... the brain. These results suggest that 13cIMH may play a key role in the gener-ation of 13cRA, as well as in the modulation of neuronal functions in the brain.AbbreviationsatRA, all-trans retinoic ... retinoic acid; atRAL, all-trans retinal; atRE, all-trans retinyl ester; atROL, all-trans retinol; 13cIMH, 13- cis isomerohydrolase;9cRA, 9-cis retinoic acid; 13cRA, 13- cis retinoic acid; 13cRAL, 13- cis ... that RA signaling is essential for neuronal cellphenotypic maintenance in the brain [19,22,24]. There-fore, treatment with 13cRA at high concentrationsmay cause an imbalance of RA in the brain,...