[125I]-alpha-bungarotoxin binding co-varies with motoneurone density during apoptosis.

During chick embryogenosis, apoptosis removes 50% of the initial population of spinal motoneurones. Administration of alpha-bungarotoxin during this critical phase arrests apoptosis. Intraperitoneally administered [125I]alpha-bungarotoxin reaches and binds to the spinal cord at the onset of motoneurone apoptosis. It is not known whether specific [125I]alpha-bungarotoxin binding is directly associated with motoneurones. This study was carried out to examine the level of toxin binding after the final number of motoneurones in the lateral motor column had been experimentally manipulated during the critical period of apoptosis. The level of specific [125I]alpha-bungarotoxin binding significantly co-varied with the number of motoneurones present, suggesting that the toxin could affect receptor-mediated aspects of motoneurone function which, in turn, could regulate final motoneurone number.