The differentiation of synaptic areas

Abstract The classical concept of the synapse, as it emerged at the end of the last century from both histological and physiological investigations, does not require us to think that nerve cells possess, in the region of their junctions, properties which differ from those in other parts of their surface. Certain observations, however, such as those made by Bernard (1856) on skeletal muscles in curare experiments and by Langley (1901) on sympathetic ganglia exposed to the action of nicotine led physiologists to the view that some drugs act selectively on the synapses,* which already suggested that the cells forming the synapses present some differentiation at their connexions. These pharmacological properties of synaptic areas can now be regarded as one of the characteristics of their specialization which is also evident from other structural and chemical peculiarities. The special properties observed at synapses may be localized on both the pre and postsynaptic sides. I shall consider principally the postsynaptic properties, and perhaps not unnaturally shall choose as examples mainly those synapses which have been studied in my laboratory, in particular neuromuscular junctions of vertebrates, nerve-electroplaque junctions, ganglionic synapses of amphibians, and retino-tectal synapses of rodents.