EFFECT OF ELECTROCHEMICAL STIMULATION IN THE OLFACTORY BULBS ON THE RELEASE OF GONADOTROPIN HORMONES IN RATS

The olfactory bulbs were electrochemically stimulated in non-anesthetized, freely moving rats, and the ovulatory response and serum luteinizing hormone (LH) levels were studied. The stimulus was applied at 11:30 h through unilateral stainless steel electrodes chronically implanted, and serial blood samples were obtained by way of a plastic cannula located in the jugular vein. Electrochemical stimulation (100 μA/60 sec) of the main olfactory bulbs in the ventral aspect of the superficial layers as well as in its central core, performed on the day of proestrus, prevented the preovulatory discharge of LH and ovulation. Blockade of ovulation also occurred when the stimulus was applied in the lateral or medial parts of the superficial layers. On the other hand, stimulation in the dorsal part blocked the preovulatory surge of LH and ovulation in only 50% of the cases. Stimulation applied in the accessory olfactory bulbs failed to interfere with ovulation and LH discharge. Stimulation of ovariectomized estrogen-primed rats applied in the superficial layers of the main olfactory bulbs had no significant effect on the release of LH, but when the stimulus was applied in the accessory olfactory bulb a release of LH took place 3-6 h following stimulation. These results indicate that stimulation of the olfactory bulbs produce a dual effect on LH release: while the response of the accessory olfactory bulb is facilitatory in nature, that of the main olfactory bulbs is inhibitory.