Ventral Premammillary Nuclei Mediate Pheromonal-Induced LH Release Stimuli in the Rat

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Abstract
The rise in the concentration of LH [luteinizing hormone] in the serum that takes place in ovariectomized, estrogen-primed rats exposed to the odors from a cage with bedding soiled by a male rat was completely prevented by bilateral lesions destroying the ventral premammillary (PMv) nuclei. The pheromonal stimuli generate stimuli that course through a pathway which involves the PMv nuclei before they reach the hypothalamus. In addition, the chemosensory information is apparently transmitted centrally by an uncrossed pathway in view of the fact that removal of 1 vomeronasal organ combined with lesions of the contralateral PMv nucleus, but not of the ipsilateral nucleus, suppressed by the release of LH in rats exposed to male odors. Since pheromonal stimuli are known to activate the accessory olfactory system, of which the medial (Me) amygdaloid nucleus and the bed nucleus of the stria terminalis (BNST) are parts, the effect of stimulating these nuclei in rats bearing lesions of the PMv nucleus was also investigated. Unilateral lesions of the PMv nucleus prevented the release of LH in ovariectomized, estrogen-primed rats and the advancement of LH surge in proestrous rats induced by electrochemical stimulation (anodic d.c. 100 .mu.A/30 s) of the ipsilateral Me amygdaloid nucleus but not those induced by stimulation of the contralateral Me amygdaloid nucleus. Similar results were obtained stimulating the medial part of the BNST in proestrous rats. The impulses evoked by pheromonal stimuli inducing LH release in the rat are conveyed by an uncrossed pathway and relay in the PMv nucleus before they reach the medial basal hypothalamus.