Abstract
Oxytocin modulates reward-related behaviors. The nucleus accumbens shell (NAcSh) is a major relay in the brain reward pathway and expresses oxytocin receptors, but the effects of oxytocin on the activity of NAcSh neurons in vivo are unknown. Hence, we used in vivo extracellular recording to show that intracerebroventricular (ICV) oxytocin administration (0.2 mu g) robustly increased medial NAcSh neuron mean firing rate; this increase was almost exclusively evident in slow-firing neurons and was not associated with any change in firing pattern. To determine whether oxytocin excitation of medial NAcSh neurons is modulated by drugs that impact the brain reward pathway, we next tested the effects of ICV oxytocin following repeated morphine treatment. In morphine-treated rats, ICV oxytocin did not affect the mean firing rate of medial NAcSh neurons. Taken together, these results show that oxytocin excites medial NAcSh neurons but does not do so after repeated morphine. This could be an important factor in oxytocin modulation of reward-related behaviors, such as drug addiction. (C) 2015 Elsevier Inc. All rights reserved.