Neurochemically distinct myenteric neurone populations containing calbindin have specific distribution patterns around the circumference of the gastric corpus

We recently described calbindin immunoreactivity in the myenteric plexus of the guinea-pig stomach. To study the neurochemical coding of calbindin D28 k (CALB)-containing myenteric neurones, the presence of calretinin (CALRET), choline acetyltransferase (ChAT), enkephalin (ENK), neuropeptide Y, serotonin (5-HT), somatostatin (SOM) and substance P(SP) was investigated immunohistochemically in colchicine-treated preparations. Nitric oxide synthase-containing neurones were detected by NADPH-diaphorase histochemistry. In addition, we investigated the neurone distribution patterns around the gastric corpus. Most CALB neurones were ChAT positive. ChAT/CALB neurones were either CALRET (ca 75%) or 5-HT positive and most contained in addition SP and/or ENK. All 5-HT neurones contained CALB. CALB labelled on average 2.3, 4.8 and 7.5 neurones per ganglion at the lesser curvature, in the central region and the greater curvature, respectively, which indicated a preferential localisation at the greater curvature. Compared to the total number of myenteric neurones, the proportion of CALB neurones increased significantly from the lesser curvature (6%) towards the greater curvature (18%). This shift, although observed for most ChAT/CALB-positive populations, was most prominent for the ChAT/CALB/CALRET/SP/ENK-encoded neurones. SOM-positive and ChAT-only encoded neurones were preferentially located at the lesser curvature. The remaining ten neurochemically defined populations did not exhibit an uneven distribution. The colocalisation of CALB with CALRET or 5-HT is specific for myenteric neurones in the stomach and represents one significant difference to the neurochemical code of CALB neurones in the guinea-pig intestine. The functional significance of the unevenness of neurone distribution along the circumference of the gastric corpus remains to be studied.