Strongly glucocorticoid receptor immunoreactive neurons in the neonatal rat brain.

Brain glucocorticoid receptor (GR) immunoreactivity was studied in the neonatal rat. Already at postnatal days 1-3 strongly GR immunoreactive (IR) neurons were found in the arcuate and paraventricular hypothalamic nuclei. Moderately to strongly GR IR neurons were found in the locus coeruleus and raphe nuclei, while only weakly GR IR neurons were present in the CA1 and CA2 areas of the hippocampus. GR IR increases steadily during the postnatal period reaching adult levels at day 16. Thus, GR may play a role in the maturation of these hypothalamic nuclei and the 5-hydroxytryptamine and noradrenaline neurons, and GR may provide a basis for the ability of stress-induced increases of glucocorticoids to influence distinct brain circuits during postnatal development.