Influence of tryptophan availability on selection of alcohol and water by men

Effects of Rumen-Protected L-Tryptophan Supplementation on Productivity, Physiological Indicators, Blood Profiles, and Heat Shock Protein Gene Expression in Lactating Holstein Cows under Heat Stress Conditions

In this study, we examined the effects of rumen-protected L-tryptophan supplementation on the productivity and physiological metabolic indicators in lactating Holstein cows under heat stress conditions. The study involved eight early lactating Holstein cows (days in milk = 40 ± 9 days; milk yield 30 ± 1.5 kg/day; parity 1.09 ± 0.05, p < 0.05), four cows per experiment, with environmentally controlled chambers. In each experiment, two distinct heat stress conditions were created: a low-temperature and low-humidity (LTLH) condition at 25 °C with 35-50% humidity and a high-temperature and high-humidity (HTHH) condition at 31 °C with 80-95% humidity. During the adaptation phase, the cows were subjected to LTLH and HTHH conditions for 3 days. This was followed by a 4-day heat stress phase and then by a 7-day phase of heat stress, which were complemented by supplementation with rumen-protected L-tryptophan (ACT). The findings revealed that supplementation with ACT increased dry matter intake as well as milk yield and protein and decreased water intake, heart rate, and rectal temperature in the HTHH group (p < 0.05). For plateletcrit (PCT, p = 0.0600), the eosinophil percentage (EOS, p = 0.0880) showed a tendency to be lower, while the monocyte (MONO) and large unstained cells (LUC) amounts were increased in both groups (p < 0.05). Albumin and glucose levels were lower in the HTHH group (p < 0.05). The gene expressions of heat shock proteins 70 and 90 in the peripheral blood mononuclear cells were higher in the ACT group (HTHH, p < 0.05). These results suggest that ACT supplementation improved productivity, physiological indicators, blood characteristics, and gene expression in the peripheral blood mononuclear cells of early lactating Holstein cows under heat-stress conditions. In particular, ACT supplementation objectively relieved stress in these animals, suggesting that L-tryptophan has potential as a viable solution for combating heat-stress-induced effects on the cattle in dairy farming.

Serotonergic function, substance craving, and psychopathology in detoxified alcohol-addicted males undergoing tryptophan depletion

Alcohol addiction is associated with alterations of central nervous dopaminergic and serotonergic functions. Acute tryptophan depletion has not yet been applied in detoxified alcohol-addicted patients in order to investigate its impact on psychopathology, psychoneuroendocrinology, and substance craving behaviour. 25 alcohol-addicted males randomly either received a tryptophan-free or tryptophan-containing amino acid drink and 7 days later the respective other drink. Anxiety, depression, and craving were assessed before and 5 h after the drink. Tryptophan, 5-HIAA, dopamine, norepinephrine, epinephrine, and HVA in serum were measured before and after both treatments. Nocturnal urinary cortisol measurements and genotyping for the HTTLPR polymorphism of the SLC6A4 gene were performed. Tryptophan depletion resulted in a significant reduction of total and free serum tryptophan while the tryptophan-rich drink increased serum levels. Both treatments caused a significant increase of serum serotonin levels, however, serum 5-HIAA was decreased after depletion but increased after sham depletion. Dopamine and norepinephrine were elevated after tryptophan depletion and sham. Depletion increased depression scores (MADRS), while the full amino acid drink improved state and trait anxiety ratings (STAI) and substance craving. Urinary cortisol excretion was not affected by both treatments. Patients with the ll genotype of the serotonin transporter gene displayed lower baseline tryptophan levels compared to patients with the heterozygous genotype. Results suggest an impaired serotonergic function in alcohol-addicted males.

Rapid depletion of plasma tryptophan: a review of studies and experimental methodology

Evidence that the neurotransmitter serotonin (5-hydroxytryptamine, 5-HT) plays a role in the pathophysiology of mood disorders has been accumulating over the past three decades. Recent studies on this neurotransmitter have extended across the spectrum of psychiatric disorder, suggesting a role for 5-HT in psychosis, aggression, eating disorders and addiction. However, much of the evidence has come from post-mortem examination of the brain or measures of peripheral rather than central 5-HT function. The technique of tryptophan depletion allows investigation of brain 5-HT function in living subjects by examining the behavioural responses to this pharmacological challenge. This review considers the current status of tryptophan depletion as an experimental technique and discusses the implications of findings both in affective disorders and in a range of other psychiatric syndromes. MEDLINE and PSYCHLIT searches were completed for the years 1966 to November 1996 using the key words 'serotonin', '5-hydroxytryptamine', 'tryptophan' and 'depletion'. In addition relevant journals were hand-searched for the period from 1980 to December 1996. Forty-four double-blind studies in humans and three clinical case reports were identified; these cover a range of psychiatric disorders including mood disorders and psychoses, anxiety and eating disorders and specific behaviours such as appetite, aggression and craving. The studies reviewed utilized a variety of differing methodologies reducing the extent to which results can be generalized. A series of studies in depressed patients (before and after treatment with antidepressants) and their first-degree relatives have shown the importance of an intact 5-HT system in the action of antidepressants and offer new insights into the biology of affective disorder. The mood change induced by tryptophan depletion may predict those patients likely to respond to 5-HT-specific drugs. Rapid tryptophan depletion has also been reported to exacerbate both panic and aggression in vulnerable individuals. Effects in other disorders are conflicting and further research is needed to clarify these findings.

Effect of ethanol on extracellular 5-HT and glutamate in the nucleus accumbens and prefrontal cortex: comparison between the Lewis and Fischer 344 rat strains

The present study investigated the impact of systemic (i.p.) ethanol administration on extracellular levels of serotonin and glutamate in the prefrontal cortex and the nucleus accumbens in Lewis and Fischer 344 rat strains using in vivo microdialysis. At 1.0 g/kg, ethanol elicited a significant increase in nucleus accumbens-dialysate levels of both 5-HT (44% +/- 16, P = 0.002) and glutmate (90% +/- 43, P = 0.009) in Lewis rats. In Fischer rats, there was no increase in 5-HT (6% +/- 7: P = 0.5), and a trend toward an increase in glutamate (88% +/- 46: P = 0.1). The 0.5 and 2.0 g/kg doses did not result in any significant change in extracellular 5-HT or glutamate in the nucleus accumbens or prefrontal cortex of either strain. The basal levels of glutamate, in both brain regions, were significantly lower in Lewis than in Fischer 344 rats. The basal levels of 5-HT were also lower in the nucleus accumbens of Lewis rats. These findings suggest that enhanced sensitivity of the mesoaccumbens 5-HT or glutamate systems to ethanol and/or inherent low basal levels of 5-HT or glutamate activity may be associated with the predisposition to alcohol-drinking behavior seen in Lewis rats.

Acute effect of altered tryptophan levels and alcohol on aggression in normal human males

Normal males received amino acid mixtures designed to raise or lower tryptophan availability, and thus to raise or lower brain serotonin synthesis. They also received alcoholic or non-alcoholic drinks. The subjects were tested in the Taylor Competitive Reaction Time Task in which they competed against a (non-existent) partner in a reaction time task. The magnitude of electric shocks that the subjects were willing to give to their bogus partner was used as a measure of aggression. Lowered tryptophan levels and ingestion of alcohol were associated with increased aggression. Our data support the idea that low serotonin levels may be involved in the etiology of aggression. They suggest that subjects with low brain serotonin levels may be particularly susceptible to alcohol-induced violence.

Serotonin and alcohol intake, abuse, and dependence: clinical evidence

A large body of literature has emerged concerning the role of the neurotransmitter serotonin (5-hydroxytryptamine, or 5-HT) in the regulation of alcohol intake and the development of alcoholism. Despite the wealth of information, the functional significance of this neurotransmitter remains to be fully elucidated. This paper, part one of a two-part review, summarizes the available clinical research along two lines: the effects of alcohol on serotonergic functioning and the effects of pharmacological manipulation of serotonergic functioning on alcohol intake in normal (nonalcohol dependent) and alcohol-dependent individuals. It is concluded that considerable evidence exists to support the notion that some alcoholic individuals may have lowered central serotonin neurotransmission.

Cardiovascular reactivity as a predictor of alcohol consumption in a taste test situation

The existence of a relationship between cardiovascular reactivity to signalled shock and alcohol consumption can be inferred from studies of males at increased familial risk for alcoholism. The present study examined two groups of nonalcoholic men--those with multigenerational histories (MGH) of alcoholism and family--history negative (FH-) controls-to determine whether reactivity was related to voluntary ethanol consumption in the context of a beverage taste test. High reactors, a significant majority of whom were MGH males, drank significantly more vodka and orange juice, rum and coke, and orange juice when asked to rate the flavor of three alcoholic and two nonalcoholic drinks. High reactors also consumed more alcohol on a weekly basis according to their self-report.

Biochemical aspects of tryptophan depletion in primates

We studied the degree of plasma tryptophan depletion produced by giving normal human males different amounts of a tryptophan-free (T-) amino acid mixture. From the results of this and other studies we concluded that the maximum degree of tryptophan depletion can be produced by a 31.5 g mixture of seven essential amino acids. Administration of a T- amino acid mixture to vervet monkeys lowered tryptophan and 5-hydroxyindoleacetic acid in the cerebrospinal fluid. Levels of tyrosine and the catecholamine metabolites were unchanged. These data support the idea that the effects of T- mixture on mental function in humans which have been reported previously are due to a decrease in 5-hydroxytryptamine.