Two populations of sympathetic neurons project selectively to mesenteric artery or vein

The objective of this study was to determine whether sympathetic neurons of the inferior mesenteric ganglion (IMG) projecting to mesenteric arteries c ould be distinguished by their localization, neurochemical phenotype, and e lectrophysiological properties from neurons projecting to mesenteric veins. In an in vitro intact vasculature-IMG preparation, neurons were labeled fo llowing intraluminal injection of Fluoro-Gold or rhodamine beads into the i nferior mesenteric artery (IMA) or vein (IMV). The somata of neurons projec ting to IMA were localized in the central part of the IMG, whereas those pr ojecting to IMV were localized more peripherally. None of the labeled neuro ns was doubly labeled. Neuropeptide Y immunoreactivity was found in 18.9% o f neurons innervating the IMA, but not in neurons innervating the IMV. Iden tified neurons were dissociated and characterized using whole cell patch-cl amp recording. After direct soma depolarization, all of the labeled arteria l and venous neurons were classified as tonic firing, compared with only 40 % of unlabeled neurons; the remaining 60% of unlabeled neurons were phasic firing. The results indicate that IMG neurons projecting to mesenteric arte ries are distinct from neurons projecting to mesenteric veins.