MN TRANSPORT ACROSS THE BLOOD-BRAIN BARRIER

The observations by Couper in 1837 are acknowledged as the earliest description of the toxic syndrome associated with chronic manganese (Mn) exposure. Since then, many of the neurotoxic aspects of manganism have been elucidated, yet, there is little known about Mn transport mechanisms across the blood-brain barrier (BBB), a crucial step in its accumulation in the CNS. The objective of this proposal is to identify the transport mechanisms of Mn across this barrier in the rat, under the general assumption that factor affecting the rate and extent of Mn transport will affect its toxicity. The working hypothesis postulates that Mn transport across the BBB is a carrier-mediated transport system, and that Mn is transported as a transferrin conjugate, in its trivalent oxidation state (Mn+3). To test this hypothesis, the "Oldendorf" single capillary passage method (1971) of in vivo common carotid artery injection, and the retrograde in situ brain perfusion technique (Takasato et al., 1984) will be employed. To provide control over the composition of the incubation media and to establish uptake, as well as, transendothelial transport kinetics, bovine brain capillary endothelial cell suspensions (Betz et al., 1978), and in vitro monolayers of cultured brain capillaries (Rutten et al., 1987) will be utilized. The cardinal criteria for a carrier-mediated transport system, such as uptake inhibition, substrate specificity, counter transport and its metabolic requirements will be evaluated. Correlation between the temporal distribution of 54 Mn in specific brain nuclei with the capillary- transferrin-receptor density, using autoradiography will be assessed as further support for the role of transferrin in the transendothelial transport of Mn. The existence of other BBB transport mechanisms for Mn, in its divalent oxidation state (Mn+2) will be also evaluated. The possibility that Mn is transported by a generic "sulfhydryl shuttle", a two step "internalization" process, or as a lipid soluble compound will be addressed in the same in vivo and in vitro transport systems.