Neuroplasticity of the Hypothalamic–Pituitary–Adrenal Axis Early in Life Requires Recurrent Recruitment of Stress-Regulating Brain Regions

Fos-immunoreactive neurons are significantly increased in PVT, ACe, and BnST of P9 handled pups after their return to the dam. Bright-field photomicrographs of coronal brain sections of PVT (left column), ACe (middle column), and BnST (right column) at the levels indicated by the atlas images in the first row (Paxinos and Watson, 1982) are shown. Fos-positive cells were few in PVT and virtually absent in ACe and BnST of P9 pups that remained undisturbed during P2 to P9 (second row) or were deprived of maternal care for 3 h on P9 (fourth row). In contrast, Fos-labeled cells (blue arrows) were abundant in PVT, ACe, and BnST of rats handled from P2 to P9 and perfused 30 min after their return to the dam (third row). Ant Comm, Anterior commissure; BLA, basolateral amygdala nucleus; Lat Vent, lateral ventricle; 3rd, third ventricle. Scale bars, 500 μm.