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Kinetic studies have been performed on the activity of the succinate oxidizing enzyme complex in living nerve cells and glial cells after increasing duration of stimulation. The nerve cells and glia of the lateral vestibular nucleus were used. The results show a clear difference between the neuron and its surrounding glia. The nerve cell reacted by highly increasing the capacity of the electron transporting system, reflecting an increased consumption of energy as a function of the stimulation. The glia, in contrast, did not change in this respect.Qualitative as well as quantitative biochemical differences have been shown to exist between the neuron and the glia immediately surrounding the neuron (1, 24). Differences were found even down to the base composition of RNA in the two types of cells (3). Physiological stimulation of the vestibular nerve was found to be followed by a significant increase of the amount of RNA, protein, and certain enzyme activities in the neuron. Inverse changes were found in the glia.The following investigation is a kinetic study of the behaviour of an enzyme reaction and its temperature dependence in the neuron and neighbouring glia, as a function of increased physiological stimulation.The comparison between the reactions in the neuron and in the glia could be made on a dry weight basis. Therefore, it was possible to study differences in energy requirement as the functional demand on the vestibular organ was changed. The activity of the succinate oxidizing enzyme complex (here called succinoxidase) was chosen because of the unique position of succinate in the Krebs cycle with direct transfer of electrons to the cytochrome system of the respiratory chain. MATERIAL AND EXPERIMENTALCONDITIONS 87 white rabbits weighing 1.6 to 1.8 kg were used. The vestibular nerve was stimulated by rotating the animal through 120 ° horizontally and 30 ° vertically with 30 turns per minute and for 25 minutes per day for 1 to 7 days. The animal was placed in a tightfitting box with the head away from the centre. Vestibular tests were used to check that the peripheral organ had not been damaged. The animals were killed by bleeding and the brain rapidly removed. The large nerve cells within the lateral vestibular nucleus, the so called Deiters' nerve cells, and the neuroglia immediately surrounding each nerve cell were used for the study. The brain material was immersed in 0.25 M sucrose solution. The cells were rapidly removed by freehand dissection under a stereomicroscope at X 100 magnification as described earlier (2, 5). The nerve cells were transferred to a clean solution of sucrose and cleaned from glia. The glia cells surrounding each nerve cell were collected in a dense cluster and trimmed down to a spheroid having a volume approximately equal to that of the nerve cell. This was checked as described earlier (2). The dry weight per unit volume of the nerve cell and the glia was determined by quantitative x-ray micro-

Abstract. The brain-specific acidic protein, S100, in the pyramidal nerve cells of the hippocampus was investigated as a possible correlate to learning during transfer of handedness in rats. The amount of S100 increased during training.

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Abstract. The study takes up the problem whether synthesis of certain protein fractions in nerve cells of the hippocampus in rats during the transfer of handedness may be specific for this learning process. Electrophoretic separation of protein was carried out on polyacrylamide gels at the microscale. The investigation encompasses the brain-specific, acidic protein S100 and two protein fractions moving close to the S100 protein during electrophoresis. The protein synthesis was studied during one month of intermittent training of the animals.The temporal link between behavior and an increase in the synthesis of nervecell protein indicates that the protein response is specific for the processes occurring in the hippocampus during learning.Introduction. Two main discoveries have evolved from biochemical studies of learning and memory. One has been the inhibition of brain protein and RNA synthesis and its effect on memory fixation and expression. The other has been the correlation between a new behavior and changes in the composition of brain cells or in labeling patterns. By now, it can be inferred from a large number of experiments in which antibiotics were used that brain protein and RNA synthesis are required for the establishment of long-term memory and that they occur during or shortly after learning.'-5 Short-term memory is not dependent upon the synthesis of intact brain protein and can persist for hours after training.The present study takes up the problem whether an increase in the synthesis of certain protein fractions in nerve cells of the hippocampus during learning, previously shown to occur,6 is or is not specific for the learning process. The data presented indicate that the synthesis of two protein fractions (4 and 5) and possibly the brain-specific acidic protein S1007 is specifically related to the learning process and is not merely an expression of sustained motor and sensory activities. The pyramidal nerve cells in the CA3 region were chosen as material, since the hippocampus is of special importance for the establishment of new