itor ▁( DD CI ), ▁in ▁this ▁case ▁car bid op a , ▁which ▁is ▁very ▁polar ▁( and ▁charged ▁at ▁phys i olog ic ▁p H ) ▁and ▁cannot ▁cross ▁the ▁blood ▁brain ▁bar rier , ▁however ▁prevents ▁peri pher al ▁conversion ▁of ▁le vod op a ▁to ▁dop am ine ▁and ▁thereby ▁reduces ▁the ▁unw anted ▁peri pher al ▁side ▁effects ▁of ▁le vod op a . ▁Use ▁of ▁car bid op a ▁also ▁increases ▁the ▁quantity ▁of ▁le vod op a ▁in ▁the ▁blood stream ▁that ▁is ▁available ▁to ▁enter ▁the ▁brain . ▁ ▁History ▁In ▁ 1 9 6 0 ▁the ▁Aust rian ▁bio chem ist ▁Ole h ▁Horn yk iew icz , ▁while ▁at ▁the ▁University ▁of ▁Vienna , ▁exam ined ▁results ▁of ▁aut ops ies ▁of ▁patients ▁who ▁had ▁died ▁with ▁Park inson ' s ▁disease . ▁He ▁suggested ▁that ▁the ▁disease ▁was ▁associated ▁with , ▁or ▁caused ▁by , ▁a ▁reduction ▁in ▁the ▁levels ▁of ▁dop am ine ▁in ▁the ▁bas al ▁gang lia ▁of ▁the ▁brain . ▁Since ▁dop am ine ▁itself ▁did ▁not ▁enter ▁the ▁brain , ▁he ▁tried ▁tre ating ▁twenty ▁patients ▁with ▁a ▁rac em ic ▁mixture ▁of ▁di h ydro xy phen yl al an ine ▁( DO PA ), ▁which ▁could ▁enter ▁the ▁brain ▁and ▁be ▁converted ▁there ▁to ▁dop am ine ▁by ▁the ▁action ▁of ▁D OP A ▁dec ar box yl ase . ▁His ▁results ▁were ▁positive , ▁as ▁were ▁those ▁of ▁another ▁trial ▁in ▁Montreal ▁run ▁by