Neuronal Activity in the Hypothalamic Paraventricular Nucleus Varies Across the Estrous Cycle in Anesthetized Female Rats: Effects of Dopamine Receptor Agonism

ABSTRACT Purpose The central nervous system plays a pivotal role in sexual behavior. The role of the paraventricular nucleus (PVN) of the hypothalamus in female sexual behavior is poorly characterized. In males, there is a correlation between PVN neuron activity and erectile activity, and in mediating dopamine receptor agonist-induced sexual arousal. Material and Methods To understand the role of the PVN in female sexual function, baseline PVN neuronal activity and responses to dopamine receptor agonism were assessed in anesthetized rats. Single unit recordings were used to assess the firing properties of individual PVN neurons; and local field potentials quantified PVN network activity (combined activity of large numbers of PVN neurons). Baseline and apomorphine-stimulated activity was measured across the estrous cycle. Results Baseline firing rates of single units were found to differ across the stages of the estrous cycle with metestrus showing the highest firing rate (3.7 vs. 0.9 Hz in diestrus). Apomorphine administration caused significant increases in firing rate in 29% of neurons, and significant decreases in 71%. Basal local field potentials also varied between estrous stages and in response to apomorphine; significant differences in the total power of alpha1 and beta1 bands were observed in both cases. Conclusions This study shows that PVN neuronal activity varies with hormonal state, and these neurons are differentially affected by apomorphine, suggesting two different populations. These data are indicative of a critical role for the PVN in female sexual function. It is important that the hormonal state should be considered when investigating sexual physiology and the effect of pharmacological agents. Richards N, Wayman C, and Allers KA. Neuronal activity in the hypothalamic paraventricular nucleus varies across the estrous cycle in anesthetized female rats: Effects of dopamine receptor agonism.