Hypothalamic involvement in the regulation of maternal behaviour in the rat: inhibitory roles for the ventromedial hypothalamus and the dorsal/anterior hypothalamic areas.

The present report examines the possible involvement of the ventromedial hypothalamus (VMH), the dorsal hypothalamus (DH), and the anterior hypothalamic area (AHA) in the regulation of maternal behaviour in the female rat. In a series of experiments it was found that either infusions of saline or lowering cannulas into the VMH stimulated a rapid onset of maternal behaviour in progesterone plus oestrogen-primed, nulliparous rats. The stimulatory effect of cannula lowering into the VMH on maternal behaviour was shown to be steroid-dependent. Next, the involvement of cell bodies located in the DH/AHA in maternal behaviour was examined after bilateral lesions of these regions with the neurotoxin, N-methyl-D-aspartic acid (NMA). NMA lesions of the DH/AHA stimulated a rapid onset of maternal behaviour in oestrogen-treated, nulliparous rats, while NMA lesions in non-steroid-treated animals or vehicle infusions in steroid or non-steroid-treated rats failed to induce a rapid onset of behaviour. In a final study the effects of NMA lesions of the VMH were evaluated. As in AHA lesioned rats, NMA lesions of the VMH stimulated a fast onset of maternal behaviour in steroid-primed females. These findings indicate that the VMH as well as the DH/AHA exert chronic steroid-dependent inhibitory influences on the induction of maternal behaviour.