A map of the location and relative concentration of a number of different proteins present in 25 distinct neuroanatomical regions of the male rat brain has been established utilizing two-dimensional polyacrylamide gel electrophoresis. The regions examined include cortical areas as well as nuclei from the hypothalamus, amygdala, thalamus, forebrain, and hindbrain. Tissue samples were obtained from each region of interest by microdissection. Proteins within these samples were first separated by charge using the technique of isoelectric focusing. In the second dimension, proteins were separated by mass on polyacrylamide slab gels containing sodium dodecyl sulfate. Proteins were visualized using a highly sensitive silver stain and quantitated by computerized scanning densitometry. The results demonstrate that all proteins examined varied somewhat in concentration among the different brain regions. The majority (53%) of polypeptides selected for quantitation were found to vary less than 4-fold in concentration between the neuroanatomical areas with the lowest and highest detected amounts. In contrast, approximately 10% of the proteins examined varied widely in the quantity measured in each brain region, with concentration values ranging more than 10-fold between the regions with the lowest and highest detected amounts. This atlas is a first attempt at systematically classifying the mass, charge, and relative concentration of proteins present in a variety of regions of the rat brain. The system presented here will serve as a basis for future studies in this area.
The beta subunit of the guanine nucleotide regulatory proteins (also termed G proteins) has been examined in both rat and human brain. Proteins contained within samples of fresh rat and human brain tissue were separated by two-dimensional gel electrophoresis and either stained with silver or reacted with various antisera raised against the G proteins. In both rat and human brain, a single protein of molecular weight 36,000 daltons and pI 5.8 reacted the antisera. This protein also comigrated with one of the proteins present in a purified preparation of bovine brain G proteins. Based upon molecular weight, pI, and reaction with specific antisera, it was concluded that this protein is the beta subunit of the G proteins in brain. Using this information, the regional and subcellular distribution of the G protein beta subunit was studied in rat brain. Of 25 distinct neuroanatomical areas examined, cortical regions were generally found to contain the largest amount of this protein. The subcellular distribution of the G protein beta subunit revealed that large amounts are present in the synaptic membrane, crude synaptic vesicles, and microsomes. These studies serve to identify another protein visible on silver-stained two-dimensional electrophoretograms of rat and human brain. The regional and subcellular distribution of the G protein beta subunit correlate well with the proposed physiological function of this protein.
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