Social and breeding status are associated with the expression of GnIH

Abstract

Discoveries of how social behavior can influence the plasticity of gonadotropin-releasing hormone (GnRH) have revolutionized the field of behavioral neuroendocrinology by providing new insights into the neural mechanisms controlling behavior. In 2000, the neuropeptide gonadotropin inhibitory hormone (GnIH) was discovered and is changing the way we view how the brain mediates reproduction and associated behaviors. GnIH acts as a reproductive 'pause button', momentarily inhibiting the activity of the reproductive system. However, how GnIH fluctuates naturally in response to social environment is unknown. We examine how the outcome of competition for limited resources needed for reproduction is associated with GnIH. We experimentally manipulated nesting opportunities for pairs of European starlings (Sturnus vulgaris) and examined brain GnIH mRNA and peptide content, as well as GnRH content and plasma testosterone and corticosterone. By limiting the number of nest boxes per enclosure and thus the number of social pairing and nesting opportunities, we observed that birds which outcompeted others for nest boxes ('winners') had significantly fewer numbers of GnIH peptide-producing cells than those without nest boxes ('losers') and this relationship changed with breeding stage. GnRH content, testosterone and corticosterone did not vary with nest box ownership. Thus, while birds appeared reproductively capable across treatments, our data indicate that GnIH may serve as a modulator of reproductive behaviors in response to social environment. Additionally, we provide some evidence of the adaptive value of this mechanism. . For all vertebrates studied, the gonadotropin-releasing hormone (GnRH) family of peptides is a key regulator of the reproductive, or hypothalamic-pituitary-gonadal (HPG), axis. Gonadotropinreleasing hormone released from the hypothalamus signals the anterior pituitary gland to release the gonadotropic hormones luteinizing hormone (LH) and follicle-stimulating hormone (FSH) into the bloodstream. Luteinizing hormone and FSH then promote testicular spermatogenesis, follicular growth and estradiol and testosterone release which feedback to and modulate all levels of the HPG axis. Several studies on how social behavior can influence the plasticity of the GnRH system have revolutionized the field of behavioral and reproductive neuroendocrinology by expanding our understanding of how social interactions can influence neural mechanisms associated with reproduction (Burmeister 2005;Fox et al. 1997;Francis et al. 1993). The discovery of the novel neurohormone gonadotropin inhibitory hormone (GnIH; Tsutsui et al.) in 2000 is changing the way we view how reproduction and sexual behavior are regulated by the brain.Found in the area of the brain responsible for reproduction, the hypothalamus, GnIH inhibits reproduction and sexual behavior. Gonadotropin inhibitory hormone decreases the activity of GnRH neurons in addition to reducing synthesis and release of the gonadotropins LH and, in some cases, FSH from the pituita...

The Impact of Exposure to a Novel Female on Symptoms of Infection and on the Reproductive Axis

“…This result fits with previous observations that the number of GnIH-ir cells is increased by LPS injection [19]. High levels of GnIH neuropeptide in the hypothalamus could mean a preparedness to ‘pause' reproduction [58], which would be a parsimonious explanation during infectious states.…”

Neuroanatomical Organization of the Brain Gonadotropin-Inhibitory Hormone and Gonadotropin-Releasing Hormone Systems in the Frog <b><i>Pelophylax esculentus</i></b>

“…Because it has been demonstrated in another bird that the GnIH system changes in response to photoperiodic manipulation experiments [Bentley et al, 2003], it is also possible that the lack of GnIH-ir fibers in the median evidence of our samples could be related to their unreproductive status. However, to confirm this hypothesis it is necessary to perform a detailed study covering the entire frog reproductive cycle, as previously reported for the European starling [Calisi et al, 2011].…”

Female competition and aggression: interdisciplinary perspectives

“…Functional individual variation in hormones is also of relevance, but is still a relatively neglected area of investigation [155]. Here, there is potential to explore mechanisms underlying individual variation in female behaviour and reproductive suppression, for example, involving gonadotropin inhibitory hormone (GnIH), which suppresses the hypothalamic-pituitary-gonadal axis and is responsive to stress and environmental cues in vertebrates [156,157].…”