Pattern of labelling of the rat brain stem after intraventricular administration of 3H-leucine; low and high resolution autoradiographic study.

: The pattern of labelling of proteins of the periventricular grey matter was studied two hours after intraventricular administration of 3H-leucine by low- and high-resolution autoradiography. The pattern was investigated by computer-controlled densitometry. The deposition of radioactive, proteins in the periventricular grey surrounding the mesencephalic part of the aquaeductus Sylvii was compared with that surrounding the fourth ventricle. In the former case, the distribution, of grains was in a circular area 500-600 micrometer in diameter; the densitometric tracing revealed a homogeneous distribution of the label; in the latter case, the distribution was nonhomogeneous and was limited by the tissue components forming the wall of the fourth ventricle. A comparison of the intensity of labelling (performed by a combination of low- and high-resolution autoradiography indicated: a) relatively substantial labelling of proteins of ependymal cells, b) very sparce labelling of subependymal layers, c) very high labelling ot neurones, adjacent to the subependymal layers. The significance of these findings for the interpretation of studies using the intraventricular administration of labelled amino acids for investigating brain macromolecular metabolism is discussed.