Differential effects of chlordiazepoxide on conditioned and unconditioned behavior in mice with septal lesions.

The time course of action of repeated daily doses of chlordiazepoxide (CDP) was examined in mice with septal lesions. Bilateral septal lesions produced changes in both conditioned and unconditioned behavior. These lesions increased rate of operant responding on a VI-40 s schedule and produced hyperreactivity to tactile stimuli. The effects of repeated administration of CDP on these two classes of behavior were observed to follow different time courses. In a dose dependent fashion, CDP first reduced VI response rates in septal mice, but after several daily doses the response rate increased above post-surgical baseline levels. The suppressant effects of CDP on septal hyper-reactivity were quite different. Hyper-reactivity was persistently attenuated by all CDP doses tested during the eight-day drug regimen. The pattern of drug effects suggested that serotonin antagonism was involved in CDP's effects on lesion produced hyper-reactivity.