Multitracer screening: brain delivery of trace elements by eight different administration methods.

Trace elements are closely associated with the normal functioning of the brain. Therefore, it is important to determine how trace elements enter, accumulate, and are retained in the brain. Using the multitracer technique, which allows simultaneous tracing of many elements and comparison of their behavior under identical experimental conditions, we examined the influence of different administration methods, i.e., intravenous (IV), intraperitoneal (IP), intramuscular (IM), subcutaneous (SC), intracutaneous (IC), intranasal (IN), peroral (PO), and percutaneous (PC) administration, on the uptake of trace elements. A multitracer solution containing 16 radionuclides (i.e., 7Be, 46Sc, 48V, 51Cr, 54Mn, 59Fe, 56Co, 65Zn, 74As, 75Se, 83Rb, 85Sr, 88Y, 88Zr, 95mTc, and 103Ru) was used. The results indicated that the 83Rb brain uptake rate with intranasal administration was approximately twice those obtained with the other administration methods. This result indicated that a portion of Rb was delivered into the brain circumventing the blood circulation and that delivery could be accomplished mainly by olfactory transport. Multitracer screening of trace element delivery revealed differences in brain uptake pathways among administration methods.