Humans are often required to maintain rigid schedules for work,school,and social activities at times when their endogenous circadian clock is signaling it is time to sleep. Alterations in the timing of the endogenous clock and the onset of sleep or activity produce significant adverse health outcomes. The long-term goal of our research is to describe the neurological mechanisms responsible for the generation and entrainment of circadian rhythms timing and identify possible targets for the therapeutic intervention of circadian-based disorders. To reach this goal we are studying the role of synaptic and extrasynaptic GABA neurotransmission in identified populations of suprachiasmatic nucleus neurons. We are also examining the role of astrocyte-neuronal interactions in responding to glutamatergic neurotransmission and regulating the strength of coupling between individual suprachiasmatic nucleus neuronal oscillators.