Optical sectioning of HRP-stained molluscan neurons

The use of high-resolution differential interference contrast(DIC) microscopy on cleared whole-mounts of the circumesophageal nervous system from Hermissenda crassicornis permits visualization of neuronal morphology in detail without the need for physical sectioning. Such optical sectioning, when preceded by intracellular iontophoresis of horseradish peroxidase (HRP) permits rapid and accurate examination of the arborization of electrically characterized neurons. Details such as varicosities and terminal swellings can readily be resolved. This method has revealed new morphological features of neurons implicated in training-specific behavioral modification in Hermissenda, and promises to be of further general use for the quantitative morphometry of electrically identified neurons.