Biocytin: intracellular staining, dye-coupling and immunocytochemistry in carp retina

Correlation of electrophysiological and morphological, including ultrastructural, characteristics of neurones is important for understanding the functional organization of neuronal systems. Further correlation with neurotransmitter content is essential for determining the neurochemical(s) used by a given neurone for propagating its signal. The two main neuronal markers presently available (lucifer yellow and horseradish peroxidase) are not satisfactory for correlating all three aspects. We have devised a new simple procedure whereby retinal interneurones can be labelled with biocytin by positive ionophoresis of an unbuffered solution. Biocytin readily crosses gap junctions thus revealing extensive networks of coupled cells. In the case of H1 horizontal cells, which are known to be GABAergic, the neurotransmitter can also be demonstrated by superimposed immunocytochemistry.