SYMPATHETIC PREGANGLIONIC NEURONS REPRESENT ONLY ONE FOURTH OF ALL CHOLINERGIC NEURONS IN THE RAT CENTRAL AUTONOMIC AREA

Abstract

All cholinergic neurons in the intermediolateral cell column (IML) and central autonomic area (CAA) of the thoracic and upper lumbar lateral horn are thought to be sympathetic preganglionic neurons (SPN). However, few CAA neurons are retrogradely labelled from sympathetic ganglia or the adrenal medulla compared to the cholinergic population, suggesting that some cholinergic CAA neurons may not be SPN. To examine this issue in rats, we first retrogradely labelled SPN with intraperitoneal Fluorogold (FG) and localized FG and choline acetyltransferase (ChAT) with double immunofluorescence. In the IML, 97–99% of ChAT-immunoreactive (IR) neurons were FG-IR. In contrast, in the CAA; only 12% of ChAT-positive neurons in T1-4 and less than 2% in T5-11 were FG-positive. In T12-L2, however, half of the cholinergic CAA neurons contained FG. Overall, in T1-L2, only one fourth of the ChAT-positive CAA neurons were retrogradely labelled with FG. Furthermore, of the ChAT-IR neurons in the intercalated nucleus (ICN), only 61% were FG-IR. These findings indicate that many of the cholinergic neurons in the CAA and ICN of thoracic and upper lumbar cord are not SPN. Since spinal interneurons innervate SPN, we injected pseudorabies virus containing a transgene encoding green fluorescent protein (GFP) into the kidney and FG intraperitoneally and did triple immunofluorescent staining for GFP, FG and ChAT. We found neurons positive for ChAT and GFP but not FG, suggesting that local cholinergic interneurons are part of spinal circuitry regulating sympathetic outflow. Supported by NHMRC Australia & NIH USA