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Environmental manipulation early in life can alter the development of the hypothalamic-pituitary-adrenal (HPA) axis by mechanisms that are still unclear. The aim of the present work was to study the acute effects of postnatal touch stimulation, in an attempt to understand the mechanism by which touch stimulation early in life alters the HPA response to stress in adult animals. Rat pups were gently brushed for 15 min daily during the 1st postnatal week. Serum corticosterone levels were determined by radioimmunoassays, while glucocorticoid receptor (GR) gene expression was assayed by semiquantitative reverse transcriptase-polymerase chain reaction. Touch stimulation induced a significant decrease (30-36%) in serum corticosteroid secretion during the 1st and 2nd postnatal day as compared to the unstimulated group. In contrast, GR gene expression in the touch stimulation group was significantly increased in several brain areas such as the hippocampus (19-21%), frontal cortex (26-34%) and midbrain (15-24%). The results thus indicate that neonatal touch stimulation causes acute hormone- secretion and gene-expression changes within the period of stimulation. These changes may be the underlying cause for the permanent changes that have been observed in adult animals touch-stimulated as neonates.
Jutapakdeegul et al. (Wed,) studied this question.