Cooperative nature of the binding of cholesterol on to synaptosomal plasma membranes of dog brain.

The 'binding' of cholesterol on to dog brain synaptosomal plasma membranes from aqueous cholesterol 'solutions' was studied. 'Binding' of exogenous cholesterol is a slow process, strictly depending on the concentration of cholesterol and the quantity of the membranes present. It appears that binding probably occurs in three distinct successive stages. The first stage occurs very rapidly, and consists of a large deposition-like accumulation of cholesterol onto the membranes. This stage is characterized by the lack of functional changes of integral proteins. It is followed or accompanied by a slower type of binding, probably at 'specific binding sites', the nature of which is, in all probability, cooperative. Thus, when the glucoside of cholesterol is used at lower concentrations as compared to cholesterol it increases the binding of cholesterol, while at higher concentrations relative to cholesterol, it antagonizes its binding. This stage, which evokes strong functional changes of integral proteins, merges without interruption into an incorporation of cholesterol as a structural element into the membranous framework (nonspecific binding).

Non-enzymic interactions of nicotinamide adenine dinucleotide, of some of its synthetic analogues and other compounds with orthophosphate.

Changes in the ultraviolet (UV) absorption spectra of nicotinamide adenine dinucleotide (NAD), of its synthetic analogues, and of adenosine and its derivatives in the presence of high concentrations of orthophosphate were studied. The role of the carboxamide group of the nicotinamide moiety of NAD on these spectral changes was investigated by replacing that group with an acetyl or aldehyde group. The effect of the 6-amino group of the purine was investigated by studying the interaction of deamino-NAD and various adenosine derivatives with orthophosphate. 2,4-Dinitrophenol was also found to give a charge transfer complex with phosphate. Molar extinction coefficients (E) and association constants (K) of these charge transfer reactions were determined.

Subsynaptosomal localization and biochemical characterization of serotonin binding sites in the brain.

The subsynaptosomal distribution of the borohydride stabilizable binding of serotonin (5-HT) in the brain was investigated using various enzyme markers, such as NAD glycohydrolase (NADase), Na+, K+-activated ATPase for synaptic membranes, and monoamine oxidase (MAO) for outer mitochondrial membranes. The gross distribution of the activity of NADase and Na+, K+-activated ATPase in various membrane fractions was found to parallel the distribution of 5-HT binding in these fractions. Radioactivity bound to brain fractions was extractable with chloroform-methanol (2:1). The membranous material was solubilized by chloroform-methanol (2:1) and the recovered material, suspended in 0.32 M sucrose was found to retain its 5-HT binding capacity. The protein-phospholipid nature of the binding subcellular macromolecule was demonstrated with proteolytic and lipolytic enzymes.

Ontogenesis of serotonergic systems in rat brain.

It was shown that the concentration of brain 5-HT rises slowly, reaching mature values by 80 days of age, while the catabolic product of 5-HT, i.e., 5-HIAA, drops from a high perinatal value to lower values by adulthood. This is indicated of poorly developed storage mechanisms at this early period in life. It was also shown that MAO develops at a rapid rate, acquiring mature values by 20 days. The activity of MAO towards substrates develops at different rates, although the general pattern of development is the same.

Subsynaptosomal distribution, inhibition, and characterization of the binding of (14C) 5-OH-indole-3-acetaldehyde to brain preparations.

The distribution of the monoamine oxidase (MAO) dependent binding of [14C] serotonin as well as of pre-formed [14C] 5-OH-indole-3-acetaldehyde to synaptic subfractions paralleled the gross distribution of MAO. The binding of [14C] serotonin and MAO activity in brain preparations was inhibited by CNS antidepressants (imipramine) or stimulants (caffeine), by hallucinogens (N,N-dimethyltryptamine), sedatives (chlorpromazine), and other drugs. The protein-lipid nature of the binding macromolecule was determined. The chemical nature of the acceptors was also investigated. Experiments with sodium borohydride indicated the partial formation of imines, those with SH-reactive compounds showed partial involvement of acceptor-SH groups in the binding.

Drug antagonism and reversibility of the binding of indoleamines in brain.

The specificity of the binding of serotonin to brain preparations was investigated with various competitive agents. A probable relationship between their structure and their capability of displacement was suggested. Bufotenine and morphine displaced serotonin (0.5 X 10(-5) M) binding to synaptic membranes 87 and 49% respectively. Dissociation constants of the binding of 5-HT and tryptamine to synaptic membranes, and displacement constants of certain drugs were determined. The binding of 5-HT and tryptamine to calf brain preparations was also investigated by equilibrium dialysis, in order to determine affinity constants and reversibility of the binding. Differences were noted in the specificity of binding sites for serotonin and tryptamine, suggesting a different binding site for tryptamine. Extrapolations of Scatchard plots were used for determination of the constants. A characteristic low dissociation constant was found for 5-HT in synaptic membranes (K approximately X 10(-6) M). Probably, the binding macromolecule (receptor?) is a proteolipid.

Ontogeny of multiple forms of monoamine oxidase in mouse brain.

MAO activities in mouse brain responsible for deamination of serotonin (5-HT) and p-dimethylaminobenzylamine (DAB) were found to follow different postnatal developmental patterns. MAO activity which deaminated 5-HT reached adult levels 15 days after birth. At this age the capacity of brain to deaminate DAB was only 50% of adult levels and did not develop fully until after the 45th postnatal day. Inhibitor studies with Deprenil and clorgyline indicated that the deamination of the two substrates was due to different forms of MAO and that these forms were similar to type A and type B MAO described previously in rat brain.

Formation of aberrant neurotransmitters and its implication for alcohol addiction and intoxication.

The possible involvement of false neurotransmitters in the biological aspects of addiction to alcohol has been reviewed and discussed. Current evidence is somewhat ambiguous, although suggestive, of a cause-effect relationship between possible metabolic products of biogenic amines (i.e., tetrahydroisoquinoline derivatives etc.) and addiction. A novel hypothesis of the mode of action of these derivatives developed on the basis of experiments in the reviewer's laboratory is also discussed. According to the latter hypothesis, alkaloid formation may occur in vivo at the membranous level in situ, by interaction of indoleamines and (or) catecholamines with the products of polypeptide chains and thereby modifying the properties of plasmalemmal membranes.

Receptors: localization and specificity of binding of serotonin in the central nervous system.

Formation of a Schiff base between the ethylamine residue of serotonin and an appropriate carbonyl residue at the receptor site may be among the forces holding serotonin onto the receptor. Reduction of this imine may provide a means of permanently labeling receptors as a preliminary to their isolation.