Antinociceptive effect of a group II metabotropic glutamate receptor antagonist in the thalamus of monoarthritic rats.

F L Neto, J M Castro-Lopes

Index: Neurosci. Lett. 296(1) , 25-8, (2000)

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Abstract

Adult rats were rendered monoarthritic (MA) by injection of 50 microl of complete Freund's adjuvant (CFA) into the tibiotarsal joint. The ankle-bend (AB) test of nociception was performed in those animals before and during 60 min after the stereotaxic injection of 2 microl of either saline (controls) or (2S)-alpha-ethylglutamic acid (EGLU, 80 nmol in 2 microl), a group II metabotropic glutamate receptors (mGluR) antagonist, in the reticular thalamic nucleus (Rt) contralateral to the arthritic joint. AB scores reached near maximum values before the stereotaxic injections (18.7+/-0.8), and remained constant throughout the entire experimental period in the control group, denoting marked allodynia. In the EGLU-treated group, AB scores gradually decreased after EGLU injection, with minimum values at 10 min (7.7+/-1.6), recovering to scores near maximum at 60 min (19.7+/-0.3). The data point to an activation of group II mGluR by noxious inputs in the Rt of MA rats, suggesting their participation in inhibiting local gamma-aminobutyric acid (GABA)ergic inhibitory neurones.