Allostasis in Neuroendocrine Systems Controlling Reproduction

Abstract

Allostasis provides a supporting role to the homeostatic control of biological variables in mammalian species. While the concept of homeostasis is related to the control of variables within a set point or range that are essential to life, allostasis refers to systems that facilitate adaptation to challenges that the organism faces and the new requirements for survival. Essential for such adaptation is the role played by the brain in eliciting neural and neuroendocrine responses. Reproductive function is fundamental for the survival of species but is costly in energetic terms and requires a synchrony with an ever-changing environment. Thus, in many species reproductive function is blocked or delayed over immediate challenges. This review will cover the physiological systems and neuroendocrine pathways that supply allostatic control over reproductive neuroendocrine systems. Light, hypoxia, temperature, nutrition, psychosocial, and immune mediators influence the neuroendocrine control of reproductive functions through pathways that are confluent at the paraventricular nucleus; however, understanding of the integrative responses to these stimuli has not been clarified. Likely, the ultimate consequence of these allostatic mechanisms is the modification of kisspeptin and gonadotropin-releasing hormone neuronal activity, thus compromising reproduction function in the short term, while preserving species survivability.

Keywords: GnRH; allostasis; homeostasis gonadotropin-releasing hormone; pulses; reproduction; stress.

Figure 1.

Comparison of luteinizing hormone (LH) profiles in mice treated with A, insulin; B, interleukin 1β; C, physical restraint; or D, corticosterone. Blood samples were collected from ovariectomized (insulin, interleukin 1β, restraint) or estrogen-treated ovariectomized (cortisol; Cort) mice before and after exposure to a stressor or a stress level of corticosterone (34, 85, 87, 88). Blood samples were analyzed at the University of Virginia assay core or an inhouse assay developed in our laboratory (89). Panels A, C, and D were originally published in refs. 34, 85, and 108 and has been adapted and reproduced by permission of Oxford University Press (http://global.oup.com/academic). Panel B was originally published in ref. 106 and has been adapted and reproduced by permission of Bioscientifica (https://www.bioscientifica.com/publishing/journals/).

Figure 2.

Schematic of allostatic factors (black boxes) suppressing GnRH and LH secretion through different hypothalamic nuclei (blue boxes). The involvement of the arcuate nucleus (Arc) or the anteroventral periventricular area (AVPV) kisspeptin neurons in the “stress” networks determines whether the LH pulse or surge secretion pattern are affected during an allostatic challenge. GnRH, gonadotrophin-releasing hormone; H, hypophysis; Kiss, kisspeptin; LH, luteinizing hormone; POA, preoptic area; PVN, paraventricular nucleus; SCN, suprachiasmatic nucleus; VMN, ventromedial nucleus.