General and Comparative Endocrinology 146 (2006) 86–94 www.elsevier.com/locate/ygcen 0016-6480/$ - see front matter  2005 Elsevier Inc. All rights reserved. doi:10.1016/j.ygcen.2005.10.017 Expression of hypothalamic GnRH-I mRNA in the female turkey at diVerent reproductive states and following photostimulation Seong W. Kang a , Aree Thayananuphat a , Israel Rozenboim b , James R. Millam c , John A. Proudman d , Mohamed E. El Halawani a,¤ a Department of Animal Science, University of Minnesota, 495 AnSci/Vet Med Bldg., 1988 Fitch Ave., St. Paul, MN 55108 ,USA b Department of Animal Science, Faculty of Agriculture, The Hebrew University of Jerusalem, P.O. Box 12, Rehovot 76100, Israel c Department of Animal Science, University of California, Davis, CA 95616, USA d Biotechnology and Germplasm Laboratory, USDA Agricultural Research Service, Beltsville, MD 20705, USA Received 4 February 2005; revised 7 September 2005; accepted 9 October 2005 Available online 19 January 2006 Abstract In birds, changes in hypothalamic gonadotropin-releasing hormone-I (GnRH-I) content and release are correlated with reproductive stages. This study examined the distribution and expression level of GnRH-I mRNA in anatomically discrete hypothalamic nuclei throughout the turkey reproductive cycle and following photostimulation. GnRH-I mRNA expression was determined using in situ hybridization in non-photostimulated (NPS), egg-laying (LAY), incubating (INC) and photorefractory (REF) hens. Overall, GnRH-I mRNA expression was greatest in the nucleus commissurae pallii (nCPa) and around the organum vasculosum lamina terminalis (OVLT), with less expression observed in the nucleus septalis lateralis (SL), cortico-habenula cortico-septum area, and within the nucleus preopticus medialis. GnRH-I mRNA expression was signiWcantly increased in nCPa, OVLT, and SL after NPS hens (6L:18D) were exposed to a 30 or 90 min pulse of light beginning 14 h after Wrst light (dawn). GnRH-I mRNA abundance within nCPa, OVLT and SL was greater in LAY than in NPS and INC hens, while mRNA expression was least in REF hens. These results indicate that GnRH-I mRNA expression in birds is sensitive to light stimulation during the photosensitive period and can be used to more precisely characterize their diVerent reproductive stages.  2005 Elsevier Inc. All rights reserved. Keywords: GnRH-I mRNA expression; Turkey reproductive cycle; Photostimulation; Avian hypothalamus; In situ hybridization 1. Introduction In birds, the secretion of luteinizing hormone (LH) is con- trolled by gonadotropin releasing hormone-I (GnRH-I) (Sharp et al., 1998). The distribution and changes in GnRH immunoreactivity has been reported in brain areas of several avian species (Deviche et al., 2000; Katz et al., 1990; Kuenzel and Blahser, 1991; Mikami and Yamada, 1984; Mikami et al., 1988; Millam et al., 1993; Parry et al., 1997). Although there are species diVerences, signiWcant populations of immu- noreactive perikarya are located in the septal, preoptic and anterior hypothalamus, lying close to midline (Kuenzel and Blahser, 1991). Several studies have reported the distribution of GnRH-I mRNA and protein in avian brains (Dawson et al., 2002; Dunn and Sharp, 1999; Millam et al., 1989; Sun et al., 2001). However, the topographical distribution pattern of avian GnRH-I mRNA has not been well coordinated with the reproductive conditions. Photic stimuli play a pivotal role in the initiation of sexually-related neuroendocrine and behavioral changes in birds (Peczely and Kovacs, 2000). The eVects of season and photostimulation on the hypothalamic- gonadal axis are well characterized, while the mechanisms that transduce relevant photic information to neuroendo- crine eVector neurons are not well established (Cho et al., 1998; Dawson and Goldsmith, 1997; Dunn and Sharp, 1999; Peczely and Kovacs, 2000). Time-course analysis of changes * Corresponding author. Fax: +1 612 625 2743. E-mail address: elhal001@umn.edu (M.E. El Halawani).