Selective Loss of Calcitonin Gene-Related Peptide-Expressing Primary Sensory Neurons of the A-Cell Phenotype in Early Experimental Diabetes

Abstract

To evaluate the possible role of neuropeptide immunoreactive primary sensory neurons on the development of nociceptive dysfunction in diabetes, the absolute numbers of immunoreactive substance P and calcitonin gene–related peptide (CGRP) dorsal root ganglion (DRG) cell bodies were estimated in diabetic and nondiabetic BALB/C (p75^+/+) and p75 receptor knockout (p75^−/−) mice with unilateral sciatic nerve crush. The total numbers of immunoreactive substance P A-cells, substance P B-cells, CGRP A-cells, and CGRP B-cells in L5DRG were estimated using semithick consecutive sections and the optical fractionator. After 4 weeks of streptozotocin-induced diabetes, the number of immunoreactive CGRP A-cells was reduced from 692 ± 122 to 489 ± 125 (P = 0.004) in p75^+/+ mice on the noncrushed side. In p75^−/− mice, there was no such effect of diabetes on the immunoreactive CGRP A-cell number. In p75^+/+ and p75^−/− mice, there was no effect of diabetes on the immunoreactive CGRP B-cell number, nor was there any effect of diabetes on the immunoreactive substance P B-cell number. Sciatic nerve crush was associated with a substantial loss of L5DRG B-cells in diabetic and nondiabetic p75^+/+ mice and with substantial loss of immunoreactive substance P cells in diabetic p75^+/+ mice. In diabetic and nondiabetic p75^−/− mice, there was no crush effect on neuropeptide expression. It is concluded that experimental diabetes in the mouse is associated with loss of immunoreactive CGRP primary sensory neurons of the A-cell phenotype, that this loss could play a role for the touch-evoked nociception in the model, and that the neuronal immunoreactive CGRP abnormality possibly is mediated by activation of the p75 neurotrophin receptor.