Neurotransmitters are generally viewed as functioning by changing the electrophysiological properties of the cells on which they act. These changes can be the direct consequence of the transmitter binding to its receptor, such as in the case of acetylcholine acting on a nicotinic receptor¹. Alternatively, they can involve the production of a second messenger inside the target cell leading to the activation of an intracellular kinase and perhaps to the covalent modification of an ion channel (e.g. Ref. 2). However, neurotransmitters are now known to produce biochemical effects in postsynaptic cells that are unrelated to such changes in membrane permeability. These biochemical changes are only beginning to be explored, but they may well form the molecular basis for many aspects of neural plasticity seen both in the developing and adult organism.