Raphe unit activity in freely moving cats: effects of benzodiazepines

Benzodiazepines (chlordiazepoxide and diazepam) produced a dose-dependent decrease in the discharge rate of serotonin-containing neurons in the dorsal raphe nucleus of freely moving cats. This ranged from no significant change at doses of 0.5 and 1.0 mg/kg (i.p.), to greater than 90% reductions in unit activity at 10 mg/kg. The effects of benzodiazepines on raphe units occurred within 15-30 min of injection and the duration of action was dose-dependent and lasted from 1 to more than 6 hr. Doses of benzodiazepines that significantly decreased raphe unit activity (i.e. 2.5-10 mg/kg) also produced ataxia and decreased EMG activity. These data suggest that benzodiazepine-induced suppression of raphe unit activity is closely related to general motor behavior. Raphe unit activity remained suppressed during phasic increases in EMG activity during eating, grooming, or predatory behavior, suggesting that benzodiazepines also have a direct inhibitory action on raphe cells. The present results are discussed in the context of the serotonergic hypothesis of anxiety.