Transmission Between Identified Pairs of Neurons

Abstract

In the previous two chapters the initiation of impulses and the importance of synaptic location were discussed. The present chapter will be concerned with transmission between identified pairs of neurons and will put the previous discussion in the context of normal function. The examples to be considered have been chosen from the mammalian nervous system. This may seem strange to those readers who consider that working with identified neurons is a specialty confined to research on the invertebrate nervous system, where individual neurons may be recognized in living preparations and examined in different members of the same species or, in the case of neurons in ganglia, in different ganglia in the same animal. In vertebrates, identification of neurons is usually in terms of the type of neuron, e.g. motoneurons, and the identification is carried out by a variety of means such as a careful examination of the inputs to the cell, stimulation of the axon terminals of the cell at known sites of projection and the recognition of an antidromic action potential recorded at the cell body, and intracellular staining of the neuron with subsequent histological verification of the cell type and location. With techniques such as this it is perfectly possible to make a rigorous identification of the type of neuron, and indeed this approach is now a most important element in many experiments, both in vivo and also in preparations where slices of nervous tissue are studied in vitro.