The adrenocortical response to stress from the pre‐hatching period to the adult state in the pigeon: Thalamic participation

The stress‐induced adrenocortical response was kinetically evaluated for 100 min after ether vapor exposure in late embryos (30 h before hatching) and in 1, 2, 3 and 6‐wk‐old squabs. An‐adult‐pattern of corticosterone profile was seen in intact 6‐wk‐old pigeons, i.e. a polyphasic increase of corticosterone including successive peaks at 12–15, 35, 60 and 90 min after stress application. In 1‐wk‐old squabs, a small adrenocortical response to stress included only a single peak of corticosterone at 12–15 min. The early peak was found again, with the same magnitude, 2 wk after hatching but it was followed by two later and smaller peaks 35 and 60 min after stress. The adult pattern was visible in 3‐wk‐old stressed pigeons, although the magnitude of the response was still smaller than in adult controls. A single, high peak of corticosterone occurred 12–15 min after stress application, without any later peak, in embryos and a similar monophasic response was seen in thalamic lesioned adult birds. Therefore, it can be suggested that the polyphasic reverberating adrenocortical response to stress depends upon relationships between the adrenocorticotrophic hypothalamus and the anterior mediodorsal thalamus. Such thalamic‐hypothalamic interrelations appear to mature during the early post‐hatching weeks.