A ROLE OF PERIAQUEDUCTAL GREY NMDA RECEPTORS IN MEDIATING FORMALIN-INDUCED PAIN IN THE RAT

In the present study we examined the role of periaqueductal grey (PAG) N-methyl-D-aspartate (NMDA) receptors in the perception of tonic and phasic pain. Under sodium pentobarbital anesthesia rats were implanted unilaterally with a guide cannula aimed at the PAG. Following a 7-14 day recovery period rats received an infusion of the NMDA antagonist, 2-amino-5-phosponopentanoic acid (AP5), or saline into the PAG. Five m inutes after the infusion of AP5 rats were tested for analgesia in the formalin test, or in the hotplate test. AP5 injections into the PAG r educed pain in the formalin test, but not the hotplate test. These dat a show that NMDA receptors within the PAG are involved in the percepti on of tonic, inescapable pain as measured in the formalin test, but no t phasic, escapable pain as measured in the hotplate test. (C) 1997 El sevier Science Ireland Ltd.