Previous studies have shown different cardiorespiratory effects induced by stimulation of nucleus raphe obscurus (NRO). The present study demonstrates the existence of c-Fos activation in the caudal pressor area (CPA) after NRO stimulation in barodenervated rats and projections from the NRO to the CPA with HRP. Male Wistar rats (300-350 g, N = 24) were used. The animals in the c-Fos group were barodenervated (chloral hydrate, 0.4 g/kg, ip). One day later the animals were instrumented for cardiorespiratory recordings (urethane 1.2 g/kg, iv, after Fluothane induction). After electrical stimulation of NRO (SNRO, 70µA, for 10s; 11.8 mm caudal to the Bregma and 7.8 mm depth) done every minute for 1 hr, the animals were killed by urethane overdose and the brains were processed for c-Fos. Control rats had the electrode only positioned. The HRP group, under anesthesia (chloral hydrate, 0.4 g/kg, ip), received unilateral HRP microinjection (50 nL, 20% saline) into the CPA (1.0 mm caudal and 1.7 mm lateral to the obex; 2.0 mm depth) and the animals were kept alive for 2-3 days. Following, they were killed by urethane overdose and the brains were processed for HRP. The experimental protocol was approved by CEUA EMESCAM (No. 021/2007). The results are presented as means ± SEM and statistical significance was assessed with t-test. SNRO caused increase in MBP (control 90 ± 5, SNRO: 156.8 ± 6 mmHg, P<0.01), bradycardia (control 416 ± 16, SNRO: 356 ± 16 bpm, P<0.01) and hypopnea (control 26.6 ± 0.9, SNRO: 16.4 ± 0.3 AU, P<0.01). C-Fos-expression was observed into the CPA ~1.0 mm caudal to the calamus scriptorius, ~2.0 mm lateral to the midline, and ~1.7 mm ventral to the medullary surface, respectively. In a total of 6 rats used for the HRP study, 5 showed markings in the NRO. This study provides additional support to the idea that NRO influences upon autonomic functions are partially mediated through projections to the CPA.