SEPARATION OF CATECHOLAMINE-STORING SYNAPTOSOMES IN DIFFERENT REGIONS OF RAT BRAIN

¹ Departments of Pharmacology and Experimental Therapeutics and Psychiatry and the Behavioral Sciences, The Johns Hopkins University School of Medicine, Baltimore, Maryland; Department of Pharmacology, Cambridge University, Cambridge, England

We have studied the subcellular localization of exogenous and endogenous norepinephrine (NE) in different regions of rat brain. When slices from different areas were incubated with H³-NE or C¹⁴-NE, combined, homogenized and centrifuged on continuous sucrose density gradients, different patterns of subcellular localization were observed in hypothalamus, striatum, cerebral cortex and medulla-pons. These separations could be confirmed using discontinuous sucrose gradients. Endogenous and exogenous NE had the same subcellular localization in the hypothalamus. In the striatum the subcellular distributions of H³-NE, protein and lactic dehydrogenase activity were closely similar, whereas in the hypothalamus some differences were observed. Experiments in which subcellular fractions isolated in discontinuous gradients were recentrifuged on continuous gradients suggested that catecholaminergic synaptosomes in each brain region are a heterogeneous population. These findings indicate that catecholamine-containing nerve terminals from different areas of the brain vary in density and can be separated by density gradient centrifugation.

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