Influence of some serotoninergic agents on nitrazepam-induced sleep in the domestic fowl (Gallus domesticus).

The influence of some serotoninergic agents on nitrazepam-induced sleep was studied in 5-8-day-old chicks. Nitrazepam (0.4-51.2 mg/kg) induced behavioural sleep in chicks dose-dependently. 5-Hydroxytryptamine (5-HT; 10-20 mg/kg) hypnotised young chicks. Similarly, 5-HT (5-20 mg/kg) shortened the onset and significantly prolonged the duration of nitrazepam-induced sleep in chicks and increased the proportion of chicks that were hypnotized by nitrazepam; these effects were dose-dependent. 5-Hydroxytryptophan (5-HTP; 2-8 mg/kg) did not induce sleep but dose-dependently shortened the onset and profoundly prolonged the duration of nitrazepam (1.6 mg/kg)-induced sleep. Cyproheptadine (0.5-2 mg/kg) delayed the onset of nitrazepam sleep and reduced the proportion of chicks that were hypnotized by nitrazepam. Parachlorophenylalanine (PCPA, 200 mg/kg) completely blocked nitrazepam-induced sleep. Nitrazepam sleep was associated with synchronization of the electroencephalogram (EEG) of the hyperstriatum, optic tectum and pontine reticular formation. 5-HT synchronized the EEG of the hyperstriatum and the pontine reticular formation while the electromyograph (EMG) activity was profoundly reduced. These behavioural and electrocortical data suggest that 5-HT may be involved in nitrazepam-induced sleep in young chicks.