Mapping pressor, depressor, and lumbar and splanchnic sympathetic nerve responses to direct stimulation of the rostral ventrolateral medulla in rats

Although sympathetic nerve activity (SNA) can be highly coordinated, there is strong evidence that sympathetic outflow is affected differentially on both an acute and chronic basis. Based on evidence primarily in the cat, the rostral ventrolateral medulla (RVLM) may serve as an important substrate in the generation of differential control of SNA. Despite limited evidence in the rat, we hypothesized that activation of the RVLM in the rat would produce patterns of differential sympathetic activation. Inactin anesthetized rats were instrumented to record arterial pressure (AP), lumbar SNA, and splanchnic SNA. Unilateral microinjections of glutamate (30 nl, 10 mM) were placed at 200 μm intervals in a rostrocaudal, mediolateral, and dorsoventral fashion from a set of predefined coordinates. Glutamate increased AP and increased SNA differentially depending on injection location. In some instances SNA responses were selective or in opposite directions. These data suggest that changes in SNA to distinct targets vary depending on the region of the RVLM activated. These data are consistent with previous reports that suggest a functional organization of the RVLM. (R01HL096787; R01HL67814)