PHARMACOLOGY OF N-METHYL-D-ASPARTATE-EVOKED [H-3] NORADRENALINE RELEASE IN ADULT-RAT SPINAL-CORD

N-Methyl-D-aspartate (NMDA) produced a concentration-related increase in [H-3]noradrenaline release from adult rat cervical spinal cord slic es. Its potency was relatively low and the response concentrated in do rsal spinal regions although also observed in ventral slices. NMDA did not increase the release of radiolabelled glutamate, aspartate, gamma -aminobutyric acid (GABA), acetylcholine or serotonin. In comparison w ith previously characterised NMDA responses in the striatum, (release of dopamine, GABA, acetylcholine or spermidine) the spinal response wa s particularly sensitive to MK-801 and magnesium and to L-689,560 but not to other glycine receptor antagonists (7-chlorokynurenate, CNQX (6 -cyano-7-nitroquinoxaline-2,3-dione), DNQX (6,7-dichloroquinoxaline-2, 3-dione), (+)-HA966). Dextrorphan and dextromethorphan produced partia l or biphasic inhibition curves suggesting a subdivision of NMDA recep tors. NMDA-evoked [3H]noradrenaline release was moderately sensitive t o CPP and CGP37849 but insensitive to arcaine. These characteristics d istinguish the native spinal NMDA receptor subtype(s) from those so fa r characterised in the striatum suggesting a unique spinal NMDA recept or subtype.