CHANGES IN SENSORY NEUROPEPTIDES IN DORSAL-ROOT GANGLION AND SPINAL-CORD OF SPONTANEOUSLY DIABETIC BE RATS - A QUANTITATIVE IMMUNOHISTOCHEMICAL STUDY

This study examined the expression of the sensory neuropeptides, calci tonin gene-related peptide (CGRP) and substance P (SP), in the lumbar 4 and 5 dorsal root ganglion (DRG) and spinal cord of spontaneously di abetic BE rats and non-diabetic controls using quantitative immunohist ochemical 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 diamete r of immunostained CGRP neurons was significantly decreased compared w ith controls, while no difference could be found for SP-immunoreactive IIR) neurons. The decrease in the CGRP-IR cell diameter appeared to o ccur mainly in medium to large neurons (30-50 mu m diameter; 2.2% cont rols, < 1% diabetes), this change being parallel to an increased frequ ency of small-size neurons (< 20 mu m diameter) in diabetic rats (62% controls, 69% diabetes; P<0.05). However, there was no statistical dif ference 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 dia betic groups. No difference could be observed for peptide immunoreacti vity in the dorsal and ventral horns of either control or diabetic ani mals. The observed changes of perikaryal size in diabetic rats might r elate to the reduced axonal calibre and conduction velocity observed i n these animals, and indicate that subpopulations of sensory neurons a re affected differently by diabetes.