The resolution of neuronal assemblies after cobalt injection into neuropil

Abstract

Co ions are incorporated by many interneurons of the insect [Calliphora erythrocephala and C. vomitoria] CNS after injection of cobalt chloride or cobalt acetate into the neuropil. Entire nerve cells are subsequently revealed by sulfide precipitation which is followed by Ag intensification of whole brains and ganglia. The number of neurons resolved depends on the optimal timing of an injection phase, followed by a period of diffusion. These and the site of injection can be adjusted so as to demonstrate arrangements within and between complete populations of morphological classes of interneurons. This novel use of cobalt reveals cytoarchitectural features of neuropil refractory to other histological procedures and shows that in columnar visual neuropil the nerve cell arrangements are limited to a few basic modes of assembly.