Dual Oxytocin Receptor-G Protein Signaling in the Autoregulation of Activities of Oxytocin Neurons

Abstract

Oxytocin (OT), a hypothalamic nonaneuropeptide, can extensively modulate mental and physical activities; however, the regulation of its secretion from hypothalamic OT neurons remains poorly understood. OT neuronal activity is generally modulated by neurochemical environment, synaptic inputs, astrocytic plasticity, and interneuronal interactions. By changing intracellular signals and ion channel activity, these extracellular factors dynamically regulate OT neuronal activity and OT release in a microdomain-specific manner. In this process, OT receptor (OTR) and OTR-coupled G proteins are pivotal, typically observed during lactation. Suckling-elicited somatodendritic release of OT causes sequential activation of G_q and G_s proteins to increase the firing rate gradually and trigger burst firing transiently, and then of G_i/o protein to cause post-burst inhibition as a result of potential bolus somatodendritic release of OT during the burst-like discharges. Under chronic social stress like mother-baby separation and cesarean section, excessive somatodendritic secretion of OT and over-excitation of OT neurons cause post-excitation inhibition of OT neuronal activity and reduction of OT secretion. In this process, dominance of G protein that couples to OTR is switched from G_q to G_i/o type because of inhibition of OTR-G_q signaling following negative feedback of downstream G_q signaling or crosstalk of G_q with G_s and G_i signals. This review summarizes our current understandings of OT/OTR signaling in the autoregulation of OT neuronal activity under physiological and pathological conditions.