Patterns of hypothalamic GnIH change over the reproductive period in starlings and rats.

Gonadotropin inhibitory hormone (GnIH) exerts powerful inhibitory effects on various levels of the vertebrate hypothalamic-pituitary-gonadal (reproductive) axis, yet little is known of how it might change naturally over the course of reproduction. We characterized patterns of hypothalamic GnIH cell abundance over the reproductive period in two popular models used for the study of reproductive endocrinology: European starlings (Sturnus vulgaris) and Sprague-Dawley rats (Rattus norvegicus). We also examined the effects on an unpredictable change in the environment on GnIH cell abundance during the reproductive period, specifically during the period of parental care, by simulating a nest predation event and removing eggs/pups. In both species, we report changes in GnIH cell abundance are occurring at similar reproductive time points but are not always directionally parallel; this may be due to a difference in life histories and physiology mediating parental care. We discovered that cells immunoreactive for the GnIH peptide in male and female starlings are most highly abundant on the first day of incubation and the first day after the first chick hatches. Conversely in rats, GnIH cell abundance decreases in dams on the first day after pups are born. In both male and female starlings and female rats, GnIH cell abundance increases in response to egg/pup loss, indicating that GnIH responds to an unpredictable change in the environment in a potentially conserved fashion. These changes in GnIH cell abundance during the reproductive period inspire further investigation of its adaptive role in reproductive physiological events and behaviors, especially parental care.

A mechanistic approach to understanding range shifts in a changing world: What makes a pioneer?

A species' range can be thought of as a manifestation of the ecological niche in space. Within a niche, evolution has resulted in traits that maximize fitness. Across millennia, natural oscillations in temperature have caused shifts in the geographic location of appropriate habitat and with corresponding changes in species' ranges. Contemporary climate change and human disturbance may lead to rapid range expansion or contractions with largely unknown consequences. Birds provide an excellent case study of this phenomenon with some taxa expanding range and others contracting even to the point of extinction. What leads some populations to expand while others contract? Are there physiological and behavioral attributes of "pioneers" at the forefront of a range shift/expansion? The concept of allostasis provides a framework with which to begin to evaluate when a species will be able to successfully expand into new habitat. This tool allows the integration of normal energetic demands (e.g. wear and tear of daily and seasonal routines) with novel challenges posed by unfamiliar and human altered environments. Allostasis is particularly attractive because it allows assessment of how individual phenotypes may respond differentially to changing environments. Here, we use allostasis to evaluate what characteristics of individuals and their environment permit successful range expansion. Understanding variation in the regulatory mechanisms that influence response to a novel environment will be fundamental for understanding the phenotypes of pioneers.

Social and breeding status are associated with the expression of GnIH.

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.

Gonadotrophin-inhibitory hormone: a multifunctional neuropeptide.

Gonadotrophin-inhibitory hormone (GnIH) was discovered 8 years ago in birds. Its identification raised the possibility that gonadotrophin-releasing hormone (GnRH) is not the sole hypothalamic neuropeptide that directly influences pituitary gonadotrophin release. Initial studies on GnIH focused on the avian anterior pituitary as comprising the only physiological target of GnIH. There are now several lines of evidence indicating that GnIH directly inhibits pituitary gonadotrophin synthesis and release in birds and mammals. Histological studies on projections from hypothalamic GnIH neurones subsequently implied direct actions of GnIH within the brain and in the periphery. In addition to actions on the pars distalis via the median eminence, GnIH axons and terminals are present in multiple brain areas in birds, and the GnIH receptor is expressed on GnRH-I and -II neurones. Furthermore, we have demonstrated the presence of GnIH and its receptor in avian and mammalian gonads. Thus, GnIH can act directly at multiple levels: within the brain, on the pituitary and in the gonads. In sum, our data indicate that GnIH and its related peptides are important modulators of reproductive function at the level of the GnRH neurone, the gonadotroph and the gonads. Here, we provide an overview of the known levels of GnIH action in birds and mammals. In addition, environmental and physiological factors that are involved in GnIH regulation are reviewed.