Is there an endogenous bungarotoxin-like molecule in the vertebrate central nervous system?

It has been postulated that there is an endogenous bungarotoxin-like ligand in rat brain which can inhibit the binding of alpha-bungarotoxin (alpha-BGT) to its target nicotinic acetylcholine (ACh) receptor. We have examined this further by testing the ability of rat and chick brain and spinal cord extracts to inhibit the binding of alpha-BGT to ACh receptors in cultured chick and rat myotubes. We find no evidence for inhibition by any of these extracts, and thus cannot support the hypothesis of an endogenous alpha-BGT-like ligand.