Regulation of Acetylcholine Release by Extracellular Matrix Proteins at Developing Motoneurons in Xenopus Cell Cultures

Integrins mediate cell-extracellular matrix connections and are particularly important during neuronal development. We here investigated the regulatory role of extracellular matrix (ECM) proteins on the synaptic transmission at developing motoneurons. Synaptic currents were recorded from innervated myocytes of 1-day-old Xenopus cultures by whole- cell recordings. Soluble fibronectin and laminin had no significant effect on the frequency of spontaneous synaptic currents (SSCs) by themselves and markedly increased SSC frequency in the presence of low concentration of protein kinase C (PKC) activators. Pretreatment with Gly-Arg-Gly-Asp -Ser peptide inhibited the SSC increasing action of 12-o- tetradecanoyl-phorbol -13-acetate (TPA, 0.5 M) plus fibronectin, but not that of TPA plus laminin. Genistein but not cytochalasin D inhibited the SSC increasing action of TPA plus fibronectin or laminin. High concentration of TPA ( 5 M ) markedly increased the SSC frequency by itself and occluded the SSC increasing action of fibronectin. Very low concentration of TPA (0.05 M) markedly enhanced the SSC frequency when the cells were plated onto fibronectin- or laminin-coated substratum for 1 day. The SSC frequency increased markedly right after a train stimulation, which was defined as post-train potentiation (PTrP), when the cultures were plated onto fibronectin substratum and chronically treated with brain-derived neurotrophic factor ( BDNF). The PTrP phenomenon is not observed upon chronic treatment with neurotrophin-3, glial cell line-derived neurotrophic factor, or ciliary neurotrophic factor. Our results suggest that the activation of PKC and tyrosine kinase but not actin reorganization plays a role in the SSC potentiating action of fibronectin. BDNF exerts synergistic effects in increasing synaptic transmission in neurons grown on fibronectin substratum. ECMs in concert with neurotrophic factor may play a role in regulating synaptic function at developing motoneurons