Pattern of Distribution of Calcitonin Gene–Related Peptide in the Dorsal Root Ganglion of Animal Models of Diabetes Mellitus

Abstract

Abstract: This article examined the pattern of distribution of calcitonin gene–related peptide (CGRP) in the dorsal root ganglion (DRG) of normal and diabetic Wistar, Zucker lean, and Goto‐Kakizaki (GK) rats to determine whether there are changes in the number and pattern of distribution of CGRP‐positive neurons after the onset of latent or overt diabetes. Type 1 diabetes mellitus was induced in Wistar rats by a single dose of streptozotocin (STZ) given intraperitoneally (60 mg/kg body weight). Four weeks after the induction of diabetes mellitus, diabetic (n= 6) and normal (n= 6), Zucker lean (n= 6), and GK (n= 6) rats were anesthetized with chloral hydrate and their DRGs were removed and processed for immunohistochemistry. CGRP‐positive neurons were observed in the DRG of normal and diabetic Wistar, Zucker lean (nondiabetic), and GK (animal model of type 2 diabetes) rats. CGRP was present in small‐, medium‐, and large‐sized neurons of the DRG in these three animal models. Only a small percentage of large‐sized neurons contains CGRP. The number of CGRP‐positive neurons was significantly (P < 0.05) reduced in STZ‐induced diabetic Wistar and GK rats compared to normal Wistar and Zucker lean rats. Moreover, the quantity of CGRP‐containing varicose nerves was less in diabetic Wistar and GK rats compared to control Wistar and Zucker lean rats. The reduced number of CGRP‐positive neurons in the DRG of GK rats indicated that subjects with latent diabetes may already have dysfunctional CGRP metabolism and thus diabetic neuropathy.