Rapid effects of corticosterone on cardiovascular neurons in the rostral ventrolateral medulla of rats

The present study has explored possible fast actions of corticosteroid horm ones on activity of cardiovascular neurons of the rostral ventrolateral med ulla. Experiments were conducted in 60 urethane-anesthetized, artificially ventilated adult rats. Extracellular recordings of unitary firings were mad e from the RVLM with multi- or single-barreled microelectrodes. Barosensiti ve cardiovascular neurons were identified through activation of the barorec eptor reflex by electrical stimulation of the aortic nerve and by intraveno us injection of phenylephrine. In 52 barosensitive cardiovascular neurons, iontophoretically applied corticosterone sulfate increased the ongoing acti vity of 30 (57.7%) neurons, the other 22 (42.3%) neurons being unaffected. In 16 bulbospinal pre-sympathetic neurons, iontophorized corticosterone inc reased the firing rate of 12 neurons. Intravenously applied corticosterone (0.2 mg) increased the firing rates of 5 out of 12 bulbospinal pre-sympathe tic neurons. The average baseline activity of cardiovascular neurons sensit ive to corticosterone was found to be significantly less than that of the c ardiovascular neurons insensitive to corticosterone. In 64 non-cardiovascul ar neurons, the firing rate of 13 (20.3%) neurons increased, 23 (36.0%) dec reased and 28 (43.7%) remained unchanged following local application of cor ticosterone. The changes in firing rates of RVLM neurons following applicat ion of corticosterone occurred rapidly and were dependent on the doses of t he agent. RU-38486 was able to reduce or block the rapid effects of cortico sterone on cardiovascular and non-cardiovascular neurons. The results demon strated that corticosterone may fast, non-genomically, modulate the activit y of central regulators of the cardiovascular system and suggested that fas t non-genomic actions of corticosteroid hormones may be an important mechan ism in the integration of the autonomic nervous and the cardiovascular syst ems during some conditions such as: stress. (C) 1999 Published by Elsevier Science B.V. All rights reserved.