Interstitial cells of Cajal and nerves in mouse colon, studies of kit expression and neurochemical conding by confocal and electron microscopy

Abstract

Interstitial cells of Cajal (ICC) are important regulatory cells in the gastrointestinal tract. We studied the distribution and ultrastructure of Kitexpressing ICC and their relationship with nerves in the adult mouse colon. Wholemounts were studied by confocal microscopy after double immunofluorescence with antibodies for Kit together with antibodies raised against either the pan-neuronal marker PGP9.5, or the neuronal NO Synthase or one of the following neuropeptides: VIP, SP, NPY, Leuor Metenkephalines. Transgenic mice carrying a lacZ reporter gene inserted in place of the first exon of the Kit gene (WlacZ/+ heterozygous mice) [1] and controls (+/+) were studied by electron microscopy after beta-galactosidase histochemistry to determine the ultrastructure of Kit expressing ceils. In the subserosa, ICC formed a 2-dimensional plexus accompanied by few nerve fibres. In the myenteric area, the ICC plexus was well-developed, especially close to ganglia and primary nerve fascicles. Tertiary nerves with various chemical coding closely followed ICC processes. The myenteric ICC plexus gradually merged with ICC in the outer half of the circular layer. These ICC had their longest axis in the direction of the circular muscle cells while forming a 3-dimensional network. The inner half of the circular muscle was devoid of ICC processes. An extensive 2-dimensional plexus of ICC and nerves was revealed in the submuscular region. These ICC had their longest axis in the circular direction while multiple processes at right angles connected them in the longitudinal direction. They were also closely followed by nerves with various chemical coding. By electron microscopy, Kitexpressing cells revealed scattered caveolae, incomplete basal lamina and many small mitochondria. Kit-expressing ICC in the mouse colon are organised into several characteristic plexus. Moreover, ICC are in close contact with nerves with different chemical coding. Altogether, Kit-expressing cells in the mouse colon are identifiable as ICC by their ultrastructure. [1] Bernex F et al. Development 1996; 122: 3023-33.