Peripheral metabolism of beta-carboline-carboxylic acid esters

3-Ethoxy-beta-carboline: a high affinity benzodiazepine receptor ligand with partial inverse agonist properties

3-Ethoxy-beta-carboline binds with high affinity to benzodiazepine receptors in the central nervous system (Ki approximately equal to 10.1, 15.3, and 25.3 nM in rat cerebellum, cerebral cortex, and hippocampus, respectively). This compound has pharmacological actions reminiscent of benzodiazepine receptor partial inverse agonists such as FG 7142 and 3-carboethoxy-beta-carboline. Thus, while not a convulsant, 3-ethoxy-beta-carboline potentiated the convulsant actions of pentylenetetrazole in mice. Furthermore, this compound reduced both the time spent and the total entries in the open arms of an elevated plus maze and also inhibited stress-induced ulcer formation, effects that are also observed with benzodiazepine receptor inverse agonists. These findings suggest that 3-ethoxy-beta-carboline is a partial inverse agonist at benzodiazepine receptors which may prove useful for in vivo studies since it has a higher affinity for benzodiazepine receptors and better solubility than the commonly used partial inverse agonist FG 7142. Furthermore, 3-ethoxy-beta-carboline appears to be less vulnerable to metabolic degradation than ester analogs with a similar pharmacological profile such as 3-carboethoxy-beta-carboline.

The effects of beta-carboline carboxylic acid ethyl ester and its free acid, administered ICV, on the anticonvulsant activity of diazepam and sodium valproate in the mouse

The effects of intracerebroventricular (ICV) beta-carboline carboxylic acid ethyl ester (beta-CCE) and its free acid on the protective effects of diazepam against leptazol- and R05-3663-induced convulsions were investigated in mice and compared with their effects on the antileptazol effect of sodium valproate, in an attempt to demonstrate a specific central effect of beta-CCE on benzodiazepine function. The results show that a small dose (1 microgram) of beta-CCE but not its free acid (in doses of up to 100 micrograms) was able to reverse the protective effects of diazepam against leptazol- and R05-3663-induced convulsions, whereas the effects of sodium valproate, a nonbenzodiazepine anticonvulsant, could not be reversed by these beta-carboline derivatives.

The effect of midazolam and beta-carboline carboxylic acid ethyl ester on behaviour, steroid hormones and central monoamine metabolites in social groups of talapoin monkeys

Established social groups of talapoin monkeys show rank-related differences in aggressive, social and sexual behaviours and visual monitoring, as well as in endocrine and monoamine profiles. Here we describe the effects on these variables of an "anxiogenic drug", beta-carboline carboxylic acid ethyl ester (beta-CCE), and an anxiolytic drug (midazolam) given to either dominant or subordinate male talapoins. In dominant animals beta-CCE increased aggression and visual monitoring but reduced sexual behaviour. Treatment of subordinate animals with beta-CCE served only to increase visual monitoring. Conversely, treatment with a non-sedative acute dose of midazolam in dominants reduced aggressive behaviour and increased sexual behaviour, whereas in subordinates no behavioural changes were noted. Significant effects on endocrine and neurochemical variables were not seen with the acute drug treatments employed. Nevertheless, the results show that drugs which modulate anxiety produce status-dependent behavioural effects.

Can drug effects on anxiety and convulsions be separated?

The effects of benzodiazepines, barbiturates, a series of novel putative anxiolytic compounds and anxiogenic compounds are reviewed in animal tests of anxiety and on experimentally-induced seizures. It is clear from the data that drug effects on anxiety and convulsions are not always in the same direction; certain compounds are apparently both anxiolytic and proconvulsant, others are anxiogenic and anticonvulsant, others have varied effects depending on the test situation. It is suggested that this work necessitates considerable revision of our traditional concepts of an "anticonvulsant." The extent to which drug-induced anxiety is correlated with weak epileptiform activity in the brain is discussed. Finally, the Discussion considers a number of possible mechanisms that could underlie the separation of drug effects on anxiety and convulsions that is observed.

Intrinsic behavioural actions of n-propyl β-carboline-3-carboxylate

The behavioural effects of n-propyl beta-carboline-3-carboxylate (beta-CCP) were assessed in the social interaction test of anxiety and in the holeboard test of exploratory behaviour. n-Propyl beta-carboline-3-carboxylate (2 mg/kg) significantly reduced the time spent in social interaction without affecting locomotor activity, indicating an anxiogenic action. This reduction was not significantly reversed by chlordiazepoxide (3 mg/kg). In the holeboard, beta-CCP (4 mg/kg) reduced exploratory head-dipping and rearing; neither of these effects was significantly reversed by chlordiazepoxide (5 mg/kg). The actions of beta-CCP in these two tests are similar to those of the structurally-related compound ethyl beta-carboline-3-carboxylate.

Lasting behavioral effects after treating rats with CGS 8216 on postnatal days 9 to 21

The lasting effects of chronic exposure to CGS 8216 in early postnatal life were studied in the social interaction test of anxiety, the holeboard test of exploratory behavior, a startle test and on convulsions induced by pentylenetetrazole. Male rat pups were treated with CGS 8216 (10 or 20 mg/kg/day) from postnatal day 9 until weaning (day 21), and tested in adulthood. In the social interaction test, the pups that had been exposed to CGS 8216 during development showed increased social interaction in both unfamiliar and familiar test conditions, (particularly the latter), in contrast to the decrease in social interaction that results when CGS 8216 is given acutely to adult animals. Conversely, the developmentally-treated rats were more sensitive to the convulsant effects of pentylenetetrazole, and this effect is in the same direction as that seen in adults after acute administration. No effects of the early treatment were detected in adult animals in the holeboard or startle tests.

Interactions of ethyl-beta-carboline-3-carboxylate and Ro 15-1788 with CGS 8216 in an animal model of anxiety

The effect of CGS 8216 (10 mg/kg) alone and in combination with the imidazodiazepine Ro 15-1788 (10 mg/kg) or ethyl-beta-carboline-3-carboxylate (beta-CCE 1 mg/kg) was tested in the social interaction test of anxiety. All 3 compounds were found to have an anxiogenic action. When Ro 15-1788 or beta-CCE was combined with CGS 8216, no mutual antagonism of the drugs' effects was observed. The failure of Ro 15-1788 to antagonize the anxiogenic action of CGS 8216 raises the possibility that CGS 8216 might be acting at a non-benzodiazepine site.

Interaction of beta-carbolines with the benzodiazepine receptor. Structure-activity relationships of amide derivatives of beta-carboline and tetrahydro-beta-carboline

1. The inhibition of specific 3H-flunitrazepam binding to rat cortical membrane preparations (benzodiazepine receptors) by a series of amide derivatives of beta-carboline and tetrahydro-beta-carboline related to the ethyl ester of beta-carboline 3-carboxylate (beta-CCE) was measured. 2. beta-Carboline amides which are unsaturated in the C ring of the beta-carboline nucleus were the most potent inhibitors of benzodiazepine receptor binding. 3. Increasing the length of the hydrocarbon moiety in the aliphatic amide side chain beyond two carbon atoms decreased potency.