The formation of 5-hydroxytryptophol in brain in vitro

Gaddum and LSD: the birth and growth of experimental and clinical neuropharmacology research on 5-HT in the UK

The vasoconstrictor substance named serotonin was identified as 5-hydroxytryptamine (5-HT) by Maurice Rapport in 1949. In 1951, Rapport gave Gaddum samples of 5-HT substance allowing him to develop a bioassay to both detect and measure the amine. Gaddum and colleagues rapidly identified 5-HT in brain and showed that lysergic acid diethylamide (LSD) antagonized its action in peripheral tissues. Gaddum accordingly postulated that 5-HT might have a role in mood regulation. This review examines the role of UK scientists in the first 20 years following these major discoveries, discussing their role in developing assays for 5-HT in the CNS, identifying the enzymes involved in the synthesis and metabolism of 5-HT and investigating the effect of drugs on brain 5-HT. It reviews studies on the effects of LSD in humans, including Gaddum's self-administration experiments. It outlines investigations on the role of 5-HT in psychiatric disorders, including studies on the effect of antidepressant drugs on the 5-HT concentration in rodent and human brain, and the attempts to examine 5-HT biochemistry in the brains of patients with depressive illness. It is clear that a rather small group of both preclinical scientists and psychiatrists in the UK made major advances in our understanding of the role of 5-HT in the brain, paving the way for much of the knowledge now taken for granted when discussing ways that 5-HT might be involved in the control of mood and the idea that therapeutic drugs used to alleviate psychiatric illness might alter the function of cerebral 5-HT.

The effect of selective type A or type B monoamine oxidase inhibition on the intrasynaptosomal deamination of (3H)serotonin in rat spinal cord tissue

The degree to which the type A and type B forms of monoamine oxidase participate in the intraneuronal deamination of (3H)serotonin (5-HT) was examined in synaptosomal-rich fractions of rat spinal cord tissue. Synaptosomes were labeled with (3H)5-HT and superfused with physiological buffers containing selective concentrations of a type A (clorgyline) or a type B (deprenyl) MAO inhibitor. The efflux of (3H)5-HT and newly-formed (3H)5-hydroxyindoleacetic acid (5-HIAA) was determined and compared to controls over time. In control samples, a slight decline in (3H)5-HT efflux occurred over the experimental superfusion period. However, a stable formation and efflux of (3H)5-HIAA was seen during this same period of time. When clorgyline was added to the superfusion buffer, a rapid decline in superfusate levels of (3H)5-HIAA was observed. Similar experiments in the presence of deprenyl were without effect. In order to elevate cytoplasmic concentrations of (3H)5-HT and therefore increase its chances for interaction with nerve terminal MAO, reserpine was added to the superfusion buffer. Reserpine caused a greater than 3-fold increase in (3H)5-HIAA formation with no change in (3H)5-HT efflux. Clorgyline inhibited this increase in (3H)5-HIAA formation but deprenyl was again without effect. In the presence of clorgyline, reserpine also caused an increase in (3H)5-HT efflux. These results strongly support the notion that 5-HT deamination within rat spinal cord nerve terminals occurs primarily, if not exclusively, through an interaction with type A MAO.

Difference in monoamine oxidase activity measured by either liquid ion exchange or ion exchange resin chromatography in rat and cat brain

Cat and rat brain monoamine oxidase (MAO) activity was measured with a radioisotopic procedure and two extraction methods. Results indicated an underestimation of MAO activity when liquid ion exchange chromatography (LIEC) was used instead of an ion exchange chromatographic method (IEC) to separate the different products of the deaminated tyramine, phenylethylamine, or serotonin. MAO produced aldehydic products which may be found in the incubation medium and may be extracted with the substrate in the chloroform phase by the LIEC method. In cat brain, the resulting underestimation of the MAO activity was prevented by the addition of nicotinamide adenine dinucleotide (10(-3) M) in the incubation medium or by allowing a 2-h period between the end of incubation and the LIEC extraction procedure. In the rat brain, the same result was obtained by the addition of an equimolar mixture of nicotinamide adenine dinucleotide and nicotinamide adenine dinucleotide phosphate in reduced form (NAD-NADPH, 10(-3) M). Using the IEC method, the NAD decreased only the deamination of tyramine and serotonin in rat brain. This study suggests that the use of an IEC method to evaluate MAO activity is more accurate for the estimation of the enzymatic activity.

Chronic ethanol administration decreases 5-HT and increases 5-HIAA concentration in rat brain

The effect of acute and chronic ethanol administration on cerebral 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) concentrations of male Sprague-Dawley and Wistar rats was studied. Acute HIAA concentration one hour after administration. In chronically treated rats the whole brain 5-HT concentration was decreased by 9% during ethanol intoxication. This fall was significant in the part of brain containing diencephalon, mesencephalon and telencephalon except cortex (by 23%; P less than 0.01) and in that containing pons and medulla oblongata (by 37%; P less than 0.001) but not in cerebral cortex. The cerebral 5-HIAA concentrations of chronically treated Wistar and Sprague-Dawley rats were increased during intoxication (4--6 hrs after last ethanol administration) and even more during withdrawal (16--18 hrs after last ethanol administration, by 24--58%; P less than 0.05--0.01). The increase was observed in all three parts into which the brain of Wistar rats were dissected. Because ethanol did not further increase the probenecid induced elevation of cerebral 5-HIAA concentration, our results suggest that ethanol increases the cerebral 5-HIAA concentration by attenuating its removal from the brain.

Determination of urinary indolic metabolites

A rapid mass spectral assay for tryptophol, 5-hydroxytryptophol, and 3-indoleacetic acid, employing stable-isotope labeled internal standards, is described. The compounds were extracted from urine or buffer with ethyl acetate and quantitatively measured by chemical-ionization mass spectrometry. The calibration curves were linear over a range of 0.06--2.8 microgram/ml. The technique was applied to the analysis of urine from patients with carcinoid tumors. In addition, the first synthesis of 5-methoxy-3-indoleacrylic acid is reported.

Cellular localization of the uptake of 5-hydroxytryptamine in the area postrema of the rabbit after injection into a lateral ventricle

1. The cellular localization of 5-hydroxytryptamine (5-HT) was investigated in the area postrema of the rabbit after intraventricular injection under different experimental conditions.2. 5-HT was found to be accumulated in different parts in and near to the area postrema, e.g. in glial cells, dorsal surface of the area postrema and ependyma of the central canal.3. The concentrations of 5-HT and 5-hydroxy indol-3-yl acetic acid (5-HIAA) were measured in different parts of the brain and CSF in control and in 5-HT treated animals with and without pargyline pretreatment. Intraventricular injection of 5-HT increased the concentration of 5-HT and 5-HIAA in the brain and in the CSF; pretreatment with pargyline further increased the concentrations of 5-HT but decreased the concentration of 5-HIAA.

5-Hydroxytryptamine metabolism in rat brain and liver homogenates

1. The metabolism of 5-hydroxyindoleacetaldehyde derived from 5-hydroxytryptamine incubated with tissue homogenates was studied as an indicator of aldehyde dehydrogenase and alcohol dehydrogenase activities.2. In liver and brain from rats, there were indications of the presence of one or more aldehyde dehydrogenases which were stimulated by NAD(+) to a greater extent than by NADP(+).3. In liver from rats, there were indications of the presence of one or more alcohol dehydrogenases, which were stimulated by NADH to a greater extent than by NADPH.4. In brain from rats, there were indications of the presence of one or more alcohol dehydrogenases which were stimulated by NADPH to a greater extent than by NADH.

Brain receptors sensitive to indole compounds: function in control of luteinizing hormone secretion

The placement of melatonin and of 5-hydroxytryptophol in the median eminence of castrated male rats is followed 5 days later by a significant decrease in pituitary stores of luteinizing hormone. Pituitary reserve of this hormone is also depleted after the implantation of melatonin, 5-hydroxytryptophol, and 5-methoxytryptophol in the reticular formation of the midbrain. It is suggested that these indole compounds, which are normally synthesized in the pineal gland, may intervene in the control of the secretion of luteinizing hormone, possibly by acting on specific receptors localized in the median eminence and in the midbrain.