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

Introduction: Dopamine (DA) is a neurotransmitter/neuromodulator found in both central and peripheral nervous systems. It plays several physiological functions in some mammalian and avian species. DA has been indicated to be associated with the neuroendocrine regulation of the reproductive cycle and maternal behaviors in the female native Thai chickens. Indeed, male birds express parental behaviors as well. To date, there are no data describing the functional aspects of the DAergic system in the male native Thai chickens. Thus, the objective of this study was to elucidate the localization of tyrosine hydroxylase (TH; a DA marker) neuronal groups in the brain of the roosters.

Material and methods: The distributions of TH immunoreactivity in the brain were detected utilizing the immunohistochemical technique.

Results: TH immunoreactivity was located throughout the brain and extensively in the diencephalon and mesencephalon. The highest density of TH-immunoreactive (-ir) neurons and fibers was found within the nucleus intramedialis (nI) and nucleus mamillaris lateralis (ML). The numbers of TH-ir neurons within the nucleus anterior medialis hypothalami (AM), nucleus paraventricularis magnocellularis (PVN), nI, and ML were then compared and revealed that the numbers of TH-ir neurons within the nI and ML were significantly higher than those of the AM and PVN.

Conclusions: These present findings suggest that the DAergic neurons within the nI and ML might play an important role in the reproductive activities of the native Thai roosters. Interestingly, the DAergic system in the nI might be involved in male reproductive activities and/or parental behaviors in this equatorial species.