Localization of catechol-O-methyltransferase in the leptomeninges, choroid plexus and ciliary epithelium: implications for the separation of central and peripheral catechols.

Catechol-O-methyltransferase (COMT) was localized in cells of the pia-arachnoid, and in epithelial cells of the choroid plexus, using an indirect immunofluorescence technique. The specific activity of COMT derived from these tissues was determined by radioenzymatic assay, and in the case of the choroid plexus was found to be 9-fold greater than that measured in whole rat brain. The level of COMT specific activity in pia-arachnoid was twice as high as that in whole brain. Indirect immunofluorescence studies also revealed an intensity of COMT immunofluorescence in the ciliary epithelium at the blood-aqueous barrier in the rat eye, similar to that visualized in the epithelium of the choroid plexus at the blood-cerebrospinal fluid barrier. The localization of COMT in the leptomeninges, choroid plexus, and ciliary epithelium is consistent with a role for this enzyme in the separation of catechol compounds synthesized in the central nervous system, from those of peripheral origin. Thus, catecholamines derived from the peripheral sympathetic system may be prevented from entering the brain parenchyma, which is innervated by the functionally distinct central catecholaminergic systems.