OMEGA-CONOTOXIN PREVENTS MYELIN-EVOKED GROWTH CONE COLLAPSE IN NEONATAL RAT LOCUS-CERULEUS NEURONS IN-VITRO

The response of neonatal rat locus coeruleus neurons to contact with m yelin extracts prepared from the CNS and PNS was examined. The growth cones of these neurons collapsed following contact with central myelin , but continued to elongate on contact with peripheral myelin. Central myelin elicited an increase in the intracellular free calcium concent ration in these growth cones, while peripheral myelin did not. This in crease appeared to require transmembrane calcium flux, since it was bl ocked by extracellular EGTA, and also by extracellular cobalt. These n eurons express N- and L-type calcium channels. Exposure to 5 mum omega -conotoxin GVIA, a specific blocker of N-type channels, prevented both the myelin-evoked increase in growth cone calcium concentration and t he collapse of growth cones.