Mood disorders tryptophan

Tryptophan depletion in healthy volunteers impairs the retrieval of learnt material (Park et al., 1994), an effect probably mediated through a selective impairment of episodic memory consolidation (Riedel et al., 1999 Schmitt et al., 2000). However, tryptophan depletion appears to have no effect on working memory (Riedel et al., 1999) and either no effect or an enhancement of tests of executive function (Park et al., 1994 Schmitt et al., 2000). Thus the abnormality in episodic memory in mood disorders could conceivably be related to an impairment in the 5-HT system, but such an impairment is unlikely to account for the abnormalities in working memory and executive function. Clearly then, changes in consciousness occurring in affective disorders are unlikely to be explainable on the basis of an abnormality in a single neurochemical system. 

Experimental tryptophan depletion studies in humans and in animals have been utilized to determine the effects of reduced serotonin levels in the brain. Since acute tryptophan depletion leads to diminished serotonin levels, it has been considered a desirable and specific way to study effects or influences of serotonin. In general, it appears that alterations in serotonin levels influence a variety of mood disorders and neuropsychiatric conditions. This raises the question of whether the administration of tryptophan may prove to be beneficial in treating some patients. This aspect is considered further in Chapter 8. 

Lucca, A., Lucini, V., Piatti, E., Ronchi, P., and Smeraldi, E., Plasma tryptophan levels and plasma tryptophan/neutral amino acids ratio in patients with mood disorder, patients with obsessive-compulsive disorder, and normal subjects, Psychiatr. Res., 44, 85, 1992. 

Klaasen T, Riedal WJ, van Someren A, Deutz NE, Honig A, van Praag HM. Mood effects of 24-hour tryptophan depletion in healthy first-degree relatives of patients with affective disorders. Biol. Psychiatry 1999 46 489-497. 

Benkelfat, C., Ellenbogen, M. A., Dean, R, Palmour, R. M., and Young, S. N., Mood-lowering effect of tryptophan depletion. Enhanced susceptibility in young men at genetic risk for major affective disorders, Arch. Gen. Psychiatr., 51, 687, 1994. 

A. M., and Benkelfat, C., The effect of tryptophan depletion on mood in medication-free, former patients with major affective disorder, Neuropsychopharmacology, 16, 294, 1997. 

The symptoms of premenstrual syndrome (PMS), also called premenstrual dysphoric disorder, include depressed mood, anxiety, affective lability, and anger or irritability.79 Since low serotonin levels are thought to be involved in the etiology of depression, aggression, and impulsivity,80 specific serotonin reuptake inhibitors have been tested in PMS. The SSRI fluoxetine was found to be better than placebo.81 Since chronic treatment with SSRIs can influence many neuron systems other than serotonin,82 Steinberg et al.83 designed a study using tryptophan, relatively specific for its effect on serotonin, on the effects of symptoms of PMS. In a randomized controlled clinical trial, 37... 

Serotonin, also known as 5-hydroxytryptamine (5-HT) is biosynthesized from tryptophan and is a neurotransmitter. Serotonin plays an important role in many behaviors including sleep, appetite, memory, and mood [52]. People with depressive disorders exhibit low levels of serotonin in the synapses. Protonated serotonin binds to a serotonin reuptake transporter protein, sometimes referred to as the serotonin transporter (SERT) and is then moved to an inward position on the neuron and subsequently released into the cjdoplasm. Selective serotonin reuptake inhibitors (SSRI) bind with high affinity to the serotonin binding site of the transporter. This leads to antidepressant effects by increasing extracellular serotonin levels which in turn enhances serotonin neurotransmission [53]. The SSRI class of antidepressants has fewer side effects than the monoamine oxidase inhibitors. 

Serotonin is derived from dietary tryptophan, an essential amino acid. A high carbohydrate (simple sugar) diet incretises the serotonin level in the brain of rats and humans. However, there is no direct evidence that an increased concentration of serotonin in the brain affects behavior. Neurologists claim that cells in the brain that reletise serotonin influence sleep. Tryptophan supplements have been used to treat various sleep disorders, and to improve the mood in depressed patients. 

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