Photoperiodically driven changes in Fos expression within the basal tuberal hypothalamus and median eminence of Japanese quail

The rapid photoperiodic response in Japanese quail is so precise that it allows neural analyses of how photoperiodic information is transduced into an endocrine response. After transfer from short [SD; 6L:18D (6:18 hr light/dark cycle)] to long (LD; 20L:4D) days, luteinizing hormone (LH) first rises 20 hr after dawn. Using Fos immunocytochemistry, we examined the basal tuberal hypothalamus (BtH) to determine the relationship between brain cell activation and the first endocrine changes. Two separate cell populations within the BtH expressed Fos-like immunoreactivity (FLI) by hour 18 of the first LD. Importantly, this activation occurred before the LH rise. Median eminence activation appeared within glial cells, whereas activated infundibular nucleus cells were neuronal, providing support to the view that gonadotropin-releasing hormone (GnRH) release can be controlled at the terminals by glia. The FLI induction parallels LH changes, suggesting that gene expression may be involved in events preceding photostimulation and is the earliest photoperiodically stimulated physiological change yet reported.Additional experiments provided further support for this hypothesis. First, photoperiodically induced activation is not a result peculiar to castrates because intact birds displayed similar results. Second, the critical length of 14 hr of light had to be exceeded to cause both BtH activation and a LH rise 30 hr from dawn. Finally, valuable evidence of the response specificity was provided by using a unique property of the quail photoperiodic clock in which exposure to 10L:26D, but not 10L:14D, causes photoinduction. The 36 hr paradigm increased both plasma LH and BtH activation.</jats:p

Distribution And Abundance Of Glucocorticoid And Mineralocorticoid Receptors Throughout The Brain Of The Great Tit (Parus Major)

The glucocorticoid stress response, regulated by the hypothalamic-pituitary-adrenal (HPA) axis, enables individuals to cope with stressors through transcriptional effects in cells expressing the appropriate receptors. The two receptors that bind glucocorticoids—the mineralocorticoid receptor (MR) and glucocorticoid receptor (GR)—are present in a variety of vertebrate tissues, but their expression in the brain is especially important. Neural receptor patterns have the potential to integrate multiple behavioral and physiological traits simultaneously, including self-regulation of glucocorticoid secretion through negative feedback processes. In the present work, we quantified the expression of GR and MR mRNA throughout the brain of a female great tit (Parus major), creating a distribution map encompassing 48 regions. This map, the first of its kind for P. major, demonstrated a widespread but not ubiquitous distribution of both receptor types. In the paraventricular nucleus of the hypothalamus (PVN) and the hippocampus (HP)—the two brain regions that we sampled from a total of 25 birds, we found high GR mRNA expression in the former and, unexpectedly, low MR mRNA in the latter. We examined the covariation of MR and GR levels in these two regions and found a strong, positive relationship between MR in the PVN and MR in the HP and a similar trend for GR across these two regions. This correlation supports the idea that hormone pleiotropy may constrain an individual’s behavioral and physiological phenotype. In the female song system, we found moderate GR in hyperstriatum ventrale, pars caudalis (HVC), and moderate MR in robust nucleus of the arcopallium (RA). Understanding intra- and interspecific patterns of glucocorticoid receptor expression can inform us about the behavioral processes (e.g. song learning) that may be sensitive to stress and stimulate future hypotheses concerning the relationships between receptor expression, circulating hormone concentrations and performance traits under selection, including behavior

Understanding the neuroendocrine mechanisms of behaviour in birds: From laboratory to field studies

I am an avian neuroendocrinologist and I have spent my research career understanding how environmental factors coordinate both the timing and the progression of reproduction and the associated behaviour. For most bird species reproduction is seasonal and breeding is regulated by environmental cues including photoperiod, food availability, temperature, and social interactions. During my presentation I will talk about my journey from an undergraduate student at the University of Bristol to Full Professor at the University of Edinburgh. There have been many adventures along the way, especially with the field work in Alaska! I have always had a passion for birds and understanding how hormones are intricately linked to behaviour. There are many advantages to studying wild birds in their natural environments especially in relation to understanding adaptations in our changing world. The laboratory setting also offers certain benefits and the technologies that are presently available to avian endocrinologists could only be dreamt of when I was an undergraduate student. We are now entering an exciting period in avian endocrinology with the annotation of many more avian species’ genomes including wild birds such as the white-crowned sparrow. Comparative genomic approaches and species-specific genetic tools can be used, as well as LC-MS and identification of the genes responsible for integrating environmental information. <br/

Late-season snowfall is associated with decreased offspring survival in two migratory arctic-breeding songbird species

While the effect of weather on reproduction has been studied for many years in avian taxa, the rapid pace of climate change in arctic regions has added urgency to this question by changing the weather conditions species experience during breeding. Given this, it is important to understand how factors such as temperature, rain, snowfall, and wind affect reproduction both directly and indirectly (e.g. through their effects on food availability). In this study, we ask how weather factors and food availability influence daily survival rates of clutches in two arctic-breeding migratory songbirds: the Lapland longspur Calcarius lapponicus , a circumpolar breeder, and Gambel’s white-crowned sparrow Zonotrichia leucophrys gambelii , which breeds in shrubby habitats across tundra, boreal and continental climates. To do this, we monitored clutch survival in these two species from egg-lay through fledge at field sites located near Toolik Field Station (North Slope, Alaska) across 5 yr (2012–2016). Our results indicate that snowfall and cold temperatures decreased offspring survival rates in both species; although Lapland longspurs were more susceptible to snowfall. Food availability, quantified by pitfall sampling and sweep-net sampling methods, had minimal effects on offspring survival. Some climate models predict increased precipitation for the Arctic with global warming, and in the Toolik region, total snow accumulation may be increasing. Placed in this context, our results suggest that changes in snow storms with climate change could have substantial consequences for reproduction in migratory songbirds breeding in the North American Arctic

Egg deposition of maternal testosterone is primarily controlled by the preovulatory peak of luteinizing hormone in quail

Differential transfer of maternal testosterone (T) into egg yolk provides a means of adjusting an offspring’s phenotype to ambient environmental conditions. While the environmental and genetic driven variability in yolk T levels is widely described, the underlying mechanisms are poorly understood. Here, we investigated whether neuroendocrine mechanisms controlling ovulatory processes are associated with the regulation of yolk T deposition. Circulatory profiles of luteinizing hormone (LH), T and estradiol levels were analysed during the last 7 h before ovulation in Japanese quail selected for contrasting yolk T concentrations. Moreover, the pituitary responsiveness to a single challenge with gonadotropin releasing hormone (GnRH) was evaluated. High egg T (HET) birds displayed higher concentrations of LH at 3.5 h before ovulation than low egg T (LET) birds while no differences were found around the time of expected ovulation. The pre-ovulatory profile of T and estradiol levels did not differ between LET and HET females but pre-ovulatory plasma T positively correlated with LH concentrations at 6.5 h and 3.5 h before ovulation. The LH response to GnRH did not differ between LET and HET females. Our results demonstrate that the pre-ovulatory LH surge can determine the amount of T transferred into the egg yolk. This link between yolk T deposition and the ovulatory cycle driven variation of reproductive hormones may explain balance between the effects of circulating T on female’s reproductive physiology and yolk T on offspring phenotype

Does male nest building in zebra finches keep peripheral testosterone production elevated through a ‘self-feedback’ mechanism?

Despite its fundamental importance for avian reproduction, the hormonal mechanisms supporting nest building remain poorly understood. While circulating sex steroids are required for nest building, it is still unclear whether sex steroids are required throughout building and whether the sharp decrease in circulating testosterone is linked to the completion of the nest or to the beginning of incubation. To answer these questions, we determined circulating testosterone dynamics in relation to nest building activities in male zebra finches (Taeniopygia guttata), a species in which the male both builds the nest and incubates. In Experiment 1, we collected plasma from males immediately before and 48 hours after pairing with a female, as well as 24 hours after building started. The nest was then removed and a plasma sample was collected 48 hours after nest building had been stopped. Any egg laid was removed upon discovery to prevent incubation. This experiment was completed with the collection of plasma and behavioural data from males that had either just started building, or that had built a whole nest (Experiment 2). Circulating testosterone levels remained high throughout pairing and nest building. 48 hours after the termination of nest building, testosterone dropped (Experiment 1), but testosterone levels of males that had completed a nest were positively associated with nesting material deposition they had performed over the last few hours preceding plasma sampling (Experiment 2). Together, our data demonstrate that circulating testosterone is important throughout male nest building in zebra finches suggesting the existence of a potential ‘self-feedback’ mechanism through which nest building activities may keep testosterone production elevated.##################################################################################This work was performed under UK Home Office licence, ARRIVE guidelines and local ethical review, and was funded by a Marie Skłodowska-Curie Action Individual Fellowship (101024039) and Biotechnology and Biological Sciences Research Council research grants (BB/Y001311/1 - BB/Y002121/1). <br/

Metabolic Regulation by the Hypothalamic Neuropeptide, Gonadotropin-Inhibitory Hormone at Both the Central and Peripheral Levels

Gonadotropin-inhibitory hormone (GnIH) is well-established as a negative regulator of reproductive physiology and behavior across vertebrates, acting on the hypothalamic–pituitary–gonadal (HPG) axis; however, recent data have also demonstrated its involvement in the control of metabolic processes. GnIH neurons and fibers have been identified in hypothalamic regions associated with feeding behavior and energy homeostasis, with GnIH receptors being expressed throughout the hypothalamus. GnIH does not act alone in the hypothalamus, but rather interacts with the melanocortin system, as well as with other neuropeptides. GnIH and its receptors are also expressed in peripheral tissues involved in important metabolic functions. Therefore, the local action of GnIH in peripheral organs, including the pancreas, gastrointestinal tract, gonad, and adipose tissue, is also suggested. This review aims to provide a comprehensive summary of the emerging role of GnIH in metabolic regulation at both the central and peripheral levels

The effect of food-restriction on the regulation of gonadotropin-releasing hormone in male house finches (Haemorhous mexicanus).

Seasonal activation of the vertebrate hypothalamic-pituitary-gonadal (HPG) axis and gonadal development is initiated by gonadotropin-releasing hormone-I (GnRH) release from the hypothalamus. In photoperiodic species, the consistent annual change in photoperiod is the primary environmental signal affecting GnRH cell activity, including changes in the synthesis and secretion of this neuropeptide. Non-photoperiodic environmental cues such as energy availability also influence HPG axis activity, but the mechanisms mediating this influence, in particular on the GnRH system, are unclear. Understanding how the neuroendocrine system integrates environmental information is critical in determining the plasticity and adaptability of physiological responses to changing environments. The primary objective of this study was to investigate GnRH-mediated changes in HPG axis activity and gonadal development in response to energy availability in a wild bird. We hypothesized that negative energy balance inhibits HPG axis activity by affecting GnRH secretion. Moderate food restriction for several weeks in male house finches, Haemorhous mexicanus, decreased body condition and inhibited photoinduced testicular growth compared to birds fed ad libitum. Food restriction did not affect plasma luteinizing hormone (LH; a correlate of GnRH release) or plasma testosterone, but it enhanced the plasma LH response to an injection of the glutamatergic agonist, N-methyl-D-aspartate (NMDA). Thus, food restriction may decrease photoinduced HPG axis activation by acting centrally, in particular by attenuating the release of accumulated GnRH stores

Transcriptomic seasonality in the hippocampus and amygdala/nucleus taeniae of quail and hamsters

Both birds and mammals use seasonal photoreception to precisely time life history transitions. The neuroendocrine control of reproductive physiology is underpinned by deep brain photoreception in birds, whereas in mammals the nocturnal melatonin signalling via retinal photoreception is essential. Light stimuli is known to impact the hippocampus and amygdala (or nucleus taeniae in birds), brain regions important for perception of social cues and emotional processing. The hippocampus in particular shows seasonal plasticity in size and dendritic complexity. The molecular basis of seasonal plasticity in these limbic brain regions is not well characterised. This study developed the transcriptomic architecture of the hippocampus and amygdala/nucleus taeniae in Japanese quail and Siberian hamsters using Oxford Nanopore RNA-sequencing to investigate photoperiodic and taxonomic differences in the seasonal plasticity of these brain regions. Physiological variation across photoperiod was apparent in body mass, testes mass, and pelage. A large number of transcripts of potential interest were identified, including TTR and MGRN1, providing solid links to the reproductive response to differential photoperiod and indicating that both brain regions respond robustly to photoperiodic manipulation. Both the hippocampus and amygdala/nucleus taeniae demonstrated primarily long-day downregulation of transcript expression. These results provide key insight into the transcriptomic architecture of two highly seasonal brain regions, suggesting a high level of unique transcript specificity across taxa. Birds and mammals respond similarly to seasonal photoperiodic cues via very different transcriptomic routes

Transcriptomic seasonality in the hippocampus and amygdala/nucleus taeniae of quail and hamsters

Both birds and mammals use seasonal photoreception to precisely time life history transitions. The neuroendocrine control of reproductive physiology is underpinned by deep brain photoreception in birds, whereas in mammals the nocturnal melatonin signalling via retinal photoreception is essential. Light stimuli is known to impact the hippocampus and amygdala (or nucleus taeniae in birds), brain regions important for perception of social cues and emotional processing. The hippocampus in particular shows seasonal plasticity in size and dendritic complexity. The molecular basis of seasonal plasticity in these limbic brain regions is not well characterised. This study developed the transcriptomic architecture of the hippocampus and amygdala/nucleus taeniae in Japanese quail and Siberian hamsters using Oxford Nanopore RNA-sequencing to investigate photoperiodic and taxonomic differences in the seasonal plasticity of these brain regions. Physiological variation across photoperiod was apparent in body mass, testes mass, and pelage. A large number of transcripts of potential interest were identified, including TTR and MGRN1, providing solid links to the reproductive response to differential photoperiod and indicating that both brain regions respond robustly to photoperiodic manipulation. Both the hippocampus and amygdala/nucleus taeniae demonstrated primarily long-day downregulation of transcript expression. These results provide key insight into the transcriptomic architecture of two highly seasonal brain regions, suggesting a high level of unique transcript specificity across taxa. Birds and mammals respond similarly to seasonal photoperiodic cues via very different transcriptomic routes