The neuropeptide galanin (GAL) causes hypotension when injected into the rostral ventrolateral medulla (RVLM). GAL-immunoreactive neurons occur in the retrotrapezoid nucleus (RTN) in the rostral ventral medulla, which is also a key site for the tonic and reflex control of blood pressure; but it is unknown how GAL neurons relate to cardiovascular neurons. In this study, we used Fos-immunoreactivity resulting from drug-induced hypotension to determine whether GAL neurons in the RTN are barosensitive and to examine the relationship of GAL axons to spinally-projecting adrenergic and non-adrenergic neurons in the RVLM. We implanted cannulae into femoral arteries and veins of isoflurane-anesthetized (3% for induction, 2.5% for maintenance) Sprague Dawley rats for recording arterial pressure (MAP) and infusing drugs, respectively. The next day, we treated conscious rats with hydralazine (HDZ, 2mg/ml) or saline (SAL) and perfused them 2 hours later with 4% formaldehyde. In some rats, we injected the lateral horn of segment T3 (under 3% isoflurane anesthesia) with the retrograde tracer, cholera toxin B subunit (CTB), 3-5 days before drug treatment. We used avidin-biotin-peroxidase to localize immunoreactivity for GAL, Fos, PNMT and CTB (where appropriate) in a 1:4 series of brainstem sections. We also made RVLM microinjections of GAL (20 nl or 40 nl of 1 ng/nl in aCSF) in isoflurane-anesthetized rats to confirm its cardiovascular effects. GAL-immunoreactive neurons were identified in the retrotrapezoid nucleus (RTN); an average of 76.6+16.2 of these neurons (14 rats) occurred caudal to the facial nucleus in the RVLM. HDZ produced significant hypotension (71±10 vs 113±10 mmHg) and induced Fos-immunoreactivity in many ventral medullary neurons. Few neurons were Fos-positive after SAL. About 15% of the GAL neurons in the RVLM expressed Fos in response to hypotension (11.0+5.6, n=8 after HDZ vs 0.7+0.8, n=6 after SAL). HDZ also induced Fos in PNMT-positive and PNMT-negative RVLM neurons. About half of the Fos-immunoreactive C1 neurons were closely apposed by GAL terminals. Of Fos-expressing neurons that had transported CTB from the spinal cord, GAL appositions were found mainly on PNMT-positive neurons and only rarely on PNMT-negative neurons. In a separate group of rats (n= 5), microinjecting 40 ng of GAL consistently decreased MAP to about 25 mmHg below baseline whereas vehicle microinjecting did not affect MAP. This study has confirmed that GAL acts as a depressor agent when injected into the RVLM. We have also shown that some GAL neurons in RTN are barosensitive and that GAL axons closely appose bulbospinal barosensitive C1 and non-C1 neurons in the RVLM. These findings suggest that barosensitive GAL-containing RTN neurons could directly innervate vasomotor presympathetic neurons in RVLM. This pathway could be a means of coupling the activity of cardiovascular and respiratory systems.