Oxygen inhalation enhances striatal dopamine metabolism and monoamineoxidase enzyme inhibition prevents it: a microdialysis study

In order to explore the effect of normobaric oxygen on the extracellular le vel of dopamine and its metabolites, oxygen (30, 60 and 90%) was administer ed to freely moving rats after the animals had been pretreated with either monoamineoxidase (MAO)-A and -B inhibitors (0.1 or 1 mg kg(-1) of clorgylin e, 1 or 10 mg kg(-1) of selegiline and 75 mg kg(-1) pargyline) or control s olution. The levels of dopamine and its metabolites were monitored in micro dialysis samples collected every 20 min and directly applied to an on-line high-performance liquid chromatograph combined with electrochemical detecti on. Normobaric oxygen inhalation decreased the level of extracellular dopam ine and increased that of 3.4-dihydroxyphenylacetic acid (DOPAC) in a conce ntration-dependent manner. These changes were partly prevented by pre-treat ment with low doses of selegiline or clorgyline, i.e. by conditions in whic h monoamineoxidase-A or -B was inhibited. When both isoforms of monoamineox idase were inhibited, there was a drastic increase in extracellular concent rations of dopamine and 3-methoxytyramine, and the levels of DOPAC and homo vanilic acid (HVA) were very low. These results indicate that the intracell ular metabolism of cytoplasmic dopamine is enhanced by normobaric hyperoxia in rat striatum. (C) 2001 Elsevier Science B.V. All rights reserved.