Intrahypothalamic infusions of a synthetic heroin substitute, N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, potentiate mating behaviour in the female rat.

Acute microinfusions of N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) bilaterally into the arcuate-ventromedial area of the hypothalamus (ARC-VMH) produced a dose-dependent facilitation of lordosis behaviour in oestrogen- and oestrogen-progesterone-treated ovariectomized female rats. This facilitation could be blocked by pretreatment of the ARC-VMH site with pargyline but not by a potent antagonist analogue of gonadotropin releasing hormone (GnRH). MPTP was not effective in potentiating lordosis when microinfused into other brain sites which are intimately involved in the neural circuitry for this oestrogen-dependent behavioural response. This action of MPTP in the ARC-VMH may be dependent upon the high MPTP receptor densities which are known to occur in the arcuate and periventricular hypothalamic nuclei. Chronic infusions of MPTP (once daily for 21 days) into the ARC-VMH did not result in any significant cell loss and did not interfere with the ability of a later acute MPTP infusion to potentiate lordosis nor with the ability of oestrogen and progesterone to promote the full display of lordosis behaviour. These results provide the first demonstration of neurally placed MPTP in the regulation of a specific hormone-dependent neuroendocrine response.