THE DETERMINATION BY QUANTITATIVE HISTOCHEMISTRY OF THE EFFECT OF PHENOTHIAZINES ON BRAIN CYTOCHROME C OXIDASE ACTIVITY

The Burstone method (1961) for the histochemical demonstration of cytochrome c oxidase was quantified and applied to the study of the effects of chlorpromazine and trifluoperazine on the activity of this enzyme in rat forebrain, hypothalamus, cerebellum and pons-medulla. Fresh frozen, 10-µ-thick sections from rat brain were incubated in a buffered medium containing p-aminodiphenylamine and 8-amino-1,2,3,4-tetrahydroquinoline. The colored oxidized product of cytochrome c oxidase activity was extracted with ethanol and the optical density determined. In one series of experiments the phenothiazine was added to the incubating medium. For 50% inhibition of cytochrome c oxidase the following average tissue concentrations of chlorpromazine were required: cerebellum, 20 mM; forebrain, 27 mM; pons-medulla, 42 mM. Trifluoperazine was required in higher concentrations: cerebellum, 38 mM; forebrain, 47 mM; ponsmedulla, greater than 70 mM. In another series the phenothiazine was given intraperitoneally, 100-200 mg/kg. No significant inhibition of the enzyme was noted. The tissue concentration in vivo of the drug was well below the tissue concentration in vitro associated with minimum enzyme inhibitions.