Nicotinic receptors in the brain are receiving increased attention due in part to the recent cloning of receptor subunits and to postmortem studies revealing alterations in receptor density associated with Alzheimer's disease. The peptide neurotoxin neuronal bungarotoxin (NBT) has been shown to block nicotinic cholinergic responses in autonomic ganglia and in retinal ganglion cells. These findings suggest that NBT may be a useful probe for studying nicotinic receptors in the brain. Therefore, we have investigated the effects of NBT on the nicotine-mediated enhancement of endogenous dopamine release from rat striatal slices. It was found that the transient increase in dopamine release caused by 100 microM nicotine was completely blocked by 100 nM NBT, indicating that NBT is a functional nicotinic antagonist in this system.