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

The dopaminergic (DAergic) system plays a pivotal role in incubation behavior via the regulation of prolactin (PRL) secretion in birds, however the role of the DA/PRL system in rearing behavior is poorly understood. The objective of this study was to investigate the relationship between the DA/PRL system and rearing behavior in a gallinaceous bird, the native Thai chicken. Incubating native Thai hens were divided into two groups. In the first group, hens were allowed to care for their chicks (rearing hens; R). In the second group, hens were deprived of their chicks immediately after hatching (non-rearing hens; NR). In both groups, blood samples and brain sections were collected at different time points after the chicks hatched (days 4, 7, 10, 14, 17, 21, 24, and 28; 6 hens/time point/group). In this study, tyrosine hydroxylase (TH) was used as a marker for DAergic neurons. The numbers of TH-immunoreactive (-ir) neurons in the nucleus intramedialis (nI) and in the nucleus mamillaris lateralis (ML), which regulate the vasoactive intestinal peptide (VIP)/PRL system, were determined in R and NR hens utilizing immunohistochemical techniques. Plasma PRL levels were determined by enzyme-linked immunosorbent assays. The results revealed that both the number of TH-ir neurons in the nI and the plasma PRL levels were significantly higher in the R hens compared with the NR hens during the first 14. days of chick rearing (P<0.05). However, there was no significant change in the DAergic activity in the ML in either the R or NR groups throughout the 28-day rearing periods. These results suggest that the DA/PRL system is involved in early rearing behavior. The additional decline in DAergic activity and plasma PRL levels during the disruption of rearing behavior further supports their involvement in rearing behavior in this equatorial precocial species.