Embryonic Thermal Manipulation Affects Ventilation, Metabolism, Thermal Control And Central Dopamine In Newly Hatched And Juvenile Chicks

The first third of incubation is critical for embryonic development, and environmental changes during this phase can affect the physiology and survival of the embryos. We evaluated the effects of low (LT), control (CT), and high (HT) temperatures during the first 5 days of incubation on ventilation ((V) over dot(E)), body temperature (Tb), oxygen consumption ((V) over dotO(2)), respiratory equivalent ((V) over dot(E)/(V) over dotO(2)), and brain monoamines on 3-days-old (3d) and 14-days-old (14d) male and female chickens. The body mass of LT animals of both ages and sexes was higher compared to HT and CT animals (except for 3d males). The heart mass of 14d HT animals was higher than that of CT animals. Thermal manipulation did not affect (V) over dot(E), (V) over dotO(2) or (V) over dot(E)/(V) over dotO(2) of 3d animals in normoxia, except for 3d LT males (V) over dot(E), which was lower than CT. Regarding 14d animals, the HT females showed a decrease in (V) over dot(E) and (V) over dotO(2) compared to CT and LT groups, while the HT males displayed a lower (V) over dotO(2) compared to CT males, but no changes in (V) over dot(E)/(V) over dotO(2). Both sexes of 14d HT chickens presented a greater Tb compared to CT animals. Thermal manipulations increased the dopamine turnover in the brainstem of 3d females. No differences were observed in ventilatory and metabolic parameters in the 3d animals of either sexes, and 14d males under 7% CO2. The hypercapnic hyperventilation was attenuated in the 14d HT females due to changes in (V) over dotO(2), without alterations in (V) over dot(E). The 14d LT males showed a lower (V) over dot(E), during hypercapnia, compared to CT, without changes in (V) over dotO(2), resulting in an attenuation in (V) over dot(E)/(V) over dotO(2). During hypoxia, 3d LT females showed an attenuated hyperventilation, modulated by a higher (V) over dotO(2). In 14d LT and HT females, the increase in (V) over dot(E) was greater and the hypometabolic response was attenuated, compared to CT females, which resulted in no change in the (V) over dot(E)/(V) over dotO(2). In conclusion, thermal manipulations affect hypercapnia-induced hyperventilation more so than hypoxic challenge, and at both ages, females are more affected by thermal manipulation than males.