Steroids modulate the release of luteinizing hormone from quail pituitary cells

At the crossroads of physiology and ecology: food supply and the timing of avian reproduction

This article is part of a Special Issue “Energy Balance”. The decision of when to breed is crucial to the reproductive success and fitness of seasonally breeding birds. The availability of food for adults prior to breeding has long been thought to play a critical role in timing the initiation of seasonal reproductive events, in particular laying. However, unequivocal evidence for such a role remains limited and the physiological mechanisms by which an increase in food availability results in seasonal activation of the reproductive system are largely speculative. This lack of mechanistic information partly reflects a lack of integration of ecological and physiological approaches to study seasonal reproduction. Indeed, most work pertaining to the role of food availability for adults on the timing of avian reproduction has been ecological and has focused almost exclusively on female traits associated with reproductive timing (e.g., lay date and clutch size). By contrast, most work on the physiological bases of the relationship between food availability and the timing of reproduction has investigated male traits associated with reproductive development (e.g., reproductive hormones and gonadal development). To advance our understanding of these topics, we review the role of proximate factors including food availability, social factors, and ambient temperature in the control of breeding decisions, and discuss the role of three potential candidates (leptin, glucocorticoids, and GnIH-neuropeptide Y) that may mediate the effects of food availability on these decisions. We emphasize that future progress in this area is heavily contingent upon the use of physiology-based approaches and their integration into current ecological frameworks.

Effect of estradiol-17β on follicle-stimulating hormone secretion and egg-laying performance of Japanese quail

The aim of this study was to measure the effect of estradiol-17β (E2) injection on follicle-stimulating hormone (FSH) secretion and egg-laying performance of Japanese quail. Female Japanese quail were housed in cages and fed ad libitum. After a 7-day adaptation period, the birds were randomly assigned to three groups, that is, one control group and two test groups. The birds were weighed, before every injection. The control group was subcutaneously injected with 0.2 ml sesame oil-ethanol mixture, whereas test groups were injected, twice in a week, with 0.2 ml sesame oil-ethanol mixture containing 0.1 or 0.2 mg E2 along the study. One day after the first injection, egg number, egg weight, eggshell strength and food conception were daily recorded. On the last day of the experiment, the birds were injected and 3 h later seven birds from each group were randomly selected for bleeding. Blood samples (2 ml/bird) were collected from the jugular vein for the measurements of serum concentrations of E2, FSH, calcium (Ca) and phosphorus (P). E2 injection did not cause any significant changes in serum FSH concentrations, daily egg laid/bird, food conception/bird, serum concentrations of the Ca and the P. Egg weight was significantly increased in the 0.1 mg E2-injected group as compared with the control and 0.2 mg E2-injected groups. Eggshell strength in the 0.2 mg E2-injected group was significantly high as compared with the control, whereas the difference between the 0.1 mg E2- and 0.2 mg E2-injected groups was not statistically important. These results show that serum FSH concentration was not increased even when slightly suppressed by subcutaneous injection of 0.1 or 0.2 mg E2. Different doses of E2 have different functions. The increase in BWs in the 0.1 mg E2-injected group was a result of the dose effect, which probably increased growth hormone secretion from the pituitary or IGF-1 synthesis from the liver or both. The dose, 0.2 mg E2, was ineffective in increasing the BW, but it significantly increased eggshell strength probably via the increase in Ca and P utilizations.

Maternal corticosterone further reduces the reproductive function of male offspring hatched from eggs laid by quail hens selected for exaggerated adrenocortical stress responsiveness

Activation of the hypothalamic-pituitary-adrenal (HPA) axis can depress the hypothalamic-pituitary-testicular axis. Male quail cloacal gland (CG) size and foam production shows androgen dependency, and males selected for exaggerated [high stress (HS)] rather than reduced [low stress (LS)] plasma corticosterone (B) stress response exhibit reduced CG and testes development. High stress hens also deposit more B into egg yolks than LS ones, and quail hens given B produce chicks that have a reduced growth rate and adults with heightened HPA responsiveness. Herein, we gave LS and HS hens no B [empty implants, control (CON)] or B-filled implants and assessed the reproductive performances of these hens and their male offspring. Mortality was similarly elevated in LS and HS B-treated hens, but only HS B-implanted hens showed reduced egg production. In male offspring, CG volume (CVOL), intensity of CG foam production (CFP), and the proportion of individuals that produced CG foam were measured from 4 to 11 wk of age. At 6 wk, BW, and at 15 wk, BW, testes weight (TWT), and TWT relative to BW were also determined. Hen treatments did not affect male chick CVOL at 4 wk, but CVOL differed thereafter as follows: LS CON > LS B = HS CON = HS B at 5 and 6 wk and LS CON > LS B > HS CON = HS B from 7 to 11 wk. By 8 wk, and thereafter, CFP differed as follows: LS CON > LS B > HS CON > HS B. Group differences in the proportion of individuals that produced CG foam generally supported CFP findings from 4 to 8 wk of age. Body weight did not differ by treatment at 6 wk of age. By 15 wk, TWT were similarly depressed in both HS groups. However, similarly higher 15-wk BW in the LS-CON and HS-B groups contributed to TWT relative to BW differences as follows: LS-B > LS-CON > HS-B; LS-CON = HS-CON; LS-B > HS-CON; and, HS-CON = HS-B. Both selection for exaggerated HPA responsiveness and maternal B treatment negatively affected the reproductive function of HS male offspring.

Testicular development during long-distance spring migration

In birds, gonadal size varies between fully functional and maximally sized during reproduction and a regressed state with limited function during the non-reproductive periods. Recent findings show that testicular mass of the long-distance migratory garden warbler begins to increase during spring migration. Therefore, we sampled garden warblers during spring migration from Tanzania to Ethiopia, and finally to Egypt to determine if this mass increase is functional in terms of sperm and hormone production. In addition, we compared these birds, with garden warblers sampled after a 9-day recovery period following the crossing of the Sahara Desert (simulation of stopover) in Egypt and a group sampled in breeding condition in the laboratory. During migration there was a significant increase in testicular mass that was correlated with seminiferous tubule area and the stage of spermatogenesis. Plasma testosterone levels were low during migration, but were significantly correlated with testicular mass. LH concentration was not related to testicular mass, and, surprisingly, remained constant during migration. We suggest that previous experiments that found a tight relationship between testicular growth and LH level in the laboratory may not reflect the situation during long-distance migration where the great physical and energetic demands of migration likely affect the reproductive axis and, consequently, the relationship between testicular growth and LH titer. However, testes do develop to a considerable extent during spring migration and the present data suggest that initiation of testicular maturation during spring migration is necessary to ensure full spermatogenetic development soon after arrival at the breeding area.

Cloacal Gland and Gonadal Photoresponsiveness in Male Japanese Quail Selected for Divergent Plasma Corticosterone Response to Brief Restraint

Corticosterone is linked to testicular depression, and in Coturnix, a relatively photorefractory species, day length and androgen dependency in cloacal gland development and foam production are evident. Furthermore, male quail selected for reduced (low stress, LS) rather than exaggerated (high stress, HS) plasma corticosterone stress response show more photo-induced reproductive development, greater resistance to reproductive declines induced by exposure to very short days, and a quicker recovery to a higher reproductive level upon return to long days. To determine whether a milder reduction in day length would also influence stress line reproductive photoresponsiveness, and perhaps photorefractoriness, males grown on 16 h of light were given 13 h of light for 4 wk followed by a return to long days for 12 wk. Cloacal gland measurements were made following the initial stimulatory photoperiod and weekly thereafter during the 2 light treatments. Plasma testosterone was determined initially, after 4 wk of light reduction, and at the end of the study, along with BW, testes weight (TWT), and TWT relative to BW. Cloacal gland volume (CVOL) was greater in LS than HS males grown on long days. Whereas exposure to 13 h of light reduced CVOL in both lines, line differences (LS > HS) persisted during the first 3 wk of light reduction. Moreover, by 2 wk of rephotostimulation, and weekly thereafter, line differences (LS > HS) in CVOL reemerged. Cloacal gland foam production and the proportion of individuals that produced cloacal gland foam responses reflected changes in CVOL. The BW did not differ by line, yet LS males had a higher TWT and TWT relative to BW than HS ones. All individuals, however, exhibited relative photorefractory responses. Whereas none of the LS males completely resisted reproductive regression induced by a 3 h light reduction, LS males showed other reproductive benefits upon mild photocastration and subsequent rephotostimulation (e.g., greater resistance to CVOL and cloacal gland foam production losses during a mild light crash and quicker restoration to full reproductive potential upon relighting).

Cloacal Gland and Testes Development in Male Japanese Quail Selected for Divergent Adrenocortical Responsiveness

The time course of sexual development in male quail from lines selected for either a reduced (low stress, LS) or an exaggerated (high stress, HS) plasma corticosterone response to brief restraint was determined. Sexual development was assessed by examination of cloacal gland area (CAREA) and volume (CVOL), proportion of individuals that produced cloacal gland foam, and the intensity of cloacal gland foam production (CFP) at 4, 5, 6, 8, 10, 14, and 16 wk of age. These intervals encompass ages during which growing, photostimulated quail would be expected to evolve from being totally prepubescent to well into adulthood. Testes weight (TW) and the proportion of individuals that had achieved a combined TW of 500 mg (PI500) were also measured at 6 and 16 wk of age. Mean CAREA and CVOL were similar in LS and HS quail at 4 wk of age. Beginning at 5 wk of age and thereafter, CAREA was greater (P < 0.05) in LS than in HS quail. Similarly, beginning at 6 wk of age and thereafter, CVOL was greater (P < 0.05) in LS than in HS quail. More LS than HS birds also expressed foam at 4 (P < 0.05), 5 (P = 0.15), and 6 wk (P < 0.05) of age. From 8 wk on, all birds were in foam production. CFP results mimicked those found for CAREA and CVOL in that LS quail tended toward higher CFP values than HS quail at all intervals of measurement. TW were higher (P < 0.02) in LS than HS quail when data from the 2 ages at which testes were harvested were combined. At 6 wk of age, the LS and HS birds showed a PI500 line difference (P < 0.08) of 1.0 and 0.91, respectively; by 16 wk, all birds exhibited a maximum PI500. The results suggest that 1) selection for reduced adrenocortical responsiveness in Coturnix is accompanied by an accelerated onset of puberty in males, and 2) enhanced reproductive development in LS males remains extant throughout early to middle-age adulthood.

Photoperiod-Induced Changes in Cloacal Gland Physiology and Testes Weight in Male Japanese Quail Selected for Divergent Adrenocortical Responsiveness

In quail, activation of the hypothalamic-pituitary-adrenal axis has been linked to depression in the hypothalamic-pituitary-testicular axis, and cloacal gland development and foam production are known to be androgen dependent. Therefore, photoperiod manipulations that induce gonadal growth (long day) and involution (short day) were used to examine changes in cloacal gland physiology in male quail from lines selected for a reduced (low stress, LS) or exaggerated (high stress, HS) plasma corticosterone response to brief restraint. Line differences in cloacal gland area (CAREA) and volume (CVOL), the proportion of individuals that produced cloacal gland foam (PICF), and the intensity of cloacal gland foam production (CFP) were initially assessed in adult males maintained on stimulatory, long photoperiods of 14L:10D. Thereafter, these variables were re-examined weekly in the same males during their subsequent exposure to 3 wk of short days (6L:18D) followed by return to long d for 3 more wk. Line differences in testes weight relative to body weight (RTW) were also measured at the end of the study. CAREA and CVOL were markedly greater in LS than HS males grown under long days. As expected, these indices of cloacal gland size were greatly reduced upon exposure to short days in both lines. However, line differences (LS > HS) in CAREA and CVOL were maintained during the first 2 wk of exposure to short days. Line differences in the depressed cloacal gland size measures were no longer evident by the third week on short days as well as after the first week of relighting wherein there were no further depressions in gland size of either line. However, by the end of 2 wk of rephotostimulation and thereafter, marked line differences (LS > HS) in CAREA and CVOL re-emerged. Photoperiod-induced line effects on CFP generally mimicked those of CAREA and CVOL. The PICF was marginally different (P < 0.07) between the lines (LS > HS) only after 1 wk of light reduction. After 3 wk of rephotostimulation, RTW was nearly 25% greater in LS quail. The results suggest that selection for reduced adrenocortical responsiveness in Coturnix has resulted in certain reproductive advantages in middle-aged, adult males maintained on stimulatory photoperiods as well as in such adults subjected to photocastration and subsequent rephotostimulation.

Short-term stress increases testosterone secretion from testes in male domestic fowl

Prolonged stress inhibits the hypothalamus-pituitary-gonadal (HPG) axis and reduces plasma testosterone (T). However, enhanced secretion of luteinizing hormone (LH) and T has been documented during the initial stages of acute stress in mammals. This study assayed the effect of short-term stress on plasma T and corticosterone (B) in juvenile, pubertal, and adult White Leghorn cockerels. Stress was induced by brief physical restraint of caged juvenile (7 weeks), pubertal (17 weeks), and adult (40 weeks) cockerels, as well as 40-week-old adults reared together in a room lined with wood shavings (group reared). Blood was sampled immediately before restraint (0 time), at the end of a 10-min restraint period, and at 30, 60, and 180 min after 0 time. Restraint resulted in an initial increase in plasma T in all groups, along with a rise in B. Whereas B generally reached its peak level at the end of the restraining period, T peaked 20 min later. The maximum increase of T and B relative to prestress levels (T and B ratios) was similar in all groups, with median T ratio reaching 1.25-1. 5-about half that of the B ratio. Thus, the extent of T and B response to short-term stress was not influenced by basal levels of T, which were highest in adults, and basal levels of B, which were higher in caged adults than in group-reared adults. Injection of ACTH did not induce a greater increase in plasma T than in sham-injected controls. Further, the elevation of T in response to stress was extinguished in castrated adults, indicating that T is secreted from the testes rather than the adrenals in response to stress. When the same regime of blood sampling was applied to adults not subjected to restraint, the T ratio rose by up to 11 times. It can therefore be stipulated that T response depends on the type of stress applied, a factor that should be considered when investigating androgen levels in plasma.

Avian LHRH during embryonic development: measurement by competitive ELISA with a monoclonal antibody

A mouse monoclonal antibody directed against chicken Gln8-luteinizing hormone-releasing hormone (cLHRH-I) was developed and characterized. This antibody was used for the development of a competitive microtiter plate enzyme-linked immunosorbent assay for avian LHRH. The assay was validated for use with tissue and was used at a working range between 5 pg and 10 ng per sample. Using this procedure, cLHRH-I and II were assayed in whole brain extracts of Japanese Quail embryos. Samples were taken at regular intervals between Day 6 of incubation through Day 1 posthatch. There were 10 samples taken at each age with 2 replicates of the entire sampling regime. Data from males and females were pooled. LHRH concentrations were low, then rose to higher levels (15 pg/mg tissue) between Days 10 through 13 and decreased thereafter. These changes are likely to be correlated with the activation of the hypothalamic-pituitary-gonadal axis. This is particularly apparent in later embryonic development.

Aggressive behavior in birds: an experimental model for studies of brain-steroid interactions

1. Although testosterone (T) stimulates aggressiveness in males of many vertebrate species, it is now known that the full expression of T actions in the central nervous system requires aromatization to estradiol (E2) and subsequent binding of formed E2 to its receptor. 2. We have recently confirmed these as rate-limiting steps in the control of sex-related and individual differences in aggressiveness of the Japanese quail (Coturnix coturnix japonica). 3. In this review, we describe some of the neuroendocrine factors which control aggression with a focus on our recent studies in quail.

Changes in pituitary responsiveness during the ovulatory cycle of the Japanese quail, in vitro

Anterior pituitary glands from ovulating Japanese quail (Coturnix coturnix) were used to investigate variation in sensitivity to chicken luteinizing hormone-releasing hormone (cLHRH I; Gln8-LHRH). Grouping the pituitaries by ovulatory stage provided preliminary evidence of changes in sensitivity to LHRH during the ovulatory cycle. Pituitaries taken from quail before the preovulatory LH surge were responsive to cLHRH I, while pituitaries from the other times of the cycle showed minimal response to cLHRH I. Female pituitary glands release less LH than those of males. These data indicate a change in sensitivity to LHRH in the female quail that may be due to changes in gonadal steroids or the pool of releaseable LH from the pituitary.