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Effects of acute tryptophan depletion on executive function in healthy male volunteers.

Gallagher P, Massey AE, Young AH, McAllister-Williams RH - BMC Psychiatry (2003)

Bottom Line: Plasma free and total tryptophan concentrations were significantly reduced by the depleting drink (P < 0.001).ATD selectively improved motor speed/ attention on the Trails A test (P = 0.027), with no effect on subjective ratings of mood.Interaction effects between drink and the order of drink administration were observed on most neurocognitive tests.

View Article: PubMed Central - HTML - PubMed

Affiliation: Stanley Research Centre, School of Neurology, Neurobiology and Psychiatry, University of Newcastle upon Tyne, NE1 4LP, UK. peter.gallagher@ncl.ac.uk

ABSTRACT

Background: Neurocognitive impairment is frequently described in a number of psychiatric disorders and may be a direct consequence of serotonergic dysfunction. As impairments in executive functions are some of the most frequently described, the purpose of this study was to examine the performance of normal volunteers on a range of executive tasks following a transient reduction of central serotonin (5-HT) levels using the method of acute tryptophan depletion (ATD).

Methods: Fifteen healthy male subjects participated in a within-subject, double-blind, counterbalanced crossover study. ATD was induced by ingestion of a 100 g amino-acid drink. Executive function was evaluated using the Wisconsin Card Sorting Test, Stroop, Verbal Fluency and Trail Making. Visual analogue scales were administered to assess mood.

Results: Plasma free and total tryptophan concentrations were significantly reduced by the depleting drink (P < 0.001). ATD selectively improved motor speed/ attention on the Trails A test (P = 0.027), with no effect on subjective ratings of mood. Interaction effects between drink and the order of drink administration were observed on most neurocognitive tests.

Conclusions: The improvement in simple motor speed/ attention following ATD is in keeping with the ascribed role of 5-HT in the cortex, however performance on tests of executive function is not robustly altered. The presence of interaction effects on most tasks suggests that subtle changes may occur but are masked, possibly by simple learning effects, in the context of a crossover design. This has implications for the design of future studies, particularly those examining executive functions.

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Related in: MedlinePlus

Drink by order interactions from the Stroop test
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Figure 2: Drink by order interactions from the Stroop test

Mentions: A similar overall pattern emerged in the interactions from the Stroop test. In subjects who were depleted on the second visit, latencies were significantly reduced for the 'CW' component (t = -2.712, df = 5, P = 0.042) and the interference index (t = -2.607, df = 5, P = 0.048) following ATD. In subjects who were depleted on the first visit, the 'CW' latency was significantly lower following the control drink (t = -2.333, df = 8, P = 0.048) although the difference in the interference index did not reach significance (t = -1.809, df = 8, P = 0.108) (See figure 2).


Effects of acute tryptophan depletion on executive function in healthy male volunteers.

Gallagher P, Massey AE, Young AH, McAllister-Williams RH - BMC Psychiatry (2003)

Drink by order interactions from the Stroop test
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC184453&req=5

Figure 2: Drink by order interactions from the Stroop test
Mentions: A similar overall pattern emerged in the interactions from the Stroop test. In subjects who were depleted on the second visit, latencies were significantly reduced for the 'CW' component (t = -2.712, df = 5, P = 0.042) and the interference index (t = -2.607, df = 5, P = 0.048) following ATD. In subjects who were depleted on the first visit, the 'CW' latency was significantly lower following the control drink (t = -2.333, df = 8, P = 0.048) although the difference in the interference index did not reach significance (t = -1.809, df = 8, P = 0.108) (See figure 2).

Bottom Line: Plasma free and total tryptophan concentrations were significantly reduced by the depleting drink (P < 0.001).ATD selectively improved motor speed/ attention on the Trails A test (P = 0.027), with no effect on subjective ratings of mood.Interaction effects between drink and the order of drink administration were observed on most neurocognitive tests.

View Article: PubMed Central - HTML - PubMed

Affiliation: Stanley Research Centre, School of Neurology, Neurobiology and Psychiatry, University of Newcastle upon Tyne, NE1 4LP, UK. peter.gallagher@ncl.ac.uk

ABSTRACT

Background: Neurocognitive impairment is frequently described in a number of psychiatric disorders and may be a direct consequence of serotonergic dysfunction. As impairments in executive functions are some of the most frequently described, the purpose of this study was to examine the performance of normal volunteers on a range of executive tasks following a transient reduction of central serotonin (5-HT) levels using the method of acute tryptophan depletion (ATD).

Methods: Fifteen healthy male subjects participated in a within-subject, double-blind, counterbalanced crossover study. ATD was induced by ingestion of a 100 g amino-acid drink. Executive function was evaluated using the Wisconsin Card Sorting Test, Stroop, Verbal Fluency and Trail Making. Visual analogue scales were administered to assess mood.

Results: Plasma free and total tryptophan concentrations were significantly reduced by the depleting drink (P < 0.001). ATD selectively improved motor speed/ attention on the Trails A test (P = 0.027), with no effect on subjective ratings of mood. Interaction effects between drink and the order of drink administration were observed on most neurocognitive tests.

Conclusions: The improvement in simple motor speed/ attention following ATD is in keeping with the ascribed role of 5-HT in the cortex, however performance on tests of executive function is not robustly altered. The presence of interaction effects on most tasks suggests that subtle changes may occur but are masked, possibly by simple learning effects, in the context of a crossover design. This has implications for the design of future studies, particularly those examining executive functions.

Show MeSH
Related in: MedlinePlus