The experiments proposed here will determine the influences of time of day and daylength on the distribution and concentrations of opiate receptors in the brain of the male golden hamster, a photoperiodic seasonal breeder, Autoradiographic methods will be used to determine the quantity and localization of mu, delta, and kappa receptors. Since radioimmunoassays indicate large effects of photoperiod on the concentrations of endogenous opiates and since peptide and receptor distributions are not always matched, we will complement these binding experiments with immunocytochemical studies of the distribution of met- enkephalin, beta-endorphin, and dynorphin in the brains of long and short day hamsters. finally, the functional significance of opiates in seasonal changes in gonadotropin secretion, male sexual behavior, and body weight will be evaluated using brain lesions and the systemic and intracranial application of opiate receptor agonists and antagonists. By manipulating photoperiod and gonadal steroid concentrations, we will determine the role of endogenous opiates in the integration of internally and externally generated signals. These studies will contribute to our understanding of the role of specific neuro-peptides in the coordination of endocrine and behavioral processes, elucidate environmental and hormonal influences on CNS function, uncover mechanisms of reproductive cyclicity which have possible applications to human and animal fertility, expand our knowledge of brain plasticity, and indicate naturally occurring controls over responsiveness to opiates and hormones which may bear implications for syndromes of abuse and addiction.
