Reduced substance P in hereditary sensory neuropathy in the mf rat.

Mutilated foot (mf) is a mutant rat with an autosomal recessive sensory neuropathy. Affected animals become ataxic and their feet become mutilated. Morphological and quantitative studies have shown a reduced number of sensory ganglion cells and of cells of secondary sensory neurons. No degeneration was seen in the peripheral nervous system. Substance P (SP) is an undecapeptide which is thought to be involved in transmission of nociceptive information. Since mf rats show, in addition to ataxia, a decreased response to painful stimuli, SP immunoreactivity was examined. The density of SP staining was decreased at all levels of the spinal cord, mainly at cervical and lumbar levels and only in areas related to sensory pathways. In other areas of the spinal cord and in the substantia gelatinosa of the trigeminal tract, no reduction of SP staining was observed. The results further support the relationship between SP and transmission of pain stimuli. There are also many similarities between the appearance in mf rats and those in animals in which sensory afferents from dorsal root ganglia had been impaired with various methods, particularly in those treated from birth with capsaicin.