Electrophysiological comparison of 5-Hydroxytryptamine1A receptor antagonists on dorsal raphe cell firing

Single-unit recording studies were undertaken in chloral hydrate-anesthetized rats to compare the effects on dorsal raphe cell firing of several putative 5-hydroxytryptamine (HT)1A receptor antagonists, including WAY 100635 (N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl) cyclohexanecarboxamide), p-MPPI (4-(2-methoxyphenyl)1-[2'-[N-(2"-pyridinyl)-p-iodobenzamido]ethyl] pip erazine), and two newly described 5-HT1A receptor antagonists, NDL-249 [(R)-3-(N-propylamino)-8-fluoro-3, 4-dihydro-2H-1-benzopyran-5-carboxamide] and NAD-299 [(R)-3-N, N-dicyclobutylamino-8-fluoro-3, 4-dihydro-2H-1-benzopyran-5-carboxamide]. Consistent with a 5-HT1A receptor antagonist profile, pretreatment with an approximately equimolar (0.02-0.03 micromol/kg) i.v. dose of each compound caused a significant rightward shift in the dose-response curve for 8-OH-DPAT [8-hydroxy-2-(di-n-propylamino)tetralin]. Antagonist potency was clearly highest for NAD-299 and WAY 100635, which caused shifts roughly 3 times greater than those for either p-MPPI or NDL-249 (ED50 for 8-OH-DPAT, 1.3 +/- 0.3 microg/kg; after NAD-299, 18.2 +/- 1.0 microg/kg; after WAY 100635, 16.9 +/- 2.9 microg/kg; after NDL-249, 6.0 +/- 1.2 microg/kg; after p-MPPI, 4.7 +/- 1.1 microg/kg). In separate studies, each of the antagonists was administered alone in increasing cumulative doses to evaluate whether they possessed intrinsic agonist activity in this system. At doses below 0.01 micromol/kg, none of the drugs altered firing by more than +/-20% basal rates. At higher doses (>0.1 micromol/kg), WAY 100635, NDL-249, and NAD-299 caused a dose-dependent suppression of dorsal raphe cell firing (ED50 = 0.6 +/- 0.2, 0.7 +/- 0.3, and 0. 9 +/- 0.4 micromol/kg, respectively). However, the ED50 values for inhibition by these drugs were roughly 30 times higher than the doses that antagonized effects of 8-OH-DPAT. Moreover, the inhibition by all three antagonists (but not 8-OH-DPAT) was readily reversed by d-amphetamine (3.2 mg/kg i.v.), a releaser of norepinephrine, suggesting that these effects were likely due to alpha adrenergic receptor blockade rather than to 5-HT1A receptor agonism. Thus, it was concluded that WAY 100635, NAD-299, NDL-249, and p-MPPI all fulfill criteria as 5-HT1A receptor antagonists lacking intrinsic efficacy in the dorsal raphe system. The newly described compound NAD-299 exhibits antagonist potency comparable to that of WAY 100635 in this electrophysiological assay.     

Nuclear-cytoplasmic interaction and development of goat embryos reconstructed by nuclear transplantation: production of goats by serially cloning embryos

We found previously that alcohol-preferring (P) rats have fewer serotonin (5-HT) neurons and fibers in key brain regions than alcohol-nonpreferring (NP) rats. Because 5-HT uptake blockers increase synaptic 5-HT content and 5-HT1A receptor antagonists increase 5-HT release by disinhibiting 5-HT autoinnervation, in the present study, our intent was to determine whether increased synaptic 5-HT content and/or 5-HT release in P rats would effectively reduce alcohol consumption. In experiment 1, the 5-HT antagonist WAY 100635 (WAY) was tested on adult female P rats maintained on 24-hr free-choice access to ethanol (10% v/v) and water. Twice daily doses of WAY (0.05, 0.1, 0.5, and 1.0 mg/kg, subcutaneously) were administered to each rat in a counterbalanced order. Baseline ethanol intake, derived from the mean ethanol intakes of the three previous non-drug days, was approximately 8 g/kg/day. Results indicated that 0.05, 0.1, and 0.5 mg/kg doses of WAY reduced 24-hr ethanol drinking by 25-30% (p < 0.01) without affecting 24-hr water intake or body weight. In the second experiment, the effects of WAY (0.5 mg/kg), fluoxetine (1.0 mg/kg), or a combination of both were tested in another group of female P rats. WAY and fluoxetine, each alone, reduced ethanol drinking by around 20% and, when combined, decreased ethanol intake by 50%, whereas the body weight and the total fluid intake were not significantly affected. Taken together, these results indicate that both fluoxetine and WAY preferentially reduce ethanol drinking in the P line of rats and, when administered together, reduce ethanol intake in an additive manner. It is proposed that coadministration of these two compounds with distinct mechanisms of action may be a new strategy for reducing alcohol intake.     

Intraventricular galanin modulates a 5-HT1A receptor-mediated behavioural response in the rat

The present studies have examined whether the neuropeptide galanin can modulate brain serotoninergic (5-HT) neurotransmission in vivo and, particularly, 5-HT1A receptor-mediated transmission. For that purpose, we studied the ability of galanin (given bilaterally into the lateral ventricle, i.c.v.) to modify the impairment of passive avoidance retention induced by the selective 5-HT1A agonist 8-hydroxy-2-(di-n-propyloamino)tetralin (8-OH-DPAT) when injected prior to training. This impairment appears to be mainly related to activation of 5-HT1A receptors in the CNS. Galanin dose-dependently (significant at 3.0 nmol/rat) attenuated the passive avoidance impairment (examined 24 h after training) induced by the 0.2 mg/kg dose of 8-OH-DPAT. This 8-OH-DPAT dose produced signs of the 5-HT syndrome indicating a postsynaptic 5-HT1A receptor activation. Furthermore, both the impairment of passive avoidance and the 5-HT syndrome were completely blocked by the 5-HT1A receptor antagonist WAY 100635 (0.1 mg/kg). Galanin (0.3 or 3.0 nmol) or WAY 100635 (0.1 mg/kg) failed by themselves to affect passive avoidance retention. 8-OH-DPAT given at a low dose 0.03 mg/kg, which presumably stimulates somatodendritic 5-HT1A autoreceptors in vivo, did not alter passive avoidance retention or induce any visually detectable signs of the 5-HT syndrome. Galanin (0.3 or 3.0 nmol) given i.c.v. in combination with the 0.03 mg/kg dose of 8-OH-DPAT, did not modify passive avoidance. The immunohistochemical study of the distribution of i.c.v. administered galanin (10 min after infusion) showed a strong diffuse labelling in the periventricular zone (100-200 microm) of the lateral ventricle. Furthermore, in the dorsal and ventral hippocampus galanin-immunoreactive nerve cells appeared both in the dentate gyrus and the CA1, CA2 and CA3 layers of the hippocampus. In the septum only endogenous fibres could be seen while in the caudal amygdala also galanin-immunoreactive nerve cells were visualized far away from the labelled periventricular zone. At the level of the dorsal raphe nucleus a thin periventricular zone of galanin immunoreactivity was seen but no labelling of cells. These results suggest that galanin can modulate postsynaptic 5-HT1A receptor transmission in vivo in discrete cell populations in forebrain regions such as the dorsal and ventral hippocampus and parts of the amygdala. The indication that galanin administered intracerebroventrically may be taken up in certain populations of nerve terminals in the periventricular zone for retrograde transport suggests that this peptide may also affect intracellular events.     

Differential regulation of somatodendritic serotonin 5-HT1A receptors by 2-week treatments with the selective agonists alnespirone (S-20499) and 8-hydroxy-2-(Di-n-propylamino)tetralin: microdialysis and autoradiographic studies in rat brain

Single treatment with the serotonin (5-hydroxytryptamine) 5-HT1A receptor agonists 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) and alnespirone (S-20499) reduces the extracellular 5-HT concentration (5-HText) in the rat midbrain and forebrain. Given the therapeutic potential of selective 5-HT1A agonists in the treatment of affective disorders, we have examined the changes in 5-HT1A receptors induced by 2-week minipump administration of alnespirone (0.3 and 3 mg/kg/day) and 8-OH-DPAT (0.1 and 0.3 mg/kg/day). The treatment with alnespirone did not modify baseline 5-HText but significantly attenuated the ability of 0.3 mg/kg s.c. alnespirone to reduce 5-HText in the dorsal raphe nucleus (DRN) and frontal cortex. In contrast, the ability of 8-OH-DPAT (0.025 and 0.1 mg/kg s.c.) to reduce 5-HText in both areas was unchanged by 8-OH-DPAT pretreatment. Autoradiographic analysis revealed a significant reduction of [3H]8-OH-DPAT and [3H]WAY-100635 [3H-labeled N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridyl)cyclohexa necarboxamide x 3HCl] binding to somatodendritic 5-HT1A receptors (but not to postsynaptic 5-HT1A receptors) of rats pretreated with alnespirone but not with 8-OH-DPAT. In situ hybridization analysis revealed no change of the density of the mRNA encoding the 5-HT1A receptors in the DRN after either treatment. These data indicate that continuous treatment for 2 weeks with alnespirone, but not with 8-OH-DPAT, causes a functional desensitization of somatodendritic 5-HT1A receptors controlling 5-HT release in the DRN and frontal cortex.     

Role of 5-HT1A receptors in the effects of acute chronic fluoxetine on extracellular serotonin in the frontal cortex

Fluoxetine 10 mg/kg i.p. significantly increased the extracellular concentrations of serotonin (5-HT) in the frontal cortex as assessed by in vivo microdialysis. This effect was significantly potentiated when 0.3 mg/kg s.c. WAY-100635, a 5-HT1A receptor antagonist, was administered 30 min before. WAY-100635 by itself had no effect on extracellular 5-HT. Twenty-four hours after chronic fluoxetine schedule (10 mg/kg/day i.p. x 14 days), basal extracellular 5-HT concentrations in the frontal cortex were higher than those of animals that had received the vehicle chronically. At 24 h after the last dose, a challenge dose of fluoxetine (10 mg/kg i.p.) raised extracellular 5-HT similarly in chronically vehicle or fluoxetine treated rats. At this same interval 25 micrograms/kg s.c. 8-OH-DPAT, a 5-HT1A receptor agonist, significantly reduced extracellular 5-HT only in the frontal cortex of rats treated chronically with the vehicle. Examining basal extracellular 5-HT, the effect of a challenge dose of fluoxetine and the effect of 25 micrograms/kg 8-OH-DPAT after 96 h washout, no differences were found between chronically fluoxetine and vehicle-treated rats. The results confirm that the ability of fluoxetine to stimulate 5-HT1A autoreceptors through an increase of endogenous 5-HT attenuates its effect on cortical dialysate 5-HT. Chronic fluoxetine increased the basal concentrations of extracellular 5-HT only when a substantial amount of its metabolite was present in the brain and during the desensitization of presynaptic 5-HT1A autoreceptors (24 h after the last dose). These effects, in fact, disappeared after 96 h washout. The continuous presence of the drug may, therefore, be necessary to maintain extracellular 5-HT at concentrations high enough to produce a therapeutic effect.     

Decrease in gastric sensitivity to distension by 5-HT1A receptor agonists in rats

Using an in vivo model for evaluation of gastric sensitivity in awake rats, we aimed to determine whether 5-hydroxytryptamine 1A (5-HT1A) agonists modify pain threshold and gastric compliance specifically through 5-HT1A receptors. Isobaric gastric distensions were performed with a barostat using steps of 5 mm Hg in male rats equipped with a gastric balloon and electrodes implanted in the neck muscles. Gastric distension at 15 or 20 mm Hg induced a typical posture associated with contractions of the neck muscles. Rats received drugs 30 min before gastric distension. The 5-HT1A receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT), administered intraperitoneally (0.5 mg/kg) increased gastric pain threshold and gastric tone. These effects were reproduced when administered centrally (0.05 mg/kg) and blocked by intracerebroventricular administration of the 5-HT1A antagonist WAY 100635. Flesinoxan (4 mg/kg, intraperitoneally), another 5-HT1A agonist reproduced the effects of 8-OH-DPAT on pain threshold and gastric tone and the alpha2-receptor antagonist yohimbine did not modify the action of 8-OH-DPAT. Our results indicate that activation of 5-HT1A receptors at the level of the central nervous system increases gastric tone and decreases gastric sensitivity to distension.     

Poor periodontal health of the pregnant woman as a risk factor for low birth weight

1. It has been hypothesized that 5-HT1A autoreceptor antagonists may enhance the therapeutic efficacy of SSRIs and other antidepressants. Although early clinical trials with the beta-adrenoceptor/5-HT1 ligand, pindolol, were promising, the results of recent more extensive trials have been contradictory. Here we investigated the actions of pindolol at the 5-HT1A autoreceptor by measuring its effect on 5-HT neuronal activity and release in the anaesthetized rat. 2. Pindolol inhibited the electrical activity of 5-HT neurones in the dorsal raphe nucleus (DRN). This effect was observed in the majority of neurones tested (10/16), was dose-related (0.2-1.0 mg kg(-1), i.v.), and was reversed by the 5-HT1A receptor antagonist, WAY 100635 (0.1 mg kg(-1), i.v.), in 6/7 cases tested. 3. Pindolol also inhibited 5-HT neuronal activity when applied microiontophoretically into the DRN in 9/10 neurones tested. This effect of pindolol was current-dependent and blocked by co-application of WAY 100635 (3/3 neurones tested). 4. In microdialysis experiments. pindolol caused a dose-related (0.8 and 4 mg kg(-1), i.v.) fall in 5-HT levels in dialysates from the frontal cortex (under conditions where the perfusion medium contained 1 microM citalopram). In rats pretreated with WAY 100635 (0.1 mg kg(-1), i.v.), pindolol (4 mg kg(-1), i.v.) did not decrease, but rather increased 5-HT levels. 5. We conclude that, under the experimental conditions used in this study, pindolol displays agonist effects at the 5-HT1A autoreceptor. These data are relevant to previous and ongoing clinical trials of pindolol in depression which are based on the rationale that the drug is an effective 5-HT1A autoreceptor antagonist.     

In vivo electrophysiological characterization of 5-HT receptors in the guinea pig head of caudate nucleus and orbitofrontal cortex

The aim of the present study was to characterize in vivo the 5-HT receptor subtypes which mediate the effect of microiontophoretic applied 5-HT in the guinea pig head of caudate nucleus and orbitofrontal cortex. 5-HT and the preferential 5-HT2A receptor agonist DOI and the preferential 5-HT2C receptor agonist mCPP, suppressed the quisqualate (QUIS)-induced activation of neurons in both structures. The inhibitory effect of DOI and mCPP was not prevented by acute intravenous administration of the 5-HT1/2 receptor antagonist metergoline (2 mg/kg) and the 5-HT2A/2C receptor antagonist ritanserin (2 mg/kg) in the two regions nor by the selective 5-HT2A receptor antagonist MDL100907 (1 mg/kg) in the head of caudate nucleus. However, the inhibitory effect of DOI, but not that of mCPP, was antagonized by a 4-day treatment with metergoline and ritanserin (2 mg/kg/day; using minipumps implanted subcutaneously) in head of caudate nucleus, but not in orbitofrontal cortex. Microiontophoretic ejection of the 5-HT1A/7 receptor agonist 8-OH-DPAT and of the 5-HT1A receptor antagonist WAY100635 both suppressed the spontaneous and QUIS-activated firing activity of orbitofrontal cortex neurons. At current which did not affect the basal discharge activity of the neuron recorded, microiontophoretic application of WAY100635 and BMY7378 failed to prevent the inhibitory effect of 8-OH-DPAT. The inhibitory effect of gepirone, which is a 5-HT1A receptor agonist but devoid of affinity for 5-HT7 receptors, was also not antagonized by WAY100635. Altogether, these results suggest the presence of atypical 5-HT1A receptors in the orbitofrontal cortex. The present results also indicate that the suppressant effect of DOI may be mediated by 5-HT2A receptors in head of caudate nucleus and atypical 5-HT2 receptors in orbitofrontal cortex.     

Anxiolytic-like actions of BW 723C86 in the rat Vogel conflict test are 5-HT2B receptor mediated

The 5-HT2B receptor agonist, BW 723C86 (10, 30(mg/kg i.p. 30 min pre-test), increased the number of punishments accepted in a rat Vogel drinking conflict paradigm over 3 min, as did the benzodiazepine anxiolytics, chlordiazepoxide (2.5-10 mg/kg p.o. 1 h pre-test) and alprazolam (0.2-5 mg/kg p.o. 1 h pre-test), but not the 5-HT2C/2B receptor agonist, m-chlorophenylpiperazine (mCPP, 0.3-3 mg/kg i.p) or the 5-HT1A receptor agonist, buspirone (5-20 mg/kg p.o. 1 h pre-test). The effect of BW 723C86 was unlikely to be secondary to enhanced thirst, as BW 723C86 did not increase the time that rats with free access to water spent drinking, nor did it reduce sensitivity to shock in the apparatus. The anti-punishment effect of BW 723C86 was opposed by prior treatment with the 5-HT2/2B receptor antagonist, SB-206553 (10 and 20 mg/kg p.o. 1 h pre-test), and the selective 5-HT2B receptor antagonist, SB-215505 (1 and 3 mg/kg p.o. 1 h pre-test), but not by the selective 5-HT2C receptor antagonist, SB-242084 (5 mg/kg p.o.), or the 5-HT1A receptor antagonist, WAY 100635 (0.1 or 0.3 mg/kg s.c. 30 min pre-test). Thus, the anti-punishment action of BW 723C86 is likely to be 5-HT2B receptor mediated. This is consistent with previous reports that BW 723C86 exhibited anxiolytic-like properties in both the social interaction and Geller-Seifter conflict tests.     

Antianxiety and behavioral suppressant actions of the novel 5-HT1A receptor agonist, flesinoxan

Flesinoxan is a potent and selective 5-HT1A receptor agonist. In this study, the effects of this compound on behavior in the murine elevated plus-maze have been assessed using a recently developed ethological scoring method. Results show that, at low doses (0.1-0.5 mg/kg), flesinoxan inhibited risk assessment behaviors (stretched attend postures and closed arm returns) indicative of a reduction in anxiety. These effects were maintained at a higher dose of 1.0 mg/kg, which also increased percent open entries and time spent on the central platform and open arms. However, this more convincing anxiolytic profile was associated with significant reductions in total arm entries and rearing, suggesting a combination of anxiolysis and behavioral suppression at high doses. The plus-maze profile observed with flesinoxan is very similar to that previously reported for 8-OH-DPAT in the same test but, despite superficial similarities, can be distinguished from that seen with buspirone. Data are discussed in relation to behavioral similarities and differences between 5-HT1A receptor agonists, and the advantages of a more detailed approach to the analysis of plus-maze behavior.     

Effect of a selective 5-HT reuptake inhibitor in combination with 5-HT1A and 5-HT1B receptor antagonists on extracellular 5-HT in rat frontal cortex in vivo

1. Selective 5-hydroxytryptamine (5-HT; serotonin) reuptake inhibitors (SSRIs) cause a greater increase in extracellular 5-HT in the forebrain when the somatodendritic 5-HT1A autoreceptor is blocked. Here, we investigated whether blockade of the terminal 5-HT1B autoreceptor influences a selective 5-HT reuptake inhibitor in the same way, and whether there is an additional effect of blocking both the 5-HT1A and 5-HT1B autoreceptors. 2. Extracellular 5-HT was measured in frontal cortex of the anaesthetized rat by use of brain microdialysis. In vivo extracellular recordings of 5-HT neuronal activity in the dorsal raphe nucleus (DRN) were also carried out. 3. The selective 5-HT reuptake inhibitor, paroxetine (0.8 mg kg-1, i.v.), increased extracellular 5-HT about 2 fold in rats pretreated with the 5-HT1A receptor antagonist, WAY100635. When administered alone neither paroxetine (0.8 mg kg-1, i.v.) nor WAY100635 (0.1 mg kg-1, i.v.) altered extracellular 5-HT levels. 4. Paroxetine (0.8 mg kg-1, i.v.) did not increase 5-HT in rats pretreated with the 5-HT1B/D receptor antagonist, GR127935 (1 mg kg-1, i.v.). GR127935 (1 and 5 mg kg-1, i.v.) had no effect on extracellular 5-HT when administered alone. 5. Interestingly, paroxetine (0.8 mg kg-1, i.v.) caused the greatest increase in 5-HT (up to 5 fold) when GR127935 (1 or 5 mg kg-1, i.v.) was administered in combination with WAY100635 (0.1 mg kg-1, i.v.). Administration of GR127935 (5 mg kg-1, i.v.) plus WAY100635 (0.1 mg kg-1, i.v.) without paroxetine, had no effect on extracellular 5-HT in the frontal cortex. 6. Despite the lack of effect of GR127935 on 5-HT under basal conditions, when 5-HT output was elevated about 3 fold (by adding 1 microM paroxetine to the perfusion medium), the drug caused a dose-related (1 and 5 mg kg-1, i.v.) increase in 5-HT. 7. By itself, GR127935 slightly but significantly decreased 5-HT cell firing in the DRN at higher doses (2.0-5.0 mg kg-1, i.v.), but did not prevent the inhibition of 5-HT cell firing induced by paroxetine. 8. In summary, our results suggest that selective 5-HT reuptake inhibitors may cause a large increase in 5-HT in the frontal cortex when 5-HT autoreceptors on both the somatodendrites (5-HT1A) and nerve terminals (5-HT1B) are blocked. This increase is greater than when either set of autoreceptors are blocked separately. The failure of a 5-HT1B receptor antagonist alone to enhance the effect of the selective 5-HT reuptake inhibitor in our experiments may be related to a lack of tone on the terminal 5-HT1B autoreceptor due to a continued inhibition of 5-HT cell firing. These results are discussed in relation to the use of 5-HT autoreceptor antagonists to augment the antidepressant effect of selective 5-HT reuptake inhibitors.     

Pollen tube localization implies a role in pollen-pistil interactions for the tomato receptor-like protein kinases LePRK1 and LePRK2

An impulsive cognitive style may affect behaviour in several different ways, including rapid decision making, intolerance of the delay of reward and a tendency to terminate chains of responses prematurely. It has been proposed to measure the last of these in rats using fixed consecutive number (FCN) schedules. The present study uses a modified version of the FCN procedure in which responding was paced by retracting the response lever for short periods between presses. In this way, the experimenter can control the maximum rate of responding. The procedure was made up of two components. In both, the schedule requirement was FCN 8, but in the Fast component lever presses were spaced by a minimum of 2.5 s and in the Slow component by a minimum of 5 s. Alterations in impulsivity were inferred from changes in the mean chain length and the distribution of chain lengths. The 5-HT1A agonist, 8-OH-DPAT (0.03-0.3 mg/kg), increased chain lengths within a narrow dose range, whereas the 5-HT1A antagonist, WAY 100 635 (0.03-0.3 mg/kg), reduced chain lengths. The 5-HT2 agonist, DOI (0.1-1.0 mg/kg), markedly reduced chain lengths, whereas the 5-HT2 antagonist, ritanserin (0.03-0.3 mg/kg), had no effect. The 5-HT1A/1b agonist, RU 24969 (0.03-0.3 mg/kg), reduced chain lengths. The 5-HT releaser, p-chloramphetamine (0.1-1.0 mg/kg), had a weak, biphasic effect, slightly reducing the number of short chains at the lowest dose tested and slightly increasing this number at the highest dose. Other drugs tested, citalopram (1.0-10.0 mg/kg), metergoline (0.3-3.0 mg/kg) and MDL-72222 (0.1-3.0 mg/kg), had no significant effects. These results suggest that stimulation of 5-HT1A receptors reduces impulsivity, whereas stimulation of 5-HT2 receptors increases it. These data are in agreement with previous results using the DRL-72 schedule, and indicate that there is no simple role for serotonin in the control of impulsivity.     

Introducing a downsized, open computer system with asynchronous transfer mode in PACS and its effect on image data transfer

(+/-)-8-Hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT), (+)-8-OH-DPAT, and (-)-8-OH-DPAT produced dose-related reversals of haloperidol-induced extrapyramidal side effects (EPS) in cebus monkeys, with all compounds producing similar almost complete reversals at 0.1 mg/kg i.m. These compounds were more potent than apomorphine, which reversed haloperidol-induced EPS at 0.3, but not 0.1, mg/kg i.m. The data indicate that the reversal of haloperidol-induced EPS by (+/-)-8-OH-DPAT and its enantiomers is mediated via effects at 5-HT1A receptors, not dopamine D2 receptors. Thus, inclusion of 5-HT1A agonist activity in novel antipsychotics may reduce EPS liability.     

Pharmacological analysis of the heterogeneous discriminative stimulus effects of ethanol in rats using a three-choice ethanol-dizocilpine-water discrimination

The present study used a three-choice operant drug discrimination procedure to determine if NMDA-mediated discriminative stimulus effects could be separated from other stimulus effects of 2.0 g/kg ethanol. Adult male Long-Evans rats (n = 7) were trained to discriminate dizocilpine (0.17 mg/kg; i.g.) from ethanol (2.0 g/kg; i.g.) from water (4.7 ml; i.g.) using food reinforcement. Substitution tests were conducted following administration of the GABA(A) positive modulators allopregnanolone (5.6-30.0 mg/kg; i.p.), diazepam (0.3-10.0 mg/kg; i.p.) and pentobarbital (1.0-21.0 mg/kg; i.p.), the non-competitive NMDA antagonist phencyclidine (0.3-10.0 mg/kg; i.p.), the 5-HT1 agonists TFMPP (0.3-5.6 mg/kg; i.p.) and RU 24969 (0.3-3.0 mg/kg; i.p.), and isopropanol (0.10-1.25 g/kg; i.p.). Allopregnanolone, diazepam and pentobarbital substituted completely (>80%) for ethanol. Isopropanol partially (77%) substituted for ethanol. Phencyclidine substituted completely for dizocilpine. RU 24969 and TFMPP did not completely substitute for either training drug, although RU 24969 partially (62%) substituted for ethanol. Successful training of this three-choice discrimination indicates that the discriminative stimulus effects of 0.17 mg/kg dizocilpine were separable from those of 2.0 g/kg ethanol. The finding that attenuation of NMDA-mediated effects of ethanol occurred without altering significantly GABA(A)- and 5-HT1-mediated effects suggests that the NMDA component may be independent of other discriminative stimulus effects of 2.0 g/kg ethanol.     

Studies on the neuronal circuits involved in the discriminative stimulus effects of 5-hydroxytryptamine1A receptor agonists in the rat

Rats were trained to discriminate 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT, 0.1 mg/kg i.p.) or 5-methoxy-N,N-dimethyltryptamine (5-OMe-DMT, 1.25 mg/kg i.p.), a selective and nonselective 5-hydroxytryptamine1A (5-HT, serotonin) receptor agonist, respectively, from saline in a two-lever procedure. The selective 5-HT1A receptor agonist ipsapirone substituted completely for 8-OH-DPAT (ED50, 1.52 mg/kg) and 5-OMe-DMT substituted partially for 8-OH-DPAT, whereas 8-OH-DPAT (ED50, 0.07 mg/kg) and ipsapirone (ED50, 4.15 mg/kg) substituted completely for 5-OMe-DMT. These results suggest that the discriminative stimulus properties of both 8-OH-DPAT and 5-OMe-DMT are 5-HT1A receptor mediated, although 5-OMe-DMT may involve an additional interaction with other 5-HT receptor subtypes. 5-OMe-DMT substituted for 8-OH-DPAT after application in the lateral ventricle (ED50, 3.0 micrograms/rat) and the dorsal raphe nucleus (DRN, 1.1 micrograms/rat). After application in the DRN (ED50 range, 1.4-5.0 micrograms/rat) and the median raphe nucleus (2.3 micrograms/rat), and after bilateral application into the CA-4 region of the dorsal hippocampus (4.1 micrograms/rat), 8-OH-DPAT also produced responding on the 8-OH-DPAT lever. Ipsapirone also substituted for 8-OH-DPAT after application into the DRN and the hippocampus (ED50S, 38 and 62 micrograms/rat, respectively). The 5-HT1A mixed agonist-antagonist (1-(2-methoxyphenyl) 4-[4-(2-pthalimido)butyl]piperazine, i.p. NAN-190) attenuated the discriminative stimulus effects of 8-OH-DPAT injected i.p. (0.1 mg/kg), into the DRN (10 micrograms) or into the hippocampus (2 x 10 micrograms).(ABSTRACT TRUNCATED AT 250 WORDS)     

The 5-HT1-like receptors mediating inhibition of sympathetic vasopressor outflow in the pithed rat: operational correlation with the 5-HT1A, 5-HT1B and 5-HT1D subtypes

1. It has been suggested that the inhibition of sympathetically-induced vasopressor responses produced by 5-hydroxytryptamine (5-HT) in pithed rats is mediated by 5-HT1-like receptors. The present study has re-analysed this suggestion with regard to the classification schemes recently proposed by the NC-IUPHAR subcommittee on 5-HT receptors. 2. Intravenous (i.v.) continuous infusions of 5-HT and the 5-HT1 receptor agonists, 8-OH-DPAT (5-HT1A), indorenate (5-HT1A), CP 93,129 (5-HT1B) and sumatriptan (5-HT(1B/1D)), resulted in a dose-dependent inhibition of sympathetically-induced vasopressor responses. 3. The sympatho-inhibitory responses induced by 5-HT, 8-OH-DPAT, indorenate, CP 93,129 or sumatriptan were analysed before and after i.v. treatment with blocking doses of the putative 5-HT receptor antagonists, WAY 100635 (5-HT1A), cyanopindolol (5-HT(1A/1B)) or GR 127935 (5-HT(1B/1D)). Thus, after WAY 100635, the responses to 5-HT and indorenate, but not to 8-OH-DPAT, CP 93,129 and sumatriptan, were blocked. After cyanopindolol, the responses to 5-HT, indorenate and CP 93,129 were abolished, whilst those to 8-OH-DPAT and sumatriptan (except at the lowest frequency of stimulation) remained unaltered. In contrast, after GR 127935, the responses to 5-HT, CP 93,129 and sumatriptan, but not to 8-OH-DPAT and indorenate, were abolished. 4. In additional experiments, the inhibition induced by 5-HT was not modified after 5-HT7 receptor blocking doses of mesulergine. 5. The above results suggest that the 5-HT1-like receptors, which inhibit the sympathetic vasopressor outflow in pithed rats, display the pharmacological profile of the 5-HT1A, 5-HT1B and 5-HT1D, but not that of 5-HT7, receptors.     

Involvement of the 5-HT1A subtype receptor in the neonatal organization of agonistic behaviour in the rat

5-hydroxytryptamine (5-HT) interacts with testosterone (T) in the development of a number of neuronal systems controlling sexually dimorphic adult behaviours. In this report, we investigated this interaction on the organization of agonistic behaviour in males, females, androgenized females (250 micrograms/pup of T proprionate on the day of birth), and males castrated on the day of birth. We have shown previously that manipulating 5-HT2 activity over the 2nd week of life modulates adult agonistic behaviour, depending on genetic sex and the presence of T. In this report, we investigated the effects seen in adulthood of a 5-HT1A agonist [8-OH-DPAT, 0.25 mg/kg, intraperitoneally (i.p.)] and antagonist (WAY100135, 0.25 mg/kg, i.p.) given over days 8-16 postpartum. The test for agonistic behaviour was carried out in a neutral territory against a matched conspecific, and introductory, offensive and defensive activities were note. Results show that neonatal administration of the 5-HT1A antagonist WAY100135 increases introductory activity and defense in the presence of neonatal T, independent of genetic sex, because these effects were seen in sham-castrated males and androgenized females. Offence followed a similar pattern, in that it was increased by WAY100135, but only in males. In the case of defence, the effects of the antagonist were reinforced by the action of the agonist (8-OH-DPAT) in both males and females, indicating an inhibitory role of 5-HT1A perinatal activity on defence in the presence of malelike levels of circulating T and a facilitatory role when levels of T are low or negligible. These findings indicate that 5-HT1A activity is involved in the development of agonistic behaviour and the effects are influenced by T. The results also show that the offensive and defensive facets of agonistic activity are controlled differently.     

Stimulated [35S]GTP gamma S binding by 5-HT1A receptor agonists in recombinant cell lines. Modulation of apparent efficacy by G-protein activation state

G-protein activation by different 5-HT receptor ligands was investigated in h5-HT1A receptor-transfected C6-glial and HeLa cells using agonist-stimulated [35S]-GTP gamma S binding to membranes in the presence of excess GDP. 5-HT (10 microM) stimulated [35S]GTP gamma S binding in the C6-glial membrane preparation to a larger extent than in the HeLa preparation; maximal responses with 30 microM GDP were 490 +/- 99 and 68 +/- 12%, respectively. With the 5-HT receptor agonists that were being investigated, the two preparations displayed the same rank order of potency for stimulation of [35S]GTP gamma S binding. In the C6-glial preparation at 0.3 microM GDP, the rank order of maximal effects was: 5-HT (1.00) > 8-OH-DPAT (0.90) = R(+)-8-OH-DPAT (0.87) = 5-CT (0.86) = L694247 (0.84) > S(-)8-OH-DPAT (0.68) = buspirone (0.67) = spiroxatrine (0.67) = flesinoxan (0.64) > ipsapirone (0.53) = (-)-pindolol (0.50) > SDZ216525 (0.25). However, differences in maximal response in the C6-glial preparation were magnified by increasing the GDP concentrations, indicating that the activity state of G-proteins can affect the maximal response. With the exception of 5-CT and L694247, increasing the amount of GDP to 30 microM and higher concentrations resulted in an attenuation of both the ligand's maximal effect (24 to 56%) and apparent potency (6 to 24-fold). Each of the [35S]GTP gamma S binding responses was mediated by a 5-HT1A receptor as indicated by the competitive blockade by WAY100635 and spiperone. Only 5-CT and L694247 in some conditions displayed an efficacy similar to that of 5-HT at the h5-HT1A receptor; the other agents with intrinsic activity are partial agonists at this receptor. The data also suggest that the activity state of the G-proteins is involved in the maximal effects that can be produced by activating the h5-HT1A receptor.     

CP-135,807, a selective 5-HT1D agonist: effects in drug discrimination and punishment procedures in the pigeon

CP-135,807 [3-(N-methylpyrrolidin-2R-ylmethyl)-5-(3-nitropyrid-2- yl)amino-1H-indole] binds with high affinity to central 5-HT1D receptors, and in functional studies produces dose-dependent decreases in extracellular serotonin. These and other findings have suggested that CP-135,807 may act as a terminal 5-HT autoreceptor agonist. In an attempt to characterize the behavioral activity of selective 5-HT1D ligands, adult male Carneau pigeons were trained to discriminate IM injections of 0.1 mg/kg CP-135,807 from saline under a two-key, fixed ratio schedule of food-reinforced key pecking. CP-135,807 and the structurally unrelated 5-HT1D agonist CP-286,601 fully and dose-dependently substituted for the training dose. In contrast, little substitution was observed following administration of 8-OH-DPAT, a potent 5-HT1A agonist, the 5-HT1B agonist CP-94,253, or the serotonin reuptake inhibitor sertraline. In addition, the discriminative stimulus produced by CP-135,807 was not blocked by WAY 100,635, a selective 5-HT1A antagonist, but was completely and dose-dependently antagonized by the selective 5-HT1D antagonist, GR 127935. In subjects trained under a multiple schedule of punished and unpunished responding, 8-OH-DPAT produced large increases in punished responding while having little effect on unpunished responding. In contrast, CP-135,807 and CP-94,253 produced no antipunishment effects, while GR 127935 produced modest increases in punished responding. Collectively, these results suggest that CP-135,807 produces centrally mediated psychoactive effects that differ distinctly from those of 5-HT1A agonists.     

Full and partial 5-HT1A receptor agonists disrupt learning and performance in rats

As a means of characterizing the role of 5-hydroxytryptamine (5-HT1A) receptors in learning, a full 5-HT1A receptor agonist, 8-hydroxy-dipropylaminotetralin (8-OH-DPAT), was administered both alone and in combination with two partial agonists (buspirone and 1-(2-methoxyphenyl)-4-[4-(2-phthalimido)butyl] piperazine hydrobromide (NAN-190)) and a 5-HT1A receptor antagonist (p-MPPI) to rats responding under a multiple schedule of repeated acquisition and performance of response sequences. In addition, the effects of another 5-HT1A receptor agonist, (LY228729), were also studied under this same procedure. When administered alone, both 8-OH-DPAT (0.1-3. 2 mg/kg) and LY228729 (0.32-3.2 mg/kg) dose dependently decreased overall response rate and increased the percentage of errors in the acquisition and performance components. At the doses of each drug tested, both buspirone (0.32 or 1 mg/kg) and NAN-190 (1 or 3.2 mg/kg) also decreased overall response rate and increased the percentage of errors. However, the effects of these drugs differed across behavioral components and dependent measures. The effects of buspirone and NAN-190 on rate and accuracy were also different when they were administered in combination with 8-OH-DPAT. In contrast, p-MPPI (3.2 or 10 mg/kg) had little or no effect when administered alone and antagonized the effects of 8-OH-DPAT; shifting the dose-effect curves for both response rate and the percentage of errors in both components to the right. Taken together, these results indicate that complex behaviors in rats are sensitive to disruption by drugs with both full and partial 5-HT1A receptor agonist properties, and that the effects of partial 5-HT1A receptor agonists on learning may be different depending on their efficacy at pre- and postsynaptic 5-HT1A receptors.