazepines interact with different receptor populations, and the present study confirms that in vivo functional consequences of this receptor selectivity exist in the form of differential behavioural responses in rats.     

Optimization and pharmacological characterization of receptor‐mediated Gi/o activation in postmortem human prefrontal cortex

The biochemical abnormalities in transmembrane signal transduction mediated through G protein‐coupled receptors (GPCRs) have been postulated as underlying pathophysiology of psychiatric diseases such as schizophrenia and mood disorders. In the present study, the experimental conditions of agonist‐induced [³⁵S]GTPγS binding in postmortem human brain membranes were optimized, and the responses induced by a series of agonists were pharmacologically characterized. The [³⁵S]GTPγS binding assay was performed in postmortem human prefrontal cortical membranes by means of filtration techniques, and standardized as to GDP concentration, membrane protein content, MgCl₂ and NaCl concentrations in assay buffer, incubation period and effect of white matter contamination. Under the standard assay conditions, the specific [³⁵S]GTPγS binding was stimulated by the addition of 15 compounds in a concentration‐dependent manner. Of these agonists, R(+)‐8‐OH‐DPAT, UK‐14,304, DAMGO and DPDPE showed apparently biphasic concentration‐response curves. As for these four responses, only higher‐potency site was pharmacologically characterized. The receptors involved in the responses investigated were 5‐HT_1A receptor (probed with R(+)‐8‐OH‐DPAT or 5‐HT), α_2A‐adrenoceptor (UK‐14,304 or (?)‐epinephrine), M₂/M₄ mAChRs (carbachol), adenosine A₁ receptor (adenosine), histamine H₃ receptor (histamine), group II mGlu (l ‐glutamate), GABA_B receptor (baclofen), μ‐opioid receptor (DAMGO or endomophin‐1), δ‐opioid receptor (DPDPE or SNC‐80) and NOP (nociceptin). Although dopamine also activated specific [³⁵S]GTPγS binding, this response was likely mediated via α_2A‐adrenoceptor, but not dopamine receptor subtypes. The present study provides us with fundamental aspects of the strategy for elucidation of probable abnormalities of neural signalling mediated by G proteins activated through multiple GPCRs in the brain of psychiatric patients.     

Mechanisms underlying the renoprotective effect of GABA against ischaemia/reperfusion‐induced renal injury in rats

Excitation of the renal sympathetic nervous system is important for the development of ischaemic acute kidney injury (AKI) in rats. We reported that intravenous treatment with GABA has preventive effects against ischaemia/reperfusion (I/R)‐induced renal dysfunction with histological damage in rats; however, the mechanisms underlying these effects on renal injury remain unknown. Thus, the aim of the present study was to clarify how GABA mechanistically affects ischaemic AKI in rats. Ischaemic AKI was induced in rats by clamping the left renal artery and vein for 45 min and then reperfusing the kidney to produce I/R‐induced injury. Treatment with the GABA_B receptor antagonist CGP52432 (100 nmol/kg, i.v., or 1 nmol/kg, i.c.v.) abolished the suppressive effects of 50 μmol/kg, i.v., GABA on enhanced renal sympathetic nerve activity (RSNA) during ischaemia, leading to elimination of the renoprotective effects of GABA. Intracerebroventricular treatment with 0.5 μmol/kg GABA or i.v. treatment with 1 μmol/kg baclofen, a selective GABA_B receptor agonist, prevented the I/R‐induced renal injury equivalent to i.v. treatment with GABA. Conversely, i.v. treatment with 10 μmol/kg bicuculline, a GABA_A receptor antagonist, failed to affect the preventive effects of GABA against ischaemic AKI. We therefore concluded that GABA_B receptor stimulation in the central nervous system, rather than peripheral GABA_B receptor stimulation, mediates the preventive effect of GABA against ischaemic AKI by suppressing the enhanced RSNA induced by renal ischaemia.     

Attenuation by electroconvulsive shock and antidepressant drugs of the 5-HT1A receptor-mediated hypothermia and serotonin syndrome produced by 8-OH-DPAT in the rat

The hypothermia and motor behavioural syndrome produced in rats by injection of the 5-HT_1A ligand 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) has been studied following administration of electroconvulsive shock under halothane anaesthesia (ECS) and during the administration of antidepressant drugs. Repeated ECS attenuated the hypothermic response to 8-OH-DPAT (0.1 mg/kg SC) immediately after the last of five shocks given spread out over 10 days with a maximal effect 21 days after the final shock. A single ECS was without effect. The serotonin syndrome produced by 8-OH-DPAT (0.75 mg/kg SC) was also attenuated, although simple motility was increased.Zimeldine (20 mg/kg) and desipramine (20 mg/kg), when given once daily for 14 days also attenuated the hypothermia and the serotonin syndrome provoked by 8-OH-DPAT. The hypothermic response was somewhat reduced 24 h after a single injection of zimeldine but not 45 min after zimeldine (5 mg/kg IP). At a high dose (20 mg/kg) tranylcypromine clearly attenuated both responses 24 h after a single injection. Tranylcypromine (6 mg/kg IP) showed a smaller effect after a single injection but attenuated the behavioural syndrome on repeated administration. Repeated injection of flurazepam (10 mg/kg IP) was without effect on either the behavioural or hypothermic response to 8-OH-DPAT.These findings are consistent with the view that responses mediated via the 5-HT_1A receptor may be involved in the mechanism of action of antidepressant treatments.     

5‐HT modulates the rat mesenteric vasopressor outflow by 5‐HT1D sympatholytic receptors

5‐hydroxytryptamine (5‐HT) modulates noradrenergic activity in different cardiovascular territories, but its effect on the mesenteric vasopressor outflow has not yet been clarified. This study investigated the in vivo serotonergic influence, characterizing 5‐HT receptors implicated, in sympathetic innervation of mesenteric vasculature. Wistar rats were anaesthetised and prepared for the in situ autoperfused rat mesentery, monitoring systemic blood pressure (SBP), heart rate (HR) and mesenteric perfusion pressure (MPP). Electrical stimulation of mesenteric sympathetic nerves resulted in frequency‐dependent increases in MPP (9 ± 1.6, 25.7 ± 3.9 and 60.2 ± 5 mmHg for 2, 4 and 8 Hz, respectively), without altering SBP or HR. 5‐HT (1‐25 μg/kg), 5‐carboxamidotryptamine (5‐HT_1/7 agonist; 25 μg/kg) or L‐694,247 (5‐HT_1D agonist; 1‐25 μg/kg) i.a. bolus inhibited vasopressor responses by mesenteric nerves electrical stimulation, unlike i.a. bolus of agonists 8‐OH‐DPAT (5‐HT_1A), CGS‐12066B (5‐HT_1B), BRL 54443 (5‐HT_1e/1F), α‐methyl‐5‐HT (5‐HT₂), 1‐PBG (5‐HT₃), cisapride (5‐HT₄) or AS‐19 (5‐HT₇) (25 μg/kg each). Interestingly, i.a. L‐694,247 (25 μg/kg) also reduced the exogenous norepinephrine‐induced vasoconstrictions. Pretreatment with selective 5‐HT_1D receptor antagonist, LY310762 (1 mg/kg, i.v.), completely abolished L‐694,247‐ and 5‐HT‐induced mesenteric sympathoinhibition. Furthermore, ELISA analysis confirmed 5‐HT_1D receptors expression in mesenteric artery. These findings suggest that serotonergic mechanisms‐induced sympathoinhibition of mesenteric noradrenergic outflow is mediated by pre and/or postjunctional 5‐HT_1D receptors.     

Differential sensitivity to the motor and hypothermic effects of the GABA<Subscript>B</Subscript> receptor agonist baclofen in various mouse strains

Rationale Comparison of different mouse strains can provide valuable information about the genetic control of behavioural and molecular phenotypes. Recent evidence has demonstrated the importance of GABA_B receptors in anxiety and depression. Investigation of the phamacogenetics of GABA_B receptor activation may aid in the understanding of mechanisms underlying the role of GABA_B in affect.Objectives The aim of current study was to determine the relative sensitivity of different mouse strains to GABA_B receptor agonism in two models of GABA_B receptor function, namely hypothermia and motor incoordination.Methods Mice each from 11 strains (BALB/cByJIco, DBA/2JIco, OF1, FVB/NIco, CD1, C3H/HeOuJIco, 129/SvPasIco, NMRI, C57BL/6JIco, A/JOlaHsd and Swiss) were trained to walk on a rotarod for 300 s. On the following day, mice received 0, 3, 6 or 12 mg/kg of l-baclofen PO. Rectal temperature and rotarod performance were measured at 0, 1, 2 and 4 h after drug application.Results l-Baclofen produced a significant dose-dependent hypothermia and ataxia in most, but not all, mouse strains examined. The magnitude and duration of response was influenced by strain, with mice of the 129/SvPasIco strain showing largest hypothermic response to 12 mg/kg l-baclofen and C3H/HeOuJIco the lowest, whereas the BALB/cByJIco strain demonstrated greatest ataxic response on the rotarod, and NMRI the least. Interestingly, some strains (notably C3H/HeOuJIco) had marked differential hypothermic and ataxic responses, with minimal body temperature responses to l-baclofen but significant ataxia on the rotarod observed.Conclusion There is differential genetic control on specific GABA_B receptor populations that mediate hypothermia and ataxia. Further, these studies demonstrate that background strain is an important determinant of GABA_B receptor mediated responses, and that hypothermic and ataxic responses may be influenced by independent genetic loci.     

Chronic treatment with meta-chlorophenylpiperazine (m-CPP) alters behavioral and cerebral metabolic responses to the serotonin agonists m-CPP and quipazine but not 8-hydroxy-2(di-N-propylamino)tetralin

The effects of the serotonin (5-HT) agonists meta-chlorophenylpiperazine (m-CPP), quipazine and 8-hydroxy-2(di-n-propylamino)tetralin (DPAT) on behavior and on regional cerebral metabolic rates for glucose (rCMRglc) were measured in control rats or in rats pretreated for 2 weeks with continuous infusion of saline or m-CPP (2.5 mg/kg/day, subcutaneously). rCMRglc was measured in 71 brain regions, using the quantitative autoradiographic [¹⁴C]2-deoxy-D-glucose technique, at 15 min after acute administration of m-CPP 2.5 mg/kg, 60 min after quipazine 20 mg/kg, or 10 min after DPAT 1 mg/kg. Behavioral effects were assessed for m-CPP with an activity monitor, for quipazine by counting head shakes and for DPAT by scoring the serotonin syndrome. Chronic m-CPP pretreatment produced tolerance to hypolocomotion induced by acute m-CPP and to head shakes caused by acute quipazine, but did not alter the serotonin syndrome produced by DPAT. m-CPP 2.5 mg/kg IP produced widespread rCMRglc reductions in control rats but failed to modify rCMRglc in any region after chronic m-CPP pretreatment. Quipazine increased rCMRglc in 4 regions in control rats, but reduced rCMRglc in 14 brain areas of chronically m-CPP-pretreated animals. DPAT altered rCMRglc to the same degree in control (25 regions affected) and in chronically m-CPP-pretreated rats (28 regions affected). Reduced behavioral and metabolic effects of acute m-CPP in chronically m-CPP-pretreated rats were not due to pharmacokinetic alterations. These results demonstrate that chronic administration of m-CPP produces behavioral and metabolic tolerance to acute administration of m-CPP, but not of DPAT. They suggest that hypolocomotion and the serotonin syndrome are mediated by different 5-HT receptor subtypes, and that chronic m-CPP administration produces functional down-regulation of 5-HT_1B/1C but not of 5-HT_1A-coupled mechanisms.     

Chronic lithium treatment enhances the postsynaptic 5-HT1A receptor-mediated 5-HT behavioral syndrome induced by 8-OH-DPAT in rats via catecholaminergic systems

The effects of antimanic agents, including lithium, carbamazepine, clonazepam and zotepine, on the postsynaptic 5-HT_1A receptor-mediated behavioral and hypothermic responses induced by 8-OH-DPAT in rats, and on [³H]8-OH-DPAT binding to 5-HT_1A receptors in the rat hippocampus were examined. Treatment with lithium (3 mEq/kg, IP) for 14 days enhanced forepaw treading, one component of the 5-HT behavioral syndrome induced by 8-OH-DPAT, and this enhancement by lithium was abolished by catecholamine depletion with reserpine or -methyl-p-tyrosine, but not by 5-HT depletion withp-chlorophenylalanine. These data suggest that lithium enhances 5-HT_1A-mediated behavior via catecholaminergic systems. In contrast, chronic lithium treatment did not alter the hypothermic response to 8-OH-DPAT in untreated rats, as well as in rats treated with reserpine. These findings strengthen the suggestion that lithium has no direct influence on the postsynaptic 5-HT_1A-mediated response. Other antimanic agents had no effect on either forepaw treading or hypothermia induced by 8-OH-DPAT. Radioligand binding studies using [³H]-8-OH-DPAT demonstrated that chronic lithium treatment, but not other antimanic agents, caused 5-HT_1A receptor down-regulation in rat hippocampus. A discrepancy therefore exists between 5-HT_1A receptor down-regulation and unaltered 5-HT_1A-mediated behavioral and hypothermic responses in catecholamine-depleted rats after chronic lithium treatment.     

Dissociating anxiolytic and sedative effects of GABA<Subscript>A</Subscript>ergic drugs using temperature and locomotor responses to acute stress

Rationale  The stress-induced hyperthermia (SIH) model is an anxiety model that uses the transient rise in body temperature in response to acute stress. Benzodiazepines produce anxiolytic as well as sedative side effects through nonselective binding to GABA_A receptor subunits. The GABA_A receptor α₁ subunit is associated with sedation, whereas the GABA_A receptor α₂ and α₃ subunits are involved in anxiolytic effects. Objectives  We therefore examined the effects of (non)subunit-selective GABA_A receptor agonists on temperature and locomotor responses to novel cage stress. Results  Using telemetric monitoring of temperature and locomotor activity, we found that nonsubunit-selective GABA_A receptor agonist diazepam as well as the α₃ subunit-selective receptor agonist TP003 dose-dependently attenuated SIH and locomotor responses. Administration of GABA_A receptor α₁-selective agonist zolpidem resulted in profound hypothermia and locomotor sedation. The GABA_A receptor α₁-selective antagonist βCCt antagonized the hypothermia, but did not reverse the SIH response attenuation caused by diazepam and zolpidem. These results suggest an important regulating role for the α₁ subunit in thermoregulation and sedation. Ligands of extrasynaptic GABA_A receptors such as alcohol and nonbenzodiazepine THIP attenuated the SIH response only at high doses. Conclusions  The present study confirms a putative role for the GABA_A receptor α₁ subunit in hypothermia and sedation and supports a role for α_2/3 subunit GABA_A receptor agonists in anxiety processes. In conclusion, we show that home cage temperature and locomotor responses to novel home cage stress provide an excellent tool to assess both anxiolytic and sedative effects of various (subunit-selective) GABA_Aergic compounds.     

GABAergic influences on plus-maze behaviour in mice

Manipulations of GABA function have been found to produce highly variable effects in animal models of anxiety. In the present series, an ethological version of the murine elevated plus-maze was used to examine in detail the behavioural profiles of diazepam (1.5 mg/kg; positive control) and a range of GABA-related compounds: valproic acid (100–400 mg/kg), No-711 (1.25–10.0 mg/kg), muscimol (0.5–3.0 mg/ kg), (+)bicuculline (4.0–8.0 mg/kg), picrotoxin (0.25– 2.0 mg/kg), R(+)baclofen (0.375–3.0 mg/kg) and CGP 35348 (25–200 mg/kg). On both conventional and ethological indices, results confirmed the anxiolytic profile of diazepam under present test conditions, and revealed substantially similar effects for the GABA-T inhibitor, valproic acid (100–400 mg/kg), and the GABA_A receptor agonist, muscimol (2 mg/kg). The GABA reuptake inhibitor, No-711, produced weak anxiolytic-like effects at low doses (1.25–2.5 mg/kg) but disrupted behaviour at the highest dose tested (10 mg/ kg). Although the GABA_A receptor antagonists, (+)bicuculline and picrotoxin, produced changes indicative of anxiety enhancement, concomitant behavioural suppression was evident at high doses (8 mg/kg and 1–2 mg/kg, respectively). Further studies suggested that the effects observed with bicuculline may be mediated by an active metabolite, such as bicucine. In contrast to the effects of valproic acid and direct GABA_A receptor manipulations, the GABA_B receptor agonist, R(+) baclofen, non-specifically disrupted behaviour at the highest dose tested (3 mg/kg) while the GABA_B receptor antagonist, CGP 35348, was inactive over the dose range studied. Although present data confirm the sensitivity of the plus-maze to agents which modify GABA_A receptor function, further studies will be required in order more fully to characterize this relationship. Received: 8 March 1996/Final version: 28 July 1996     

Synthesis and evaluation of anticonvulsant activities of 7‐phenyl‐4,5,6,7‐tetrahydrothieno[3,2‐b ]pyridine derivatives

A series of 7‐phenyl‐4,5,6,7‐tetrahydrothieno[3,2‐b]pyridine derivatives containing triazole and other heterocycle substituents (methyltriazole, tetrazole, and triazolone) is described. Two experimental methods, maximal electroshock (MES) and subcutaneous pentylenetetrazole (scPTZ), were used to evaluate the anticonvulsant activity of the target compounds. Moreover, the neurotoxicity (NT) was tested using the Rotarod test. 5‐(4‐Chlorophenyl)‐4,5‐dihydrothieno[2,3‐e][1,2,4]triazolo[4,3‐a]pyridine ( 6c ) showed the best anticonvulsant activity. In the MES and PTZ experiments, the 50% effective dose (ED₅₀) values of compound 6c were 9.5 and 20.5 mg/kg, respectively. From the therapeutic index (PI) values, 6c (MES and PTZ with PI values of 48.0 and 22.2, respectively) showed better safety than the clinical drugs carbamazepine (MES with PI value of 6.4) and ethosuximide (PTZ with PI value of 3.2). The biological activities of the compounds were verified by using molecular docking studies. Compound 6c showed significant interactions with residues at the benzodiazepine‐binding site on gamma‐aminobutyric acid A (GABA_A) receptors. The results of in vivo GABA estimation and bicuculline‐induced seizures showed that 6c may have an effect on the GABA system. The physicochemical and pharmacokinetic properties of the target compounds were predicted.     

Involvement of GABAA receptor sites in diazepam hypothermia

1. Intraperitoneal (i.p.) injection of diazepam (1.5-6 mg/kg) decreased the core body temperature (BT) of the rats. The effect was dose-dependent. 2. The hypothermia produced by diazepam (6 mg/kg, i.p.) was decreased in animals pretreated with high doses of bicuculline (BIC, 3 mg/kg, i.p.), while low doses of BIC (1.5 mg/kg, i.p.) potentiated the hypothermia. 3. Picrotoxin (PIC, 1 and 2 mg/kg, i.p.) pretreatment also decreased the hypothermic effect of diazepam. 4. Pretreatment of animals with atropine (AT, 10 mg/kg, i.p.) or propranolol (PRO, 10 mg/kg, i.p.) potentiated the hypothermic response of diazepam. Phenoxybenzamine (PHEN, 0.5 mg/kg, i.p.), methergoline (METH, 0.5 mg/kg, i.p.) or pimozide (PIM, 0.5 mg/kg, i.p.) did not change the diazepam hypothermia. 5. Single administration of BIC, PIC, PRO, PIM or METH also induced hypothermia. 6. One can postulate that diazepam hypothermia may be induced through GABAA receptor sites. However, further studies will clarify this hypothesis.     

Pharmacological evidence that 5‐HT1D activation induces renal vasodilation by NO pathway in rats

5‐HT is a powerful vasoconstrictor substance in renal vasculature (mainly by 5‐HT₂ activation). Nevertheless, 5‐HT is notable for its dual cardiovascular effects, producing both vasodilator and vasoconstrictor actions. This study aimed to investigate whether, behind the predominant serotonergic vasoconstrictor action, THE 5‐HT system may exert renal vasodilator actions, and, if so, characterize the 5‐HT receptors and possible indirect pathways. Renal perfusion pressure (PP), systemic blood pressure (SBP) and heart rate (HR) measurement in in situ autoperfused rat kidney was determined in phenylephrine infused rats. Intra arterial (i.a.) bolus administration of 5‐HT (0.00000125–0.1 μg/kg) decreased renal PP in the presence of a phenylephrine continuous infusion (phenylephrine‐infusion group), without modifying SBP or HR. These vasodilator responses were potentiated by 5‐HT₂ antagonism (ritanserin, 1 mg/kg i.v.), whereas the responses were abolished by 5‐HT_1/7 antagonist (methiothepin, 100 μg/kg i.v.) or 5‐HT_1D antagonist (LY310762, 1 mg/kg i.v.). The i.a. administration (0.00000125 to 0.1 μg/kg) of 5‐CT or L‐694,247 (5‐HT_1D agonist) mimicked 5‐HT vasodilator effect, while other agonists (1‐PBG, α‐methyl‐5‐HT, AS‐19 (5‐HT₇), 8‐OH‐DPAT (5‐HT_1A) or CGS‐12066B (5‐HT_1B)) did not alter baseline haemodynamic variables. L‐694,247 vasodilation was abolished by i.v. bolus of antagonists LY310762 (5‐HT_1D, 1 mg/kg) or L‐NAME (nitric oxide, 10 mg/kg), but not by i.v. bolus of indomethacin (cyclooxygenase, 2 mg/kg) or glibenclamide (ATP‐dependent K⁺ channel, 20 mg/kg). These outcomes suggest that 5‐HT_1D activation produces a vasodilator effect in the in situ autoperfused kidney of phenylephrine‐infusion rats mediated by the NO pathway.