Peter J Sharp

• Ph.D
• Head of Department at University of Edinburgh

Increased TSHβ expression in the pars tuberalis is thought to be an early step in the neuroendocrine mechanism transducing photoperiodic information. This study aimed to determine the relationship between long-photoperiods (LP) and diurnal TSHβ gene expression in the juvenile chicken by comparing LP-photostimulated birds with groups kept on short p...

Background: A major step towards the success of chickens as a domesticated species was the separation between maternal care and reproduction. Artificial incubation replaced the natural maternal behaviour of incubation and, thus, in certain breeds, it became possible to breed chickens with persistent egg production and no incubation behaviour; a ty...

A central goal in evolutionary ecology is to characterize and identify selection patterns on the optimal phenotype in different environments. Physiological traits, such as hormonal responses, provide important mechanisms by which individuals can adapt to fluctuating environmental conditions. It is therefore expected that selection shapes hormonal t...

Many bird species have advanced their seasonal timing in response to global warming, but we still know little about the causal effect of temperature. We carried out experiments in climate-controlled aviaries to investigate how temperature affects luteinizing hormone, prolactin, gonadal development, timing of egg laying and onset of moult in male an...

In vertebrates, reproductive output often increases with age. Unlike older birds, first-year photoperiodic birds lack experience with the reproductively stimulatory effects of long day lengths (photostimulation). We examined whether age-related differences in annual reproductive development could be partially attributed to previous experience with...

The reproductive status of adult Pekin drakes is very sensitive to nutritional status. Thus, the purpose of this study was to increase our understanding of the neurobiology underlying the depressive effect of fasting on the secretion of reproductive hormones. It was hypothesized that this effect was mediated by gonadotropin-inhibitory hormone (GnIH...

Most animals reproduce seasonally. They time their reproduction in response to environmental cues, like increasing photoperiod and temperature, which are predictive for the time of high food availability. Although individuals of a population use the same cues, they vary in their onset of reproduction, with some animals reproducing consistently earl...

The Challenge Hypothesis postulates that male vertebrates can respond to social challenges, such as simulated territorial intrusions, by rapidly increasing their concentrations of plasma androgens, such as testosterone (T). This increase may facilitate the expression of aggressive behavior and lead to persistence of this behavior even after withdra...

Gonadotropin-releasing hormone (GnRH) is central to the control of vertebrate reproductive cycles and since GnRH orthologs are also present in invertebrates, it is likely that the common ancestor of bilateral animals possessed a GnRH-like peptide. In order to understand the evolutionary and comparative biology of GnRH peptides we cloned the cDNA tr...

Timing of reproduction in temperate-zone birds is strongly correlated with spring temperature, with an earlier onset of breeding in warmer years. Females adjust their timing of egg laying between years to be synchronized with local food sources and thereby optimize reproductive output. However, climate change currently disrupts the link between pre...

The Challenge Hypothesis postulates that male vertebrates can respond to social challenges, such as simulated territorial intrusions, by rapidly increasing their concentrations of plasma androgens, such as testosterone (T). This increase may facilitate the expression of aggressive behavior and lead to persistence of this behavior even after withdra...

Many seasonal breeders adjust the timing of reproduction in response to year-to-year variations in supplementary environmental cues, amongst which ambient temperature is thought to be most influential. However, it is possible that for species such as the great tit (Parus major L.), phenological cues from sprouting vegetation and the consequent abun...

In mammals, photoreception is restricted to cones, rods and a subset of retinal ganglion cells. By contrast, non-mammalian vertebrates possess many extraocular photoreceptors but in many cases the role of these photoreceptors and their underlying photopigments is unknown. In birds, deep brain photoreceptors have been shown to sense photic changes i...

Seasonal changes in gonad weights, concentrations of plasma luteinizing hormone (LH), prolactin, thyroxine (T 4 ) and triiodothyronine (T 3 ), and 5β reductase activity in the neuroendocrine tissues were measured in the Grey partridge ( Perdix perdix ) in northern Italy. Seasonal changes in the birds' photoperiodic responses were investigated by tr...

1. Annual variation in the timing of avian reproduction is associated with predictive cues related to ambient temperature. Understanding how these cues affect timing, and estimating the genetic variation in sensitivity to these cues, is essential to predict the micro-evolutionary changes in timing which are needed to adapt to climate change. 2. We...

Some components of male sexual and agonistic behaviours are considered to be regulated by the same neurocircuitry in the medial preoptic nucleus (POM) and the medial portion of bed nucleus of the stria terminalis (BSTM). To better understand this neurocircuitry, numbers of aromatase- (ARO) or arginine vasotocin- (AVT) immunoreactive (ir) neurones e...

Hormones mediate major physiological and behavioural components of the reproductive phenotype of individuals. To understand basic evolutionary processes in the hormonal regulation of reproductive traits, we need to know whether, and during which reproductive phases, individual variation in hormone concentrations relates to fitness in natural popula...

We used a free-ranging, seasonally breeding adult male songbird, the rufous-winged sparrow, Aimophila carpalis, to investigate the effects of acute stress-induced by capture followed by restraint, on the hypothalamo-pituitary-testicular axis. Intra- and interindividual comparisons revealed that males decreased their plasma testosterone (T) by 37-52...

In a study on starlings (Sturnus vulgaris) kept on a simulated annual cycle in photoperiod, temperature had no effect on the timing or rate of testicular maturation but high temperature resulted in an advance in the timing of testicular regression and molt (Dawson, 2005). This study asks whether the earlier gonadal regression in response to higher...

Many birds have highly sophisticated photoperiodic mechanisms and show robust responses to changing photoperiod. William Rowan is generally credited with the first demonstration of the avian photoperiodic response when he photostimulated dark eyed juncos (Junco hyemalis) during the Canadian winter and observed stimulation of testicular growth. The...

The chicken ovary is organized into a hierarchy of yellow yolky follicles that ovulate on successive days. Active or passive immunization of laying hens against testosterone blocks ovulation without affecting follicle development. Testosterone may play a role in pre-ovulatory follicle maturation by stimulating granulosa progesterone production. We...

The chicken ovary is organized into a hierarchy of yellow yolky follicles that ovulate on successive days, and their steroid secretion is dependent on the developmental degree of the follicle. Testosterone has been recently described to have an important role in follicle ovulation. Active or passive immunization of laying hens against testosterone...

In order to further advance the understanding of genes involved in avian photoperiodic signaling, a chicken hypothalamic cDNA microarray was made to identify changes in gene expression in the whole hypothalamus of juvenile male domestic chickens after 4 days' photostimulation. The most robust change was a depression in heat shock protein 90B1 (HSP9...

Broodiness is a nuisance and sometimes a serious problem in some poultry. The behaviour is recognized as persistent nesting, usually associated with cessation of egg laying. Broodiness has two components: incubation and brooding behaviour; the former can only be induced in laying hens, while the latter can be induced in both laying and non-laying h...

The aim of the study was to test the hypothesis that decreasing plasma prolactin stimulates or permits the initiation of avian molt. Changes in the concentration of plasma prolactin in Mute swans (Cygnus olor) were compared in non-breeding singletons and breeding pairs. In breeding swans, the onset of molt is delayed compared to non-breeders, and i...

In vertebrates, the neuropeptide control of gonadotrophin secretion is primarily through the stimulatory action of the hypothalamic decapeptide, gonadotrophin-releasing hormone (GnRH). Gonadal sex steroids and inhibin inhibit gonadotrophin secretion via feedback from the gonads, but a hypothalamic neuropeptide inhibiting gonadotrophin secretion was...

Seasonal breeding in two Sonoran desert passerines, the Cassin's (Aimophila cassinii) and Rufous-crowned (Aimophila ruficeps) Sparrows is thought to be terminated by the development of a decrease in responsiveness to photostimulation, a condition known as relative photorefractoriness. It was predicted that the development of relative refractoriness...

Many birds and mammals show changes in the hypothalamo-pituitary-gonadal (HPG) axis in response to social or sexual interactions between breeding partners. While alterations in GnRH neuronal activity play an important role in stimulating these changes, it remains unclear if acute behaviorally-induced alterations in GnRH release are accompanied by p...

The objective of this work was to define precisely the response curve for photoinduced luteinizing hormone (LH) release in feed-restricted meat-type (broiler) breeder females and to compare it with the photoperiodic response curve for advance in age at first egg (AFE). Birds with a mean body weight of 2.0kg at 20 weeks of age were transferred from...

Molecular mechanisms regulating animal seasonal breeding in response to changing photoperiod are not well understood. Rapid induction of gene expression of thyroid-hormone-activating enzyme (type 2 deiodinase, DIO2) in the mediobasal hypothalamus (MBH) of the Japanese quail (Coturnix japonica) is the earliest event yet recorded in the photoperiodic...

We tested the hypothesis that adult male rufous-winged sparrows, Aimophila carpalis, exhibit relative photorefractoriness. This condition results in partial loss of sensitivity to photoperiod as a reproductive stimulus after prolonged exposure to long photoperiods and is similar to the mammalian condition called photoperiodic memory. Captive birds...

We investigated the regulation of luteinizing hormone (LH) in the male Rufous-winged Sparrow,Aimophila carpalis, a resident of the Sonoran desert that breeds after irregular summer rains. Although the testes develop in March due to increasing photoperiod and regress in September due to decreasing photoperiod, LH does not consistently increase in th...

Prolonged exposure to conspecific song stimulates gonadal function and reproductive hormone secretion in female birds but few studies have investigated the physiological effects of conspecific song exposure on males outside of short-term, aggressive interactions. We exposed male Rufous-winged Sparrows, Aimophila carpalis, either to conspecific song...

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) in vertebrates. Until recently, no neuropeptide that directly inhibits gonadotropin secretion had been identified. In 2000, we discovered a nove...

It is now known that circadian clocks are localized not only in the central pacemaker but also in peripheral organs. An example of a clock-dependent peripheral organ is the ovary of domestic poultry in which ovulation is induced by the positive feedback action of ovarian progesterone on the neuroendocrine system to generate a preovulatory release o...

Avian breeding seasons vary in length and in the degree of asymmetry with respect to the annual cycle in photoperiod to suit species-specific food resources. Asymmetry is the result of photorefractoriness. The degree of photorefractoriness, absolute or relative, is related to the length and asymmetry of the breeding season. Absolute photorefractori...

The decapeptide gonadotropin-releasing hormone (GnRH) is the primary factor responsible for the hypothalamic control of gonadotropin secretion. Gonadal sex steroids and inhibin inhibit gonadotropin secretion via feedback from the gonads, but a neuropeptide inhibitor of gonadotropin secretion was, until recently, unknown in vertebrates. In 2000, we...

The aim of this study, in 36 week-old laying broiler breeder hens, was to establish the effects on reproductive neuroendocrine gene expression of reinstating ad libitum food intake after moderate food restriction from 2 weeks of age. Seven days of ad libitum feeding increased the number of large pre-ovulatory ovarian follicles and gonadotropin rele...

1. Broiler breeders were given a 3-h increase in photoperiod to 11 h at 20 week and then a series of increases to reach 16 or 17 h either immediately after the initial increment or in 30-min, 1- or 2-h increments starting at various ages after peak rate of lay. Controls were maintained on 11 h from 20 weeks. Changes in plasma LH concentration (afte...

This study examined effects of exogenous melatonin on osmoregulatory hormones and water and sodium secretion by salt glands and excretion via the kidneys of Glaucous-winged gulls (Larus glaucescens). Six saline acclimated gulls were injected with inulin and paraminohippuric acid and then infused with 500 mM NaCl to stimulate salt gland secretion. E...

We investigated reproductive regulation in male Rufous-winged Sparrows, Aimophila carpalis, a Sonoran Desert passerine that breeds after irregular summer rains. Field and captive data demonstrate that increased photoperiod stimulates testicular development in March and maintains it until early September. Free-living birds caught in July and placed...

In mammals, alternative splicing of the leptin receptor (LEPR) produces several C-terminal truncated isoforms that are believed to play a role in the transport, cellular internalisation and degradation of the hormone leptin. The chicken leptin receptor (chLEPR) is similar to its mammalian counterparts in terms of its intron/exon structure and conse...

The leptin binding domain of the chicken leptin receptor gene was analyzed for alternative splicing. Polymerase chain reaction (PCR) primers were designed to amplify exons 8-14 of the gene which is known to encode the leptin binding domain. Four cDNA products from reverse transcribed chicken anterior pituitary and basal hypothalamic RNA were genera...

Rufous-winged Sparrows, Aimophila carpalis, reside in the Sonoran desert and although testicular development is initiated in the spring under the influence of increasing day length, breeding occurs opportunistically in summer in association with heavy rainfall or "monsoon". The aim of this study in free-living male Rufous-winged Sparrows was to est...

How much effort to expend in any one bout of reproduction is among the most important decisions made by an individual that breeds more than once. According to life-history theory, reproduction is costly, and individuals that invest too much in a given reproductive bout pay with reduced reproductive output in the future. Likewise, investing too litt...

Melatonin (MT) inhibits salt gland secretion of Pekin ducks [Ching, A.C.T., Hughes, M.R., Poon, A.M.S., Pang, S.F., 1999. Melatonin receptors and melatonin inhibition of duck salt gland secretion. Gen. Comp. Endocrinol. 116, 229-240]. The present study examined simultaneous diurnal changes in plasma concentrations of MT and four osmoregulatory horm...

Animal populations living in geographically variable environments respond to different selection pressures. The adaptive character of the responses to environmental information determines the degree of synchrony of the breeding period with local optimal conditions. An example is provided by two populations of Mediterranean blue tits (Parus caeruleu...

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, r...

Testosterone (T) in male birds generally inhibits the activity of the hypothalamo-pituitary-gonadal axis, but the androgen can also be gonadostimulatory. The mechanisms responsible for this stimulation are unknown. To address this question, adult male House Finches, Carpodacus mexicanus, held on short day length to inhibit reproductive function, re...

The preovulatory release of luteinizing hormone (LH) in the domestic hen occurs after the initiation of a preovulatory surge of testosterone. The objective of this study was to determine whether this testosterone surge has functional significance in the endocrine control of ovulation. Groups of laying hens (n = 10-22) were treated with the androgen...

Leptin is well established as a multifunctional cytokine in mammals. However, little is known about the evolution of the leptin gene in other vertebrates. A recently published set of ESTs from the tiger salamander (Ambystoma tigrinum) contains a sequence sharing 56% nucleotide sequence identity with the human leptin cDNA. To confirm that the EST is...

Gambel's white-crowned sparrow is a long distance migrant that undergoes spontaneous gonadal regression as a result of long day exposure. This termination of breeding is caused by the development of photorefractoriness and the birds become insensitive to long days, including continuous light. The present study investigated its possible mechanisms b...

Until recently, any neuropeptide that directly inhibits gonadotropin secretion had not been identified. We recently identified a novel hypothalamic dodecapeptide that directly inhibits gonadotropin release in quail and termed it gonadotropin-inhibitory hormone (GnIH). The action of GnIH on the inhibition of gonadotropin release is mediated by a nov...

Egg production declines with advancing age in the domestic chicken and this is particularly pronounced in breeding stocks of meat type hens (broiler breeders). The objective of this study was to establish whether declining egg production with reproductive ageing in broiler breeders is correlated with plasma LH and FSH, and with mRNAs encoding hypot...

Seasonal breeding in the emu occurs in winter and is associated with anorexia and a loss of 20-30% body weight. In order to establish whether decreasing day length induces winter breeding and associated anorexia, photoperiodic experiments were carried out on emus held in light-controlled rooms. Transfer from long to short days stimulated reproducti...

Day length predicts changing of seasons at mid-latitudes, but additional environmental cues (e.g., temperature, rainfall) give more precise information about timing of food peaks critical for offspring survival. We tested the effects of temperature on seasonal reproductive development of male song sparrows (Melospiza melodia morphna) from two popul...

1. Shaver White and ISA Brown pullets were reared to 140 d in cage groups of 8 on a 10-h photoperiod of incandescent light and maintained at an illuminance of 3 or 25 lux, or transferred from 3 to 25 lux or from 25 to 3 lux at 63 or 112 d of age. 2. Plasma follicle stimulating hormone (FSH) concentration at 63 and 112 d was higher in both breeds fo...

The aim of this study was to determine in the ring dove, the effects of aromatase inhibition on the expression of aggressive courtship and nest-soliciting behaviours in relation to the distribution of cells containing immunoreactive androgen (AR) and progesterone (PR) receptor in the hypothalamus and pituitary gland. Isolated sexually experienced r...

In domestic juvenile chickens kept on short days, photoinduced luteinsing hormone (LH) release, and by inference gonadotrophin-releasing hormone (GnRH) release, are readily detectable within 4 days of photostimulation.2 The molecular mechanisms responsible for the rapid photoinduced release of LH and GnRH in avian species are unknown. It has been s...

Egg production by meat-type fowl is markedly inferior to that from commercial laying hens, and so, to assess the degree to which photorefractoriness might be a contributing factor, male- and female-line broiler breeders were maintained on 8-, 11- or 16-h photoperiods. In addition, to determine the age-related rate of change in response to an increm...

On or before Jul 19, 2011 this sequence version replaced gi:67527825, gi:67527826, gi:67527824.

Day length-dependent breeding in birds commonly occurs in spring and summer, but may occur after exposure to complex changes in day length, as for example in transequatorial migrants. More rarely, some photoperiodic birds breed when day lengths are decreasing or are short. The flexibility of avian photoperiodic breeding strategies may reflect modif...

The compartmentalization of body fluids was measured in three species of ducks that differ in saline tolerance. Half of the birds of each species drank freshwater, while the other half drank saline (300 mM NaCl). Among ducks that drank freshwater, total body water (TBW) was similar among all species, but Barrow's goldeneyes (Bucephala islandica), t...

Studies performed in vitro suggest that a novel 12 amino acid RF amide peptide, isolated from the quail hypothalamus, is a gonadotrophin inhibitory hormone (GnIH). The aim of the present study was to investigate this hypothesis in the domestic chicken. Injections of GnIH into nest-deprived incubating hens failed to depress the concentration of plas...

Seasonal temperate zone breeders respond to increasing day length to anticipate the approach of spring breeding conditions. Other (supplementary) environmental cues, such as temperature and precipitation, were historically thought to play unimportant roles in reproductive timing. We demonstrate variation in reproductive timing across small geograph...

Understanding the relationships among variables can be difficult if the variables covary with time. Using a simple, commonly used statistical procedure to control for the passage of time, we demonstrate that some hormonal changes traditionally assumed to be causally related to the transition from sexual to parental behaviour can be explained by sea...

1. Shaver White and ISA Brown pullets were reared to 140 d in groups of 8 in cages on a 10-h photoperiod of incandescent light and maintained at an illuminance of 3 or 25 lux, or transferred from 3 to 25 lux or from 25 to 3 lux at 63 or 112 d of age. 2. There was no significant difference in sexual maturity, measured as eggs per 100 bird.d at 139 a...

We investigated the hypothesis that species differences in paternal care in birds may result from differences in concentrations of circulating testosterone (T) and prolactin (PRL). Concentrations of plasma T and PRL were compared in breeding Blue-headed Vireos (Vireo solitarius) and Red-eyed Vireos (Vireo olivaceus), passerine congeners with bipare...

Table 1 is being rerun to correct the table footnote.

Egg laying begins in domestic hens, reared on short daylengths, at about day 147 of age and is advanced by photostimulation after but not before about day 42 of age. The development of this response at day 42 may be facilitated by oestrogen. This hypothesis was investigated in prepubertal hens, reared on short daylengths, by comparing the effects o...

Research in mammals has established the existence of a neuronal network that lies within the hypothalamus and that regulates energy homeostasis. However, it is unknown whether this system has been evolutionarily conserved. The objective of the present study was therefore to examine the influence of the agouti-related peptide (AGRP), pro-opiomelanoc...

On Mar 28, 2005 this sequence version replaced gi:34980140.

On Mar 28, 2005 this sequence version replaced gi:34980146.

On Mar 28, 2005 this sequence version replaced gi:34980142.