Lipopolysaccharide injection induces rapid decrease of hypothalamic GnRH mRNA and peptide, but does not affect GnIH in zebra finches

Lipopolysaccharide (LPS) is frequently used experimentally to mimic acute infection. Through activation of the host's immune response, an LPS injection has profound effects on the adrenocortical response to stress and on behaviors including reduction in activity, water and food intake, and libido. These behavioral changes occurring during infection are collectively called "sickness behavior." It is thought that adoption of sickness behavior reallocates energy from other fitness-enhancing activities, such as reproduction, for use in the immune response. Although the behavioral effects of LPS treatment are well-known, less information is available regarding the effects of LPS on the brain in terms of controlling reproductive behavior, specifically concerning a newly discovered neuropeptide, gonadotropin-inhibitory hormone (GnIH). This study investigated the effects of an LPS injection on the behavior and the hypothalamic neuropeptides controlling reproduction [GnIH and gonadotropin-releasing hormone (GnRH)] of zebra finches (Taeniopygia guttata). Overall, there was a decrease in activity in birds injected with LPS. The number of GnRH-immunoreactive neurons was significantly reduced in birds injected with LPS when compared to controls, while the number of GnIH-releasing neurons remained unchanged. At the level of gene expression, a similar pattern was found: there was reduced expression of GnRH mRNA in LPS-injected animals, whereas GnIH expression remained unchanged. Plasma testosterone did not change significantly in LPS-injected animals, nor did plasma corticosterone. Taken together, these results indicate a rapid (within 3h) inhibition of the reproductive axis during an immune challenge mimicking an infection, specifically acting on the GnRH system. The present study expands our knowledge on the interaction between the immune system and the reproductive system.     

Rapid inhibition of female sexual behavior by gonadotropin-inhibitory hormone (GnIH)

Gonadotropin-releasing hormone (GnRH) is largely responsible for the initiation of sexual behaviors; one form of GnRH activates a physiological cascade causing gonadal growth and gonadal steroid feedback to the brain, and another form is thought to act as a neurotransmitter to enhance sexual receptivity. In contrast to GnRH, gonadotropin-inhibitory hormone (GnIH) inhibits gonadotropin release. The distribution of GnIH in the avian brain suggests that it has not only hypophysiotropic actions but also unknown behavioral actions. GnIH fibers are present in the median eminence (ME) and are in apparent contact with chicken GnRH (cGnRH)-I and -II neurons and fibers. In birds, cGnRH-I regulates pituitary gonadotropin release, whereas cGnRH-II enhances copulation solicitation in estradiol-primed females exposed to male song. In the present study, we determined the effects of GnIH administered centrally to female white-crowned sparrows. A physiological dose of GnIH reduced circulating LH and inhibited copulation solicitation, without affecting locomotor activity. Using rhodaminated GnIH, putative GnIH binding sites were seen in the ME close to GnRH-I fiber terminals and in the midbrain on or close to GnRH-II neurons. These data demonstrate direct effects of GnIH upon reproductive physiology and behavior, possibly via separate actions on two forms of GnRH.     

Interactions of gonadotropin-releasing hormone (GnRH) and gonadotropin-inhibitory hormone (GnIH) in birds and mammals

Gonadotropin-releasing hormone (GnRH) regulates secretion of both of the gonadotropins, luteinizing hormone (LH) and follicle-stimulating hormone. Thus, it is a key hormone for vertebrate reproduction. GnRH was considered to be unusual among hypothalamic neuropeptides in that it appeared to have no direct antagonist, although some neurochemicals and peripheral hormones (opiates, GABA, gonadal steroids, inhibin) can modulate gonadotropin release to a degree. Five years ago, a vertebrate hypothalamic neuropeptide that inhibited pituitary gonadotropin release in a dose-dependent manner was discovered in quail by Tsutsui et al. (2000. Biochem Biophys Res Commun 275:661-667). We now know that this inhibitory peptide, named gonadotropin-inhibitory hormone, or GnIH, is a regulator of gonadotropin release in vitro and in vivo. Its discovery has opened the door to an entirely new line of research within the realm of reproductive biology. In our collaborative studies, we have begun to elucidate the manner in which GnIH interacts with GnRH to time release of gonadotropins and thus time reproductive activity in birds and mammals. This paper reviews the distribution of GnIH in songbirds relative to GnRHs, and our findings on its modes of action in vitro and in vivo, based on laboratory and field studies. These data are simultaneously compared with our findings in mammals, highlighting how the use of different model species within different vertebrate classes can be a useful approach to identify the conserved actions of this novel neuropeptide, along with its potential importance to vertebrate reproduction.     

Cavity-nesting birds are limited by nesting habitat in Neotropical agricultural landscapes

Most studies comparing biodiversity between natural and human-modified landscapes focus on patterns in species occurrence or abundance, but do not consider how different habitat types meet species' breeding requirements. Organisms that use or nest in tree cavities may be especially threatened by habitat conversion due to the loss of their nesting sites. Although cavity-nesting bird diversity is highest in the tropics, little is known about how tropical birds use cavities, how agriculture affects their reproductive biology, and how effective nest boxes could be as a conservation strategy in tropical agriculture. Here, we explored how habitat conversion from tropical forests to pasture affects the abundance, nesting habitat availability, and nest success of cavity-nesting birds in Northwest Ecuador. We conducted bird surveys and measured natural cavity availability and use in forest and agriculture. We also added artificial nest boxes to forest and agriculture to see whether cavity limitation in agriculture would elicit higher use of artificial nest boxes. We found evidence of cavity limitation in agriculture—there were many more natural cavities in forest than in agriculture, as well as more avian use of nest boxes placed in agriculture as compared to forest. Our results suggest that it is important to retain remnant trees in tropical agriculture to provide critical nesting habitat for birds. In addition, adding nest boxes to tropical agricultural systems could be a good conservation strategy for certain species, including insectivores that could provide pest-control services to farmers. Abstract in Spanish is available with online material.     

RNA interference of gonadotropin-inhibitory hormone gene induces arousal in songbirds

Gonadotropin-inhibitory hormone (GnIH) was originally identified in quail as a hypothalamic neuropeptide inhibitor of pituitary gonadotropin synthesis and release. However, GnIH neuronal fibers do not only terminate in the median eminence to control anterior pituitary function but also extend widely in the brain, suggesting it has multiple roles in the regulation of behavior. To identify the role of GnIH neurons in the regulation of behavior, we investigated the effect of RNA interference (RNAi) of the GnIH gene on the behavior of white-crowned sparrows, a highly social songbird species. Administration of small interfering RNA against GnIH precursor mRNA into the third ventricle of male and female birds reduced resting time, spontaneous production of complex vocalizations, and stimulated brief agonistic vocalizations. GnIH RNAi further enhanced song production of short duration in male birds when they were challenged by playbacks of novel male songs. These behaviors resembled those of breeding birds during territorial defense. The overall results suggest that GnIH gene silencing induces arousal. In addition, the activities of male and female birds were negatively correlated with GnIH mRNA expression in the paraventricular nucleus. Density of GnIH neuronal fibers in the ventral tegmental area was decreased by GnIH RNAi treatment in female birds, and the number of gonadotropin-releasing hormone neurons that received close appositions of GnIH neuronal fiber terminals was negatively correlated with the activity of male birds. In summary, GnIH may decrease arousal level resulting in the inhibition of specific motivated behavior such as in reproductive contexts.     

Surplus nest boxes and the potential for polygyny affect clutch size and offspring sex ratio in house wrens

Females of many species can gain benefits from being choosy about their mates and even exhibit context-dependent investment in reproduction in response to the quality of their breeding situation. Here, we show that if a male house wren is provided with surplus nest boxes in his territory, his mate lays a larger clutch with a significantly higher proportion of sons. This response to a territory characteristic directly associated with male competitive ability, and ultimately to male reproductive success, suggests that male competition over access to high-quality territories with surplus nest boxes (i.e. those able to support polygyny) may influence female reproductive investment decisions. The results of this study have interesting implications, particularly considering the important role that studies of cavity nesting birds utilizing nest boxes have played in advancing our understanding of behaviour, ecology and evolution.     

Defending the Weak: Parental Defense Peaks When Chick Vulnerability is Greatest in the Herring Gull (Larus argentatus)

Successful reproduction often depends upon parents providing offspring with resources and protection. In birds, reproductive success can often be enhanced by parents engaging in antipredator behaviors, but these behaviors can be costly. Theoretically, individuals should temporally modify the intensity of nest defense behavior to balance the costs and benefits of current and future reproductive success. More specifically, nest defense should vary throughout a nesting attempt to maximize fitness of the adults. Here, we consider the relationship between nest defense behavior and chick vulnerability in the herring gull (Larus argentatus), where chicks are under high predation risk. We estimated chick vulnerability by quantifying survival probabilities at different periods of the nestling stage. Simultaneously, we quantified changes in parental aggression throughout the nesting cycle by simulating predation attempts using a human predator model. We found that chick survival probabilities were lowest (i.e., vulnerability was highest) and parental aggression in nest defense was greatest during the first 10 days after hatching. Thus, we show that parents are most defensive when chicks are most vulnerable and that adults optimize nest defense behaviors in a way that maximizes their fitness.     

Mode of action and functional significance of avian gonadotropin-inhibitory hormone (GnIH): a review

Neuropeptide control of gonadotropin secretion at the level of the anterior pituitary gland is primarily through the stimulatory action of the hypothalamic decapeptide, gonadotropin-releasing hormone (GnRH). However, a hypothalamic neuropeptide acting at the level of the pituitary to negatively regulate gonadotropin secretion has, until recently, remained unknown in any vertebrate. In 2000, we discovered a novel hypothalamic neuropeptide inhibiting gonadotropin release at the level of the pituitary in quail and termed it gonadotropin-inhibitory hormone (GnIH). A gonadotropin-inhibitory system is an intriguing concept and provides us with an unprecedented opportunity to study the regulation of avian reproduction from an entirely novel standpoint. To elucidate the mode of action of GnIH, we further identified the receptor for GnIH and characterized its expression and binding activity in quail. The identified GnIH receptor possessed seven transmembrane domains and specifically bound to GnIH in a concentration-dependent manner. The expression of GnIH receptor was found in the pituitary and several brain regions including the hypothalamus. These results suggest that GnIH acts directly on the pituitary via GnIH receptor to inhibit gonadotropin release. GnIH may also act on the hypothalamus to inhibit GnRH release. To understand the functional significance of GnIH in avian reproduction, we also investigated the mechanism that regulates GnIH expression. Interestingly, melatonin induced dose-dependently GnIH expression and melatonin receptor (Mel(1c)) was expressed in GnIH neurons. Thus melatonin appears to act directly on GnIH neurons via its receptor to induce GnIH expression. Based on these studies, GnIH is likely an important neuropeptide for the regulation of avian reproduction.     

Reproduction in shark-attacked sea turtles is supported by stress-reduction mechanisms

Vertebrates exhibit varied behavioural and physiological tactics to promote reproductive success. We examined mechanisms that could enable female loggerhead turtles to undertake nesting activities and maintain seasonal reproduction despite recent shark injuries of varying severity. We proposed that endocrinal mechanisms that regulate both a turtle's stress response and reproductive ability are modified to promote successful and continued reproduction. Irrespective of the degree of injury, females did not exhibit increased levels of the stress hormone corticosterone, nor decreased levels of the reproductive steroid testosterone; hormone responses consistent with stress. When exposed to a capture stressor, females with shark injury did not exhibit any greater corticosterone response than controls. In addition, breeding females showed a reduced corticosterone stress response compared to non-breeding females. Reduced endocrinal responses following shark injury, and during breeding in general may, in part, enable females to maintain behavioural and physiological commitment to reproduction.     

Gonadotropin releasing hormone (GnRH) and gonadotropin inhibitory hormone (GnIH) in the songbird hippocampus: Regional and sex differences in adult zebra finches

Hypothalamic gonadotropin releasing hormone (GnRH) and gonadotropin inhibitory hormone (GnIH) are vital to reproduction in all vertebrates. These neuropeptides are also present outside of the hypothalamus, but the roles of extra-hypothalamic GnRH and GnIH remain enigmatic and widely underappreciated. We used immunohistochemistry and PCR to examine whether multiple forms of GnRH (chicken GnRH-I (GnRH1), chicken GnRH-II (GnRH2) and lamprey GnRH-III (GnRH4)) and GnIH are present in the hippocampus (Hp) of adult zebra finches (Taeniopygia guttata). Using immunohistochemistry, we provide evidence that GnRH1, GnRH2 and GnRH4 are present in hippocampal cell bodies and/or fibers and that GnIH is present in hippocampal fibers only. There are regional differences in hippocampal GnRH immunoreactivity, and these vary across the different forms of GnRH. There are also sex differences in hippocampal GnRH immunoreactivity, with generally more GnRH1 and GnRH2 in the female Hp. In addition, we used PCR to examine the presence of GnRH1 mRNA and GnIH mRNA in micropunches of Hp. PCR and subsequent product sequencing demonstrated the presence of GnRH1 mRNA and the absence of GnIH mRNA in the Hp, consistent with the pattern of immunohistochemical results. To our knowledge, this is the first study in any species to systematically examine multiple forms of GnRH in the Hp or to quantify sex or regional differences in hippocampal GnRH. Moreover, this is the first demonstration of GnIH in the avian Hp. These data shed light on an important issue: the sites of action and possible functions of GnRH and GnIH outside of the HPG axis.     

American Kestrel reproduction: evidence for the selection hypothesis and the role of dispersal

Many hypotheses attempt to explain why younger, less experienced birds have a relatively low reproductive output. We evaluated reproductive patterns of marked American Kestrels Falco sparverius nesting in boxes in southwestern Idaho from 1992 to 2006 to test predictions of these hypotheses. Results were consistent with the selection (differential mortality) hypothesis and did not support the constraint, restraint or recruitment hypotheses. Most known-age Kestrels nested in their first year of life, and there was no apparent short-term or long-term reproductive advantage to delayed breeding. The number of years that Kestrels nested in study area boxes ranged from 1 to 6 years, with most Kestrels nesting in only 1 year. Reproductive rates were higher for birds with at least 1 year of nesting experience than for birds nesting in boxes for the first time. After 2 years of nesting, reproductive rates levelled off; there was no evidence for additional improvement or for senescence. Differences in reproductive output with experience/age were due to variation among and not within individuals. Individuals that nested in more than 1 year had similar reproductive rates in their first and second years. Poor producers either died or dispersed after 1 year of nesting in study area boxes. Successful females that nested early in the season and successful males that had been produced locally had the highest probability of returning to nest in a subsequent year.     

Perceived risk of ectoparasitism reduces primary reproductive investment in tree swallows Tachycineta bicolor

Many birds have been shown to reduce their reproductive investment in response to infestation of nest sites by ectoparasites. Nest-dwelling parasite populations increase throughout the breeding season, and can reduce the condition and future survival of both breeding adults and their offspring. Thus, avian hosts should be capable of assessing early cues that predict future ectoparasitism risk, and should be able to facultatively adjust their primary reproductive investment in response to anticipated future costs of parasites. We tested this hypothesis in the tree swallow Tachycineta bicolor , a cavity nesting passerine, by presenting a visual cue of avian fleas on the outer surface of nest boxes. This treatment manipulated perceived ectoparasitism risk without exposing birds to parasites, thereby allowing us to examine facultative responses in the absence of early physiological effects of parasites on female reproductive investment. During one of the study years, birds preferentially occupied control boxes, however, across both years, birds nesting in treatment boxes produced significantly smaller clutches, resulting in smaller broods at hatching, relative to those in control boxes. This difference in clutch size could not be explained by differences in phenotypic quality of breeding birds, indicating that for cavity nesting birds such as tree swallows, the perception of future ectoparasitism risk may be sufficient to induce a facultative reduction in reproductive investment early in the breeding season, before nest-dwelling parasite populations have grown very large.     

Nest sites as limiting resources for cavity‐nesting birds in mature forest ecosystems: a review of the evidence

ABSTRACT Assumptions that populations of cavity‐nesting birds are limited by access to nest sites have largely been based on anecdotal reports or correlative data. Nest‐box‐addition experiments or tree‐cavity‐blocking experiments are potentially rigorous ways to investigate how densities of breeding birds are affected by access to nest cavities. Experimental evidence indicates that natural tree holes are limited in human‐altered landscapes, but the possibility that cavity nests are limited in old growth (unmanaged) forests is less clear. I reviewed 31 nest‐cavity‐removal or addition experiments conducted with 20 species of cavity‐nesting birds in mature forests. Of these 31 experiments conducted with a variety of different species of birds, only 19% reported statistically significant changes in breeding densities. However, none of these studies included data about the reproductive history of individuals colonizing the boxes (i.e., whether birds using the boxes would have otherwise been floaters or that birds excluded from blocked cavities on the plots did not simply move elsewhere), so they provided no strong evidence that the number of breeding pairs was limited by availability of nest sites at the population scale. Although some studies indicate that nest sites are limited at local (plot) scales in old growth forests, there is still little empirical evidence for nest‐site limitation at the population‐ and landscape‐level in mature, unmanaged forests. I review the challenges in designing and interpreting box‐addition experiments and highlight the main gaps in knowledge that should be targeted in the future.     

Elevated plasma corticosterone decreases yolk testosterone and progesterone in chickens: linking maternal stress and hormone-mediated maternal effects

Despite considerable research on hormone-mediated maternal effects in birds, the underlying physiology remains poorly understood. This study investigated a potential regulation mechanism for differential accumulation of gonadal hormones in bird eggs. Across vertebrates, glucocorticoids can suppress reproduction by downregulating gonadal hormones. Using the chicken as a model species, we therefore tested whether elevated levels of plasma corticosterone in female birds influence the production of gonadal steroids by the ovarian follicles and thus the amount of reproductive hormones in the egg yolk. Adult laying hens of two different strains (ISA brown and white Leghorn) were implanted subcutaneously with corticosterone pellets that elevated plasma corticosterone concentrations over a period of nine days. Steroid hormones were subsequently quantified in plasma and yolk. Corticosterone-implanted hens of both strains had lower plasma progesterone and testosterone levels and their yolks contained less progesterone and testosterone. The treatment also reduced egg and yolk mass. Plasma estrogen concentrations decreased in white Leghorns only whereas in both strains yolk estrogens were unaffected. Our results demonstrate for the first time that maternal plasma corticosterone levels influence reproductive hormone concentrations in the yolk. Maternal corticosterone could therefore mediate environmentally induced changes in yolk gonadal hormone concentrations. In addition, stressful situations experienced by the bird mother might affect the offspring via reduced amounts of reproductive hormones present in the egg as well as available nutrients for the embryo.     

Latitudinal trends in within-year reoccupation of nest boxes and their implications

Multiple brooding can substantially increase the annual reproductive output of birds, and the propensity for multiple brooding can vary geographically. Thus, studies attempting to understand the evolution of geographic variation in nesting success need to account for variation in re‐nesting potential. However, direct assessment of rates of multiple brooding requires individually recognizable breeding adults, which are not generally available. We explore the possibility of comparing relative indices of multiple broodedness across a latitudinal gradient from studies of un‐banded birds locally restricted to nest boxes. We analyzed nest box reoccupation by a multiple‐brooding species, the eastern bluebird Sialia sialis, reported by volunteers in a citizen‐participation project (1998–2002) in which nest boxes were monitored throughout much of the breeding range of the bluebirds. We found nest boxes in the southern portion of the bluebird range (30° latitude) had, on average 17–33% higher likelihood of repeated egg‐laying, brooding, and successful fledging events than boxes in the north (48° latitude). Latitudinal variation in the reoccupation of nest boxes may indicate that either (1) the number of broods per female varies with latitude, (2) female breeding dispersal/site fidelity varies with latitude, (3) the density, distribution, and/or availability of suitable nest sites varies with latitude, or (4) observer bias varies with latitude. Various lines of evidence suggest that nest re‐occupancy is a useful index of latitudinal variation in re‐nesting. During the time‐frame of second attempts, first‐time box occupancy was as likely as second occupancy and approximately 45% more likely in the south than north, suggesting that, despite considerable breeding dispersal, observed trends in box reoccupation conservatively reflect latitudinal trends in the number of nest attempts/broods per female. Furthermore, despite a compressed nesting cycle in the north (shorter incubation and re‐nesting interval), the shorter duration of the breeding season in the north restricted the potential number of broods. Studies of banded birds are necessary to confirm the behavior underlying the latitudinal trends in box reoccupation.     

Breeding orange-winged Amazon parrots in captivity

Captive propagation of parrots for the companion bird trade provides a potential means of reducing the economic incentive to capture these birds from the wild. To test whether environmental and social manipulations might stimulate reproduction in captive, wild-caught orange-winged Amazon parrots (Amazona amazonica), we compared reproductive performance in pairs presented with nest boxes (controls) or nest boxes plus additional environmental and social manipulations (enriched group) consisting of misting, fruit supplementation, nest hole restriction, enlarged nest boxes, and pair separation/reunification. In the first breeding trial, in 1990, enriched pairs were more likely to lay eggs (six of seven enriched pairs vs. one of eight control pairs; P < 0.09). When treatments were reversed the following years (e.g., 1990 controls were exposed to enriched conditions in 1991), reproductive performance was not different between the groups (four of seven enriched pairs laid eggs vs. five of seven control pairs), although three pairs in the 1991 enriched group laid eggs which had not laid eggs before. These results are consistent with the idea that while enriched environments may enhance the probability of a first episode of egg laying in captivity, once pairs have laid eggs in captivity, little stimulation beyond that provided by nest box presentation is required to reinitiate egg laying. The environmental and social manipulations of the enriched conditions could be useful in increasing reproductive performance of captive Amazon parrots for the companion bird trade. © 1995 Wiley-Liss, Inc.     

Nest site competition between cavity nesting passerines and golden paper wasps Polistes fuscatus

Nest boxes provide sheltered nesting sites for both passerines and paper wasps. Although neither wasps nor birds appear to evict the other once one is fully established, it is unclear which is the dominant competitor at the onset of the breeding season. Using wire mesh, we excluded birds but not golden paper wasps Polistesfuscatus from alternating boxes along a transect through edge habitat in North Carolina from 2006 – 2008. If wasps dominate Carolina chickadees Poecile carolinensis and eastern bluebirds Sialia sialis during the early spring (all have similar nest initiation dates), we would expect wasps to settle in both box types at equal frequencies. However, if birds dominate wasps, we would expect wasp nests to be concentrated in “bird‐proof” boxes. We found wasps in bird‐proof boxes significantly more often than in bird‐accessible boxes, indicating that secondary‐cavity nesting birds are able to exclude wasps from available nest sites. Additionally, we found that during the period of nest initiation, birds usurp wasps more often than vice versa.     

Nest Mosquito Trap quantifies contact rates between nesting birds and mosquitoes

Accurate estimates of host-vector contact rates are required for precise determination of arbovirus transmission intensity. We designed and tested a novel mosquito collection device, the Nest Mosquito Trap (NMT), to collect mosquitoes as they attempt to feed on unrestrained nesting birds in artificial nest boxes. In the laboratory, the NMT collected nearly one-third of the mosquitoes introduced to the nest boxes. We then used these laboratory data to estimate our capture efficiency of field-collected bird-seeking mosquitoes collected over 66 trap nights. We estimated that 7.5 mosquitoes per trap night attempted to feed on nesting birds in artificial nest boxes. Presence of the NMT did not have a negative effect on avian nest success when compared to occupied nest boxes that were not sampled with the trap. Future studies using the NMT may elucidate the role of nestlings in arbovirus transmission and further refine estimates of nesting bird and vector contact rates.     

Hormonal and behavioral responses of starlings during a confrontation with males or females at nest boxes during the reproductive season

We investigated in an aviary experiment the behavioral and hormonal responses of European starlings (Sturnus vulgaris) that were moved from a same sex group to an aviary containing either a nest box alone, a nest box and another male, or a nest box and a female. Luteinizing hormone (LH) and testosterone (T) levels increased significantly and independently of the situation, suggesting that nest boxes were the most important stimulus affecting the levels of these hormones. Some birds occupied more than two boxes (winners), and others a single or no box (losers). Levels of T increased less in males that did not acquire a nest box. However, the increase in LH was similar in all males after the test. Singing was positively correlated with T levels. Winners started singing earlier and sang more during a contest than losers. In the presence of females LH increased more in winners than in losers, while the increase in T was similar in both groups. In females, there was no increase in T but LH increased in the presence of males. Levels were higher in females paired with winners than in females paired with losers. Finally, winners advertised their nest boxes more frequently than losers. These results indicate that within a relatively short time frame levels of LH and T increase following the transfer from a flock to a territorial situation and can react independently from each other depending on reproductive circumstances. For males, the possession of a nest box and, for females, the qualities of the male seemed to be the most important factors stimulating reproduction.     

Gonadotropin-inhibitory hormone reduces sexual motivation but not lordosis behavior in female Syrian hamsters (Mesocricetus auratus)

Reproductive success is maximized when female sexual motivation and behavior coincide with the time of optimal fertility. Both processes depend upon coordinated hormonal events, beginning with signaling by the gonadotropin-releasing hormone (GnRH) neuronal system. Two neuropeptidergic systems that lie upstream of GnRH, gonadotropin-inhibitory hormone (GnIH; also known as RFamide related peptide-3) and kisspeptin, are potent inhibitory and excitatory modulators of GnRH, respectively, that participate in the timing of the preovulatory luteinizing hormone (LH) surge and ovulation. Whether these neuropeptides serve as neuromodulators to coordinate female sexual behavior with the limited window of fertility has not been thoroughly explored. In the present study, either intact or ovariectomized, hormone-treated female hamsters were implanted for fifteen days with chronic release osmotic pumps filled with GnIH or saline. The effect of GnIH on sexual motivation, vaginal scent marking, and lordosis was examined. Following mating, FOS activation was quantified in brain regions implicated in the regulation of female sexual behavior. Intracerebroventricular administration of GnIH reduced sexual motivation and vaginal scent marking, but not lordosis behavior. GnIH administration altered FOS expression in key neural loci implicated in female reproductive behavior, including the medial preoptic area, medial amygdala and bed nucleus of the stria terminalis, independent of changes in circulating gonadal steroids and kisspeptin cell activation. Together, these data point to GnIH as an important modulator of female proceptive sexual behavior and motivation, independent of downstream alterations in sex steroid production.