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

Kirsteen N. Browning, William E. Renehan and R. Alberto Travagli

The electrophysiological properties of rat dorsal motor nucleus of the vagus (DMV) neurones (n = 162) were examined using whole cell patch clamp recordings from brainstem slices. Recordings were made from DMV neurones whose projections to the gastrointestinal tract had been identified by previously applying fluorescent retrograde tracers to the gastric fundus, corpus or antrum/pylorus, or to the duodenum or caecum.

The neuronal groups were markedly heterogeneous with respect to several electrophysiological properties. For example, neurones which projected to the fundus had a higher input resistance (400 ± 25 M), 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 potentials s^-1) following injection of depolarizing current (270 pA) when compared with caecum-projecting neurones (302 ± 22 M; 23·5 ± 0·87 mV and 81·1 ± 5·3 ms; 9·7 ± 1·1 action potentials s^-1; P < 0·05 for each parameter). Differences between neuronal groups were also apparent with respect to the distribution of several voltage-dependent potassium currents. Inward rectification was present only in caecum-projecting neurones, for example.

Neurones (n = 82) were filled with the intracellular stain Neurobiotin allowing post-fixation morphological reconstruction. Neurones projecting to the caecum had the largest cell volume (5238 ± 535 µm³), soma area (489 ± 46 µm²) and soma diameter (24·6 ± 1·24 µm) as well as the largest number of dendritic branch segments (23 ± 2).

In summary, these results suggest that DMV neurones are heterogeneous with respect to some electrophysiological as well as some morphological properties and can be divided into subgroups according to their gastrointestinal projections.