Sympathoexcitatory CVLM neurons mediate responses to caudal pressor area stimulation

Neurons in the caudal pressor area (CPA) are a source of tonic sympathoexci tation that is dependent on activation of cardiovascular sympathetic premot or neurons in the rostral ventrolateral medulla (RVLM). In the present stud y, we sought to clarify the mechanism through which CPA neurons elicit incr eases in RVLM neuronal discharge, vasoconstrictor sympathetic tone, and art erial pressure. In urethan-chloraloseanesthetized, paralyzed, and artificia lly ventilated rats, bilateral disinhibition of CPA with bicuculline (Bic) after bilateral disinhibition of caudal ventrolateral medulla (CVLM) caused increases in splanchnic sympathetic nerve activity (+277% control) and art erial pressure (+54 mmHg). Inhibition of CVLM neurons with muscimol abolish ed the pressor response to activation of CPA neurons, suggesting that neuro ns within CVLM mediate the excitatory responses from CPA. Disinhibition of CVLM and CPA with Bic enhanced the sympathoexcitatory responses to stimulat ion of CPA with DL-homocysteic acid, which were blocked by microinjections of kynurenic acid into CVLM. We conclude that the pathway from CPA to RVLM involves an obligatory glutamatergic activation of sympathoexcitatory neuro ns in the vicinity of CVLM.