Effects of N-methyl-D-aspartate on luteinizing hormone release and Fos-like immunoreactivity in the male White-crowned sparrow (Zonotrichia leucophrys gambelii)

Seasonal breeding is terminated in the White-crowned sparrow by the onset o f absolute photorefractoriness, a condition in which the reproductive syste m is switched off indefinitely until it is dissipated by short day lengths. Absolute photorefractoriness is controlled by the central nervous system; however, the mechanisms underlying GnRH quiescence in photorefractory birds have get to be elucidated. Using the excitatory amino acid glutamate agoni st N-methyl-D-aspartate (NMDA), plasma LH levels in White-crowned sparrows were significantly elevated regardless of the reproductive or photoperiodic condition. NMDA also significantly induced Fos-like immunoreactivity (FLI) within the infundibular nucleus and median eminence, regions previously sh own to express FLI after a photoperiodically driven LH rise. NMDA did not i nduce FLI within GnRH I neurons; instead, it significantly activated cells within the organum vasculosum of the lamina terminalis in close proximity t o GnRH I perikarya. These findings provide the first evidence that photorefractoriness is not d ue to depletion of GnRH stores, as LR and presumably GnRH were secreted in response to excitatory amino acid stimulation. NMDA activation of FLI in th e region of the organum vasculosum of the lamina terminalis and the basal t uberal hypothalamus suggests that seasonal reproductive neuroendocrine cont rol may be mediated via cells in the region of the GnRH I perikarya and ter minals.