The antibiotic, puromycin, caused loss of memory of avoidance discrimination learning in mice when injected intracerebrally. Bilateral injections of puromycin involving the hippocampi and adjacent temporal cortices caused loss of short-term memory; consistent loss of longer-term memory required injections involving, in addition, most of the remaining cortices. Spread of the effective memory trace from the temporal-hippocampal areas to wide areas of the cortices appears to require 3 to 6 days, depending upon the individual animal. Recent reversal learning was lost while longer-term initial learning was retained after bilateral injections into the hippocampal-temporal areas.

ON the assumption that learning and memory may have a biochemical basis, the suggestion has become increasingly frequent during recent years that they may depend in some way on macromolecules such as nucleic acid or protein. The discovery by YARMOLINSKY and DE LA HABA (1960) that puromycin produces profound inhibition of protein synthesis in a cell-free system and the later demonstration that it efficiently suppresses protein synthesis in vivo (GORSKI, AIZAWA and MUELLER, 1961) led us to investigate its effect on the central nervous system. This report deals primarily with the substantial suppression of protein synthesis which has been produced in the brains of mice with puromycin, and with the performance of these mice in tests of their ability to learn and to retain memory of the learning experience. MATERIAL A N D METHODS Biochemical studiesYoung adult, albino mice weighing about 30 g were used. We are indebted to Dr. LEON GOLDMAN of the Lederle Laboratories Division of the American Cyanamid Company for our supply of puromycin dihydrochloride pentahydrate. L-Valine uniformly labelled with 14C with a specific radioactivity of 1.0 mc per mg was obtained from the New England Nuclear Corporation.Subcutaneous injection of puromycin and treatment of tissues. Our first experiments were directed towards establishing the maximum amount of puromycin which could be tolerated in a single, subcutaneous injection and then towards following, as a function of time after injection, the degree of suppression of incorporation of ['*C]valine into protein.Just before use, puromycin dihydrochloride was dissolved in 0.15 ml of water and the solution brought to pH 6 with 1 N-NaOH. This solution was injected subcutaneously over the middle of the back of the animal. At various times after administration of the puromycin, 0.10 ml of [14C]valine (4 p c per 30 g mouse) was injected subcutaneously over the back of the mouse. Forty minutes later the animal was killed by asphyxiation. Previous experience had shown that the rates of incorporation of labelled essential amino acids into the proteins of liver and cerebral cortex are approximately constant during this time interval (ROBERTS, FLEXNER and FLEXNER, 1959). In control experiments, the same amount of [Wlvaline was injected in the same way and the animal was killed 40 min later.In the earliest experiments, samples of cerebral cortex, liver, spleen, kidney (including cortex and medulla) and abdominal muscle were taken for analysis. In later experiments we confined our interests to several regions of the brain. In these last experiments, the brain was removed from the skull and samples were taken of the cerebellar cortex, the two thalami, corpora striata, hippocampi, and the cerebral cortex, the latter divided roughly into rostra1 and caudal halves. Blunt dissection of the brain to separate these regions required about 3 min. With few exceptions, samples of fresh tissue * This work was supported by grants B-514, M-3571 and RG-6970 from the U.S. Public Health Service, National Institutes ...

Learning and memory are important elements of our daily lives, familiar to all through introspection. Yet the mechanisms underlying these processes are still for the most part unknown. Here are problems which combine a maximum of intrinsic and practical interest with a minimum of actual knowledge and understanding. Years of our lives are dedicated to the formation of certain long-term memories and behaviour patterns, yet we have only rudimentary notions of how such ‘schooling’ is best accomplished. There is no certainty in any aspect of the process. We are not sure whether relatively few cells or millions participate in a memory trace; whether these cells change as a whole, or whether the changes are limited to synaptic regions. In fact, we cannot be certain whether the changes are confined to the neurones or whether the glia also participate.