Filling Selected Neurons with Cobalt through Cut Axons

Abstract

The introduction of cobalt chloride as an intracellular marker (Pitman et al., 1972) and the demonstration that it could be introduced into neurons through the cut ends of their axons (Pitman et al., 1973; Sandeman and Okajima, 1973) have established cobalt staining as an extremely powerful tool for the analysis of connectivity in insect neuropils. Both central and peripheral ends of cut axons can be filled and, by careful choice of nerve branches, single functionally identified neurons can be demonstrated (Tyrer and Altman, 1974; Altman and Tyrer, 1977a). In the short time since its introduction, the use of cobalt chloride has enormously advanced our understanding of the organization of insect neuropils, especially tangled ones and, together with improvements in microelectrode recording techniques, is providing the basis for new concepts of functional organization in the insect central nervous system.