Metabolic and respiratory chemosensitivity and brain monoaminergic responses to cold exposure in chicks subjected to thermal manipulation during incubation

We evaluated ventilation (VE), body temperature (TB), oxygen consumption (V O2), respiratory equivalent (VE/ V O2), and monoamine concentrations of 14-day-old (14d) male and female chicks from eggs incubated at low (LT, 36 degrees C), control (CT, 37.5 degrees C) and high (HT, 39 degrees C) temperature during the early embryonic phase, to normoxia, hypercapnia and hypoxia under exposure to cold environment (20 degrees C). At normoxia, acute cold exposure did not affect the ventilatory variables, with the exception of HT males, in which cold prevented the reduced VE observed under thermoneutral conditions. Exposure to 20 degrees C caused a decrease in TB in both sexes, and LT and HT females presented a greater hypothermic response. Hypercapnia combined with cold did not alter the ventilatory vari-ables, but LT females and CT males and females showed a blunted CO2-induced hyperventilation due to a higher V O2, compared to the same groups in thermoneutral conditions. Unlike with thermoneutral conditions, the blunted hypercapnic hyperventilation observed in the HT groups was not observed during cold challenge. CO2 exposure promoted a similar decrease in TB in the thermoneutral and acutely cold exposed groups, while LT females under cold condition presented a blunted hypothermic response. During hypoxia, cold challenge attenuated the increase in VE in LT females and HT males, due to changes in VT. Hypoxic metabolic depression was greater in LT females and males and HT males during cold exposure, while no change in VE/ V O2 was observed. The only alteration in monoaminergic concentration under cold challenge was an increase in brain -stem 5-HIAA and 5-HIAA/5-HT ratio in HT females, and an enhanced 5-HT concentration in HT males. In summary, thermal manipulation during embryogenesis induces 14d old chicks to respond differently to cold stress with LT females and HT males being more sensitive.

Automated summary

In this study, we evaluated the response of 14-day-old chicks to cold stress under different thermal conditions during embryogenesis. The results indicate that LT females and HT males are more sensitive to cold stress.