Critical Evaluation of the Use of Radioautography as a Tool in the Localization of Amino Acids in the Mammalian Central Nervous System

Abstract

In this chapter we describe a method for analyzing the distribution of silver grains over electron microscopic autoradiography by comparing the frequency with which silver grains formed clusters of 0,l,2,3,4 or more silver grains over the tissue which is thought to accumulate the label most avidly with that which occurred over the rest of the tissue present on the autoradiograph. Since in a large number of studies with GABA and β-alanine in various regions of the brain the frequency with which the different sizes of clusters occurred over both areas of the electron microscopic autoradiographs was as predicted by the Poisson’s theorem it appears that the increase in clusters over the more densely labelled tissue is the natural consequence of a random process involving rare events. It therefore, follows that the clusters over nerve terminals are unlikely to be the result of an all or none phenomenon and that a fairly careful analysis is required to determine the probability with which each cluster size will be over the tissue which is presumed to accumulate the label most avidly. In this study, for instance, the probability that a single silver grain would lie over the tissue which accumulated the label most avidly was only rarely better than 2:1.