Neurotransmitter release in the male rat brain quantitated by in vivo microdialysis

Abstract

The study of synaptic transmission in the central nervous system of the living animal is of fundamental importance in the field of neuroscience. The neurotransmitters that are released induce a wide range of physiologic responses. Research indicates that several brain areas have been implicated in playing a role in regulating male sexual behavior. Among these areas are the Medial Preoptic Area (MPOA) and the Nucleus Accumbens (NAc). The MPOA serves as an integration center for the consummatory state of the animal. The NAc functions as an interface between the forebrain areas and the motor systems. Researchers have reported that in these two brain areas Dopamine (DA) and/or Norepinephrine (NE) have been found. The precise roles of these neurotransmitters remains to be determined. This study used microdialysis probes to measure the release of neurotransmitters during sexual behavior. The microdialysis probes were inserted into either the Medial Preoptic-Diagonal Band of Broca areas (MPOA-DBB) or the Nucleus Accumbens (NAc) of sexually experienced male rats. Samples were collected while the male rat was exposed to an estrous female or an ovariectomized female. In the Nucleus Accumbens, DA levels tended to increase during copulation with an estrous female. In contrast, when males were exposed to an ovariectomized female levels of DA tended to be low. In the MPOA-DBB area the levels of Homovanillic Acid (HVA), NE, and Epinephrine (EPI) showed a substantial increase when the males were exposed to an estrous female. Upon exposure to the ovariectomized female, the levels of these neurotransmitters were decreased below basal levels. These results support the hypothesis that catecholamines in the MPOA-DBB and NAc play a role in mediating the complex neural mechanisms that regulate copulatory behavior in male rats.