Microdialysis in combination with HPLC and fluorescence detection was used to measure the release of endogenous amino acids from the region of the intermediolateral cell column of rat thoracic spinal cord in response to electrical stimulation of the rostral ventrolateral medulla (RVLM). Stimulation of the RVLM led to a marked rise in blood pressure (74 +/- 6 mm Hg) accompanied by an immediate increase in the release of glutamate (80%) and aspartate (50%). Small increases in the release of glycine and taurine were found, but there were no changes in alanine and serine release. These results suggest that the RVLM pressor pathway to the thoracic spinal cord may use, at least in part, excitatory amino acids as neurotransmitters, supporting previous pharmacological and neuroanatomical investigations of this bulbospinal pathway.