FORMALIN-INDUCED RELEASE OF EXCITATORY AMINO-ACIDS IN THE SKIN OF THERAT HINDPAW

Application of glutamate to skin evokes pain-related behaviors [S.M. C arlton, G.L. Hargett, R.E. Coggeshall, Localization and activation of glutamate receptors in unmyelinated axons of rat glabrous skin, Neuros ci. Lett., 197 (1995) 25-28; D.L. Jackson, C.B. Graff, J.D. Richardson , K.M. Hargreaves, Glutamate participates in the peripheral modulation of thermal hyperalgesia in rats, fur. J. Pharmacol., 284 (1995) 321-3 25.] and peripherally-administered glutamate antagonists can prevent t he nociception produced by inflammation [E.M. Davidson, R.E. Coggeshal l, S.M. Carlton, Peripheral NMDA and non-NMDA glutamate receptors cont ribute to nociceptive behaviors in the rat formalin test, NeuroReport, 8 (1997) 941-946; Jackson et al., 1995.] In this study, the concentra tions of glutamate and aspartate in the plantar of the rat hindpaws we re measured before and after the subcutaneous administration of formal in. increases in glutamate and aspartate concentrations were observed on the ipsilateral side, but not on the contralateral side, to the inj ection. This shows that nociception and inflammation caused by formali n injection induces the release of peripheral glutamate and aspartate, which would contribute to nociception and inflammatory pain. (C) 1998 Elsevier Science B.V.