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.

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.