The pre-sympathetic neurons in the rostral ventrolateral medulla (RVLM) are the source of the sympathetic activity and there is evidence that these cells present intrinsic pacemaker activity. However, there are few electrophysiological studies in the literature involving these neurons in neonatal rats and no studies on these neurons in the brainstem slices from adult rats. Herein we studied slices from adult rats (5-6 weeks old) presenting viable RVLM pre-sympathetic neurons for patch-clamp recordings, previously labeled by injection of fluorescent microbeads into the intermediolateral column of spinal cord (T3-T6). Our data show that after application of antagonists of ionotropic glutamate, GABA and glycine receptors in the bath perfusion, these neurons present spontaneous firing action potentials in a regular pattern [frequency: 9.4±1.0 Hz; CV of the inter-spike interval: 0.12±0.01 (n=19)]. In comparison, RVLM respiratory neurons projecting to phrenic nucleus in spinal cord (C3-C5) fired spontaneous action potentials more irregularly and with a lower frequency when compared to pre-sympathetic neurons [frequency: 4.4±0.8 Hz; CV of inter-spike interval: 0.38 ± 0.11 (n=15); P=0.001]. Considering that CIH in rats induces hypertension due to sympathetic overexcitation, we hypothetized that the pre-sympathetic neurons in these animals should present changes in their intrinsic membrane properties and an increase in their frequency discharge. However, our data clearly indicate that the intrinsic membrane properties and the frequency discharge of the pre-sympathetic neurons in rats submitted to 10 days of CIH were not changed: resting membrane potential [Con: -63.9±0.8 mV, (n=21) vs. CIH: -64.8±0.7 mV, (n=23); P=0.41]; input resistance [Con: 341±21 MOhm, (n=18) vs. CIH: 392±34 MOhm, (n=20); P=0,21] and intrinsic frequency discharge [Con: 9.4±1,0 Hz, (n=19) vs. CIH: 9.9±1.2 Hz, (n=21); P=0.74]. The present study shows that: a) it is feasible to record the electrophysiological properties of RVLM pre-sympathetic neurons in brainstem slices from adult rats, b) these neurons present characteristics of pacemakers, and c) their passive and active intrinsic properties were not altered in rats submitted to CIH.