Changes in metabotropic glutamate receptor expression following spinal cord injury

Spinal cord injury (SCI) initiates biochemical events that lead to an incre ase in extracellular excitatory amino acid concentrations, resulting in glu tamate receptor-mediated excitotoxic events. These receptors include the th ree groups of metabotropic glutamate receptors (mGluRs). Group I mGluR acti vation can initiate a number of intracellular pathways that increase neuron al excitability. Group II and III mGluRs may function as autoreceptors to m odulate neurotransmission. Thus, all three groups may contribute to the mec hanisms of central sensitization and chronic central pain. To begin evaluat ing mGluRs in SCI, we quantified the changes in mGluR expression after SCI in control (naive), sham, and impact injured adult male Sprague-Dawley rats (200-250 g). SCI was produced at spinal segment TIO with a New York Univer sity impactor (12.5-mm drop, 10-g rod of 2-mm diameter). Expression levels were determined by Western blot and immunohistochemistry analyses at the ep icenter of injury, as well as segments rostral and caudal. The group I subt ype mGluR1 was increased over control levels in segments rostral and caudal by postsurgical day (PSD) 7 and remained elevated through PSD 60. The grou p I subtype mGluR5 was unchanged in all segments rostral and caudal to the injury at every time point measured. Group Il mGluRs were decreased compare d to control levels from PSD 7 through PSD 60 in all segments. These result s suggest that different subtypes of mGluRs have different spatial and temp oral expression patterns following SCI. The expression changes in mGluRs pa rallel the development of mechanical allodynia and thermal hyperalgesia fol lowing SCI; therefore, understanding the expression of mGluRs after SCI may give insight into mechanisms underlying the development of chronic central pain. (C) 2001 Academic Press.