Neuropeptides in physiologically identified mammalian sensory neurones.

In cats, intracellular dye injection of single sensory neurones of known fibre type and sensory modality has been combined with peptide immunohistochemistry. There was no clear relationship between the sensory function of a neurone and the presence of the neuropeptides substance P, somatostatin, cholecystokinin and vasoactive intestinal polypeptide, in its cytoplasm. In particular, substance P was not detected in many nociceptive sensory neurons even though it could be demonstrated with the same technique in many sensory neurones which did not have cutaneous receptive fields. These results mean that the role, if any, of these neuropeptides in the transmission of pain, must be regarded as complex.