The dopaminergic system in the brain of the native Thai chicken, Gallus domesticus: localization and differential expression across the reproductive cycle

Dopamine (DA) has a pivotal role in avian prolactin (PRL) secretion, acting centrally through D₁ DA receptors to stimulate PRL secretion by operating through vasoactive intestinal peptide (VIP). DA also inhibits PRL secretion by activating D₂ DA receptors at the pituitary level. This study was designed to investigate the distribution of DA neurons in the native Thai chicken, utilizing tyrosine hydroxylase (TH) as a marker for dopaminergic neurons. The differential expression of hypothalamic TH immunoreactive (TH-ir) neurons was also compared across the reproductive cycle. The results revealed that TH-ir neurons and fibers were found throughout the brain of the laying hen and were predominantly located within the diencephalon and mesencephalon. The observed distribution pattern of TH immunoreactivity was consistent with that reported previously in several avian species. However, changes in the number of TH-ir neurons in the nucleus intramedialis (nI) were observed across the reproductive cycle and correlated directly with variations in PRL levels. The population of TH-ir neurons in the nI increased significantly during the egg incubation period, where circulating PRL levels were the greatest. This study indicates, for the first time, that an association exists between DA neurons and the regulation of the reproductive system in the native Thai chicken. There is a paucity of information about the reproductive neuroendocrine regulation of tropical non-seasonally breeding avian species and it is suggested that the differential expression of DA neurons in the nI might play a role in the control of VIP secretion and subsequent PRL release in such birds.     

Differential roles of hypothalamic serotonin receptor subtypes in the regulation of prolactin secretion in the turkey hen

In the turkey, exogenous serotonin (5-hydroxytryptamine, 5-HT) increases prolactin (PRL) secretion by acting through the dopaminergic (DAergic) system. In the present study, infusion of the 5-HT_2C receptor agonist, (R)(−)-DOI hydrochloride (DOI), into the third ventricle stimulates PRL secretion, whereas the 5-HT_1A receptor agonist, (+/−)-8-OH-DPAT hydrobromide (DPAT), inhibits PRL secretion. Using the immediate-early gene, c-fos, as an indicator of neuronal activity, in situ hybridization histochemistry showed preferential c-fos co-localization within tyrosine hydroxylase immunoreactive neurons (the rate limiting enzyme in DA synthesis) in the areas of the nucleus preopticus medialis (POM) and the nucleus premammillaris (PMM), in response to DPAT and DOI, respectively. To clarify the involvement of 5-HT_1A and 5-HT_2C receptors in PRL regulation, their mRNA expression was determined on hypothalamic tissue sections from birds in different reproductive stages. A significant difference in 5-HT_1A receptor was observed, with the POM of hypoprolactinemic short day and photorefractory birds showing the highest expression. 5-HT_2C receptors mRNA did not change during the reproductive cycle. The data presented support the notion that DA neurons in the PMM and POM mediate the stimulatory and inhibitory effects of 5-HT, respectively, on PRL secretion and the 5-HTergic system can both stimulate and inhibit PRL secretion.     

Serotonin receptor subtypes influence prolactin secretion in the turkey

Serotonin (5-HT) stimulation of prolactin (PRL) secretion is mediated through the dopaminergic (DAergic) system, with 5-HT ligands having no direct effect on pituitary PRL release. Infusion of 5-HT into the third ventricle (ICV) or electrical stimulation (ES) of the medial preoptic area (POM) or the ventromedial nucleus (VMN) induces an increase in circulating PRL in the turkey. These increases in PRL do not occur when a selective antagonist blocks the D₁ dopamine (DA) receptors in the infundibular area (INF). In this study, the ICV infusion of (R)(−)-DOI hydrochloride (DOI), a selective 5-HT_2A eceptor agonist, caused PRL to increase. Pretreatment with Ketanserin tartrate salt (KETAN), a selective 5-HT_2A receptor antagonist, blocked DOI-induced PRL secretion, attesting to the specificity of the response. DOI-induced PRL secretion was prevented when the D₁ DA receptors in the INF were blocked by the D₁ DA receptor antagonist, R(+)-SCH-23390 hydrochloride microinjection, suggesting that the DAergic activation of the vasoactive intestinal peptide (VIP)/PRL system is mediated by a stimulatory 5-HT_2A receptor subtype. The DOI-induced PRL increase did not occur when (±)-8-OH-DPAT (DPAT) was concurrently infused. DPAT is a 5-T_1A receptor agonist which appears to mediate the inhibitory influence of 5-HT on PRL secretion. When DPAT was microinjected directly into the VMN, it blocked the PRL release affected by ES in the POM. These data suggested that when 5-HT_2A receptors are activated, they influence the release of DA to the INF. When 5-HT_1A receptors are stimulated, they somehow inhibit the PRL-releasing actions of 5-HT_2A receptors. This inhibition could take place centrally, or it could occur postsynaptically at the pituitary level. It is known that D₂ DA receptors in the pituitary antagonize PRL-releasing effect of VIP. A release of DA to the pituitary, initiated by 5-HT_1A receptors, could effectively inhibit PRL secretion.     

Predictive factors for Gnathostoma seropositivity in patients visiting the Gnathostomiasis Clinic at the Hospital for Tropical Diseases, Thailand during 2000-2005

This was a retrospective study of patients having Gnathostoma antibody testing at the Hospital for Tropical Diseases, Bangkok during 2000-2005 to investigate predictive factors for Gnathostoma seropositivity in patients attending the Gnathostomiasis Clinic. Out of 849 patients tested, 531 (62.5%) were Gnathostoma seropositive. The median absolute eosinophil counts were 464 (0-16,796) and 326.5 (0-10,971) cells/mm3 in seropositive and seronegative patients, respectively (p<0.001). Differences in a history of cutaneous swelling, the habit of eating raw meat, eosinophilia (>500 cells/mm3), and the frequency of cutaneous swellings between seropositive and seronegative patients were all statistically significant. Patients with a history of eating raw meat and a history of cutaneous swelling were at 2.1 and 1.8 times more likely to be Gnathostoma seropositive, respectively. Logistic regression analysis showed eosinophilia was not a predictive factor for Gnathostoma seropositivity.     

Viral hepatitis infections among dialysis patients: Thailand registry report

BACKGROUND: Patients on dialysis are at high risk of acquiring viral hepatitis infections. However, there were only few data from Thailand. The aim of the present study was to assess the prevalence, incidence and associated risk factors of viral hepatitis infections among dialysis patients. METHODS: A retrospective study was conducted to evaluate 5179 medical records of dialysis patients from the Thailand Renal Replacement Therapy Registry. RESULTS: In 2002, the seroprevalence of hepatitis B virus (HBV) and hepatitis C virus (HCV) infections were 6.3% (n = 2454) and 4.8% (n = 2167), respectively. HBV and HCV seroprevalence became 6.5% (n = 2585) and 4.3% (n = 2399) in 2003. The incidence of HBV and HCV infections were 1.5 and 2.4 cases per 1000 patient-years, respectively. Logistic regression analysis showed that age and gender were significant risk factors for HBV infection, but not for HCV infection. CONCLUSION: In Thailand, it was not uncommon for dialysis patients to acquire viral hepatitis infections. However, our prevalence is similar to reports from some other South-East Asian countries.     

Role of vitelline envelope during fertilization in the black tiger shrimp, Penaeus monodon

Animal eggs possess investments through which sperm must penetrate. The aim of the present study was to investigate the role of the egg coating, the vitelline envelope, during sperm-egg interactions in the black tiger shrimp, Penaeus monodon. The site(s) of primary binding between sperm and egg and the possible binding molecule(s) for sperm were identified. In vitro adsorption of the vitelline envelope protein onto the sperm surface showed that primary binding occurred between the sperm anterior spike of acrosome intact sperm and the vitelline envelope. Results from streptavidin blotting revealed that the component of the vitelline envelope that interacts with the sperm integral membrane protein is a 370 kDa protein. In addition, it was shown that the vitelline envelope protein had no ability to induce acrosome reaction. These results suggest that the function of the vitelline envelope is as a primary binding site for sperm in shrimp, but not a sole trigger for the acrosome reaction.     

Neuropeptide Y and maternal behavior in the female native Thai chicken

Maternal care behaviors in birds include incubation and rearing behaviors. During incubating period, the hens stop laying and eating less due to food restriction as a natural fasting when compared with the rearing hens, resulting in low production of eggs and chicks. Neuropeptide Y (NPY), a neurotransmitter/neuromodulator, is very well known to be involved in food intake regulation in birds and mammals. The objective of this study is to elucidate the association between NPY and maternal behaviors in the female native Thai chicken. The distributions of NPY-immunoreactive (-ir) neurons and fibers in the brain of the incubating (INC), nest-deprived (ND), and replaced-egg-with-chicks (REC) hens at day 6 were determined utilizing immunohistochemistry technique. The results revealed that the distributions of NPY-ir neurons and fibers were observed within the septalis lateralis, nucleus rotundus, and nucleus dorsolateralis anterior thalami, with predominantly located within the the nucleus paraventricularis magnocellularis (PVN). NPY-ir fibers were located throughout the brain and the densest NPY-ir fibers were distributed in a discrete region lying close to the ventriculus tertius (third ventricle) through the hypothalamus. Changes in the number of NPY-ir neurons within the PVN of the INC, ND, and REC hens were compared at different time points (at days 6 and 14). Interestingly, the number of NPY-ir neurons within the PVN was significantly higher (P < 0.05) in the INC hens when compared with those of the ND and REC hens at day 14 but not day 6. In addition, the number of NPY-ir neurons within the PVN of the INC hens was significantly increased (P < 0.05) from day 6 to day 14 but not the ND and REC hens. These results indicated, for the first time, the asscociation between NPY and maternal behaviors in the femle native Thai chicken. Change in the number of NPY-ir neurons within the PVN during the transition from incubating to rearing behavior suggested the possible role of NPY in the regulation of the maternal behaviors in this equatorial species. In addition, the native Thai chicken might be an excellent animal model for the study of this phenomenon.     

Distribution and variation in gonadotropin releasing hormone-I (GnRH-I) immunoreactive neurons in the brain of the native Thai chicken during the reproductive cycle

Gonadotropin releasing hormone-I (GnRH-I) is known to regulate the avian reproductive system. We investigated the roles of GnRH-I in the regulation of the reproductive system of the native Thai chicken. The distribution of GnRH-I neurons and changes in GnRH-I-immunoreactive (-ir) neurons throughout the reproductive stages and between incubating and nest-deprived hens were analyzed utilizing immunohistochemical techniques. The results revealed that GnRH-I-ir neurons were distributed in a discrete region lying close to the third ventricle from the level of preoptic area through the anterior hypothalamus, with the greatest abundance found within the nucleus commissurae pallii (nCPa). The number of GnRH-I-ir neurons in the nCPa was highest in laying hens when compared with that in the other reproductive stages. Nest deprivation caused an increase in the number of GnRH-I-ir neurons in the nCPa of nest-deprived hens when compared with incubating hens. These results indicate that GnRH-I expression is correlated with the reproductive state in the native Thai chicken and may be, in part, regulated by it. This study also confirms a pivotal role of GnRH-I in controlling avian reproduction of this non-seasonal breeding, equatorial species.     

Vasoactive Intestinal Peptide Concentrations in Turkey Hypophysial Portal Blood Differ across the Reproductive Cycle

Hypophysial portal blood was collected for the first time in an avian species using a dorsal approach through the third ventricle and median eminence of the turkey. This was done to test for the presence of the prolactin (PRL)-releasing factor vasoactive intestinal peptide (VIP) in the portal blood and to determine whether VIP concentrations there varied with and corresponded to plasma PRL levels across the reproductive cycle. VIP concentrations in hypophysial portal blood were 2.5- to 13.5-fold greater than in the general circulation. VIP concentrations were lowest in portal blood of nonphotostimulated, reproductively inactive hens (231.8 ± 26.4 pg/ml) and highest in incubating hens (1108.1 ± 363.7 pg/ml), while laying, and photorefractory hens were intermediate at 372.5 ± 95.6 and 715.3 ± 338.5 pg/ml, respectively. These differences in concentration of VIP in portal blood mirrored those of PRL in the general circulation and support other evidence that VIP is the avian PRL-releasing factor.