Changes in sensory neuropeptides in dorsal root ganglion and spinal cord of spontaneously diabetic BB rats. A quantitative immunohistochemical study.

This study examined the expression of the sensory neuropeptides, calcitonin gene-related peptide (CGRP) and substance P (SP), in the lumbar 4 and 5 dorsal root ganglion (DRG) and spinal cord of spontaneously diabetic BB rats and non-diabetic controls using quantitative immunohistochemical analysis. In both animal groups immunoreactivities for CGRP and SP were widely distributed within the neurons of DRG and in nerve fibres of the dorsal spinal cord. Image analysis of each neuropeptide subpopulation in the DRG showed that in diabetic rats the cell diameter of immunostained CGRP neurons was significantly decreased compared with controls, while no difference could be found for SP-immunoreactive (IR) neurons. The decrease in the CGRP-IR cell diameter appeared to occur mainly in medium to large neurons (30-50 microns diameter; 2.2% controls, < 1% diabetes), this change being parallel to an increased frequency of small-size neurons (< 20 microns diameter) in diabetic rats (62% controls, 69% diabetes; P < 0.05). However, there was no statistical difference in the total number of cells immunostained for either CGRP or SP between control and diabetic rats. The ratio of CGRP or SP neurons compared to total cells in the ganglion was similar in control and diabetic groups. No difference could be observed for peptide immunoreactivity in the dorsal and ventral horns of either control or diabetic animals. The observed changes of perikaryal size in diabetic rats might relate to the reduced axonal calibre and conduction velocity observed in these animals, and indicate that subpopulations of sensory neurons are affected differently by diabetes.