INVESTIGATION OF THE SCHWANN CELL LINEAGE IN THE MOUSE SCIATIC NERVE: AN ELECTROPHYSIOLOGICAL AND MORPHOLOGICAL STUDY

Abstract

Two Schwann cell (SC) types are present in the peripheral nervous system: myelinating and non-myelinating SCs. Both types originate from the same progenitor, the immature SC, which develops from neuronal crest cells. The sequential expression of transcription factors and developmental markers characterize the distinct SC types in the lineage. The electrophysiological properties of these cells are only rarely studied in ex vivo slices so far. Furthermore, only a few studies investigated the different SC types in embryonic and early postnatal vertebrate. We want to determine and characterize SCs in ex vivo slices. We developed a new preparation of sciatic nerve slices of late embryonic (E16-18) and early postnatal mice (P0-P2). Using patch clamp recording and immunohistological analyses, we could (dependent on the age) characterize two (E16-E18) or four (P0-P2) electrophysiologically different SC types. These SC types differ in their expression of voltage-dependent Na+ and K+ channels. First analyses show that they express TEA and 4-AP sensitive delayed rectifing K+ channels. During patch-clamp recordings we included a fluorescent dye into the pipette solution, so we could combine the electrophysiological properties of the different SC types with their morphological features. These analyses show that SCs before birth display higher number of processes and branches whereas SCs after birth have longer but a lower number of processes and less branches. First hint that SCs could express neurotransmitter receptors for glutamate was shown in invertebrate. Furthermore, neurotransmitters, including glutamate, are able to induce changes of SC membrane potential in the giant squid axons (Villegas, Evans et al. 1987, Lieberman and Sanzenbacher 1992). Moreover, different studies done in cell culture (Liu and Bennett 2003) or with immunohistochemical methods (Dememes, Lleixa et al. 1995) show that SCs in vertebrates could express different types of glutamate receptors. Using the fast pressure-application system, we want to investigate whether SCs in acute slices express functional ionotropic glutamate receptors and whether SC types differ in their expression. Application of 1mM Glutamate induced an inward current in at least two SC types and in both developmental stages/age groups. The majority of the evoked current is sensitive to the AMPA/kainate blocker GYKI53655, indicating that functional glutamate receptors of the AMPA/kainate type are expressed.