Ultrastructural identification of VIP-containing nerve fibres in the myenteric plexus of the rat ileum.

Vasoactive intestinal polypeptide (VIP)-containing nerve fibres of myenteric plexus of the rat ileum were investigated using the pre-embedding peroxidase-antiperoxidase technique for electron microscopy. The VIP-positive fibres were characterized by a predominance of spherical agranular vesicles with a diameter of 40-55 nm. The immunoprecipitate was largely localized on the vesicle membrane. Large granular vesicles (100-144 mm) containing labelled dense cores were also present within labelled nerve profiles. Quantitative data indicate that the vesicles appeared in the following proportions: 93% small agranular vesicles and 7% large granular vesicles.