Motor fibre organization in the intratemporal portion of cat and rat facial nerve studied with the horseradish peroxidase technique.

The intra-axonal transport of horseradish peroxidase (HRP) was used to label fibres in the intratemporal facial nerve portion (ITFN) in the rat and cat. HRP was applied to the proximal cut end of facial nerve branches innervating different facial muscles. Following appropriate survival periods, the animals were fixed by perfusion. The ITFN was processed histochemically for demonstration of intra-axonal HRP, using tetramethylbenzidine as substrate. The distribution of labelled fibres was analyzed in serial longitudinal sections and in photographic transverse-like reconstructions from three selected levels. HRP-labelled fibres from all examined motor branches were found to be diffusely distributed almost throughout the entire ITFN, leaving only a narrow zone free of label. By applying HRP to the chorda tympani nerve, it was shown that this zoe harbours fibres of this nerve. The findings support the conclusion that the motor fibres to the facial muscles are diffusely organized in the ITFN.