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Influence of Estradiol on NADPH Diaphorase/Neuronal Nitric Oxide Synthase Activity and Colocalization with Progesterone or Type II Glucocorticoid Receptors in Ovine Hypothalamus¹

^a Department of Clinical Veterinary Science, University of Bristol, Langford BS40 5DU, United Kingdom ^b Department of Zoology and Physiology, University of Wyoming, Laramie, Wyoming 82071

Nitric oxide (NO) has been shown to play an important role in both the neuroendocrine reproductive and stress axes, which are closely linked. Because progesterone (P₄) receptors (PRs) and glucocorticoid receptors (GRs) are not found in GnRH neurons and the NOergic system has been implicated in the control of GnRH secretion, this study aimed to ascertain whether steroids altered the NOergic system. Our first objective was to map the distribution of NO synthase (NOS) cells in the ovine preoptic area (POA) and hypothalamus and to determine whether NOS activity is enhanced by estradiol (E₂) treatment. Using NADPH diaphorase (NADPHd) histochemistry, we found that NADPHd-positive neurons were spread throughout the ovine POA and hypothalamus, and that all NADPHd cells were immunoreactive for NOS. In response to estradiol, a significant increase in the number of NADPHd cells was noted only in the ventrolateral region of the ventromedial nucleus (VMNvl), with no significant difference in the POA or arcuate nucleus. Progesterone and glucocorticoid receptors were colocalized with NADPHd reactive neurons in the POA, arcuate nucleus, and VMNvl of ewes in both treatment groups. In ewes receiving estradiol, the number of NADPHd-positive cells containing steroid receptors in the POA (PR, 81%; GR, 79%) and arcuate nucleus (PR, 89%; GR, 84%) was similar, but in the VMNvl, fewer NADPHd-positive cells contained GR (PR, 88%, GR, 31%). These data show that estradiol up-regulates NOS activity in a site-specific manner and that the influence and possible interaction of progesterone and corticosteroids on NO producing cells may differ according to the neural location.

First decision: 8 March 2002.

¹ L.D. was supported by Wellcome Trust Travelling Fellowship 061765/Z/00/Z.

² Correspondence: Laurence Dufourny, University of Wyoming, Department of Zoology and Physiology, Biological Science Building, Room 428, PO Box 3166, Laramie, WY 82071-3166. FAX: 307 766 5625; dufourny{at}uwyo.edu

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