ALL CALBINDIN-IMMUNOREACTIVE MYENTERIC NEURONS PROJECT TO THE MUCOSA OF THE GUINEA-PIG SMALL-INTESTINE

The projections of Dogiel type II myenteric neurons to the mucosa of t he guinea-pig ileum were quantified by combining retrograde transport of DiI, in vitro, with immunohistochemistry. After DiI application to the mucosa over an area of 1.5 x 10 mm(2), virtually all (>97%) calbin din-immunoreactive Dogiel type II neurons in the myenteric plexus unde rneath the mucosal DiI application site were labelled, indicating that essentially all of these neurons project to the mucosa. From cell cou nts, on average 5 calbindin-immunoreactive neurons project to each vil lus, and each calbindin-immunoreactive neuron supplies on average 10 v illi. Since Dogiel type II neurons that were not immunoreactive for ca lbindin (19% of all labelled nerve cells) also projected to the mucosa , it is likely that all Dogiel type II neurons, which are putative sen sory neurons of the gut, project to the mucosa.