Effects of corticosterone on neurons of reticular formation in rats

The effects of microelectrophoretic application of corticosterone (CS) on single neurons of the brain stem reticular formation (RF) were investigated and then compared with the effects produced on the same neurons by intravenous administration of CS. The experiments were done in two groups of rats, one anesthetized with urethan and the other with pentobarbital sodium because these anesthetics cause different increases of basal concentration of plasma CS. Microelectrophoretic application of CS to neurons in the caudal portion of RF caused primarily excitatory effects, whereas inhibitory effects were observed in neurons of the rostral portion of the RF. The intravenous injection of CS (5 micrograms/100 g body wt) always produced the same effects as microelectrophoretic application. Under our experimental conditions the increase in plasma CS concentration produced by the intravenous injection of CS was found to be within the physiological range for the rat. The different anatomical distribution of units within the RF responding with either excitation or inhibition may be related to functional differences of the two RF areas.