The long-term effects of taxol on explants of developing chick optic tectum in culture.

The long term effects on cellular ultrastructure and survival of exposure to the antimitotic drug taxol were investigated using explant cultures of embryonic chick optic tectum. After 7-8 days of continuous exposure the major changes were similar to those previously reported for shorter periods of exposure (Bird, 1984), i.e. the presence of increased numbers of microtubules in large bundles, associated with networks of filamentous cytoskeletal elements (inter-microtubule substance). With longer periods of exposure microtubule numbers increased further, the inter-microtubule substance became displaced towards the periphery of the microtubule bundles and filamentous cross-bridges between microtubules, other microtubules and membranous organelles became more numerous. Further microtubule accumulation, darkening of the cytoplasmic matrix, compression of endoplasmic cisterns and neuronal cell death were increasingly evident after 15 days and longer, and the numbers of synaptic profiles fell drastically. Few neurons survived beyond 28 days and return of cultures to normal medium after 7-14 days continuous exposure to taxol had limited effects on neuronal survival and none on synaptic profile numbers.