Expression and localization of the CYP2B subfamily predominantly in neurones of rat brain

Despite the very small amounts of cytochrome P450 (P450, CYP) enzymes expre ssed in different areas and cell populations of the brain as compared with the liver, there is significant evidence for their specific involvement in brain development, function and plasticity. Nevertheless, the current discu ssion about occurrence and importance of cerebral cytochrome P450s is deter mined by inconsistent interpretations of their function in general and with respect to single isoforms. Continuing a series of publications about brai n P450 isoforms, we now present evidence for the constitutive expression of CYP2B1 and CYP2B2 mRNAs in rat brain. Immunocytochemical and non-radioacti ve in situ hybridization studies revealed the same expression pattern throu ghout the brain predominantly in neuronal populations, but to some extent i n astrocytes of corpus callosum and olfactory bulb. The well known testoste rone-metabolizing capacity and the presence of CYP2B isoforms shown in ster oid hormone-sensitive areas and neurones (e.g. hippocampus) clarify the sig nificance of isoforms like CYP2B1 and CYP2B2 for impairment of steroid horm one actions by P450 inducing environmental substances. We argue that cerebr al P450 isoforms which are induced by xenobiotics and are able to metaboliz e these as well as endogenous substrates help us to understand fundamental aspects of brain's functioning.