Brain Ribosomal RNA Synthesis Inhibited by Chlorpromazine

The influence of chlorpromazine (CPZ) on cerebral turnover of catecholamines has been well established (1-3). Evidence that a specific increase in tyrosine–dopamine transfer is caused by the drug has also been reported (4, 5). Recently a protein–chlorpromazine complex has been demonstrated and an effect of the CPZ-free radicals on ATPase has been shown (6, 7). Previous studies have indicated that CPZ inhibits brain mitochondrial oxidative phosphorylation, acting as an uncoupler (8) and inhibiting oxidation of tricarboxylic acid cycle substrate (9). The drug inhibits orotic acid incorporation into nucleic acids in Bacillus megaterium, but it does not affect incorporation of adenine or thymidine. The present study deals with the effect of CPZ on in vivo RNA synthesis in rat brain.

Materials and Methods. Male, Charles River rats, weighing 200-300 g were used. Plastic cannulas (Yeda, Rehovot, Israel. Cat. No. 92-103) were implanted 2.5 mm lateral and 2.0 mm posterior to the bregma. The rats were paired at random into controls and experimental animals. Seven days after cannulation, 2 mg CPZ in 0.5 ml were injected ip twice a day during 10 days. Control rats were also injected ip with the same volume of saline. The rats were kept at 20-25° and fed ad libitum.

After CPZ treatment the animals were superficially anesthetized with ether and 50 μCi of ³H-uridine (15 Ci/mmole, Israel Nuclear Research Center) in 5 μl saline were injected with an 11 mm needle into the lateral ventricle through the cannula with a microsy-ringe.

Eighteen hours later the rats were decapitated. The brain was homogenized in TMKB buffer (Tris–HCl buffer 0.05 M (pH 7.8), 0.01 M MgAc; 0.5 M KCl Bentonite 2%). All manipulations were done at 4°. The amount of radioactive precursor in the brain was quantitated by counting 0.1 ml of each brain homogenate as described below.