GABA synchronizes clock cells within the suprachiasmatic circadian clock

The master clock in the suprachiasmatic nuclei (SCN) is composed of multiple, single-cell circadian clocks. We test the postulate that these individual "clock cells" can be synchronized to each other by the inhibitory transmitter gamma-aminobutyric acid (GABA). For these experiments, we monitored the firing rate rhythm of individual clock cells on fixed multielectrode plates in culture and tested the effects of GABA. The results show that the daily variation in responsiveness of the SCN to phase-shifting agents is manifested at the level of individual neurons. Moreover, GABA, acting through A-type receptors, can both phase shift and synchronize clock cells. We propose that GABA is an important synchronizer of SCN neurons in vivo.