Central regulation of physiological and metabolic responses in neonatal chicks

Birds maintain their body temperature a few degrees Celsius higher than mammals, and young birds may have somewhat higher body temperatures than adult birds. In many newborn mammals, the first active mechanism of heat production against cold is thermogenesis in brown adipose tissues. While there is evidence for non-shivering thermogenesis in birds, it is clear that adipose tissue does not participate in this response. Mammals and birds also differ in other aspects of thermoregulation. Our previous findings suggested that even in the same species of birds thermoregulation may differ due to stage of life. Intracerebroventricular injection of thyrotropin-releasing hormone increased body temperature, but did not change plasma T3 and T4 concentrations in neonatal chicks which suggested that thermoregulatory response to thyrotropin-releasing hormone may differ in neonatal stages being dependent upon the stimulation of the hypothalamus-pituitary-adrenal axis rather than the hypothalamus-pituitary-thyroid axis. Even under lower environmental temperature, the hypothalamus-pituitary-adrenal axis functions to keep body temperature. We have recently shown that exposure of neonatal chicks to low-temperature resulted in increased oxidative damage to the brain and intracerebroventricular injection of corticotropin-releasing factor played a putative neuroprotective role in the brain of low-temperature-exposed neonatal chicks. There is evidence in birds that stress resulting from high environmental temperature decreases food intake. It was found that food intake was not affected by high environmental temperature until 7-d of old in chicks; however, it depressed from 14-d suggested some different thermoregulatory mechanism in neonatal chicks as young and adult birds reduce their food intake under high environmental temperature to survive. Metabolism of neonatal chicks is also regulated by different factors and different ways. For instance, central Neuropeptide Y modifies peripheral carbohydrate and lipid metabolism in chicks. In sum, regulation of physiological and metabolic responses of neonatal chicks differs from young and adult birds.