Phenylethanolamine‐ N ‐methyltransferase‐immunoreactive cells in developing rat superior cervical ganglion and the effect of hydrocortisone on their number

Rats were subcutaneously injected with hydrocortisone acetate. Control rats were similarly injected with saline. PNMT‐immunoreactive cells in the superior cervical ganglia were immunohistochemically demonstrated, and the cell densities (number/mm 3 ) of the PNMT‐immunoreactive cells were counted. PNMT‐immunoreactive cells were detected in ganglia of all age groups of the saline‐treated control rats. With increasing age, there was a tendency to cluster formation. The number of the PNMT immunoreactive cells dramatically increased if hydrocortisone administration was initiated during the first two postnatal weeks. Hydrocortisone also caused appearance of numerous PNMT‐immunoreactive fibres, which were not seen in controls. The cell density of the PNMT‐immunoreactive cells in the hydrocortisone‐treated rats was still increased, although less, if the hydrocortisone injections were started during the third postnatal week, as compared with the saline‐injected control rats of the same age. After discontinuation of the first, early postnatal hydrocortisone treatment on days 2–6, the number of the PNMT‐immunoreactive cells decreased during the following 2 weeks, but a second treatment with hydrocortisone daily for 7 days initiated as late as on postnatal day 63 caused a new significant increase in cell density and the appearance of immunoreactive fibres from them. It is concluded that PNMT‐immunoreactive cells are present in the normal rat superior cervical ganglion during the whole postnatal developmental period. Their number can be increased with hydro‐cortisone, as assessed on the basis of counted cell densities, during the first three postnatal weeks. Early postnatal hydrocortisone treatment preserves some cells in a stage in which they, on second exposure to glucocorticoids, can express PNMT immunoreactivity and increase in cell density.