GABAergic mechanisms in the suprachiasmatic nucleus that influence circadian rhythm

The mammalian central circadian clock is located in the suprachiasmatic nucleus (SCN) of the hypothalamus. The SCN contains multiple circadian oscillators which synchronize with each other via several neurotransmitters. Importantly, an inhibitory neurotransmitter, gamma-amino butyric acid (GABA), is expressed in almost all SCN neurons. In this review, we discuss how GABA influences circadian rhythms in the SCN. Excitatory and inhibitory effects of GABA may depend on intracellular Cl- concentration, in which several factors such as day-length, time of day, development, and region in the SCN may be involved. GABA also mediates oscillatory coupling of the circadian rhythms in the SCN. Recent genetic approaches reveal that GABA refines circadian output rhythms, but not circadian oscillations in the SCN. Since several efferent projections of the SCN have been suggested, GABA might work downstream of neuronal pathways from the SCN which regulate the temporal order of physiology and behavior.

Automated summary

The central circadian clock in the mammalian suprachiasmatic nucleus (SCN) is regulated by the inhibitory neurotransmitter gamma-amino butyric acid (GABA), which influences circadian rhythms through intracellular Cl- concentration. The excitatory and inhibitory effects of GABA in the SCN are influenced by factors such as day-length, time, and region within the SCN. GABA mediates oscillatory coupling of circadian rhythms and refines circadian output rhythms, suggesting a downstream role in regulating the physiological and behavioral temporal order.