Distribution of galanin receptor-2 immunoreactive neurones in the ovine hypothalamus: no evidence for involvement in the control of gonadotrophin-releasing hormone secretion.
Galanin is a small neuropeptide that mediates its effects via three receptor isoforms: galanin receptor-1, galanin receptor-2 and galanin receptor-3 (Gal-R1, Gal-R2 and Gal-R3). Galanin is thought to be an important intermediate in signalling in the hypothalamic-pituitary-gonadal axis and has been widely detected in the ovine hypothalamus. The expression of galanin and Gal-R1 has been reported to fluctuate during the reproductive cycle. Although the distribution of Gal-R1 has been determined in the ovine hypothalamus, the distribution of Gal-R2 was hitherto unknown. Using immunohistological and immunofluorescence techniques, we have mapped the distribution of Gal-R2 in the ovine hypothalamus, collected during the follicular phase of the oestrous cycle and examined colocalisation of Gal-R2 with oestrogen receptor alpha (ERalpha) and gonadotrophin-releasing hormone (GnRH). Gal-R2 was expressed in several regions of the hypothalamus (supraoptic nucleus, paraventricular nucleus, ventromedial nucleus, arcuate nucleus) but not as widely expressed as Gal-R1. Areas of Gal-R2 expression overlapped with those reported for Gal-R1. We observed that, in certain defined regions of the hypothalamus, up to 50% of neurones that express Gal-R2 also express ERalpha. No neurones coexpressed Gal-R2 and GnRH. Thus, we conclude that, in follicular phase animals, this receptor plays little or no role in direct intermediary signal transmission in GnRH-mediated control of the reproductive cycle.
Chambers
G
G
Division of Cell Sciences, Institute of Comparative Medicine, Faculty of Veterinary Medicine, University of Glasgow, UK.
Whitelaw
C M
CM
Robinson
J E
JE
Evans
N P
NP
D000818:Animals; D047628:Estrogen Receptor alpha / Q000378:metabolism / Q000502:physiology; D030762:Estrous Cycle / Q000502:physiology; D005260:Female; D019084:Fluorescent Antibody Technique, Indirect; D007987:Gonadotropin-Releasing Hormone / Q000096:biosynthesis / Q000378:metabolism*; D007031:Hypothalamus / Q000166:cytology / Q000378:metabolism*; D007150:Immunohistochemistry; D009474:Neurons / Q000378:metabolism*; D044092:Receptor, Galanin, Type 2 / Q000096:biosynthesis / Q000378:metabolism*; D012756:Sheep
D047628:Estrogen Receptor alpha; D044092:Receptor, Galanin, Type 2; D007987:Gonadotropin-Releasing Hormone