Retrograde filling of pyramidal neurons in postmortem human cerebral cortex using horseradish peroxidase

A method for retrograde filling of neurons in the postmortem human brain is described. Fresh human brains with minimal postmortem delay (3-11 h) were used. Horseradish peroxidase (HRP) crystals were applied directly to white matter underlying the cerebral cortex. After 5 min, the HRP was washed off and the tissue incubated in the cold for 24-48 h prior to frozen sectioning and development with 3,3'-diaminobenzidine. Reaction product filled pyramidal neurons and fibers in laminae V and VI. The method appears to be useful for labelling cortical projection neurons and cortical afferent fibers and should be applicable to other brain areas.