Brain polysomes: response to environmental stimulation

Stimulation-dependent development of neuronal cytoplasm in mouse cochlear nucleus

The extent of neuronal development in the mouse ventral cochlear nucleus was examined in normal and developmentally auditory deprived mice. Mice were unilaterally deprived on postnatal day three by external auditory meatus removal and sacrificed with controls on day 45, which is after the developmental period. Light microscopic morphometry of neuronal nucleus and cytoplasm areas demonstrated that the normal spherical and globular cells were larger in their low frequency regions than in their high frequency regions. This size difference occurred mainly in the cytoplasm. Developmental deprivation reduced neuronal cytoplasm areas similarly in the high and low frequency regions of both neuronal types, but had no effect on the size of the neuronal nucleus. It was interpreted that cytoplasmic metabolic events are dependent on developmental levels of stimulation and high and low frequency regions normally are differentially stimulated. Furthermore, these stimulation-dependent cytoplasmic events are impaired by developmental hypostimulation, which retards neuronal metabolism and growth. No changes were observed in the cochlear nucleus contralateral to the deprived side, suggesting that compensatory changes, such as hypertrophy, did not occur.

ACTH and the stress-induced changes of lysine incorporation into brain and liver proteins

When mice were subjected to footshock treatment and subsequently injected with [3H] lysine, the cerebral uptake of [3H] lysine, its incorporation into brain protein and the relative radioactivity (RR = protein radioactivity divided by amino acid radioactivity) were all increased. In the liver, footshocked mice showed decreased free lysine radioactivity, and increased protein radioactivity and relative radioactivity compared to quiet mice. The possibility that ACTH mediated these effects was investigated. The injection of saline had no effect in the brain but partially mimicked the footshock responses in the liver. Injections of ACTH 1--24 mimicked the effects of footshock in the brain, and further augmented the saline-induced effect on the RR in the liver. ACTH 4--10 increased the RR of brain protein, but produced no significant change in brain free lysine radioactivity or in any measure in the liver. Pretreatment of mice with the synthetic glucocorticoid, dexamethasone, did not enhance these effects and diminished the effect of ACTH 4--10 in the brain. ACTH treatment did not alter the profiles of brain polyribosomes. Lysine vasopressin, which is also released during stress, did not alter the incorporation of [3H] lysine into brain or liver protein, except at high doses when it decreased plasma radioactivity. These results suggest that secretion of ACTH at least partially mediates the stress-induced changes of [3H] lysine incorporation into brain and liver proteins, but that it is probably not the only factor involved.

Stimulation increases incorporation of [3H]lysine into rat brain and liver proteins

Exposure of rats to electric footshocks or merely to the footshock apparatus increased the incorporation of [3H]lysine into brain and liver protein. The effect was present in both fore-and hindbrain. The footshock treatment was the more effective stimulus, producing larger and more significant changes. These results resemble those previously observed in C57Bl/6J mice, and thus suggest that altered protein or amino acid metabolism is a general response to stress in rodents.

Free and membrane-bound ribosomes and polysomes in hippocampal neurons during a learning experiment

The ribosomes of the CA1 and CA3 pyramidal cells of hipocampus were investigated by morphometric methods after the acquisition of a shock-motivated brightness discrimination in rats. A significant increase in the total number of ribosomes was observed in CA1 cells of trained animals and in CA3 cells of both active controls and trained rats. A significant increase in membrane-bound ribosomes was obtained in CA1 and CA3 cells after training only. The results confirm the suggestion of an increased protein synthesis in hippocampal neurons during and after the acquisition of a brightness discrimination, as we have concluded from out previous investigations on the incorporation of labeled amino acids under identical experimental conditions. The results lead to the assumption that the protein synthesis in some neuronal cells may probably differ not only quantitatively, but also qualitatively in trained and untrained animals.

The effect of electrical stimulation on the incorporation of L-[U-14C] valine into the protein of chopped tissue from guinea-pig cerebral cortex

1. Chopped tissue from guinea-pig cerebral cortex carried out an energy-dependent incorporation of [(14)C]valine into protein. 2. At all times studied the nuclear fraction of the homogenized tissue accounted for about 25% of the total labelled protein. 3. Electrical stimulation at first increased, but subsequently decreased, the rate of incorporation of [(14)C]valine into protein of the chopped tissue. 4. The initial increase in the incorporation of [(14)C]valine into protein occurred in the nuclear fraction. At later times electrical stimulation decreased the incorporation into all the subcellular fractions, but the relative contribution of the nuclear fraction to the total labelled protein increased. 5. These changes are discussed in relation to the changes in the rates of respiration, glycolysis, high-energy phosphate content and intracellular Na(+) and K(+) concentrations, which were measured under the same experimental conditions as those used to study protein synthesis.

Brain function and macromolecules. 3. Uridine incorporation into polysomes of mouse brain during short-term avoidance conditioning

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