Increase in rat striatal extracellular dopamine and vacous chewing produced by two σ receptor ligands

Abstract The present studies were carried out to analyze the neurochemical and behavioral effects of peripheral σ ligand administration in the rat. Based upon previous studies which showed an increase in turning behavior following unilateral intranigral administration of σ ligands, we determined the effects of two σ ligands, 1,3-di-o-tolylguanidine (DTG) and (+)-pentazocine, on extracellular dopamine levels in the rat striatum. Dopamine levels were monitored via microdialysis in awake freely moving animals following i.p. injection of the ligands. Both DTG (1 and 3 mg/kg) and (+)-pentazocine (10 mg/kg) produced a significant (30–50%) increase in extracellular dopamine. Given the relatively high concentration of σ receptors in brain nuclei involved in facial and mouth movements, we have also determined the effects of the two σ ligands on facial movements. Both ligands produced a significant increase in vacuous chewing movements, suggesting that studies on the consequences of σ receptor activation may have relevance to animal models of human dystonia and/or dyskinesia.