Neuroendocrine regulation of maternal behaviours in birds

Avian reproductive system is regulated by the integrated system, the hypothalamo-pituitary-gonadal (HPG) axis. The HPG axis involves two major neuroendocrine systems controlling avian reproduction. These neuroendocrine systems include the chicken gonadotropin releasing hormone/follicle stimulating hormone-luteinizing hormone (GnRH/FSH-LH), and vasoactive intestinal peptide/prolactin (VIP/PRL) neuroendocrine systems. Both systems are influenced by dopamine (DA). There is a paucity of information about the reproductive neuroendocrine regulation of tropical non-seasonally breeding avian species. Hyperprolactinemia has been associated with incubation behavior and ovarian regression in the native Thai chicken, an equatorial continuous breeding species. To elucidate the association GnRH-I, VIP, PRL, and DA with the neuroendocrine regulation of incubation behavior, changes in the number of GnRH-Iimmunoreactive (GnRH-I-ir) in the nucleus commissurae pallii (nCPa), VIP-immunoreactive (VIP-ir) neurons in the nucleus inferioris hypothalami (IH) and nucleus infundibuli hypothalami (IN), and tyrosine hydroxylase-immunoreactive (TH-ir) neurons in the nucleus intramedialis (nI) and nucleus mamillaris lateralis (ML) of incubating native Thai hens (INC) were compared with those of nest-deprived hens (ND). Disruption of broodiness in INC hens was accompanied by a precipitous decline in plasma PRL levels. The numbers of VIP-ir neurons in the IH-IN and TH-ir neurons in the nI and ML were high during incubation period and decreased when hens were deprived of their nests. Nest deprivation caused an increase in the number of GnRH-I-ir in the nCPa of ND hens when compared with INC hens. These results indicated an association between GnRH neurons in the nCPa, VIP neurons in the IH-IN, and DA neurons in the nI and ML with the degree of hyperprolactinemia, suggesting that the expression of incubation behavior in the native Thai chicken might be, in part, regulated by the differential expression of GnRH neurons in the nCPa, VIP neurons in the IH-IN, and DA neurons in the nI and ML and subsequent PRL release. L7.2