Immediate effects of procaine and pentobarbital on placodal and non-placodal head ectoderm of the chick embryo in vitro.

The effects of procaine and pentobarbital on lens placodes, otic placodes and non-placodal head ectoderm of the chick embryo in vitro have been examined by scanning and transmission electron microscopy. Both types of placode cells were less sensitive to both drugs than non-placodal cells. Cellular responses to pentobarbital were microvilli formation, reduction in cetylpyridinium chloride-stainable surface coat and epithelial dissociation with thinning of the basement membrane. Procaine treatment induced the formation of large cytoplasmic blebs and cytoskeletal condensations but did not affect the surface coat. Examination of head ectoderm appears to be of value in the evaluation and comparison of drug effects on differentiating tissues. Anaesthetics also form useful probes for structural and functional changes in the cells of such developing systems.