Rapid, corticosterone-induced disruption of medullary sensorimotor integration related to suppression of amplectic clasping in behaving roughskin newts (Taricha granulosa)

Endogenously secreted or injected corticosterone (CORT) rapidly suppresses courtship clasping in male roughskin newts (Taricha granulosa) by an action on a specific neuronal membrane receptor. Previous studies, using immobili zed newts, showed that CORT administration rapidly depresses excitability o f reticulospinal neurons and attenuates medullary neuronal responsiveness t o clasp-triggering sensory stimuli. The present study used freely moving ne wts to examine clasping responses and concurrently record sensorimotor prop erties of 67 antidromically identified reticulospinal and other medullary r eticular neurons before and after CORT injection. Before CORT, reticulospin al neurons fired in close association with onset and offset of clasps elici ted by cloacal pressure. Reticulospinal neurons also showed firing correlat es of nonclasping motor events, especially locomotion. Neuronal activity wa s typically reduced during clasping and elevated during locomotion. Medulla ry neurons that were not antidromically invaded (unidentified neurons) usua lly showed sensorimotor properties that resembled those of reticulospinal n eurons. Intraperitoneal CORT (but not vehicle) reduced the probability and quality of hindlimb clasping in response to cloacal pressure, especially wi thin 5-25 min of injection. Simultaneously, responses of reticulospinal and unidentified neurons to cloacal pressure and occurrence of clasping-relate d activity were attenuated or eliminated. CORT effects were relatively sele ctive, altering clasping-related neuronal activity more strongly than activ ity associated with nonclasping motor events. The properties of CORT effect s indicate that the hormone impairs clasping by depressing processing of cl asp-triggering afferent activity and by disrupting the medullary control of clasping normally mediated by reticulospinal neurons. The rapid onset of t hese CORT effects implicates a neuronal membrane receptor rather than genom ic action of the steroid. (C) 1998 Academic Press.