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NEUROPHARMACOLOGY of BETA-CARBOLINE ALKALOIDS

Beta-carbolines are a class of indole alkaloids which are structurally similar and biosynthetically derived from the amino acid L-tryptophan. Trypophan derivatives are very important in Central Nervous System (CNS) function and include the neurotransmitter, serotonin, the Pineal metabolite, melatonin, the potent hallucinogen, dimethyl tryptamine (DMT); and the mono amine oxidase inhibitors (MAOI), the beta-carbolines.

A clue as to the beta-carboline's mode of action can be seen by examining their relationship to serotonin. It seems that ingestion of beta-carbolines raises serotonin levels and this increase is a result of the inhibited action of mono amine oxidase (MAO). Normally, MAO degrades the neurotransmitters serotonin, dopamine, and epinepherine. Therefore, inhibition of this enzyme seriously affects brain chemistry.

MAO inhibitors fall into two classes: Irreversible and reversible MAOIs. In addition they can inhibit either or both of the two types of the MAO enzyme, MAO-A and MAO-B which are associated with serotonergic and dopaminergic neurons respectively [8] . Irreversible MAOIs (e.g. the hydrazides iproniazid and phenelzine) bind permanently to the enzyme and cause MAO inhibition lasting 1-2 weeks after ingestion. They are used clinically to treat depression. Reversible MAOIs, such as moclobemide, which is used as an antidepressant, and the beta-carbolines harmine and harmaline, are effective for a much shorter time, usually less than twenty-four hours. There are significant dangers in using MAO inhibitors. Most MAOIs potentiate the cardiovascular effects of tyramine and other monoamines found in foods. There are therefore several foods that should be avoided when on MAOIs. Ingestion of aged cheese, beer, wine, pickled herring, chicken liver, yeast, large amounts of coffee, citrus fruits, canned figs, broad beans, chocolate or cream while MAO is inhibited can cause a hypertensive crisis including a dangerous rise in blood pressure. Effects of amphetamines, general anaesthetics, sedatives, anti-histamines, alcohol, potent analgesics and anticholinergic and antidepressant agents are prolonged and intensified. Overdosage of MAOIs by themselves is also possible with effects including hyperreflexia and convulsions[8].

Another result of ingesting beta-carbolines or other MAOIs at high doses is the occurrence of vivid visual hallucinations. It is not understood whether this hallucinatory effect is related directly to the inhibition of MAO, but due to the structural similarity to serotonin, it is possible that beta-carbolines are acting as serotonin antagonists in much the same way LSD does. The current theory implicates LSD temporarily binding to the serotonin receptor. Upon the release of LSD an over abundance of serotonin is present in the CNS and affects perception. It is notable, however, that the hallucinations experienced from ingestion of beta-carbolines differ from those experienced with LSD.

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