Expression of metabotropic glutamate receptors mRNA in the thalamus and brainstem of monoarthritic rats

Evidence for the involvement of metabotropic glutamate receptors (mGluR) in sensory processing has been emerging. Additionally, the differential distr ibution of distinct mGluR subtypes mRNA in particular thalamic nuclei of no rmal rats suggests that they could be involved in the processing of somatos ensory information. In the present study, mGluR1, 3, 4 and 7 mRNAs expressi on was investigated by in situ hybridisation in selected brainstem and thal amic nuclei of adult monoarthritic rats at different time points of the dis ease (2, 4 and 14 days). Monoarthritic rats displayed behavioural and physi cal signs of painful arthritis at all time points. At 2 days of monoarthrit is the mGluR1 mRNA expression was decreased mainly in the ventrobasal compl ex (VB) and in the posterior thalamic nuclei (Po) contralateral to the infl amed joint. The mGluR4, mRNA expression was also reduced, but minimum value s were found at 4 days of monoarthritis, when no changes could be found in mGluR1 mRNA expression. At 14 days, mGluR4 mRNA expression was similar to c ontrols, while mGluR1 mRNA was again reduced. Similar decreases of mGluR7 m RNA expression in the VB and Po were found at all time points, while mCluR3 mRNA expression was bilaterally increased in the reticular thalamic nucleu s (Rt). In the brainstem no changes could be found in the expression of any mGluR subtype mRNA. The reduced expression of mGluR1, 4 and 7 transcripts in VB and Po, and the increases of mGluR3 mRNA in the Pt may contribute to counteract the increased noxious input arising from the periphery. (C) 2000 Elsevier Science B.V. All rights reserved.