Effect of hydrocortisone on the number of small intensely fluorescent cells in the rat superior cervical ganglion during pre- and postnatal development.

During the first postnatal week hydrocortisone causes a massive increase in the number of small intensely fluorescent (SIF) cells. The purpose of the present study was to investigate whether the number of SIF cells can be increased with hydrocortisone also prenatally and after the first postnatal week. Because it was desirable to apply the same kind of treatment before and after birth, the embryos and neonatal rats were injected only once and were studied 4 days later. Pregnant rats were injected daily during the last 7 days of pregnancy and the superior cervical ganglia of their embryos were studied thereafter. After birth, the effect of 7 daily injections of hydrocortisone was also studied. The number of embryonal brightly fluorescent cells, the probable prenatal precursors of the SIF cells. could not be increased either with a single injection into the embryos, or in embryos of pregnant rats treated with hydrocortisone. A single injection of hydrocortisone into newborn and 4-day-old rats caused a massive increase in the number of SIF cells as studied in 4- and 8-day-old rats, respectively. The increase in the number of SIF cells was smaller but still statistically significant in 12-day-old rats injected with hydrocortisone on postnatal day 8. Daily injections of hydrocortisone for 7 days caused on the second, but not on the third postnatal week, a statistically significant increase in the number of SIF cells. After 7 injections of hydrocortisone. on postnatal days 3-9 or 40-46. no increase in the number of SIF cells was observed in 47-day-old rats, as compared with saline-treated controls of the same age, but 7 injections of hydrocortisone both on days 3-9 and 40-46 resulted in a significant increase in the number of small intensely fluorescent cells on day 47. It is concluded that hydrocortisone-induced increase in the number of SIF cells is limited in vivo to the first two postnatal weeks, while exposure to hydrocortisone at birth restores the responsiveness of these cells to increase in number even later after a second exposure to hydrocortisone.