The Role of Brain Extracellular Proteins in Learning and Memory
In mammalian brain, the cellular and biochemical mechanisms of learning and memory have the capacity to store information for long periods, in man, this may be upwards of 50 years. How is this achieved? If we search the components of the CNS looking for molecules that can fulfill this criterion of long-term stability, we find that everything except the DNA is in a dynamic state. The average half-life of proteins ranges between 6 and 14 days (Lajtha and Toth, 1966); the RNA turnover can vary from 1.5 to 24 hr (Appel, 1967); lipids and carbohydrates are in a rapid state of flux (Bourre et al., 1977). Essentially we find that there are no biochemical components present in the CNS, except the DNA, that have a lifetime stability comparable to that required for long-term memory. Since no evidence indicating DNA has been found as yet, it would seem therefore that only the structure and connectivity patterns of the CNS have features with sufficient stability for use in establishing a long-term memory. Such a concept, first proposed in 1893 by Tanzi, reduces the search for the biochemical correlates of memory to the identification of specific physiological, metabolic, and molecular components that can ultimately lead to permanent alterations of neural circuits. These may be processes common to all cells but specially adapted for the CNS, or they may be unique to the CNS requiring specific molecules (Shashoua, 1976). Whether one or both of these types are used, the processes must have the additional property of being controllable by individual cells or parts of cells within the CNS.
KeywordsSucrose Carbohydrate Cysteine Electrophoresis Fractionation
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