Dopamine and prolactin involvement in the maternal care of chicks in the native Thai hen (Gallus domesticus)

A test of context and sex-dependent dopaminergic effects on the behavior of a gregarious bird, the common waxbill Estrilda astrild

The Dopaminergic (DAergic) system has well known influences on behavioral and cognitive functions. Previous work with common waxbills (Estrilda astrild) reported context-specific DAergic effects that could have been due to social environment. Manipulating the dopamine D2-like receptor family (D2R) pathways had opposed effects on behavior depending on whether waxbills were tested alone or in a small cage with a mirror as social stimulus. Since waxbills are highly gregarious, it was hypothesized that being alone or perceiving to have a companion might explain this context-dependence. To test context-dependent DAergic effects, we compared behavioral effects of D2R manipulation in waxbills in the same familiar environment, but either alone or with a familiar, same-sex companion. We found that D2R agonism decreased movement and feeding, similarly to previous results when testing waxbills alone. However, contrary to the hypothesis of dependence on social context, we found that the behavioral effects of the D2R agonist were unchanged when waxbills were tested with a companion. The context-dependence reported earlier might thus be due to other factors, such as the stress of being in a novel environment (small cage) or with an unfamiliar social stimulus (mirror image). In tests with a companion, we also found a sex-specific social effect of D2R manipulation: D2R blocking tended to decrease aggression in males but to increase in females. Together with past work, our results suggest that DAergic effects on behavior involve different types of context- or sex-dependence.

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.

Involvement of prolactin in newborn infant irritability following maternal perinatal anxiety symptoms

BACKGROUND

Newborn irritability could be an unique and special status and/or adverse neurobehavioral outcomes which was independent of serious disease. To determine whether maternal perinatal anxiety symptoms was associated with newborn irritability, and whether the alteration of serum prolactin in newborns were involved in newborn irritability.

METHODS

205 pregnant women were recruited: normal group (n = 100), and anxiety group (n = 105), which was randomly divided to Newborn Behavioral Observations (NBO)+anxiety group(n = 65) and control+anxiety group(n = 40). Newborn Irritability was assessed by Neonatal Behavioral Assessment Scale(NBAS). Serum prolactin, cortisol and 5-HT in mothers and infants were measured.

RESULTS

1. The scores of irritability items in the newborns of anxiety group were higher than that of the normal group (p < 0.05). 2. Lower serum PRL, 5-HT and higher serum cortisol were found in the newborns of anxiety group compared with that of the control group both postpartum 2d and 15 (p < 0.05). 3. The level of serum PRL in newborn infants were significantly and negatively correlated to the scores of irritability items (p < 0.05). 4. After 7 rounds of NBO interventions, the anxiety scores of mothers and the scores of irritability items of newborns in the NBO intervention group were all lower than those of the control group (p < 0.05) .

LIMITATIONS

In future experiments, we should explore the effect of PRL in the breast milk on newborn infant serum PRL.

CONCLUSIONS

Prolactin could be a potential mediator in newborn irritability following maternal perinatal anxiety symptoms.

The effects of replacing eggs with chicks on mesotocin, dopamine, and prolactin in the native Thai hen

The mesotocinergic (MTergic) and dopaminergic (DAergic) systems have been documented to play pivotal roles in maternal behaviors in native Thai chickens. In native Thai chickens, plasma prolactin (PRL) concentrations are associated with maternal behaviors, which are also controlled by the DAergic system. However, the role of MT in conjunction with the roles of DA and PRL on the neuroendocrine regulation of the transition from incubating to rearing behavior has never been studied. Therefore, the aim of this study was to investigate the association of MT, DA, and PRL during the transition from incubating to rearing behavior in native Thai hens. Using an immunohistochemistry technique, the numbers of MT-immunoreactive (-ir) and tyrosine hydroxylase-ir (TH-ir, a DA marker) neurons were compared between incubating hens (INC; n = 6) and hens for which the incubated eggs were replaced with 3 newly hatched chicks for 3 days after 6, 10, and 14 days of incubation (REC; n = 6). Plasma PRL concentrations were determined by enzyme-linked immunosorbent assay. The results revealed that the numbers of MT-ir neurons within the nucleus supraopticus, pars ventralis (SOv), nucleus preopticus medialis (POM), and nucleus paraventricularis magnocellularis (PVN) increased in the REC hens when compared with those of the INC hens at 3 different time points (at days 9, 13, and 17). On the other hand, the number of TH-ir neurons in the nucleus intramedialis (nI) decreased in the REC13 and REC17 hens when compared with those of the INC hens. However, the number of TH-ir neurons in the nucleus mamillaris lateralis (ML) only decreased in the REC13 hens when compared with the INC13 hens. The decrease in the numbers of TH-ir neurons within the nI and ML is associated with the decrease in the levels of plasma PRL. This study suggests that the presence of either eggs or chicks is the key factor regulating the MTergic system within the SOv, POM, and PVN and the DAergic system within the nI and ML during the transition from incubating to rearing behavior in native Thai chickens. The results further indicate that these two systems play pivotal roles in the transition from incubating to rearing behavior in this equatorial species.

Role of vasoactive intestinal peptide during the transition from incubation behavior to rearing behavior in the female native Thai chicken

It is well documented that vasoactive intestinal peptide (VIP) is an avian prolactin-releasing factor, regulating the reproductive cycle, that initiates and maintains incubation behavior in avian species. Native Thai chicken has strong maternal behaviors. Thus, it is an excellent animal model to study this phenomenon. Changes in the numbers of VIP neurons within the nucleus inferioris hypothalami (IH) and nucleus infundibuli hypothalami (IN) are associated with maternal behaviors in the native Thai chicken. The objective of this study was to elucidate the role of VIP during the transition from egg incubation to rearing behavior in this species. The distributions of VIP-immunoreactive (-ir) neurons and fibers within the nucleus septalis lateralis (SL), nucleus anterior medialis hypothalami (AM), regio lateralis hypothalami (LHy), nucleus commissurae pallii (nCPa), nucleus ventromedialis hypothalami (VMN), and IH-IN were compared between incubating (INC) hens and replaced-egg-with-chicks (REC) hens, in which eggs were replaced by 3-day-old chicks after 6, 10, and 14 d of incubation period for 3 days. Using an immunohistochemistry technique, the results revealed that VIP-ir neurons and fibers were found within the SL, AM, LHy, nCPa, VMN, and IH-IN, with the greatest expression observed in the IH-IN in both groups. The number of VIP-ir neurons in the IH-IN was markedly decreased (P < 0.05) in the REC hens when compared with those of the INC hens at 3 different time points (at d 9, 13, and 17). However, changes in the number of VIP-ir neurons between the INC and REC hens were not observed within other hypothalamic areas tested. These findings indicate that the presence of eggs and chicks affects the VIPergic system, and VIP neurons in the IH-IN might play a role in the transition from incubating to rearing behavior in the native Thai chicken.

Post-partum concentrations of serum progesterone, oestradiol and prolactin in Arabian mares demonstrating normal maternal behaviour and Arabian mares demonstrating foal rejection behaviour

The aim of this prospective study was to investigate possible endocrine components to foal rejection behaviour in post-partum Arabian mares. Arabian mares were divided into two groups based on their maternal behaviour: (1) mares with normal post-parturient behaviour (8 mares); and (2) mares that demonstrated foal-rejecting behaviour post-partum (15 mares). Most mares were visited and sampled twice, in the first and third days post-partum. Serum samples were used for measurement of progesterone, oestradiol and prolactin concentrations. There were no statistically significant differences in oestradiol, progesterone or prolactin concentrations between the groups. In the rejecting mares, there was a statistically significant decrease in the progesterone (mean±standard deviation, SD, 3.14±6.2ng/dL on day 1 and 0.49±0.18ng/dL on day 3) and prolactin (mean±SD 216.2±325.4ng/mL on day 1 and 145.2±311.4ng/mL on day 3) concentrations between days 1 and 3, while the oestradiol concentration did not change significantly. In the non-rejecting mares, progesterone concentrations decreased significantly (mean±SD 0.8±0.23ng/dL on day 1 and 0.43±0.22 on day 3) while the oestradiol and prolactin concentrations did not change significantly. The oestradiol to progesterone ratio was significantly higher in non-rejecting mares on day 1 (mean±SD 114.8±140.2 on day 1 and 143.4±72.6 on day 3) and this ratio increased significantly from days 1 to 3 in the rejecting mares (mean±SD 47.3±21.1 on day 1 and 122.1±123.7 on day 3).

Dopamine D2-like receptors (DRD2 and DRD4) in chickens: Tissue distribution, functional analysis, and their involvement in dopamine inhibition of pituitary prolactin expression

Dopamine (DA) D2-like (and D1-like) receptors are suggested to mediate the dopamine actions in the anterior pituitary and/or CNS of birds. However, the information regarding the structure, functionality, and expression of avian D2-like receptors have not been fully characterized. In this study, we cloned two D2-like receptors (cDRD2, cDRD4) from chicken brain using RACE PCR. The cloned cDRD4 is a 378-amino acid receptor, which shows 57% amino acid (a.a.) identity with mouse DRD4. As in mammals, two cDRD2 isoforms, cDRD2L (long isoform, 437 a.a.) and cDRD2S (short isoform, 408 a.a.), which differ in their third intracellular loop, were identified in chickens. Using cell-based luciferase reporter assays or Western blot, we demonstrated that cDRD4, cDRD2L and cDRD2S could be activated by dopamine and quinpirole (a D2-like receptor agonist) dose-dependently, and their activation inhibits cAMP signaling pathway and stimulates MAPK/ERK signaling cascade, indicating that they are functional receptors capable of mediating dopamine actions. Quantitative real-time PCR revealed that cDRD2 and cDRD4 are widely expressed in chicken tissues with abundant expression noted in anterior pituitary, and their expressions are likely controlled by their promoters near exon 1, as demonstrated by dual-luciferase reporter assays in DF-1 cells. In accordance with cDRD2/cDRD4 expression in the pituitary, DA or quinpirole could partially inhibit vasoactive intestinal peptide-induced prolactin expression in cultured chick pituitary cells. Together, our data proves the functionality of DRD2 and DRD4 in birds and aids to uncover the conserved roles of DA/D2-like receptor system in vertebrates, such as its action on the pituitary.

Distribution of mesotocin-immunoreactive neurons in the brain of the male native Thai chicken

Mesotocin (MT), a homolog of oxytocin (OT) in mammals, is a nonapeptide neurohypophysial hormone that is mainly synthesized in specific neuronal groups within the hypothalamus and released from the posterior pituitary gland in amphibian, reptilian, and avian species. MT is associated with the neuroendocrine regulation of reproductive cycle and maternal behaviors in female native Thai chickens. Male birds exhibit parental behaviors as well. However, there are limited data regarding the role(s) of the MTergic system in males. Thus, the objective of this study was to elucidate the localization of the MT neuronal groups in the brain of male native Thai chickens. The distributions of MT-immunoreactive (-ir) neurons and fibers in the brain were studied utilizing immunohistochemistry technique. The results revealed that MT-ir neurons and fibers were distributed throughout the brain and extensively in the diencephalon. MT-ir neurons and fibers were predominantly located within the nucleus supraopticus, pars ventralis (SOv), nucleus preopticus medialis (POM), nucleus ventrolateralis thalami (VLT), nucleus paraventricularis magnocellularis (PVN), and regio lateralis hypothalami (LHy), suggesting that MT neurons in these nuclei might be involved in the reproductive activities and/or parental behavior in the male chickens. In addition, the numbers of MT-ir neurons within the SOv and POM were significantly higher than those of the VLT, PVN, and LHy. More importantly, the number of MT-ir neurons in the SOv was high in the male brain when compared with the female brain, indicating that the MTergic system in the SOv might play a significant role in male reproductive activities in this equatorial species.

Effects of nest-deprivation on hypothalamic mesotocin in incubating native Thai hens (Gallus domesticus)

Avian mesotocin (MT) is homologous to oxytocin in mammals. Native Thai chickens (Gallus domesticus) strongly express maternal behaviors including incubation and rearing. However, the role of MT during incubation behavior has never been studied. The objective of this study was to determine the physiological function(s) of the MTergic system in incubation behavior in native Thai chickens. The brains were collected from incubating (INC) and nest-deprived (ND) hens at different time points (days 3, 6, 8, 10, 14, 18, and 21; n=6). Immunohistochemistry technique was used to compare the numbers of MT-immunoreactive (-ir) neurons between the INC and ND hens within the Nucleus supraopticus, pars ventralis (SOv), Nucleus preopticus medialis (POM), and Nucleus paraventricularis magnocellularis (PVN). The results revealed that the numbers of MT-ir neurons within the SOv, POM, and PVN remained high during the incubating stage. The number of MT-ir neurons in the SOv was lower than that of the POM and PVN. Disruption of incubation behavior by nest deprivation caused the numbers of MT-ir neurons within the SOv, POM, and PVN to decrease throughout the observation periods. For the first time, this study demonstrates that the MTergic system within the SOv, POM, and PVN may be involved with incubation behavior. In addition, these results further suggest that the MTergic neurons in these nuclei are not only regulated by rearing behavior but also might have a role in the initiation and maintenance of incubation behavior in this tropical species.

Distribution of hypothalamic vasoactive intestinal peptide immunoreactive neurons in the male native Thai chicken

Avian prolactin (PRL) secretion is under stimulatory control by the PRL-releasing factor (PRF), vasoactive intestinal peptide (VIP). The neuroendocrine regulation of the avian reproductive system has been extensively studied in females. However, there are limited data in males. The aim of this study was to elucidate the VIPergic system and its relationship to PRL and testosterone (T) in the male native Thai chicken. The distributions of VIP-immunoreactive (-ir) neurons and fibers were determined by immunohistochemistry. Changes in VIP-ir neurons within the nucleus inferioris hypothalami (IH) and nucleus infundibuli hypothalami (IN) areas were compared across the reproductive stages. Plasma levels of PRL and T were determined by enzyme-linked immunosorbent assay and then compared across the reproductive stages. The results revealed that the highest accumulations of VIP-ir neurons were concentrated only within the IH-IN, and VIP-ir neurons were not detected within other hypothalamic nuclei. Within the IH-IN, VIP-ir neurons were low in premature and aging males and markedly increased in mature males. Changes in VIP-ir neurons within the IH-IN were directly mirrored with changes in PRL and T levels across the reproductive stages. These results suggested that VIP neurons in the IH-IN play a regulatory role in year-round reproductive activity in males. The present study also provides additional evidence that VIP is the PRF in non-seasonal, continuously breeding equatorial species.

Ovarian steroids involvement in maternal care in the native Thai hen (Gallus domesticus)

Maternal care in birds generally includes incubation, brooding and rearing behavior. The neuroendocrine regulation of such maternal behavior is not fully understood for many bird species. The aim of this study was to elucidate whether changes in the circulating levels of ovarian steroids might be associated with brooding behavior in the female native Thai chicken. Changes in the levels of ovarian steroids of rearing hens were compared with those of non-rearing ones. Plasma estradiol, progesterone, and testosterone levels were determined by enzyme-linked immunosorbent assays. The results revealed differences in circulating levels of ovarian steroids between hens rearing their chicks and those deprived of their young after hatching. The non-rearing hens had higher circulating estradiol, progesteron, and tertosterone levels than those of the rearing hens. These differences were significant during the first two weeks after hatching. The results of the present study demonstrate the inhibitory effect of brooding behavior on ovarian steroids in the native Thai chickens. Indeed, disruption of brooding behavior by removing the chicks from the hens increased circulating levels of ovarian steroids and reinitiated reproductive and egg laying activities.