ABSTRACT
Previous studies by others have shown that administration of hypertonic saline (HS) induces c-fos expression in rat brain and old fibroblast cells are defective in transcription of c-fos in response to serum. The present immunohisto-chemical studies were undertaken to determine 1) the time that c-fos is expressed during the postnatal development of rat brain and 2) if there is aging-related change of c-fos expression in the osmoresponsive neurons after osmotic stimulus. Fos-like immunoreactivity (FLI) in response to HS treatment began to be detected dramatically at postnatal day (P) 14 in hypothalamic paraventricular nucleus (PVN), supraoptic nucleus (SON), and organum vasculosum lamina terminalis (OVLT). Intensity of FLI and number of Fos immunoreactive cells induced by HS were substantially reduced as rats age. Our data demonstrate for the first time that c-fos induction is decreased in aging-dependent manner and the time of c-fos induction during postnatal development is coincided with the status of differentiation in rat brain. We will interpret these findings in relation to synaptogenesis, and maturation or disability of signal transduction pathways in osmoresponsive neurons in rat brain.