In the present research project, we have employed a combination of physiological and immunocytochemical approaches to the study of somatosensory systems. Two major groups of experiments are described. The activity of lumbar spinal dorsal horn lamina I neurons with afferent drive from the sciatic nerve was studied in intact cats and in cats with acute sciatic nerve transection or chronic sciatic nerve transection with neuroma formation. The majority of neurons recorded ipsilateral to a neuroma had no receptive field; those that did respond to peripheral stimuli had irregular response properties in comparison to the cells recorded in control animals. In addition, the characteristic somatotopy of lamina T cells was not observed in some cats with neuromata-indicating that some cells had altered receptive fields following chronic nerve transection. Immunocytochemical examination of spinal cord tissue from cats with neuromata revealed a decrease in the staining of substance P, somatostatin, cholesystokinin (CCK) and calcitonin gene-related peptide-containing fibers ipsilateral to the neuroma. The neuropeptide content of long ascending somatosensory projection neurons was examined in the rat and cat. Separate populations of retrogradely labeled rat spinoreticular neurons were found to contain CCK, vasoactive intestinal polypeptide, dynorphin (DYN) or enkephalin (ENK)-like material. The highest yield of double-labeled cells occurred for CCK; up to 30% of intrinsic CCK neurons also contained the retrograde marker, decreasing to 2-5% for ENK-labeled cells. Retrogradely labeled spinomesencephalic neurons were found to contain ENK (cells located in laminae I, V, VII and X) and DYN (cells located in lateral lamina V).
