Differential regional brain responses to induced maternal behavior in rats measured by cytochrome oxidase immunohistochemistry.

Maternal behavior (MB) in rats is expressed under neural control of vomeronasal structures. Some of these regions exert an inhibitory role, such as the accessory olfactory bulb (AOB), while others exert an excitatory role, such as the medial preoptic area (MPOA). In previous studies, using 2-DG as a marker for neuron activity at neuron terminal level, we reported that AOB showed a decrease and MPOA an increase when compared with control rats (non-exposed to pups) during the display of MB. In the present study we used a different indicator of neuronal metabolic activity - cytochrome oxidase (COx) - to assess the activity of the same brain regions in relation to induced MB. The induced-MB females showed increased COx expression in the MPOA and reduced COx activity in the AOB in comparison with the control, non-MB group, consistent with our previous findings using 2-DG. Present results provide further evidence of a facilitatory role of MPOA and an inhibitory role of AOB in MB induction.