EXCITATORY AMINO-ACID RECEPTORS MEDIATE THE OROFACIAL STEREOTYPY ELICITED BY DOPAMINERGIC STIMULATION OF THE VENTROLATERAL STRIATUM

stereotypy induced by direct amphetamine microinjection into the ventr olateral striatum. In these experiments, the influence of prior intra- ventrolateral striatum treatment with various excitatory amino acid an tagonists on the expression of amphetamine-stimulated oral stereotypy was observed. In all experiments, behavioral observations were conduct ed in the home cage using a time-sampling procedure. In the first expe riment, different groups of rats received bilateral microinfusions of either kynurenic acid, 2-amino-5-phosphonopentanoic acid, 6,7-dinitroq uinoxaline or dizocilpine maleate. The excitatory amino acid antagonis ts were administered immediately prior to bilateral microinfusions of d-amphetamine. Both N-methyl-D-aspartate and non-N-methyl-D-aspartate antagonists dose-dependently attenuated or blocked the expression of d opamine-mediated stereotypy. 2-Amino-5-phosphonopentanoic acid was the most potent of these compounds, totally suppressing stereotypy at a d ose of 0.3 mu g (equivalent to 1.5 nmol). In the second experiment, th e same compounds were tested for their ability to suppress physostigmi ne-induced mouth movements. Cholinergic stimulation of the ventrolater al striatum has previously been shown to elicit non-directed mouth mov ements, quite distinguishable from stimulus-directed, amphetamine-indu ced biting. Excitatory amino acid antagonists were administered in the same doses prior to bilateral infusion of physostigmine(2.5 mu g/0.5 mu l). The expression of physostigmine-induced mouth movements was for the most part not affected by excitatory amino acid antagonists, alth ough dizocilpine maleate slightly reduced this oral behavior. In a thi rd experiment, behavior was observed following infusion of the antagon ists alone, using the same doses as in the previous experiments. No be havioral alterations were observed with the exception of a small incre ase in nonspecific mouth movements induced by kynurenic acid and 2-ami no-5-phosphonopentanoic acid. These findings indicate that the express ion of dopamine-mediated oral stereotypy, induced by amphetamine stimu lation of the ventrolateral striatal region, is highly dependent on ac tivation of striatal excitatory amino acid receptors. In contrast, ora l behavior induced by cholinergic stimulation of the ventrolateral reg ion is not mediated by glutamate input. These results are discussed in relation to the synaptic organization of neuronal elements within the striatum. Moreover, the relevance to further understanding of orofaci al dyskinesias is noted.