Electrophysiological and morphological heterogeneity of rat dorsal vagal neurones which project to specific areas of the gastrointestinal tract

1. The electrophysiological properties of rat dorsal motor nucleus of the v agus (DMV) neurones (n = 162) were examined using whole cell patch clamp re cordings from brainstem slices. Recordings were made from DMV neurones whos e projections to the gastrointestinal tract had been identified by previous ly applying fluorescent retrograde tracers to the gastric fundus, corpus or antrum/pylorus, or to the duodenum or caecum. 2. The neuronal groups were markedly heterogeneous with respect to several electrophysiological properties. For example, neurones which projected to t he fundus had a higher input resistance (400 +/- 25 M Omega), a smaller and shorter after-hyperpolarization (16.7 +/- 0.49 mV and 63.5 +/- 3.9 ms) and a higher frequency of action potential firing (19.3 +/- 1.4 action potenti als s(-1)) following injection of depolarizing current (270 pA) when compar ed with caecum-projecting neurones (302 +/- 22 M Omega; 23.5 +/- 0.87 mV an d 81.1 +/- 5.3 ms; 9.7 +/- 1.1 action potentials s(-1); P < 0.05 for each p arameter). Differences between neuronal groups were also apparent with resp ect to the distribution of several voltage-dependent potassium currents. In ward rectification was present only in caecum-projecting neurones, for exam ple. 3. Neurones (n = 82) were filled with the intracellular stain Neurobiotin a llowing post-fixation morphological reconstruction. Neurones projecting to the caecum had the largest cell volume (5238 +/- 535 mu m(3)), soma area (4 89 +/- 46 mu m(2)) and soma diameter (24.6 +/- 1.24 mu m) as well as the la rgest number of dendritic branch segments (23 +/- 2). 4. In summary, these results suggest that DMV neurones are heterogeneous wi th respect to some electrophysiological as well as some morphological prope rties and can be divided into subgroups according to their gastrointestinal projections.