Rat Brain Tissue Slices Research Articles

Potassium-induced release of tritiated histamine from rat brain tissue slices

The release of exogenous histamine was studied by superfusing brain slices following incubation with the radiolabeled amine. Histamine was released in calcium-dependent way by 40 mM potassium. This release was high in hypothalamus and striatum and low in hippocampus and cortex. Compound 48/80, a mast cell histamine releasing agent, also induced histamine release, but only from hypothalic tissue slices. It is suggested that the potassium-induced of accumulated exogenous histamine is mainly from glial cells.

Regional cyclic GMP content in incubated tissue slices of rat brain

Incubated tissue slices from different regions of the rat brain contained cyclic guanosine 3′,5′-monophosphate (cyclic GMP) in the following descending order of content: cerebellum hypothalamus striatum thalamus-midbrain brain stem hippocampus cerebral cortex. Cholinomimetic agents at 10 −5 M (carbamylcholine, pilocarpine, acetylcholine and eserine) and papaverine at 10 −4 M significantly elevated cyclic GMP accumulation in the cerebral cortex. Three min incubation with carbamylcholine (10 −5 M) did not increase cyclic nucleotide accumulation in the remaining brain regions.

Studies on the distinction between uptake inhibition and release of [ 3H]dopamine in rat brain tissue slices

There exists some confusion over the classification of drugs as either uptake inhibitors or releasing agents for biogenic amines. We have evaluated this problem with rat brain tissue slices (neostriatum and cortex), using [ 3H]dopamine and the following compounds: potassium chloride, tyramine, d-and l-amphetamine, cocaine, amantacline, desipramine. amitriptyline, nortriptyline and protriptyline. Additional experiments were performed with l-dopa and [ 3H]serotonin in slices from whole rat brain. Potassium chloride and tyramine. both strong releasing agents, diminished the accumulation of [ 3H]dopamine during uptake studies. l-Dopa also caused release of [ 3H]serotonin and an inhibition of [ 3H]serotonin accumulation. Whenever a releasing action was observed, there was always a diminution in the amount of [ 3H]amine accumulation and this action (expressed as a per cent effect) was at least equal in magnitude to the per cent released. On the other hand, cocaine was an example of a pure uptake inhibitor; it did not evoke a releasing action at concentrations where a powerful uptake inhibition was seen. From these data, it was possible to conclude that, in the tissue slice system, an experimentally observed release was real (that is. not materially affected by blockade of reuptake), whereas a releasing action evoked an apparent inhibition of uptake equal in magnitude to the releasing action. Before a drug can be designated as an uptake inhibitor, the dose-response curve for inhibition of [ 3H]amine accumulation should be distinctly to the left of the dose-response curve for release. Our data indicate that, in the neostriatum, all of the drugs studied except cocaine were pure releasing agents and that drugs previously designated as uptake inhibitors were releasing agents. In the cortex, strong inhibition of uptake without significant releasing action was evident for many of the drugs.

The inhibition of 3H-biogenic amine uptake by 5,6-dihydroxytryptamine: A comparison with the effects of 6-hydroxydopamine

5,6-Dihydroxytryptamine was a competitive inhibitor of both 3H-serotonin and 3H-dopamine uptake into rat brain tissue slices. In contrast, 6-hydroxydopamine inhibited 3H-dopamine uptake but did not inhibit 3H-serotonin uptake even at a 6-Hydroxydopamine concentration of 10 −4 M. In these experiments, catalase was present in the incubation medium to decompose hydrogen peroxide which is a product of the autoxidation of 6-hydroxydopamine and an inhibitor of biogenic amine uptake systems. These above data may help to explain the relative specificity of 6-hydroxydopamine for adrenergic nerve terminals in contrast to the effects of 5,6-dihydroxytryptamine on both adrenergic and serotonergic nerve terminals. Kinetic analyses showed that 5,6-dihydroxytryptamine had almost the same affinity for the 3H-serotonin transport system as did 3H-serotonin itself. In contrast, 5,6-dihydroxytryptamine had an affinity for the 3H-dopamine transport system approximately 1/30 that of 3H-dopamine.

Isolation of cerebroside containing glucose (Glucosyl ceramide) and its possible significance in ganglioside synthesis

A small amount of cerebroside containing glucose (glucosyl ceramide) was isolated from bovine brain by Florisil column chromatography and thin-layer chromatography. The fatty acids of the glucosyl ceramide were palmitic and stearic acids; small amounts of oleic and linoleic acids were present.Rat brain tissue slices, incubated with U-(14)C-glucose, incorporated more radioacivity into glucosyl ceramide than into galactosyl ceramide. From these results the possible metabolic significance of the brain glucosyl ceramide in ganglioside metabolism is discussed.

EFFECT OF EXPERIMENTAL ENCEPHALOMYELITIS SERUM ON FATTY ACID OUTPUT OF BRAIN SLICES.

THE injection of preparations of spinal cord into certain animals has been shown to cause the development of an allergic encephalomyelitis1,2. We have been examining the effects of the addition of serum from guinea pigs suffering from experimental allergic encephalomyelitis (EAE) serum on the metabolic activity of slices of rat brain tissue, as measured by in vitro techniques. Other workers have shown that serum from affected animals can cause tissue breakdown in tissue cultures3,4, and the results of our experiments, in which we measure net free fatty acid output of brain slices incubated in a balanced medium are consistent with the hypothesis that EAE serum causes a degenerative change.