Scotostimulation of reproductive neural pathways and gonadal maturation are not correlated with hypothalamic expression of deiodinases in subtropical spotted munia

Effect of immunization against OPN5 on the reproductive performance in Shan Partridge ducks under different photoperiods

Photoperiod is an important environmental factor that influences seasonal reproduction behavior in birds. Birds translate photoperiodic information into neuroendocrine signals through deep brain photoreceptors (DBPs). OPN5 has been considered candidate DBPs involved in regulating seasonal reproduction in birds. We found that OPN5 could mediate light to regulate the follicle development in ducks. In this study, we further verified the effect of OPN5 on follicular development in Shan Partridge ducks by immunizing against the extracellular domain (ECD) of OPN5. We investigated the specific regulatory mechanism of photoperiod mediated by OPN5 on the reproductive activity of ducks. The trial randomly divided 120 Shan Partridge ducks into 3 groups with different treatments: the immunization of OPN5 group was done at d0, d15, d30, and d40 with 1 mL of vaccine containing OPN5 protein (thus containing 1, 1, 0.5, and 0.5 mg of OPN5-KLH protein), and the control group (CS and CL groups) was injected at the same time with the same dose of OPN5-uncontained blank vaccine. The group of CS (900 lux), OPN5 (600 lux), and CL (600 lux) lasted for 40 d in 12 L:12 D photoperiods, respectively. Then, the groups of CS, OPN5, and CL subsequently received 12 L:12 D, 12 L:12 D, and 17 L:7 D light treatments for 33 d, respectively. The ducks were caged in 3 constant rooms with the same feeding conditions for each group, free water, and limited feeding (150 g per duck each day). Duck serum and tissue samples were collected at d 40, d 62, and d 73 (n = 12). It was found that before prolonged light, the group of immunization (group OPN5) and the group of strong light intensity (group CS) were higher than the group of CL in egg production. Subsequent to prolonged light, the group CL in egg production rose about the same as the group immunization, while the strong light group (group CS) was lower. Group OPN5 increased the ovarian index of ducks, and both the immunization of group OPN5 and group CL (extended light) increased the thickness of the granular layer and promoted the secretion of E2, P4, LH, and PRL hormones. Compared with group CS, group CL and OPN5 increased the mRNA level and protein expression of OPN5 in the hypothalamus on d 62 and d 73 (P < 0.05). The gene or protein expression patterns of GnRH, TRH, TSHβ, DIO2, THRβ, VIP, and PRL were positively correlated with OPN5, whereas the gene expression patterns of GnIH and DIO3 were negatively correlated with OPN5. The results showed that immunization against OPN5 could activate the corresponding transmembrane receptors to promote the expression of OPN5, up-regulate the expression of TSHβ and DIO2, and then regulate the HPG axis-related genes to facilitate the follicular development of Shan Partridge ducks. In addition, in this experiment, prolonging the photoperiod or enhancing the light intensity could also enhance follicle development, but the effect was not as significant as immunizing against OPN5. Our results will offer beneficial data and more supportive shreds of evidence in favor of elucidating the role of OPN5 in relation to photoperiods and reproduction.

Three different seasonally expressed opsins are present in the brain of the Eared Dove, an opportunist breeder

Birds living at high latitudes perceive the photoperiod through deep-brain photoreceptors (DBP) located in deep-brain neurons. During long photoperiods the information transmitted by these photoreceptors increases the activity of the hypothalamic-pituitary-gonadal (HPG) axis, leading to gonadal development. The presence of photopigments such as VA-Opsin, Opn4, Opn5 and Opn2 in brain areas implicated in reproductive behaviors has been firmly established in several avian species with seasonal breeding, whereas their existence in opportunistic breeding birds remains unconfirmed. The Eared Dove is an urban and peri-urban dove that breeds throughout the year. Males of this species do not exhibit the typical gonadal regression/recrudescence cycle, thus posing the question of what occurs upstream of the HPG axis. We addressed this issue by first studying the presence of diverse opsins located in DBP in the brains of Eared Dove males and whether these photopigments changed their expression throughout the year. We carried out an immunohistochemistry analysis on three different opsins: Opn2 (rhodopsin), Opn3 and Opn5. Our results demonstrate the discrete neuroanatomical distribution of these opsins in the brain of Eared Dove males and strongly indicate different seasonal expressions. In the anterior region of the hypothalamus, Opn2-positive cells were detected throughout the year. By contrast, Opn5 was found to be strongly and seasonally expressed during winter in the anterior and the hypothalamic region. Opn3 was also found to be significantly and seasonally expressed during winter in the hypothalamic region. We thus demonstrate for the first time that males of the Eared Dove, have three different deep-brain opsin-expressing photoreceptors with differential location/distribution in the anterior and hypothalamic region and differential seasonality. The persistence of Opn2 and the strong seasonal expression of nonvisual photopigments Opn3 and Opn5 in two areas of the avian brain, which are associated with reproduction, could be the primary distinction between seasonal and opportunistic breeders.

Differential effects of continuous and intermittent daytime food deprivation periods on metabolism and reproductive performance in diurnal zebra finches

We investigated whether food availability effects on metabolism and reproduction are the result of the sum effect of daily feeding (food availability) and starvation (food deprivation) periods. Adult zebra finches were paired and subjected to a time-restricted feeding (TRF) regimen consisting of continuous and intermittent daytime food deprivation periods. Birds were given food during the 12-h day for a total of 4-h in the evening (1 *4-h, hour 8-12), or in 2 splits of 2 h each (2 * 2-h) or 4 splits 1 h each (4 * 1-h), with controls on food ad libitum, until they had the first egg clutch. TRF caused significant changes in hepatic expression of metabolism-associated sirt1, egr1, pparα and foxo1 genes despite no difference in the food intake, body mass and blood glucose levels. Importantly, TRF resulted in a significant reduction in plasma testosterone and estradiol levels, delayed nest-building and egg laying, and reduced clutch size. Concurrently, under TRF regimes, we found a significantly lower expression of th and mtr genes linked with motivation and affiliation (but not of dio2, dio3, gnrh1 and gnih genes linked with gonadal maturation) in the hypothalamus, and of star and hook 1 genes in the testes and star, cyp19 and erα genes in the ovary. These results demonstrate the importance of daily food deprivation times on the metabolism and reproduction, and suggest a possible provisioning of energy available from daily feeding for the maintenance of body condition at the expense of reproduction performance in diurnal animals.

Seasonal Differences in Expression of Neuropeptide Y (NPY) in Visual Centers of Spotted Munia (Lonchura punctulata)

The visual perception of birds is an incredibly exciting subject of research. Birds have significantly higher visual acuity than most other animals, which helps them stay safe in flight and detect their prey. Understanding how the eyes send information to the brain for additional processing is crucial. The brain has sections (nuclei) that accept input from the retina. The key areas where information is processed are the hyperpallium apicale (HA), hippocampus (HP), optic tectum (TeO), nucleus rotundus (RoT), and the geniculatus lateralis ventralis (Glv); among these, the RoT is one of the most investigated nuclei for vision. This study looked at how the visual centers of non-photoperiodic songbirds (Spotted Munia) adapt in different life history stages by looking at NPY expression. We immunohistochemically quantified NPY expression in four different seasons, including pre-breeding (June), breeding (September), post-breeding (December), and regressed (March) in the brain of Spotted Munia. We evaluated changes in the expression levels of the peptide throughout the year, by determining the expression at four different periods throughout the year. Peptide expression levels were projected to fluctuate within photoperiod-induced seasons. It was discovered that the parts of the brain related to vision (RoT, HA, and HP) have a higher number of immunoreactive cells during their mating season, i.e., during the summer. The appearance of NPY, a non-photic marker, in brain areas linked with light perception, was fascinating. Indirectly, NPY aids avian reproduction in a variety of ways. These findings demonstrate the importance of these nuclei in the process of reproduction, as well as the involvement of NPY in the visual brain areas of Spotted Munia.

OPN5 Regulating Mechanism of Follicle Development Through the TSH-DIO2/DIO3 Pathway in Mountain Ducks Under Different Photoperiods

Abstract: Photoperiod is an important environmental factor that influence seasonal reproduction behavior in bird. Birds translates photoperiodic information into neuroendocrine signals through deep brain photoreceptors (DBPs). OPN5 has been considered as candidate DBPs involving in regulation of seasonal reproduction in birds. However, little is known about the effect of OPN5 in non-seasonal breeding birds. Thus, we pondered on whether OPN5 regulating follicular development through TSH-DIO2/DIO3 system responds to different photoperiods in non-seasonal laying ducks. As an ideal non-seasonal breeding bird, a total of 120 mountain ducks were randomly divided into three groups and treated respectively to a different photoperiod: group S (8 L:16D), group C (17 L:7D), and group L (24 L:0D). The ducks were caged in a fully enclosed shelter with the same feeding conditions for each group, free water and limited feeding (150 g per duck each day). Samples were collected from each group at d 0, d 5, d 8, d 20, and d 35 (n = 8). The ducks in 24 h photoperiod had the highest laying rate and the lowest feed-to-egg ratio, while the ducks in 8 h photoperiod had the lowest laying rate and the highest feed-to-egg ratio. Long-day photoperiod for 24 h significantly increased the ovarian index and GnRH, LH, E2, and P4 levels in serum; short-day photoperiod for 8 h increased testosterone levels in serum. Compared with 8 h photoperiod, long-day photoperiod significantly or highly significantly increased the mRNA level and protein expression of OPN5 in the hypothalamus of long-day photoperiod on d 35 (p &lt; 0.05). The gene or protein expression patterns of GnRH, TRH, TSHβ, DIO2, THRβ, VIP, and PRL were positively correlated with OPN5, whereas the gene expression patterns of GnIH and DI O 3 were negatively correlated with OPN5. The results revealed that OPN5 mediated the effect of light on follicular development through the TSH-DIO2/DIO3 pathway, the expression of OPN5 increased with light duration and improved the efficiency of the HPG axis to promote follicular development in mountain ducks.

Neuromorphometric changes associated with photostimulated migratory phenotype in the Palaearctic-Indian male redheaded bunting

Neural substrates, including brain areas, differential gene expression and neuroendocrine basis, of migration are known. However, very little is known about structural changes in the brain that underlie the development and cessation of migration in long-distance avian migrants. Towards this, we investigated neuromorphological changes in the higher-order associative areas in male redheaded bunting (Emberiza bruniceps), which is a Palaearctic-Indian night migrant with wintering grounds in India. Photosensitive birds (8L:16D; SD) were exposed to stimulatory long days (16L:8D; LD), with controls retained on non-stimulatory short days. LD birds depicted shifts to, and sustained night-time activity as recorded by actograms. LD birds demonstrated increased body mass, fat deposition and testicular volume in keeping with the migratory phenotype. When LD birds had exhibited 10.0 ± 2.4 cycles of Zugunruhe (intense nighttime activity in captives, akin to night migratory flight in the wild), bird brains were fixed by transcardial perfusion, and changes in the neuronal morphometry of pallial, sub-pallial and hypothalamic brain regions studied using rapid Golgi technique with modifications, as used and validated in our laboratory. There were significant differences in both area and perimeter of soma in the visual hyperpallium apicale implicated in migratory orientation and the neuroendocrine control region for timing of migration, the mediobasal hypothalamus. We attribute these neuromorphometric changes in the soma area and perimeter to the photostimulated changes associated with the development of migration and reproductive phenotypes in redheaded buntings. It is suggested that changes in the neuronal plasticity in brain control regions parallel photoperiod-induced physiological responses.

Effects of timed food availability on reproduction and metabolism in zebra finches: Molecular insights into homeostatic adaptation to food-restriction in diurnal vertebrates

Food availability affects metabolism and reproduction in higher vertebrates including birds. This study tested the idea of adaptive homeostasis to time-restricted feeding (TRF) in diurnal zebra finches by using multiple (behavioral, physiological and molecular) assays. Adult birds were subjected for 1 week or 3 weeks to food restriction for 4 h in the evening (hour 8-12) of the 12 h light-on period, with controls on ad lib feeding. Birds on TRF showed enhanced exploratory behavior and plasma triglycerides levels, but did not show differences from ad lib birds in the overall food intake, body mass, and plasma corticosterone and thyroxine levels. As compared to ad lib feeding, testis size and circulation testosterone were reduced after first but not after third week of TRF. The concomitant change in the mRNA expression of metabolic and reproductive genes was also found after week 1 of TRF. Particularly, TRF birds showed increased expression of genes coding for gonadotropin releasing hormone (GnRH) in hypothalamus, and for receptors of androgen (AR) and estrogen (ER-alpha) in both hypothalamus and testes. However, genes coding for the deiodinases (Dio2, Dio3) and gonadotropin inhibiting hormone (GnIH) showed no difference between feeding conditions in both hypothalamus and testes. Further, increased Sirt1, Fgf10 and Ppar-alpha, and decreased Egr1 expression in the liver suggested TRF-effects on the overall metabolism. Importantly, TRF-effects on gene expressions by week 1 seemed alleviated to a considerable extent by week 3. These results on TRF-induced reproductive and metabolic effects suggest homeostatic adaptation to food-restriction in diurnal vertebrates.

Molecular correlates of hypothalamic development in songbird ontogeny in comparison with the telencephalon

Development of the songbird brain provides an excellent experimental model for understanding the regulation of sex differences in ontogeny. Considering the regulatory role of the hypothalamus in endocrine, in particular reproductive, physiology, we measured the structural (volume) and molecular correlates of hypothalamic development during ontogeny of male and female zebra finches. We quantified by relative quantitative polymerase chain reaction (rqPCR) the expression of 14 genes related to thyroid and steroid hormones actions as well as 12 genes related to brain plasticity at four specific time points during ontogeny and compared these expression patterns with the expression of the same genes as detected by transcriptomics in the telencephalon. These two different methodological approaches detected specific changes with age and demonstrated that in a substantial number of cases changes observed in both brain regions are nearly identical. Other genes however had a tissue-specific developmental pattern. Sex differences or interactions of sex by age were detected in the expression of a subset of genes, more in hypothalamus than telencephalon. These results correlate with multiple known aspects of the developmental and reproductive physiology but also raise a number of new functional questions.

Changes in brain peptides associated with reproduction and energy homeostasis: Putative roles of gonadotrophin-releasing hormone-II and tyrosine hydroxylase in determining reproductive performance in response to daily food availability times in diurnal zebra finches

Previous studies have demonstrated 'quality-quantity' trade-offs with daily food availability times in zebra finches. Compared with food access ad lib., zebra finch pairs with restricted food access for 4 hours in the morning produced poor quality offspring, whereas those with the same food access in the evening produced fewer but better quality offspring. The present study investigated whether food-time-dependent differential effects on reproductive performance involved brain peptides associated with reproduction and energy homeostasis in zebra finches. We measured peptide/protein expression of gonadotrophin-releasing hormone (GnRH)-I, GnRH-II, gonadotrophin-inhibitory hormone (GnIH), tyrosine hydroxylase (TH), neuropeptide Y (NPY), cocaine- and amphetamine regulated transcript (CART) and ZENK (a neuronal activation marker) by immunohistochemistry and mRNA expression of genes coding for the type 2 (DIO2) and type 3 (DIO3) deiodinase by a quantitative polymerase chain reaction in male and female zebra finches that were paired and kept under a 12:12 hour light/dark photocycle at 24 ± 2°C temperature for > 12 months with access to food ad lib., or for only 4 hours in the morning or evening. In both sexes, GnRH-I, DIO2 and DIO3 expression did not differ significantly between the three feeding conditions, although levels showed an overall food effect. However, in males, GnIH expression was significantly higher in evening-fed birds compared to ad lib. fed birds. Interestingly, GnRH-II and TH levels were significantly lower in restricted feeding compared to the ad lib. group and, importantly, GnRH-II and TH-immunoreactivity levels were negatively and positively correlated with egg laying latency and reproductive success (offspring/brood/pair), respectively. At the same time, we found no effect on the hypothalamic expression of orexigenic (NPY) and anorexigenic (CART) peptides, or ZENK protein (ie, the neuronal activity marker). These results suggest the involvement of reproductive neuropeptides, with putative roles for GnRH-II and TH, in the food-time-dependent effect on reproductive performance, albeit with subtle sex differences, in diurnal zebra finches, which possess the ability to reproduce year-round, in a manner similar to other continuously breeding vertebrates.

Light at night disrupts diel patterns of cytokine gene expression and endocrine profiles in zebra finch (Taeniopygia guttata)

Increased exposure to light pollution perturbs physiological processes through misalignment of daily rhythms at the cellular and tissue levels. Effects of artificial light-at-night (ALAN) on diel properties of immunity are currently unknown. We therefore tested the effects of ALAN on diel patterns of cytokine gene expression, as well as key hormones involved with the regulation of immunity, in zebra finches (Taeniopygia guttata). Circulating melatonin and corticosterone, and mRNA expression levels of pro- (IL-1β, IL-6) and anti-inflammatory (IL-10) cytokines were measured at six time points across 24-h day in brain (nidopallium, hippocampus, and hypothalamus) and peripheral tissues (liver, spleen, and fat) of zebra finches exposed to 12 h light:12 h darkness (LD), dim light-at-night (DLAN) or constant bright light (LLbright). Melatonin and corticosterone concentrations were significantly rhythmic under LD, but not under LLbright and DLAN. Genes coding for cytokines showed tissue-specific diurnal rhythms under LD and were lost with exposure to LLbright, except IL-6 in hypothalamus and liver. In comparison to LLbright, effects of DLAN were less adverse with persistence of some diurnal rhythms, albeit with significant waveform alterations. These results underscore the circadian regulation of biosynthesis of immune effectors and imply the susceptibility of daily immune and endocrine patterns to ALAN.