Abstract. The aim of this study was to investigate the effect of luteinizing hormone (LH) surge on expression of nerve growth factor (NGF), trkA, p75 and inhibin α-subunit in ovarian interstitial cells of golden hamsters after human chorionic gonadotropin (hCG) treatment. NGF, two NGF receptors (trkA, p75) and inhibin α-subunit were immunolocalized by immunohistochemistry, and gonadotropins, steroid hormones and immunoreactive (ir-) inhibin concentrations were measured by radioimmunoassay. Stronger positive staining of NGF, trkA and p75 were found in interstitial cells at 6, 12 and 18 h after hCG injection in the treated group compared with the control groups. Inhibin α-subunit staining was found in interstitial cells at 12 and 18 h after hCG injection in the treatment group, but not in the control group. Plasma concentrations of progesterone increased significantly from 6 to 18 h after hCG treatment, whereas plasma concentrations of estradiol-17β significantly decreased compared with the control group. An increased plasma concentration of FSH and decreased concentrations of ir-inhibin from 6 to 18 h after hCG treatment verified the negative relationship. There were no significant changes in the concentrations of LH in the hCG-treated group. In contrast, the typical preovulatory LH surge was found at 1700 h on day 4 (proestrus) in the control group. These results suggested that LH surge can induce expression of NGF, trkA, p75 and inhibin α-subunit in ovarian interstitial cells and that NGF, trkA, p75 and inhibin α-subunit may have a paracrine or autocrine role in modulation of ovarian interstitial cell function in golden hamsters. Key words: Golden hamster, Inhibin α-subunit, Interstitial cell, Nerve growth factor (NGF), p75 and trkA (J. Reprod. Dev. 55: [622][623][624][625][626][627][628] 2009) erve growth factor (NGF) belongs to a family of related proteins required for survival, maintenance and development of discrete neuronal populations in the central and peripheral nervous systems [1][2][3]. The effect of NGF has been shown to be mediated through a specific high-affinity membrane receptor, tyrosine kinase A (trkA), that is responsible for NGF's biological activities [4,5]. Furthermore, the effect of NGF is also mediated via low affinity p75 receptor, which is also a receptor of other neurotropins [6]. It is now well known that the mammalian ovary not only contains four of the known neurotropins [7][8][9][10][11][12], but also expresses the receptors for each of them [13,14]. Previous papers have indicated that NGF and its receptors play a critical role in the development of mammalian ovary, oogenesis and folliculogenesis [15][16][17][18][19][20][21]. Inhibin and activins are dimeric glycoproteins formed by two of three different subunits (α, βA and βB). Inhibins consist of either of the β-subunits dimerized with a common α-subunit (α:βA and α:βB; inhibin A and inhibin B, respectively). Activins are dimers of β-subunits (βA:βA, βA:βB and βB:βB; activin A, activin AB and activin B, respectively). Inhibin/...