Possible origins of substance P-like immunoreactive axons within Onuf's nucleus of the cat.

The double immunofluorescence method revealed that 30-50% of substance P-like immunoreactive (SP-LI) axons within Onuf's nucleus of cats exhibited enkephalin (ENK)-LI, and that about 5% of SP-LI axons within the nucleus showed serotonin (5-HT)-LI. After hemicordotomy, axons with both SP- and 5-HT-LI, as well as those with only 5-HT-LI, were profoundly depleted in Onuf's nucleus ipsilateral to the lesion, but no changes were detectable in axons with SP-LI and/or ENK-LI in the nucleus.