Response of the chick ciliary ganglion-iris neuromuscular preparation to botulinum neurotoxin.

Response of the chick ciliary ganglion-iris muscle neuromuscular junction (NMJ) preparation to the botulinum neurotoxin (NT) was investigated. The 150 kDa serotypes A and E NTs inhibited muscle contraction in a dose dependent fashion. Neurotoxicity of type E NT increased 20-40 fold after mild digestion with trypsin. The 50 kDA light and 100 kDa heavy chains of type A NT, following separation, applied individually, did not paralyze the tissues. Preincubation of the NMJ preparations with the isolated type A heavy chain delayed (antagonized) the paralytic action of the 150 kDa dichain type A NT. Sequential administration of type A heavy chain, followed by type A light chain mimicked the action of the parent NT. The chick ciliary preparation therefore is a useful NMJ preparation to study neurotoxicity of botulinum neurotoxins.