The phase-shifting effects of pentobarbital on the circadian rhythm of locomotor activity in the mouse: strain differences.

The phase response curves (PRCs) generated by pentobarbital injections (30 mg/kg) were obtained in SK and C57BL mice. Pentobarbital injections induced both advance and delay phase-shifts in the circadian rhythm of locomotor activity in SK mice but no phase-shifts were observed at any circadian time (CT) for pentobarbital injections in C57BL mice. The observation that a higher dose of pentobarbital (80 mg/kg) does not induce phase-shifting in C57BL mice has indicated that the differences in phase-shifting effects of pentobarbital are not quantitative but qualitative. These strains may be useful for studying the neurochemical regulation of the mammalian circadian rhythm.