Behavioral interactions have rapid effects on immunoreactivity of prohormone and gonadotropin-releasing hormone peptide

Abstract

The nervous system responds to both internal and external cues, integrating these signals to coordinate behavior and physiology. Mating interactions can promote dramatic changes in neuroendocrine cells which trigger successful copulation, ovulation, fertilization, and pregnancy. The neurons that transduce behavioral cues into neuroendocrine signals are distributed in a loose continuum along the medial ventral forebrain where they produce and secrete gonadotropin-releasing hormone (GnRH). In the past we have reported changes in GnRH-immunoreactive (GnRH-ir) cell numbers in brains of female musk shrews sacrificed during, and after, brief mating interactions. The purpose of the current study was twofold: first to determine which aspect of intracellular GnRH production is stimulated by behavioral interactions; second, to characterize the specific aspects of the social exchange that trigger GnRH production. We report that 1 h after copulation the production of proGnRH protein is stimulated. Non-copulatory behavioral interactions resulted in a rapid decrease in the numbers of neurons containing GnRH-ir peptide. This change was accompanied by an increase in the GnRH-ir fibers in the median eminence, but no surge in luteinizing hormone. These data suggest that behavioral interactions stimulate release of mature GnRH peptide from cell bodies followed by accumulation of available GnRH in cell terminals. Copulation triggers increased production of proGnRH in cell bodies. The data highlight the usefulness of behavioral paradigms for the examination of the dynamics of neuropeptide production.