The photoperiodic control of reproduction inCoturnix quail. The temporal pattern of LH Secretion

Photoperiod dependent expression of estrogen receptor alpha in testes of Japanese quail: Involvement of Withania somnifera in apoptosis amelioration

Light plays important function in the regulation of reproduction in vertebrates including birds. The prolonged long day length exposure causes reproductively inactive state or photorefractoriness in many avian species including Japanese quail. Withania somnifera (WS) is a medicinal plant known to have beneficial effects on stress and infertility. The study investigates the physiological effect of WS on the light-induced stress in quail mediated by estrogen receptor alpha. Quails were exposed to long day length for three months and then transferred into intermediate day length to make them photorefractory (PR) while controls under natural day length. Administration of Withania somnifera root extract (WSRE) in PR quail induces estrogen and decreases corticosterone in male Japanese quail. Immunoreactivity of ERα decreased in testis of PR quail and increased after oral administration of WSRE compared to control. Expression of ir-Caspase-3 and ir-p53 in the testis increased in PR while decreased in PR + WS. Histologically, seminiferous tubules size decreased in PR whereas increased in PR + WS quails. Scanning electron microscopic study reveals sperms in clusters with proper head and tail in control. In PR quails sperms were few and distorted while WSRE improved the sperm morphology. From the study, it is concluded that during photorefractoriness gonadal regression occurs due to testicular apoptosis which causes stress. WSRE helps to overcome stress and improve reproductive performance via increase in expression of ir-ERα during PR condition. Further, the stress ameliorating effect of WSRE in reducing apoptosis mediated by ir-Caspase-3 and ir-p53 in the testes is clearly evident in Japanese quail.

Time course of photo-induced Egr-1 expression in the hypothalamus of a seasonally breeding songbird

Many seasonally-breeding species use daylength to time reproduction. Light-induced release of progonadal hormones involves a complex cascade of responses both inside and outside the brain. In this study, we used induction of early growth response 1 (Egr-1), the protein product of an immediate early gene, to evaluate the time course of such responses in male white-throated sparrows (Zonotrichia albicollis) exposed to a single long day. Induction of Egr-1 in the pars tuberalis began ∼11 h after dawn. This response was followed ∼6 h later by dramatic induction in the tuberal hypothalamus, including in the ependymal cells lining the third ventricle. At approximately the same time, Egr-1 was induced in dopaminergic and vasoactive intestinal peptide neurons in the tuberal hypothalamus and in dopaminergic neurons of the premammillary nucleus. We noted no induction in gonadotropin-releasing hormone (GnRH) neurons until 2 h after dawn the following morning. Overall, our results indicate that Egr-1 responses in GnRH neurons occur rather late during photostimulation, compared with responses in other cell populations, and that such induction may reflect new synthesis related to GnRH depletion rather than stimulation by light cues.

Anticipating spring: wild populations of great tits (Parus major) differ in expression of key genes for photoperiodic time measurement

Measuring day length is critical for timing annual changes in physiology and behavior in many species. Recently, rapid changes in several photoperiodically-controlled genes following exposure to a single long day have been described. Components of this 'first day release' model have so far only been tested in highly domesticated species: quail, sheep, goats and rodents. Because artificial selection accompanying domestication acts on genes related to photoperiodicity, we must also study this phenomenon in wild organisms for it to be accepted as universal. In a songbird, the great tit (Parus major), we tested whether a) these genes are involved in photoperiodic time measurement (PTM) in a wild species, and b) whether predictable species and population differences in expression patterns exist. Using quantitative RT-PCR, we compared gene expression after a single long day in male great tits from Sweden (57°42'N) with that from a German (47°43'N) population. Hypothalamic gene expression key for PTM changed only in the northern population, and occurred earlier after dawn during the single long day than demonstrated in quail; however, gonadotropins (secretion and synthesis) were stimulated in both populations, albeit with different timing. Our data are the first to show acute changes in gene expression in response to photostimulation in any wild species not selected for study of photoperiodism. The pronounced differences in gene expression in response to a single long day between two populations raise exciting new questions about potential environmental selection on photoperiodic cue sensitivity.

Differential regulation of gene expression and release of FSH and prolactin by long day and sulfamethazine in chicks

In several avian species long day exposure results in plasma elevation of gonadotropins and prolactin (PRL). We examined the early (12-72h) effects of photostimulation on mRNA transcripts and plasma levels of follicle stimulating hormone (FSH) and PRL in three-week old cockerels. In addition, the neuroendocrine influence of the compound, sulfamethazine (SMZ), known to enhance light-induced gonadal development in chicks, was studied when applied with or without long-day photostimulation. Both long day exposure and SMZ intake caused a rapid increase in FSHbeta mRNA transcripts at Zeitgeber time 48 (ZT48), while only SMZ stimulated secretion of the hormone into plasma during the course of the study. In contrast to SMZ treatment, photostimulation was more effective at stimulating PRL mRNA transcripts and secretion of PRL. Results demonstrate a differential role of long day exposure and SMZ intake on the regulation of FSH and PRL synthesis and secretion and suggest that some effects of SMZ on gonadal development may be mediated by the pituitary.

Photoperiodism in birds

Birds show a circadian rhythm in melatonin secretion and, as expected, the pattern of output changes with photoperiod. Somewhat surprisingly then, in view of the mechanisms in mammals, birds do not seem to use this seasonal message in the photoperiodic control of reproduction. Some further experiments are needed, however, because in birds the pineal gland is not the only source of melatonin. Another difference from mammals is that birds detect the photoperiodic light not with the retina but by brain photoreceptors, which probably lie in the hypothalamus. An action spectrum for these receptors has now been obtained for the quail and this shows a peak absorption at 492 nm, suggesting that the photoreceptor is rhodopsin-based. The sensitivity of the brain receptors to 500 nm light was calculated at 2 X 10(4) photons mm-2s-1. For light to induce the photoperiodic response it must be interpreted by the bird's clock as a long day. This happens if the light falls 12-20 h after dawn and coincides with a rhythm of photosensitivity. The subsequent neuroendocrine response to the light signal is both precise and relatively long-term. A single 4 h light pulse initiates a wave of gonadotropin secretion lasting for 10 days. The light stimulus can be replaced by a brief (2 min) daily electrical stimulus given to the hypothalamus 10-12 h after dawn. Over the next few years it should be possible to disentangle further the neural processes involved.

Light-induced reduction of cytoplasmic free calcium in neurons proposed to be encephalic photoreceptors in chick brain

A population of cerebrospinal fluid-contacting neurons (CSFcn) in the lateral septal organ (LSO) may serve as encephalic photoreceptors (EPRs) functioning to signal the onset of seasonal reproductive development in birds. Previous studies on CSFcn in the LSO have focused on identification of retinal protein components in fixed brain tissue. In order to understand better the mechanisms underlying the light-induced photosexual response in birds, a physiological characterization is required. In this study, changes of intracellular free calcium concentration ([Ca2+]i) were monitored during light stimulation of CSFcn in the LSO in live brain slices from embryonic chicks. Using the fluorescent calcium indicator fluo-4, a reduced [Ca2+]i within CSFcn was recorded in response to photostimulation, which is consistent with what has been demonstrated in rods and cones following illumination. Results support the hypothesis that CSFcn in the LSO function as EPRs in the avian brain.

Effect of one or two pre-pubertal long days on age at first egg in domestic pullets

1. Two trials were conducted, using 288 brown-egg hybrid pullets in each, to determine the effect on age at first egg (AFE) of exposure to one or two 'long days' during the rearing period. In the first trial, birds were given a single 'long day' of 10, 12 or 14 h at 75, 89 or 103 d of age, with controls maintained on 8-h photoperiods. All treatment groups were transferred to cages at 110 d, and half the birds from each treatment combination given a 6-h increment in photoperiod at 116 d, with the remainder held on 8-h photoperiods. In the other trial, birds were given one or two long days of 14 or 16 h at 96, 107, 117 or 128 d of age; controls were again held on 8-h photoperiods. All groups were moved to cages at 130 d but maintained on 8-h photoperiods. 2. AFE was not significantly affected by one or two pre-pubertal long days, irrespective of when the long day was given or its length. AFE was advanced by 2 to 3 weeks following a transfer from 8 to 14 h at 116 d, independently of whether or not the birds had received a previous long day exposure. 3. It appears that a full-fed egg-type hybrid requires more than two cycles of long days to initiate rapid gonadal development, and that exposure to a single long day during the rearing period will have minimal effect on the timing of sexual maturation and no influence on the response to a subsequent permanent transfer to long days.

The behavior of the Japanese or domestic quail Coturnix japonica

This paper reviews the literature pertaining to the behavior of the Japanese or domestic quail Coturnix japonica. Details are given of the classification, characteristics, domestication and the economic and research potential of the species. Further sections deal with sensation and perception (including taste and smell, vision and hearing), maintenance behavior (including feeding and drinking, dust bathing and thermoregulation), development and aging (including vocalization, filial imprinting, sexual imprinting, fear and avoidance responses, sexual maturation and aging), adult learning (including habituation, instrumental conditioning, Pavlovian conditioning and observational learning), photoperiodism, reproductive behavior (including courtship and mating, hormonal control and ontogeny of sexual differentiation, and male and female sexual behavior), parental behavior (including nest-site selection and nest building, incubation behavior and its hormonal control, and hen-chick relationships), and aggressive behavior and dominance (including agonistic behavior and the hormonal control of aggressive behavior).

Photoperiodic induction in quail as a function of the period of the light-dark cycle: implications for models of time measurement

The earliest detectable event in the photoperiodic response of quail is a rise in luteinizing hormone (LH) secretion beginning at about hour 20 on the first long day. The timing of this rise was measured in castrated quail after entrainment to short daylengths which cause significant phase angle differences in the circadian system: (1) LD 2:22 and LD 10:14, and (2) LD 3:21 (T = 24 hr) and LD 3:24 (T = 27 hr). The quail were then exposed to 24 hr of light (by delaying lights-off), and the time of the first LH rise was measured; it was similar in all schedules. Quail were also entrained to LD 3:21 or LD 3:24 and then given a single 6-hr nightbreak 6-12, 7-13, or 13-19 hr after dawn. The earlier pulse was marginally more inductive in the 27-hr cycle. Thus the entrainment characteristics of the photoinducible rhythm (phi i) in quail appear very different from those of the locomotor circadian rhythm, and raise doubts as to whether phi i is a primary circadian oscillator.

Reproductive behavior and LH levels of cockatiels (Nymphicus hollandicus) associated with photostimulation, nest-box presentation, and degree of mate access

To determine the relative contribution of mate access and environmental cues in stimulating egg-laying and plasma luteinizing hormone (LH) secretion in cockatiels (Nymphicus hollandicus), and of mate access on nest-inspection and bowl-formation, mated pairs were permitted different degrees of mate access (full contact, auditory plus visual contact, auditory contact only, or no contact) and sequentially exposed to three environmental conditions (8L:16D without nest-box access for 6 weeks; 15L:9D without nest-box access for 3 weeks; 15L:9D with nest-box access for 3 weeks). The results indicate that a high degree of mate access is essential for the performance of nesting behaviors, since birds allowed no mate access or only auditory mate access were significantly less likely to inspect the nest or form a nest-bowl. Furthermore, pairs permitted no contact, auditory contact only, or auditory and visual contact delayed nest-inspection and bowl-formation and were significantly less likely to lay eggs than pairs with total mate contact. LH levels were significantly elevated only in photostimulated females of pairs of permitted full mate and nest-box access. These results suggest that maximal sexual activity in cockatiels requires an array of behavioral and environmental cues and that a linear relationship exists between extent of social cues and sexual activity.

Periodicity of death feigning by domestic fowl in response to simulated predation

The presence and extent of periodicity in the manifestation of death feigning duration was assessed in 137 week-old White Leghorn chicks. Chicks were reared on an LD 12:12 regimen with light onset at 0800 hr. Each was tested only once at one of 13 clock hours spanning a 24 hr period. Death feigning duration varied significantly with clock hour of induction, being longest from 1300-1400 hr and briefest from 0600-1100 hr. Variability was also cyclic but was distributed bimodally, being greatest in the latter half of each L and D phase. There was no significant influence of management hour on death feigning duration. The adaptive significance of the periodicity for predator-prey interactions was discussed, as were methodological implications.