Responses of type II spiral ganglion neurites to stripes of laminin and fibronectin

The goal of this study was to evaluate the role of extracellular matrix proteins in the guidance of type II spiral ganglion neurons. To accomplish this, we investigated the effect of stripes of extracellular matrix proteins laminin (LN) and fibronectin (FN) on the outgrowth of mouse type II SG neurites in vitro. Little is known about the guidance cues that direct the type II SG neurites to the outer hair cells in the Organ of Corti. However, laminin and fibronectin have both been found to be expressed in tracts leading to and beneath the Organ of Corti, and are thus potential candidate guidance molecules. Growth cone targeting was determined for fibers extending from spiral ganglion explants cultured on stripes of LN and FN in alternation with poly-L-lysine (PLL) or on alternating stripes of LN and FN. Type II SG neurites grown on alternating stripes of LN and PLL tended to avoid LN at all but the lowest concentration. Neurites tended to avoid high concentrations of FN relative to PLL, and showed no preference at intermediate and lower FN concentrations. When explants were grown on alternating stripes of LN and FN there was no significant difference in the number of type II neurite endings on either ECM molecule. The results indicate that both LN and FN can serve as guidance cues for type II spiral ganglion neuron neurites. Moreover, the responses of type II neurites differ from those of type I neurites, and may contribute to differences in the innervation patterns of the two neurite type