Ultrastructural characteristics of Glial and Interstitial cells of Cajal in the Lizard intestine: presence of primary cilium

In mammals, enteric nervous system consists of neurons and glial cells which are mainly organized in two ganglionated plexuses: the myenteric plexus, and the inner and outer submucosal plexuses. Enteric glial cells establish a direct contact with neurons; their cytoplasm prolongations surround the unmyelinated axons. The interstitial cells of Cajal (ICCs) are located around enteric ganglia and in both muscular layers forming an interconnected network. It is now known that some ICCs and glial cells in mammals present a single cilium but its presence in the rest of vertebrate classes has been not still demonstrated. The aim of the present study is to characterize, at the ultrastructural level, the enteric glial cells and ICCs in the lizard intestine. Material and methods: We used ten adult lizards Podareis hispanica (Reptilia). Small and large intestine wall samples were fixed with 2.5% glutaraldehyde in PB buffer (pH 7.3) and routinely processed for TEM visualization. Results: Lizard intestinal ganglia show a lower number of neurons than those from mammals. Glial cells were smaller than neurons and they showed dark nuclei because of their condénsate heterochromatin. These glial cells surround axons mainly containing mixed both cholinergic and peptidergic vesicles. Occasionally, some axons were found surrounded by myelin sheaths. We found ICCs around enteric ganglia of the myenteric plexus. They present triangular or spindle forms and a very voluminous nucleus, with scarce marginal heterochromatin, surrounded by a thin perinuclear cytoplasm that expands with long cytoplasmic processes. ICC processes penetrate and connect with other ICCs located in the connective tissue of the both muscle layers by gap-like junctions forming a three-dimensional network. In addition, we demónstrate the presence of a primary cilium in ICCs as well as in glial cells. We describe their ultraestructural features: basal foot and cap in the basal corpuscle, (9+0) axonema, and a characteristic domain of membrane: the ciliary pocket. Conclusions: Our data support that the single cilium is present in both kinds of cells and consequently, this is a phylogenetically preserved structure