Simultaneous visualization of chromatolytic neurons and neurons retrogradely labeled with horseradish peroxidase.

A method is described for visualization of neurons retrogradely labeled with horseradish peroxidase (HRP) in celloidin-embedded brain slabs. The preservation of cellular detail obtained with this technique facilitates (1) accurate delimination of nuclei or laminae in which HRP-positive neurons are found and (2) simultaneous identification of cells of origin of two central fiber systems, by combining the retrograde transport of HRP and the retrotrade degeneration technique. The latter approach has been used in adult cats and in kittens to identify cortical neurons which project to the dorsal column nuclei and to the spinal cord.