Behavioral evidence for the role of noradrenaline in putative anxiolytic and sedative effects of benzodiazepines

Acute, subchronic and discontinuation effects of zopiclone on sleep EEG and nocturnal melatonin secretion

Zopiclone is a new short half-life cyclopyrrolone hypnotic agent acting at the GABA-benzodiazepine receptor complex. In order to characterize its pharmacological profile, the effects of 7.5 mg zopiclone on nocturnal melatonin secretion were investigated under polysomnographic control in 11 healthy subjects following acute and subchronic administration as well as after abrupt discontinuation of the drug. No effect of zopiclone on the melatonin plasma levels could be observed. Regarding both total melatonin production and the temporal pattern of melatonin secretion during the night, there was no difference between placebo baseline condition, acute and subchronic administration, and discontinuation. In contrast, the sleep EEG data demonstrated the hypnotic efficacy of zopiclone under acute administration and indicated a rebound insomnia after abrupt discontinuation. Moreover, alterations of sleep architecture were found under treatment as well as after discontinuation. Whereas, with regard to sleep EEG parameters, zopiclone appears to be comparable with some short-acting benzodiazepines, a discrepancy between the missing effect of zopiclone on pineal function and the suppressing influence of benzodiazepines known from the literature becomes obvious. The fact that zopiclone does not interfere with nocturnal melatonin secretion at pharmacologically active doses as indicated by alterations in sleep EEG parameters might possibly point to a pharmacodynamic difference between the two drug classes.

Anxiolytic-like effects of alpha-2-adrenoceptor agonists on conflict behavior in the rat: pre- versus postsynaptic receptor mechanisms

The effects of acute pretest administration and chronic posttest administration of clonidine or the selective alpha 2-adrenoceptor agonist UK-14,304 on conflict behavior were investigated. In daily 10-min sessions, water-deprived rats were trained to drink water from a tube that was occasionally electrified (0.25 mA); electrification was signaled by a tone. Prior to treatment, subjects accepted 25-30 shocks/session (punished responding) and consumed approximately 12-15 ml/session (unpunished responding). Acute pretest administration of clonidine or UK-14,304 did not increase punished responding. In contrast, chronic posttest clonidine administration (40 micrograms/kg, IP, twice daily for 8 weeks) resulted in a robust and time-dependent increase in punished responding (60-70 shocks/session) relative to saline-treated controls. Moreover, the selective alpha 2-adrenoceptor agonist UK-14,304 also increased punished responding when administered chronically (1.0 mg/kg, BID). Administration of the noradrenergic neurotoxin N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine HCl (DSP4, 65 mg/kg, IP) significantly decreased punished responding in control conditioned suppression of drinking sessions. The anticonflict effect associated with chronic posttest clonidine treatment was not altered by DSP4 pretreatment. These findings suggest that chronic posttest alpha 2-adrenoceptor agonist treatment produces an anticonflict effect independent of its actions at presynaptic alpha 2-adrenoceptors.

Neuroleptic-induced changes in the anxiolytic and myorelaxant properties of diazepam in the rat

Diazepam (2.0 mg/kg) was injected (IP) into rats 30 min before chlorpromazine (2.5, 5.0, or 10.0 mg/kg) on ten occasions. All doses of chlorpromazine enhanced the capacity of diazepam to increase rats' exploration of the exposed arms of an elevated plus-maze, an animal screening test for anxiolytic and anxiogenic substances. When maze testing occurred during each of the ten diazepam----chlorpromazine trials (after diazepam but before chlorpromazine), this enhancement effect appeared on Trial 6 and persisted thereafter. Haloperidol (3.0 mg/kg, IP) changed diazepam-elicited plus-maze activity in the same manner as chlorpromazine; however, thioridazine (10.0 mg/kg) and pimozide (2.0 mg/kg) were ineffective. Additionally, haloperidol, like chlorpromazine, was found to reduce diazepam's muscle relaxation effect (inclined plane test) as a consequence of diazepam----haloperidol pairings; once again, thioridazine and pimozide proved ineffective. These results suggested that not all neuroleptics will alter diazepam activity, and also that dopamine blockade per se is not sufficient to induce such changes. While the reasons for the enhanced plus-maze effects of diazepam induced by haloperidol and chlorpromazine remain elusive, the diminished myorelaxant effect may be linked to a neuroleptic's capacity to induce muscular side effects: thioridazine and pimozide are far less likely to yield such effects than are chlorpromazine and haloperidol. Haloperidol administered chronically by itself was found to have an effect on diazepam-induced myorelaxation. Administration of this butyrophenone either orally (2.0 mg/kg daily for 22 days) or in depot form (haloperidol decanoate, 60.0 mg/kg IM once a month for four months) caused a diminished effect of diazepam in rats subjected to the inclined plane test.(ABSTRACT TRUNCATED AT 250 WORDS)

Antidepressant and anxiolytic effects of alprazolam versus the conventional. antidepressant desipramine and the anxiolytic diazepam in the forced swim test in rats

The antidepressant and anxiolytic effects of alprazolam were compared to those of desipramine, diazepam and buspirone in the forced swim test. Subchronic alprazolam induced a reduction in immobility similar to that of desipramine in 'non-pretested' and 'pretested' rats. In 'non-pretested' rats, the anti-immobility effect of desipramine was potentiated by diazepam and alprazolam, given before subchronic desipramine, while the anti-immobility effect of subchronic alprazolam was counteracted by diazepam. Diazepam, administered before the pretest session, counteracted, 24 h later, the anti-immobility effect of subchronic desipramine and alprazolam; alprazolam counteracted the anti-immobility effect of alprazolam but not of desipramine, buspirone at the highest doses tested potentiated the anti-immobility effect of subchronic desipramine but not of alprazolam. These data provide further support for the hypothesis that the GABA/benzodiazepine/Cl complex is directly implicated in the action of antidepressants and that systems other than the GABA system are involved in the antidepressant and anxiolytic effects of alprazolam.

Pharmacological dissociation between the spatial learning deficits produced by morphine and diazepam

This study sought to determine whether the place learning deficits produced by diazepam are a secondary result of opioid release. Rats pretreated with diazepam (3 mg/kg) or morphine (15 mg/kg) were trained in the Morris water maze. Diazepam impaired place learning-slowing acquisition and preventing the formation of a quadrant preference. Morphine also slowed acquisition, but did not prevent place learning, and impaired escape to a visible platform. Flumazenil blocked the deficits produced by diazepam, but not morphine. Naloxone (2 mg/kg) blocked the deficits produced by morphine, but not diazepam. A high dose of naloxone (10 mg/kg) slowed acquisition, and exacerbated the deficit produced by diazepam. These results demonstrate that diazepam interferes with mnemonic processes through endogenous benzodiazepine receptors, independently of opioidergic systems. Further, they suggest that morphine interferes with motivational processes through opioidergic systems, independently of endogenous benzodiazepine systems.

Antagonism of ethanol intoxication in rats by inhibitors of phenylethanolamine N-methyltransferase

The probable involvement of brain epinephrine in the expression of the acute sedative and intoxicating effects of ethanol and pentobarbital is demonstrated. Two selective inhibitors of phenylethanolamine N-methyltransferase (PNMT), LY134046 and LY78335, proved to be potent and long-lasting antagonists of ethanol intoxication in rats. Acute antagonism of pentobarbital-induced intoxication was observed with LY134046. The present results are compatible with a role for central epinephrine synthesis in ethanol and pentobarbital-induced sedation and intoxication in rats.