Behavioural pharmacology of nicotine: multiple mechanisms.

It is widely accepted that nicotine serves as a major reinforcer of tobacco use, but how it does so is obscure. Little is known about the nature of the reinforcing effect of nicotine in psychobiological terms, or about the mechanism of reinforcement at the level of neuropharmacology. Several ideas about the nature of the reinforcement are current, including mood changes such as euphoria, learning, memory and attention improvements, ability to help smokers deal with or adapt to stressors, and capacity to terminate symptoms of a nicotine withdrawal syndrome. These psychobiological effects are not mutually exclusive; different effects may be important for different people, or for the same person under different circumstances. Similarly, the neuropharmacology of nicotine reinforcement remains largely unexplored; nicotinic-cholinergic receptors seem to play a primary role but evidence implicating particular subtypes of nicotinic receptor is not available. Evidence points to the release of dopamine as an important link in the chain of events that transduce effects at nicotinic receptors into behaviour and nicotine-seeking responses, but the dopamine hypothesis addresses only one part of a complex system. The possibility has to be faced that neuropharmacologically, several mechanisms are involved that parallel the several psychobiological effects mentioned above; multiple types of receptor, brain structures and indirectly activated neurotransmitter systems may contribute to the maintenance of nicotine-seeking behaviour.