A hierarchy of manganese competition and entry in organotypic hippocampal slice cultures.

Contrast agents improve clinical and basic research MRI. The manganese ion (Mn(2+) ) is an essential, endogenous metal found in cells and it enhances MRI contrast because of its paramagnetic properties. Manganese-enhanced MRI (MEMRI) has been widely used to image healthy and diseased states of the body and the brain in a variety of animal models. There has also been some work in translating the useful properties of MEMRI to humans. Mn(2+) accumulates in brain regions with high neural activity and enters cells via voltage-dependent channels that flux calcium (Ca(2+) ). In addition, metal transporters for zinc (Zn(2+) ) and iron (Fe(2+) ) can also transport Mn(2+) . There is also transfer through channels specific for Mn(2+) . Although Mn(2+) accumulates in many tissues including brain, the mechanisms and preferences of its mode of entry into cells are not well characterized. The current study used MRI on living organotypic hippocampal slice cultures to detect which transport mechanisms are preferentially used by Mn(2+) to enter cells. The use of slice culture overcomes the presence of the blood brain barrier, which limits inferences made with studies of the intact brain in vivo. A range of Mn(2+) concentrations were used and their effects on neural activity were assessed to avoid using interfering doses of Mn(2+) . Zn(2+) and Fe(2+) were the most efficient competitors for Mn(2+) uptake into the cultured slices, while the presence of Ca(2+) or Ca(2+) channel antagonists had a more moderate effect. Reducing slice activity via excitatory receptor antagonists was also effective at lowering Mn(2+) uptake. In conclusion, a hierarchy of those agents which influence Mn(2+) uptake was established to enhance understanding of how Mn(2+) enters cells in a cultured slice preparation.