Involvement of NMDA receptors in the ventrolateral striatum of rats in apomorphine-induced jaw movements

The role of NMDA receptors in the ventrolateral striatum to modulate dopamine receptor-mediated jaw movements was investigated in freely moving rats, using a magnetic sensor system combined with intracerebral microinjection of drugs. Apomorphine (1 mg/kg i.v.) induced repetitive jaw movements that were reduced, in a dose-dependent manner, by bilateral microinjections of the NMDA receptor agonist NMDA (0.1 and 1 μg/0.2 μl bilaterally) into the ventrolateral striatum. Apomorphine-induced repetitive jaw movements were also reduced, in a dose-dependent manner, by bilateral microinjections of the NMDA receptor antagonists d-APV (0.01 and 0.1 μg) or MK-801 (0.5 and 5 μg). The inhibitory effect of NMDA (1 μg) was reduced by co-administration of MK-801 (0.5 μg). Microinjections of drugs into the ventrolateral striatum in the absence of apomorphine did not affect jaw movements. These results suggest that NMDA receptors in the ventrolateral striatum play an important modulatory role in the expression of dopamine receptor-mediated jaw movements. However, similar effects of NMDA and NMDA antagonists echo previous paradoxical findings and indicate that interactions between dopamine and NMDA receptors are complex and multifaceted. Cellular mechanism(s) may involve differential effects of NMDA agonism and antagonism on dopamine D1-like vs D2-like receptors and, possibly, on related GABAergic processes.