Relationships between stress and brain 5-hydroxytryptamine and their possible significance in affective disorders

L-tryptophan: a rational anti-depressant and a natural hypnotic?

L-tryptophan is an essential amino acid which is the metabolic precursor of serotonin. Because of the evidence that serotonin deficiency may be an aetiological factor in some sorts of affective disorder and that serotonin is important in the biochemistry of sleep, L-tryptophan has been suggested as a "rational" anti-depressant and as a "natural" hypnotic. This paper reviews the biochemistry and pharmacology of L-tryptophan as well as the literature of the clinical trials that have been conducted with it and suggests that, by itself, L-tryptophan may be useful in mild cases of depression accompanied by endogenous features and cases of bipolar disorder resistant to standard treatments. It also potentiates the monoamine oxidase inhibitors and possibly the serotonergic tricyclic drugs. L-tryptophan may improve the depressed mood of Parkinsonian patients and has a clinically useful hypnotic action. There is evidence it may be useful in organic mental disorders induced by levodopa. Dosage schedules, contraindications and complications are discussed.

Clinical and biochemical effects of citalopram, a selective 5-HT reuptake inhibitor--a dose-response study in depressed patients

Citalopram is a bicyclic phtalane derivative. In animal experiments, citalopram has been demonstrated to possess a potent and highly selective inhibitory effect on serotonin reuptake. Several studies in man have indicated that citalopram given in daily doses of 40-60 mg has antidepressant properties and few side effects. The present double-blind study investigated the effects of three doses of citalopram (5 mg, 25 mg, and 50 mg) on depressive symptoms and various biochemical variables in 26 depressive patients. A significant reduction of the clinical ratings of depressive symptoms occurred at all dose levels. In endogenously depressed patients, a dose of 25 or 50 mg daily seemed to have the most pronounced antidepressive effect. The side effects were few and not related to dose level. A highly significant decrease in 5-HIAA in the CSF was found. MO-PEG in the CSF was also significantly decreased, while HVA in the CSF was increased. In addition, a significant decrease in the plasma concentrations of valine, leucine, tyrosine, and histidine was found. None of the biochemical effects was dose-dependent. The complex pattern of biochemical effects indicate that the amelioration of depressive symptoms might be related to effects of citalopram on central monoaminergic mechanisms and peripheral amino acid concentrations.

Effect of brain monoamine precursors on stress-induced behavioral and neurochemical changes in aged mice

Male CF-1 mice aged 22 months showed approximately the same level of motor activity and aggressive behavior as 3-month-old mice under control (no stress) conditions, or 45 min following cold swim stress. Increasing brain catecholamine activity by dietary L-tyrosine treatment had no effect on these two age groups either under control conditions or after stress. In contrast, 30-month-old mice showed lower motor activity under control conditions which was raised significantly by supplementation of the diet with L-tyrosine. However, marked reductions in activity and aggression following stress were observed in the 30-month-old animals and these deficits were not reversed by L-tyrosine treatment prior to stress. Reduction in motor activity was greatest in stressed, 30-month-old mice on L-tyrosine supplemented diets. Compared to 3-month-old mice, the 30-month-old animals had lower brain tyrosine following dietary L-tyrosine treatment, lower brain tryptophan, norepinephrine (NE), dopamine (DA) and DOPAC, but higher HVA, serotonin (5-HT) and 5-HIAA levels. Under both control (no stress) and stress conditions, L-tyrosine pretreatment decreased brain 5-HT in the young animals, but increased 5-HT in the old mice. After stress the 30-month-old animals evidenced only slight increases in levels of blood corticosterone. Brain tyrosine was reduced by stress in the young animals but increased by stress in the old animals. Stress-induced decreases in brain NE and increases in serotonin and 5-HIAA levels were observed in both age groups. These results are consistent with hypotheses concerning age-related alterations in brain monoamine functions and adrenocortical control mechanisms.

Inhibition of rat liver tryptophan pyrrolase activity and elevation of brain tryptophan concentration by acute administration of small doses of antidepressants

1 Administration to rats of a 0.5 mg/kg dose of any of 19 antidepressants, but not that of many other drugs, causes a significant inhibition of the total enzyme and apoenzyme activities of liver tryptophan pyrrolase (of 24-48% and 37-65% respectively) and elevates brain tryptophan concentration by 13-66%. 2 When liver tryptophan pyrrolase activity is enhanced by pretreatment with cortisol or haematin, subsequent administration of a 0.5 mg/kg dose of some, but not other, antidepressants causes inhibition, which is weak (up to 38%). 3 This weak inhibition of the enhanced pyrrolase activity together with other pharmacological and physiological factors could explain the time lag between the start of antidepressant medication and the occurrence of a therapeutic response. 4 The cortisol-induced and haematin-activated pyrrolases respond differentially to inhibition by imipramine and amitriptyline, and this may explain the differential response to these two drugs of depressed patients in relation to urinary excretion of the noradrenaline metabolite 3-methoxy-4-hydroxyphenylglycol. 5 The results are discussed in relation to the mechanism of action of antidepressants and the possible involvement of disturbed hepatic tryptophan metabolism in depressive illness.

Studies of CSF 5-HIAA in depression and suicidal behaviour

The present series of studies of CSF monoamine metabolites support the hypothesis of a role for serotonin in depressive illness, insofar that depressed patients have slightly lower CSF 5-HIAA concentrations than normal controls. Apparently a normal association between CSF 5-HIAA and platelet MAO activity is disrupted in depression. The importance of serotonin does not, however, appear to be confined to depressive illness. There is a strong association between a low CSF 5-HIAA and a tendency to suicidal behaviour, also outside the setting of depression. The nature of this relationship is unclear, but it is suggested that certain personality features may form a mediating link. A connection between a low serotonin turnover and a weakened control of aggressive or hostile impulses is one possibility.

Tryptophan-nicotinamide, imipramine and their combination in depression. A controlled study

In a double-blind controlled study lasting 4 weeks 25 newly admitted severely depressed patients were randomly assigned to tryptophan-nicotinamide or imipramine or tryptophan-nicotinamide-imipramine combination. Nicotinamide was given to reduce peripheral breakdown of tryptophan. Although there were no substantial differences between the three treatments, the efficacy of tryptophan-nicotinamide tended to diminish after 2 weeks when the dose of tryptophan was increased from 4 g/day to 6 g/day and that of nicotinamide from 1.0 g/day to 1.5 g/day. The therapeutic response of patients treated with tryptophan-nicotinamide was significantly correlated with the rise in plasma tryptophan. For the tryptophan-nicotinamide-imipramine group, however, therapeutic response and rise in plasma tryptophan were negatively correlated, implying that tryptophan levels were too high in some patients. The data suggest that tryptophan-nicotamide may be as effective as imipramine in unipolar patients providing the dose is kept within the therapeutic window, and that at low doses it could also potentiate the action of tricyclic antidepressants. Bipolar patients seem to require higher doses of tryptophan than unipolar patients.

5-Hydroxytryptamine content of the whole blood in psychiatric illness and alcoholism

5-Hydroxytryptamine (5HT, serotonin) content of the whole blood has been measured in hospitalized groups of manic, depressed, schizophrenic and alcoholic patients; values were compared to non-psychotic controls. Only depressives had significantly different values. Alcoholics occupied an intermediate position between depressives and controls. Schizophrenics had virtually the same average level. Manic patients showed a very weak tendency toward higher values. Neuroleptic drugs in mania did not alter the blood 5HT levels, but in depression tricyclic antidepressants caused an elevation after 3 weeks of treatment. These post-treatment levels no longer differed significantly from those of non-psychotic controls.