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The capacity for binding dimethyl d-tubocurarine-C(14) was studied in isolated nerve-ending membranes from cerebral cortex and myelin. After treatment of the membrane with organic solvents most of the radioactivity was recovered in the extract. Preliminary evidence indicates that dimethyl d-tubocurarine-C(14) is not bound to lipids or glycolipids. While the proteolipids of myelin have a low binding capacity, the results obtained with the nerve-ending membranes rich in acetylcholinesterase suggest that the cholinergic receptor may be a special type of proteolipid.

Zn vitro binding experiments with 5-hydro~y[~T]tryptamine (3-3 x 10-o M) were carried out on subcellular fractions of the cat brain. The highest specific activity was observed in some fractions of nerve-ending membranes isolated from the hypothalamus, basal ganglia, and gray areas of the mesencephalon. The specificity of this high affinity binding was demonstrated by competition with reserpine, butanolamide of lysergic acid, and desmethylimipramine. With butanol-water extraction the [14C]5-HT was found in the butanol while the gangliosides were separated in the water phase. Several experiments with thin layer and column chromatography suggest that in the organic phase the [I4C]5-HT is not bound to the lipids but to a special proteolipid. This proteolipid is different from that found in myelin and has similar chromatographic properties to that previously observed in the proteolipid which binds d-['*C]tubocurarine in nerve-ending membranes of the cere-bra1 cortex.THE USE of electron microscopy in conjunction with cell fractionation methods has led to the isolation from the CNS of nerve endings and finer synaptic structures such as synaptic vesicles, nerve-ending membranes, and junctional complexes. These methodological advances have provided ways of investigating the localization of biogenic amines and other active substances and to study their binding capacity for drugs that may influence synaptic transmission (see, DE ROBERTIS, 1967). In an attempt to elucidate the role of indolalkylamines in brain function these two approaches have been used. Endogenous 5-HT was found to be concentrated in nerve terminals (MICHAELSON and WHITTAKER, 1963; CARLINI and GREEN, 1963; RYALL, 1964 and MAYNERT, LEVI, DE LORENZO, 1964). ZIEHER and DE ROBERTIS (1963) observed that 5-HT is present in the same nerve ending fractions which contain other biogenic amines and is practically absent from the non-aminergic nerve endings (DE ROBERTIS, PELLEGRINO DE IRALDI, RODR~GUEZ DE LORES ARNAIZ and SALGANICOFF, 1962). MARCHBANKS (1966) investigated the binding capacity for 5-HT of isolated nerve endings from brain. Three major components were distinguished by their association constants; i.e. a high affinity binding with a K, = lo6 to 5 x lo6, observed only in nerve endings, a medium affinity binding with K, = 5 x lo4 associated with monoaminoxidase, and a low affinity one that was ubiquitous.