Selective upregulation of the flip-flop splice variants of AMPA receptor subunits in the rat spinal cord after hindpaw inflammation

Glutamate receptors are involved in spinal nociceptive transmission and the development of persistent inflammatory hyperalgesia. It is unclear, howeve r, whether there are changes in glutamate receptor gene expression associat ed with tissue injury. In the present study, we used reverse transcription- polymerase chain reaction (RT-PCR) to examine the modulation of alpha -amin o-3-hydroxy-5-methyl-4-isox-azolepropionic acid (AMPA) receptor gene expres sion in the rat spinal cord by inflammation. Inflammation was introduced in to the hindpaw by intraplantar injection of 0.2 mi of complete Freund's adj uvant (CFA). At 2 h-14 d after inflammation, total RNAs from L4,5 spinal co rd were used for RT-PCR with primers targeted at eight flip-flop splice var iants of the AMPA receptor subunits. It was found that the GluR1-flop mRNA was up-regulated at 2 h-5 h (P<0.05), down-regulated at 3 d (P=0.05), and r eturned to control levels at 7 d following inflammation. The GluR2-flip and GluR3-flop mRNAs were up-regulated at 5 h-l d (P<0.05) and returned to con trol levels at 3 d after inflammation. The GluR1-flip mRNA was not detected in the samples and the mRNAs for other splice variants did not exhibit sig nificant changes. Immunocytochemical analysis of GluR1 and GluR2 subunits i ndicate that the protein translation products of these subunits were also i ncreased in the spinal cord. These results demonstrate an increased express ion of AMPA receptor subunits that correlates with the acute phase of CFA-i nduced inflammation and hyperalgesia. Selective changes in the expression o f the flip-flop splice variants of the AMPA receptor suggest a reorganizati on of the composition of the AMPA receptor complex and its involvement in t he development of inflammatory hyperalgesia. (C) 2001 Elsevier Science B.V. All rights reserved.