QUANTITATIVE AND QUALITATIVE CHANGES IN RIBONUCLEIC ACIDS OF RAT BRAIN DEPENDENT ON AGE AND TRAINING EXPERIMENTS

—Investigations of rat brain RNA were carried out by phenol extraction of the whole brain and chromatographic fractionation into ribosomal RNA and transfer RNA. (1) The amounts of both RNA species increase in the course of the animal's development reaching a maximum at about the tenth week of life. The ratio of both species remains constant throughout the growth to the twentieth week. After the rats had been trained how to reach their forage by balancing on a stressed rope, the rRNA content was found to be significantly higher, whereas the tRNA content was unchanged. (2) The portion of ribosomes bound in polysome complexes decreases with increasing age of rats. Conditioning of the animals brings about again an increase in polysome content. It is supposed that this reflects an enhanced synthesis of specific proteins in young developing rats and in the course of conditioning. (3) In young rats a second valine specific tRNA could be found as a minor component in addition to the major valyl-tRNA. This additional component disappears as the animals advance to an age of 3 weeks and it could not be detected in the brains of rats after training experiments. In tRNAs specific for the amino acids leucine, lysine and phenylalanine no kind of deviation could be stated.