Author's personal copy Sociosexual stimuli and gonadotropin-releasing hormone/ luteinizing hormone secretion in sheep and goats P.A.R. Hawken a,b, *, G.B. Martin a,b a School of Animal Biology, University of Western Australia, Crawley, West Australia, Australia b UWA Institute of Agriculture (Animal Production), University of Western Australia, Crawley, Western Australia, Australia Received 26 August 2011; received in revised form 18 January 2012; accepted 13 March 2012 Abstract Sociosexual stimuli have a profound effect on the physiology of all species. Sheep and goats provide an ideal model to study the impact of sociosexual stimuli on the hypothalamic-pituitary-gonadal axis because we can use the robust changes in the pulsatile secretion of luteinizing hormone as a bioassay of gonadotropin-releasing hormone secretion. We can also correlate these changes with neural activity using the immediate early gene c-fos and in real time using changes in electrical activity in the mediobasal hypothalamus of female goats. In this review, we will update our current understanding of the proven and potential mechanisms and mode of action of the male effect in sheep and goats and then briefly compare our understanding of sociosexual stimuli in ungulate species with the “traditional” definition of a pheromone. © 2012 Published by Elsevier Inc. Keywords: Pheromones; Olfactory; Reproduction; Kisspeptin; GnRH; LH 1. Introduction All mammals, particularly those that live in large groups, are immersed in a rich and complex social envi- ronment that is full of the sights, sounds, and smells of their neighbors, mates, and offspring [1]. These sensory inputs, the sociosexual signals, can profoundly alter many physiological and behavioral processes, includ- ing reproduction [2,3]. For example, in both female and male ungulates, exposure to a prospective mate induces an almost immediate increase in gonadotropin-releas- ing hormone (GnRH)/luteinizing hormone (LH) secre- tion, phenomena termed the “male effect” and “female effect,” respectively (Fig. 1). Olfactory signals, often called “pheromones,” are among the most potent of the sociosexual stimuli and can stimulate GnRH/LH secre- tion and induce ovulation in females, even in the ab- sence of additional sociosexual stimuli [4–6]. Changes in GnRH secretion into the hypophyseal circulation have not been measured directly in female sheep or goats exposed to males. However, the well-established relationship between GnRH and LH secretion [7] makes the measurement of LH secretion in the periph- eral circulation a reliable bioassay of GnRH secretion. Nonolfactory stimuli also help to achieve the optimum neuroendocrine and ovulatory response of females to males [8 –10], but recent work has shown that these stimuli play a relatively minor role and are unable to substitute for the full complement of sociosexual stim- uli in sheep or goats [10 –12]. The field of pheromone research has evolved dramatically since the initial con- cept of pheromones was proposed by Karlson and * Corresponding author. M085, School of Animal Biology, Uni- versity of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia. Tel: +61 (0)8 6488 3588; fax: +61 (0)8 6488 1029. E-mail address: penny.hawken@uwa.edu.au (P.A.R. Hawken). Available online at www.sciencedirect.com Domestic Animal Endocrinology 43 (2012) 85–94 www.domesticanimalendo.com 0739-7240/12/$ – see front matter © 2012 Published by Elsevier Inc. http://dx.doi.org/10.1016/j.domaniend.2012.03.005