Geniculo-hypothalamic tract lesions block chlordiazepoxide-induced phase advances in Syrian hamsters

Administration of the benzodiazepine triazolam at the appropriate time in the circadian cycle has been shown to induce phase shifts in hamster circadian rhythms. These phase shifts can be blocked by geniculo-hypothalamic tract (GHT) ablation or by restraint of activity. The present study examined the effects of the benzodiazepine chlordiazepoxide on running-wheel activity rhythms of hamsters. The phase-advancing effect of intraperitoneal injections of chlordiazepoxide administered at circadian time 6 (CT 6) was dose-dependent. Average shifts ranged from 6 min at a dose of 0.05 mg/kg to 135 min at a dose of 200 mg/kg. Four of twenty hamsters did not show a phase shift to any dose tested. Phase advance shifts to chlordiazepoxide (CT 6; 100 mg/kg) were blocked by GHT lesions. Chlordiazepoxide injections at doses which induced phase shifts were often followed by sedation. These results indicate that chlordiazepoxide is similar to triazolam, in that its ability to induce phase shifts at circadian time 6 is blocked by GHT lesions.