Are serotonergic neurons involved in the control of anxiety and in the anxiolytic activity of benzodiazepines?

Several studies have shown that, like benzodiazepines (BZP), treatments able to reduce or block the activity of CNS serotonergic (5-HT) neurons released punished behavior. Therefore, 5-HT mechanisms have been tentatively implicated in the anti-punishment (anxiolytic?) activity of BZP. Numerous data, however, are not in keeping with this hypothesis. Since not responding enables the animals to avoid punishment but also delays the receipt of food-reward, one of these factors could be an alteration of waiting capacities. Indeed, we have shown that diazepam released behavioral suppression in conflict schedules only when the duration of the punished periods exceeded 1 minute. Moreover, in rats allowed to choose in a T-maze between immediate-but-small vs. delayed-but-large reward, BZP significantly decreased the frequency with which the delayed reward was chosen, with 5-HT uptake blockers producing opposite effects. Therefore, one can hypothesize that BZP render the animals less prone than controls to tolerate delay of reward and that 5-HT mechanisms may be involved in this phenomenon. An altered tolerance to delay of reward should be taken into account when interpreting the BZP-induced release of behavioral inhibition in classical conflict procedures.