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

Time course of Fos expression in PVT, ACe, and BnST of daily handled pups after their return to the dam. Quantification and bright-field photomicrographs of Fos-labeled neurons (blue arrows) in PVT (A), ACe (B), and BnST (C) of pups handled recurrently (P2–P9) and perfused at 5, 30, 60, 90, or 120 min after their return to the dam on P9 are shown. A, Fos induction in PVT peaked 30–60 min after the pups’ return to the dam and disappeared by 120 min (compared with 120 min, F_(4,15) = 23.3; p < 0.005). B, The number of Fos-immunoreactive neurons in ACe was maximal at 5 min and declined over the next 2 h (F_(4,9) = 8.54; p < 0.01). C, Fos induction in BnST followed a time course similar to that in the PVT (F_(4,12) = 14.63; p < 0.05). ACe, n = 3 brains per time point; AD-BnST, n = 3–4 brains per time point; PVT, n = 4–7 brains per time point. Lat Vent, Lateral ventricles. Scale bars, 500 μm. *p < 0.05, values statistically differ from those at 120 min.