Distribution of protein-bound radioactivity in brain slices of the adult rat incubated with labelled leucine.

The distribution of protein-bound labelled leucine in brain cortex slices, prepared from adult rats by various methods and incubated with [14C]- or [3H]leucine, was investigated by autoradiography. In the first and second slices a marked gradient of incorporated radioactivity from the cut surface to the slice interior was observed. Very high labelling of leptomeningeal cells and vessels enhanced further the inhomogeneity of radioactivity distribution. Light microscopic examination of incubated slices revealed morphological alterations of neurones, especially in the vicinity of the cut surface. The comparison of grain density over neurones and their satellite glia indicated markedly higher incorporation into the latter. The ATP level in slices at the end of incubation reflected the method of slice preparation and morphological integrity. Inhomogeneity of incorporated radioactivity distribution in brain slices contrasted with the uniform labelling of cortical cells in vivo, and may represent at least one reason for the low estimates of protein synthesis rate in brain cortex slices.