Motor effects of intracaudate injection of excitatory amino acids

In a study of the role of excitatory amino acid receptors in movement disorders, the effect of the injection of glutamate (Glu), aspartate (Asp), N-methyl-D-aspartate (NMDA), quisqualate (Qu), or kainate (K) into the rat striatum was investigated. Rats were microinjected unilaterally through chronically implanted guide cannulas and their motor behavior was recorded. After 10-25 min L-Glu produced reversible periodic choreiform movements lasting 5-10 sec and contraversive rotation lasting 1-2 min. Both episodes were repeated every 2-3 min: the duration of motor effects was 60-80 min. L-Asp had an effect similar to that of L-Glu and in addition produced barrel rolling. The L-isomers of both Glu and Asp were active and the D-isomers were inactive. NMDA, Qu, and K were more potent than Glu or Asp. Each produced effects similar to that of Glu, and in addition NMDA and K produced wet-dog-shakes and masticatory movements. The motor behavior produced by Qu was identical to that of Glu, but it lasted longer. The motor effects of L-Glu were blocked by L-glutamic acid diethyl ester (GDEE) and by a larger sedative dose of 2-amino-5-phosphonopentanoic acid (AP5), but not by haloperidol, GABA, glycine (Gly), or a smaller nonsedative dose of AP5. The results suggest that the motor effects of L-Glu were produced by activation of the Qu-type (glutamatergic) receptors, not involving the dopamine and GABA systems. However, activation of the K-type receptors by L-Glu cannot be ruled out.