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 hy pothalamus (VMH), the dorsal hypothalamus (DH), and the anterior hypothalam ic 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 lo wering cannulas into the VMH stimulated a rapid onset of maternal behaviour in progesterone plus oestrogen-primed, nulliparous rats, The stimulatory e ffect of cannula lowering into the VMH on maternal behaviour was shown to b e steroid-dependent. Next, the involvement of cell bodies located in the DH /AHA in maternal behaviour was examined after bilateral lesions of these re gions with the neurotoxin, N-methyl-D-aspartic acid (NMA). NMA lesions of t he DH/AHA stimulated a rapid onset of maternal behaviour in oestrogen-treat ed, nulliparous rats, while NMA lesions in non-steroid-treated animals or v ehicle 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 th e VMH were evaluated, As in AHA lesioned rats, NMA lesions of the VMH stimu lated a fast onset of maternal behaviour in steroid-primed females. These f indings indicate that the VMH as well as the DH/AHA exert chronic steroid-d ependent inhibitory influences on the induction of maternal behaviour.