title: Amphetamine and D1 dopamine receptor agonists produce biphasic effects on glutamate efflux in rat ventral tegmental area: modification by repeated amphetamine administration.
abstract: Amphetamine or selective D1 and D2 dopamine receptor agonists and antagonists were administered to the ventral tegmental area (VTA) through a microdialysis probe to determine their effects on glutamate and aspartate efflux in rats pretreated for 5 days with vehicle or 5 mg/kg (+)-amphetamine sulfate. In vehicle rats, glutamate efflux declined during 2 h of perfusion with the D1 receptor agonist SKF-82958 (10 and 100 microM). After SKF-82958 perfusion ended, glutamate efflux rebounded to basal levels and continued to increase gradually over the next 2 h. A similar biphasic pattern was observed with intra-VTA amphetamine (10 and 100 microM) and with another D1 agonist (100 microM SKF-38393). The biphasic effects of SKF-82958 were prevented by coperfusion with a D1 antagonist (SCH-23390; 30 microM). Glutamate efflux was unaffected by a D2 agonist (100 microM quinpirole) and by D1 or D2 antagonists administered alone (SCH 23390 and eticlopride; 30 microM). In amphetamine-pretreated rats tested 2 days after the last injection, both the decrease during SKF-82958 perfusion and the delayed increase in glutamate efflux were attenuated. In rats tested 12-14 days after the last amphetamine injection, only the decrease during SKF-82958 perfusion was attenuated. None of these drug treatments produced consistent effects on aspartate efflux. We showed previously that systemic amphetamine (5 mg/kg, i.p.) has no immediate effect on VTA glutamate efflux but produces a delayed increase in glutamate efflux that reaches statistical significance 2-3 h after injection. Because behavioral sensitization can be elicited either by repeated systemic or repeated intra-VTA administration, neurochemical effects common to both routes (such as the delayed increase in glutamate efflux) are most likely to contribute to its induction.
authors.affiliation: Department of Neuroscience, FUHS/Chicago Medical School, Illinois 60064-3095, USA.
authors.forename: M E
authors.initials: ME
authors.lastname: Wolf
authors.forename: C J
authors.initials: CJ
authors.lastname: Xue
mesh_terms: D015647:2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine / Q000494:pharmacology; D000661:Amphetamine / Q000008:administration & dosage / Q000494:pharmacology*; D000818:Animals; D001552:Benzazepines / Q000494:pharmacology; D018698:Glutamic Acid / Q000378:metabolism*; D008297:Male; D017551:Microdialysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D017447:Receptors, Dopamine D1 / Q000819:agonists*; D013997:Time Factors; D017557:Ventral Tegmental Area / Q000378:metabolism*
chemical_list: D001552:Benzazepines; D017447:Receptors, Dopamine D1; D018698:Glutamic Acid; D015647:2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine; C071262:SK&F 82958; D000661:Amphetamine