“Binding” of γ-aminobutyric acid and glycine to synaptic particles of the brains of differentially-housed mice; Evidence for morphological changes

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Using subcellular fractionation and a double-isotope method, it was shown that differential housing of male Swiss albino mice for 6 to 7 weeks caused pronounced neurochemical changes in a region of discontinuous sucrose gradient fractions which contains synaptosomes. The “binding” of the possible inhibitory neurotransmitters, [ 14C]GABA (2.4 × 10 −5 m) and [ 3H] glycine (9 × 10 −8 m), and the total protein content of these fractions were significantly lower for the brains of aggressive “isolated” mice than for those of their “aggregated” counterparts. These differences in protein content and in amino acid binding (when expressed in mole amino acid/fraction) occurred in particles that were localized just above the 1.2:1.6 m sucrose interface of the gradients. However, when the “binding” data were expressed in mole amino acid/mg protein, no differences existed between gradient subfractions of the brains of isolated and aggregated mice. Because the protein content and total amino acid binding capacities of synaptosomal fractions were lower for the brains of isolated mice than for those of their aggregated counterparts, while no differences existed in amino acid binding on a protein basis, it seems apparent than an environmentally-induced morphological change had been produced in the brain—the brains of isolated mice contained a lesser number of subcellular binding sites for GABA and glycine. These environmentally-sensitive subcellular structures may reside on “heavy” synaptosomes, as they were localized just above the 1.2:1.6 m sucrose (“mitochondrial”) interface. This demonstration of environmentally-sensitive constituents of cerebral nerve-ending particles further validates the view that the brain exhibits structural plasticity when an animal is adapting to conditions which produce dramatic changes in behavior.