Evidence that the hyperphagic response to 8-OH-DPAT is mediated by 5-HT1A receptors.

The 5-HT1A agonist, 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT) at a dose of 1 mg/kg s.c. increased food intake in free feeding rats. 8-OH-DPAT-induced feeding was blocked by metergoline which has comparable affinity for 5-HT1A, 5-HT1B, 5-HT1C and 5-HT2 receptors. This is consistent with the hyperphagia being mediated by an action at 5-HT receptors. Evidence against the involvement of 5-HT2 or 5-HT3 receptors was provided by the lack of effect of methysergide, ketanserin, MDL 72222 and ICS 205930 on the feeding response. Blockade of the hyperphagia by (-)- but not (+)pendolol which stereoselectively interacts with 5-HT1 receptors indicated an involvement of this receptor type. The lack of effect of ketanserin suggests that the 5-HT1C site is not involved as it has high affinity for both 5-HT2 and 5-HT1C receptors. Blockade of the hyperphagia by spiperone suggests mediation by 5-HT1A rather than 5-HT1B receptors. Although spiperone also blocks dopamine and alpha 2-adrenoreceptors, involvement of these sites is unlikely as neither the DA antagonist haloperidol nor the alpha 2-adrenoceptor antagonist idazoxan blocked 8-OH-DPAT-induced feeding. These results indicate that 8-OH-DPAT-induced feeding is mediated by 5-HT1A receptors.

Neurochemical and behavioural evidence for mediation of the hyperphagic action of 8-OH-DPAT by 5-HT cell body autoreceptors.

Administration of 60 micrograms/kg s.c. of the 5-HT1A agonist 8-hydroxy-2-(di-n-propylamino)-tetralin (8-OH-DPAT), a dose previously shown to cause hyperphagia in satiated rats (but not to cause the 5-HT behavioural syndrome) decreased 5-HIAA and 5-HIAA/5-HT ratio in several brain regions, the most marked effects being in pons + medulla oblongata, a region containing 5-HT cell bodies and ascending 5-HT axons. Micro-infusion of 8-OH-DPAT (250 and 500 ng) into the dorsal or medial raphe nuclei significantly increased food intake and feeding duration but did not produce the 5-HT behavioural syndrome. Results suggest that 8-OH-DPAT induced hyperphagia is mediated via a agonist action on somatodendritic 5-HT autoreceptors.

Biopterin and neurotransmitter amine metabolism in children with acute lymphoblastic leukemia receiving methotrexate therapy.

To test the hypothesis that some of the neurologic sequelae of treatment for acute lymphoblastic leukemia (ALL) might be related to abnormalities in biopterin metabolism associated with methotrexate (MTX) therapy, total biopterin levels in cerebrospinal fluid (CSF) and plasma, and homovanillic acid (HVA) and 5-hydroxyindoleacetic acid (5HIAA) were measured in a cross-sectional study of 80 children with ALL. For comparison, biopterins were also measured in a group of children of similar age undergoing investigation for neurologic disease. In children with ALL studied before therapy, no significant difference was found between the means of plasma biopterin or CSF biopterin concentrations and the means in the control group. In children receiving MTX, plasma biopterin values were higher in the group given maintenance therapy than in children observed before treatment. CSF levels were significantly increased only in those patients who had completed 2 years of maintenance therapy. CSF concentrations of HVA and 5HIAA in patients with ALL who had received no treatment (median values 52 and 18 ng/ml, respectively) showed a wide scatter and were inversely related to age. In patients receiving MTX, concentrations of these metabolites were higher than in the untreated group, again reaching a peak in patients just completing 2 years of treatment (median HVA 110 ng/ml, 5HIAA 34 ng/ml). These results provide no support for the idea that neurotransmitter amine deficiency occurs in children with ALL receiving MTX, and indicate, rather, that amine and biopterin synthesis increases in such patients.

A comparison of an improved o-phthalaldehyde fluorometric method and high pressure liquid chromatography in the determination of brain 5-hydroxyindoles of rats treated with L-tryptophan and p-chlorophenyl-alanine.

1 The determination of 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) by reaction with o-phthalaldehyde (OPT) in the presence of cysteine and subsequent fluorometry was compared with determination by a new high pressure liquid chromatography (h.p.l.c.) electrochemical method. 2 The methods were used to investigate a claim that the OPT method gives falsely high brain 5-HT values for rats given tryptophan (greater than 25 mg/kg i.p.) and as a consequence an inhibition of 5-HT synthesis by tryptophan is obscured. 3 High concentrations of tryptophan caused some increase of fluorescence when added to 5-HT solutions and carried through the OPT method, e.g. tryptophan (80 micrograms/ml) gave fluorescence identical to 5-HT (0.13 micrograms/ml). This interference was decreased by more than half and the sensitivity of the method increased if cysteine was added at more stages and fluorescence developed at 77 degrees C instead of 100 degrees C. 4 The h.p.l.c. and modified OPT methods did not give significantly different mean brain 5-HT or 5-HIAA values in rats given 0,25,100,250 mg/kg L-tryptophan though values were somewhat higher by the OPT method with the highest dose. This method gave significantly higher residual brain 5-HT values (12% of control) than did the h.p.l.c. method (8% of control) after inhibiting 5-HT synthesis by p-chlorophenylalanine (150 mg/kg X 3). 5 There was no indication that tryptophan inhibited 5-HT synthesis even when brain tryptophan was increased about 30 fold (from 3.8 to 124 micrograms/g). 6 Results confirm the general reliability of the OPT method although h.p.l.c. has some advantages i.e. separation of 5-hydroxyindoles from tryptophan, greater sensitivity, ease of automation.

Metabolism of an oral tryptophan load. II: Effect of pretreatment with the putative tryptophan pyrrolase inhibitors nicotinamide or allopurinol.

1 The effect of seven days administration of either allopurinol (300 mg daily) or nicotinamide (500 mg twice daily) on the metabolism of an oral L-tryptophan load (50 mg/kg) has been investigated. 2 Administration of either drug failed to alter the plasma total or free tryptophan or plasma kynurenine curve. Nor was the urinary excretion of tryptophan, kynurenine, 5-hydroxyindoleacetic acid or indole acetic acid influenced. 3 Allopurinol pretreatment did increase the volume of distribution of tryptophan. 4 These data suggest that allopurinol and nicotinamide are unlikely to be of value as tryptophan pyrrolase inhibitors in vivo and therefore would not increase the therapeutic effect of L-tryptophan when it is given to treat depressive illness.

Accelerated ageing or selective neuronal loss as an important cause of dementia?

Extensive biochemical analysis of whole temporal lobe from cases of dementia and controls suggests that Alzheimer's disease is a primary degenerative nerve-cell disorder and not the result of accelerated ageing. There is selective loss of neocortical cholinergic neurones. Transmitter systems apart from the cholinergic system appears to be affected, but to a lesser extent, and there are no significant changes in the caudate nucleus. The change in cholinergic neurones has been confirmed in biopsy samples.

Effects on plasma and brain tryptophan in the rat of drugs and hormones that influence the concentration of unesterified fatty acid in the plasma.

1 The effects on tryptophan distribution and metabolism of drugs altering plasma unesterified fatty acid (UFA) concentration were investigated in the rat.2 UFA and plasma free (i.e. ultrafilterable) tryptophan altered in the same direction.3 Catecholamines and L-DOPA increased both plasma UFA and free tryptophan. L-DOPA also increased brain tryptophan and 5-hydroxyindoleacetic acid (5-HIAA) but decreased brain 5-hydroxytryptamine (5-HT).4 Aminophylline increased plasma UFA and free tryptophan and also brain tryptophan, 5-HT and 5-HIAA. Food deprivation had qualitatively similar effects.5 Insulin decreased plasma UFA and free tryptophan in both fed and food-deprived rats. However, while in fed rats these changes were associated with small decreases of brain indoles, in food-deprived animals small increases occurred.6 Nicotinic acid had only small effects in fed rats but it opposed both the UFA and indole changes in food-deprived animals. Total plasma tryptophan increased in nicotinic acid treated, food-deprived rats.7 There was a tendency towards inverse relations between changes of plasma free and total tryptophan.8 The results suggest that drugs which influence plasma UFA through actions on cyclic AMP thereby alter the binding of tryptophan to plasma protein and that this leads to altered distribution and metabolism of tryptophan.

Rapid method for the determination of 5-hydroxytryptamine and 5-hydroxyindoleacetic acid in small regions of rat brain.

A rapid and sensitive method for measuring 5-hydroxytryptamine and 5-hydroxyindoleacetic acid, using o-phthalaldehyde and L-cysteine, is presented, enabling both compounds to be measured in small areas of rat brain.

Effects of immobilization on rat liver tryptophan pyrrolase and brain 5-hydroxytryptamine metabolism.

1. Rat liver tryptophan pyrrolase increased on immobilization. The concentration of 5-hydroxyindoleacetic acid in the brain also rose and that of 5-hydroxytryptamine fell.2. When adrenalectomized rats were immobilized pyrrolase activity did not rise and brain 5-hydroxytryptamine concentration fell to a lesser extent but the 5-hydroxyindoleacetic acid concentration rose as in intact animals.3. When intact rats were injected with the pyrrolase inhibitor Allopurinol both the increase of pyrrolase and the fall of 5-hydroxytryptamine on immobilization were less prominent but the concentration of 5-hydroxyindoleacetic acid rose as before. Allopurinol did not affect the changes in immobilized adrenalectomized rats.4. Immobilization thus appears to cause (a) decreased brain 5-hydroxytryptamine synthesis resulting from pyrrolase induction and (b) increased 5-hydroxytryptamine breakdown by a more direct effect on the brain. Results of experiments on rats injected with lysergic acid diethylamide, and with alpha-methyltryptophan or probenecid are consistent with the above interpretation.5. The 5-hydroxytryptamine and 5-hydroxyindoleacetic acid changes were maximal after 5-6 hours' immobilization and became less on more prolonged immobilization, which suggests regulatory changes.