GABA_B Receptor Stimulation Phase-shifts the Mammalian Circadian Clock In Vitro

The mammalian circadian clock in the suprachiasmatic nucleus (SCN) generates 24-h rhythms in vitro. Here we show that the GABA_B agonist baclofen resets the SCN pacemaker in vitro in a phase-dependent manner: advances were induced at zeitgeber time (ZT) 6, and delays were induced at ZT 22. Both effects were blocked the GABA_B antagonist, 2-hydroxysaclofen, while the GABA_A antagonist, bicuculline was ineffective. Thus, the SCN pacemaker is sensitive to resetting by GABA_B stimulation.