THIAMINE PYROPHOSPHATE-DEPENDENT AND THIAMINE METABOLIZING ENZYMES INTHE DEAFFERENTED CEREBELLUM AND IN THE INTACT CEREBRAL-CORTEX OF RAT

The effects of chemical (CD) and surgical (SD) deafferentation of the cerebellum on thiamine pyrophosphate (ThPP)-dependent enzymes (transke tolase, TK; pyruvate-, PDH, and alpha-ketoglutarate, alpha KGDH, dehyd rogenases) and thiamine (Th) metabolizing enzymes (thiamine pyrophosph okinase, ThPK; thiamine mono-, ThMPase, and pyrophosphatases, ThPPase) were evaluated in vitro in rats in steady state conditions. The enzym es were also determined in the intact cerebral cortex of the same anim als. CD was carried out by i.p. injection of 3-acetylpyridine, followe d by harmaline and niacinamide. SD was carried out by complete dissect ion of the peduncles of the left cerebellar hemisphere. Chemical and s urgical cerebellar deafferentations significantly lowered the contents of both Th-metabolizing and ThPP-dependent enzymes in the cerebellum without modifying those of the cerebral cortex. ThPK and TK, which are particularly concentrated in neurons, were the most affected enzymes. The decrease in ThPP-dependent enzymes shown here is associated with the slowing down of the Th phosphorylation-dephosphorylation cycle and with no modification in the ThPP content in the cerebellum, both of w hich were found in a previous study. Cerebellar deafferentation seems to only affect the apoenzyme moiety of the enzymes.