c-fos expression in the parabrachial nucleus following cardiovascular and blood volume changes

c-fos expression was analyzed by means of Fos-immunocytochemistry in the parabrachial (PB) nucleus of rats anesthetized and submitted to blood pressure or volume changes. The objective was to determine if neurons of the PB are differentially activated following increase or decrease of arterial pressure or blood volume. Hypertension or hypotension were induced by continuous intravenous infusion of phenylephrine hydrochloride or sodium nitroprusside, respectively. Changes in blood volume were induced by volume load caused by infusion of isotonic saline or hemorrhage. Both an increase and a decrease in blood pressure resulted in elevated levels of Fos-IR neurons in the central lateral, dorsal lateral, and external lateral (outer section) subnuclei of the PB. No Fos-IR cells were observed in the external medial, internal lateral and ventral lateral PB. Only occasionally we could see few Fos-immunoreactive (Fos-IR) neurons in the medial and superior lateral PB subnuclei. A very similar pattern of c-fos expression was seen after volume load or hemorrhage. Our results demonstrate that blood pressure or volume changes elicit c-fos expression in specific and apparently identical sets of neuron populations in the parabrachial nucleus. We conclude that these neurons, which seem to receive a stimulatory drive, are involved in the central neural control of both cardiovascular and blood volume regulation.