Polarised innervation pattern of the mucosa of the guinea pig distal colon

A neuronal retrograde tracing method with the dye Dil in combination with the immunohistochemical detection of vasoactive intestinal polypeptide (VIP) and choline acetyltransferase (CHAT) was used to characterise the mucosal projection of neurones located in the submucosal plexus of the guinea pig distal colon. VIP and ChAT immunoreactivity labelled separate populations. The mucosa was innervated by descending (59.7 ± 7.4%), ascending (8.7 ± 5.0%) and circumferential (31.7 ± 6.1%) pathways. Descending neurones had longer projections than ascending ones. Descending Dil-labelled neurones were in their vast majority VIP-positive (88.4 ± 3.6%) and only 3.5 ± 4.8% of them were ChAT-positive. Conversely, the ascending pathways were predominantly ChAT-positive (90.9 ± 20.3%) and only 7.8 ± 20.6% of them were VIP-positive. A significantly larger proportion of Dil- neurones with circumferential projection were CHAT- than VIP-positive (70.9 ± 15.6 vs. 27.8 ± 15.7%). The proportion of ascending, descending and circumferential ChAT-positive Dil-neurones was 23:7:70%, respectively, whereas the proportion for VIP-positive Dil-neurones was 2:84:14%, respectively. The results suggest a conservation of the submucosal innervation pattern along the guinea pig colonic mucosa but also reveal differences in the mucosal enteric innervation of other regions of the gastrointestinal tract.