Upregulation of mRNAs coding for AMPA and NMDA receptor subunits and metabotropic glutamate receptors in the dorsal horn of the spinal cord in a rat model of diabetes mellitus.

Recent studies suggest that glutamate plays a pivotal role in the processing of sensory information in the spinal cords of patients with diabetic neuropathy. However, the specific glutamate receptors that that are involved have yet to be determined. We therefore conducted a study to characterize the expression of messenger RNAs (mRNAs) coding for subunits of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors and N-methyl-d-aspartate (NMDA) receptors and for metabotropic glutamate receptors (mGluRs) in the dorsal horn of the lumbar segment of the spinal cord in a rat model (streptozotocin [STZ]-induced) of diabetic neuropathy. The levels of mRNAs coding for AMPA receptor subunits, GluR1, GluR2, and GluR3, were significantly increased in all layers (laminae I-V) of the dorsal horn in diabetic (STZ-injected) rats compared to control (vehicle-injected) rats. The hybridization signals for NR2A mRNA and NR2B mRNA were significantly elevated in the deep layer of the dorsal horn of diabetic rats. In diabetic (STZ-induced) rats, the levels of expression of mGluR1 mRNA and mGluR5 mRNA were significantly increased in all layers of the dorsal horn. These results suggest that abnormal expression of multiple glutamate receptors is involved in the development of diabetic neuropathy and that glutamate receptors are promising targets in the treatment of this disorder.