Improved transport of horseradish peroxidase after injection with a non-ionic detergent (Nonidet P-40) into mouse cortex and observations on the relationship between spread at the injection site and amount of transported label.

Addition of the non-ionic detergent Nonidet P-40 (NP-40) to horseradish peroxidase (HRP) injected in small quantities into barrelfields of mouse somatosensory cortex results in a significant increase of labeled neurons in the contralateral barrelfield cortex as compared to normal HRP. Comparisons with lysolethicin as an additive to HRP show that with NP-40 neurons are labeled more reliably and spread of label is less extensive at the injection site. Using NP-40, the region of dense label spread at the injection site as revealed by the diaminobenzidine/cobalt procedure coincides rather precisely with the contralateral cortical region containing labeled neurons as visualized by tetramethylbenzidine.