Quantitative microlocation of lithium in the brain by a (n, α) nuclear reaction

Abstract

Although lithium has long been used in psychiatric practice^1–4, its exact mechanism of action remains largely unknown. The reason is mainly methodological. Lithium has no radioisotope, and it is too light to be detectable by electron-probe micro-analysis. To study the distribution of lithium in the brain, most authors⁵ have proceeded by dissecting the brain into small fragments and determining the mean Li content of each fragment by photometric methods. However, the resolving power by this method has remained poor. Our group⁶ and others⁷ have recently described the possibility of using the stable isotopes of lithium as tracers for estimating unidirectional fluxes. To study Li-location, there is the theoretical possibility of using the specific nuclear reaction ⁶Li(n, α)³H. The method cannot be used as a conventional radioactivation because the induced ³H has negligible radioactivity compared with the many other radioisotopes also induced in a biological sample bombarded by neutrons. The detection then consists of laying sections of the ⁶Li-containing samples in contact with a convenient detector, and irradiating the whole arrangement with neutrons; the distribution of lithium in the sample is revealed by the tracks of the α and ³H particles in the detector. Some authors have already attempted to use such methods for various biological applications^8–15. By taking advantage of different independent technical advances^16–22 , we can now give a precise quantitative picture of the distribution of lithium in the brain of a lithium-treated mouse.