Nicotine

Normal conditions 4

Once the message has been transmitted, the acetylcholine unbinds from the receptor. The surrounding cells then release an enzyme called acetylcholinesterase into the synaptic cleft.

This enzyme breaks down acetylcholine into choline and acetic acid, thus inactivating it. The choline is reabsorbed into the axon with the aid of reuptake proteins. It is recycled, as it were.