Effect of Electrochemical Stimulation in the Olfactory Bulbs on the Release of Gonadotropin Hormones in Rats

Abstract

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.

Release of LH in the Female Rat by Olfactory Stimuli

“…Lesioning this site suppressed the release of LH evoked by olfactory stimuli in the present study, whereas its stimulation was shown to produce opposite effects [3]. The AOBs in turn project to the corticomedial nuclei of the amygdala and the bed nucleus of the stria terminalis con necting via the stria terminalis with the hypothalamus.…”

“…The AOBs in turn project to the corticomedial nuclei of the amygdala and the bed nucleus of the stria terminalis con necting via the stria terminalis with the hypothalamus. In terestingly, stimulation of these sites also resulted in the se cretion of LH [2][3][4],…”

Olfactory Bulb Removal Does Not Prevent Gonadotropin or Prolactin Responses to Changing Photoperiod in the Ewe

“…Studies investigating pheromonal in fluences on the hypothalamopituitary-gonadal axis sug gest species differences in the source of the pheromones and in the specific olfactory system mediating the re sponses. In rodents, male pheromones in the urine mod ulate behavioral and pituitary hormone responses of the female via the accessory (stimulatory) [40][41][42][43] and main (inhibitory) [40] olfactory systems. Substances present in skin secretions of rams, but not in their urine, are effective in stimulating LH secretion in the ewe via the main olfac tory system [15,44], Severing the vomeronasal input to the accessory olfactory bulb in rats prevents pheromonal cues from activating the hypothalamopituitary axis [45,46], while in ewes such procedures are ineffective [44].…”

Removal of the Vomeronasal Organ Impairs Lordosis in Female Hamsters: Effect Is Reversed by Luteinising Hormone-Releasing Hormone

“…Additionally, LHRH immunoreactive fibers project to the interpeduncu lar nucleus and dorsal midbrain, regions which contain neurons strongly responsive to lordosis trigger stimuli, and where lesions impair lordosis in hamsters [29,30]. We can not say whether vomeronasal signals normally lead to the release of LHRH, or whether LHRH influences lordosis in dependently: however, there is evidence which implicates the accessory olfactory system in LHRH release [2][3][4]10] and in raised serum luteinising hormone, an effect that can be prevented by vomeronasal organ removal [5].…”