Monoamine oxidase and catechol-o-methyltransferase enzyme activity and gene expression in response to sustained glucocorticoids

We previously reported changes in DA neurochemical estimates after sustained corticosterone (CORT) administration or adrenalectomy (ADX) that are consistent with glucocorticoid-induced inhibition of DA metabolism. The present investigation measured monoamine oxidase type A (MAO-A), type B (MAO-B) and catechol-o-methyltransferase (COMT) activity by enzymatic assay and levels of gene expression by real-time quantitative polymerase chain reaction (rt-PCR) in tissues from sham, ADX, or ADX+CORT-replaced Lewis rats. One week of ADX had no significant effect on either enzyme activity or gene expression for any of the three enzymes examined in the medial prefrontal cortex, striatum, or liver. One week of CORT administration (100 mg-21 day release pellet) in ADX rats produced statistically significant decreases in MAO-A enzyme activity and MAO-B gene expression in the liver but no significant changes for any of the three enzymes in either activity or gene expression in the medial prefrontal cortex or striatum. The results do not support inhibition of DA metabolism as a mechanism by which glucocorticoids influence DA-mediated behaviors.