A wealth of functional data confirms the involvement of hypothalamic vasoactive intestinal peptide (VIP) and gonadotropin releasing hormone (GnRH) in the regulation of the avian reproductive cycle. However, very little is known about the neurotransmitters or the anatomical locations of the hypophysiotropic neurons mediating the transition from one reproductive state to the next. Dopamine (DA) stimulates prolactin (PRL) and luteinizing hormone (LH) secretion by acting on VIP and GnRH neurons, respectively. DA may inhibit PRL secretion by antagonizing the action of VIP at the level of the pituitary, and limits LH secretion through presynaptic inhibition of GnRH release at the median eminence (ME) level. The stimulatory and inhibitory effects of DA are mediated via D1 and D2 DA receptors, respectively. However, the dopaminergic neuronal groups/subgroups which regulate the VIP/PRL and GnRH/LH systems remain to be clarified. Studies utilizing electro-pharmacological techniques in combination with radioimmunoassay, immunocytochemistry, and in situ hybridization histochemistry yield results suggesting the presence of a stimulatory dopaminergic pathway from the preoptic area (POA) to the infundibular nuclear complex (INF) area, where VIP neurons preside over the regulation of PRL secretion, as well as DA projections within the preoptic area-anterior hypothalamus (POA-AM) areas where the GnRH neurons reside that control LH secretion. DA neurons projecting to the ME which mediate the inhibition of the VIP/PRL and GnRH/LH systems remain to be identified.
The aim of this study was to determine whether the expressions of MHC class I and II in the ovarian follicles change with follicular growth and aging of birds. Theca layer of white follicles (WF), the largest and the third largest preovulatory follicles (F1 and F3, respectively) and the largest postovulatory follicle (POF) were collected from laying hens. Localization of MHC class I and II cells was examined by immunocytochemistry. Changes in the MHC class I and II mRNA expressions in the theca were examined by semi quantitative RT-PCR. MHC class I+ cells were observed mostly in the theca interna of WF, F3, F1 and POF, whereas MHC class II+ cells were observed in both theca interna and externa of those follicles. In addition, MHC class II+ cells were observed not only in theca layer but also in granulosa layer in POF. The expression level of MHC class I mRNA was similar in the theca layers among WF, F3, F1 and POF within young and old birds as well as between young and old birds within each type of follicles. The expression level of MHC class II mRNA was significantly lower in old birds than in young birds (P<0.01). However, there was no significant difference in that level among the follicles within young and old hens. These results suggest that the expressions of MHC class I and II may not be changed with follicular growth, whereas the expression of MHC class II is declined with age in the theca layer.
Compared to studies on the cockerel and the domestic laying hen, little information is available concerning the progressive alteration to acid-base balance in broiler chickens exposed to acute heat stress. The primary objective of this study was to determine the time course of changes to core temperature, respiratory rate and blood acid-base parameters of broiler chickens during an episode of acute heat exposure (36 or 38°C). Acute exposure of chickens to 36 and 38°C resulted in significant increases in core temperature, with maximum values reaching 44 and 46°C, respectively. In the first 30min when rectal temperature increased significantly in the 38°C heat-exposed group, a clear and significant concomitant increase in blood pH was also identified. Conversely, pCO2 and bicarbonate concentration in the heat-exposed animals had decreased significantly 60min after the onset of exposure to heat, but not at the 30min time point. In contrast to previous findings of the time course of changes in arterial pH and pCO2 of hens exposed to acute heat stress, there was evidence here of a time lag for pCO2 to decrease after the onset of heat exposure and no compensation for the blood alkalosis at the 90- and 120-min time points after heat exposure. These findings imply the absence of a mechanism for pH compensation in broiler chickens.
Sex reversal effects of 17 beta-estradiol (E2), diethylstilbestrol (DES) and ethynylestradiol (EE2) on male gonads in F1 (AWE×WE) Japanese quail (Corturnix japonica) embryos were comparatively evaluated in a newly developed in vivo screening model called as the sex reversal test. Male and female offspring of F1 (AWE×WE) Japanese quail exhibit exactly wild and albino plumage colors, respectively, ruled by a criss-cross inheritance. The natural and synthetic estrogens were injected into egg white just before the incubation. At 16 days of incubation, embryos were subjected by a complete necropsy and their gonads were grossly observed and examined histopathologically and morphometrically. Grossly, genetic sex confirmed by plumage colors coincided completely with external sex phenotype of the gonads in all embryos of the control group and E2 and DES-treated groups. However, several male embryos with wild plumage in the EE2 2000ng group possessed an ovary-like gonad in the left side and a vestigial right gonad. Histopathologically, E2, DES and EE2 exposures induced a dose-dependent sex reversal effect, i.e. ovotestis development, in the left testis. The left testes showing an ovary-like morphology in the EE2 2000ng group consisted of the most of area replaced with ovarian tissue and the small area of remaining testicular cords. The incidence and morphometric analysis of the ovotestis revealed that the order of potency of sex reversal effect in Japanese quail embryos was EE2>DES>E2. E2, DES and EE2 exposures induced no noticeable changes in the ovaries of any embryos. The present study suggests that the sex reversal test using F1 (AWE×WE) Japanese quail embryo is possible to evaluate feminization effects of endocrine disrupting chemicals with estrogenic activities in avian male embryos.
Three different lines (normal, brown and crossbred) of Japanese quail were used in this study to examine the effects of dietary protein level on the production and quality of eggs. In all lines, poor egg production was evident throughout the experiment on a diet with 16% crude protein (CP). Egg production increased as the CP levels of diets increased. Until 32 weeks, normal (N) and brown (B) lines showed higher egg production at 24% CP, while the crossbred (BN) line showed higher egg production at 22% CP. The cumulative egg production at 24% CP was higher than or similar to that at 26% CP. A comparison of egg production among different lines showed that BN produced significantly (P<0.05) more eggs than N at the lower protein levels of 20% and 22% CP. Weight of eggs was lowest in all lines at 16% CP, and tended to increase with increasing protein level. No difference in egg weight was observed among lines. Egg weight and yolk color were significantly (P<0.05) affected by different levels of protein. It appears that 24% CP was optimal for higher egg production and egg weight for N and B lines and 22% CP for BN lines. Furthermore, our data indicate that heterosis was obtained in BN for egg production at the lower protein levels.
Fertilised ova, obtained from the anterior region of the magnum of the oviduct 60-80min after the preceding egg had been laid, were cultured in vitro with dense albumen adjusted to pH 7.0 after removing a thin layer of dense albumen capsule surrounding the ovum. The ova were then cultured in recipient eggshells until hatching. Of 80 cultured embryos, about half developed to the blastoderm stage, 25% survived to day 4 of incubation, and 7.5% survived to hatching. The embryo culture technique developed in this study enables precise manipulation of the germinal disc just after ovulation.
Seasonal changes occur in the plumage of male mallard ducks, and this phenomenon is referred to as seasonal dimorphism of the plumage. However, no information is available, especially morphological, about the mechanisms that control these changes. The present study was conducted to study the morphological changes in the head feathers of mallard drakes. Samples were collected from a total of 43 drakes from April to August, 2002. About 100 to 200 feathers were randomly extracted from the occipital region of the head. The collected head feathers could be classified into two main types ; the nuptial plumage type and the eclipse plumage type. It was observed that the whole feather (rachis, barb and barbules) was heavily pigmented in the nuptial plumage type feather, whereas pigmented and non-pigmented areas gave a dotted-line appearance in the barbs of the eclipse plumage type feather. The plumage type could therefore be distinguished by the proportion of nuptial and eclipse plumage type feathers. The length of the feather and proportion of nuptial plumage type feathers also decreased seasonally from the nuptial plumage to eclipse plumage. It was found that the length of the barb and barbules showed similar seasonal changes. These findings suggest that different mechanisms regulate the color and length of the feathers. The nuptial plumage showed significantly longer feathers, barbs and barbules than those of the eclipse plumage.
Since it is impossible to distinguish germline chimeric chickens by appearance only, a progeny test is required for analyzing germline chimerism. To reduce the labor, time and expense involved in such test, a new screening test for male putative germline chimeric chickens by polymerase chain reaction (PCR) was developed that uses single nucleotide polymorphism (SNP) detection primers. Putative germline chimeric chickens were produced by the transfer of stage X blastodermal cells or circulating primordial germ cells from Barred Plymouth Rocks (BPR) to White Leghorns (WL). For screening prior to the progeny test, DNA was extracted from the semen and used for PCR analysis, using SNP detection primers at position 686 in the chicken mitochondrial DNA D-loop region (DNA database, AB091008). In this study, the type of SNP in all BPR at position 686 was fixed as base G, and as base A in all WL. When the PCR product was typed as both donor (base G)- and recipient (base A)-derived, the male was determined as the germline chimera. The male and female putative germline chimeric chickens produced in this study were given the progeny test. The results of the male screening test showed good agreement with the progeny test for detecting germline chimeric chickens.