Resolution of intraneuronal and transynaptic migration of cobalt in the insect visual and central nervous systems
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Conventional cobalt chloride procedures, using either diffusion into cut nerves or application via an electrode, can only incompletely resolve nerve cells for light microscopical observation. Enhanced resolution can be obtained by the addition of small quantities of serum albumin to the cobalt chloride. This allows sufficient contrast many nerve cells and enhances the details of thin fibres and their appendages. That this should be possible is of cardinal importance for combined electrophysiological and structural studies.
The present account also illustrates that in Dipterous insects there are certain conditions where cobalt chloride will move from one neuron into another. This movement is between functionally contiguous neurons and is here described from the visual system, with reference to electrophysiological studies that employ procion yellow identifications. Transynaptically filled neurons are only faintly resoluble in whole mounts. A block modification of the Timm's enhancement procedure is described which will reveal the finest details of neurons in thick sections and will also reveal nerve cells that have taken up minute quantities of CoCl2 after passage across at least two synapses. These observations are discussed with reference to their implications and applications for electrophysiological mappings of structural pathways.
KeywordsCobalt Nerve Cell CoCl2 Fine Detail Minute Quantity
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