QUANTITATIVE BIOLOGY SEMINAR<br>The Role of GABAergic Synapses in the Generation of Circadian Rhythms

The hypothalamic suprachiasmatic nucleus (SCN) is the master circadian oscillator responsible for aligning circadian clocks located through the body. GABAergic neurotransmission is a fundamental component of the SCN neural network and virtually all SCN neurons communicate using GABA as a neurotransmitter. GABAergic neurotransmission plays a critical role in light-induced phase shifts, and synchronization of the dorsal and ventral SCN. Data will be presented from in vivo and in vitro experiments demonstrating that GABAergic neurotransmission plays an important role synchronization of the circadian phase of individual SCN neurons. While GABAergic neurotransmission is critical for the generation of circadian timing, the strength of GABAA receptor-mediated neurotransmission and the polarity of the GABA signal. In the SCN, the postsynaptic GABAA receptor-mediated currents may be excitatory or inhibitory depending on the time of day. The polarity of the GABA currents is important regulators of intracellular signaling pathways mediated by intracellular calcium. GABA released from axon terminals acts on synaptic GABAA receptors producing postsynaptic currents that have a rapid onset and offset, and desensitize in the continued presence of GABA. Once released, GABA is removed from the extracellular space by specific sodium-chloride dependent transporters (GAT). The activity of the GATs regulate the activity of GABA acting on extrasynaptic GABAA receptors.