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Lack of behavioural effects after acute tyrosine depletion in healthy volunteers

Neuroscience and Psychiatry Unit, School of Psychiatry and Behavioural Sciences, Manchester, UK, karen.lythe{at}student.manchester.ac.uk

I. M. Anderson

Neuroscience and Psychiatry Unit, School of Psychiatry and Behavioural Sciences, Manchester, UK

J. F. W. Deakin

Neuroscience and Psychiatry Unit, School of Psychiatry and Behavioural Sciences, Manchester, UK

R. Elliott

Neuroscience and Psychiatry Unit, School of Psychiatry and Behavioural Sciences, Manchester, UK

P. L. Strickland

Neuroscience and Psychiatry Unit, School of Psychiatry and Behavioural Sciences, Manchester, UK

Acute dietary tyrosine depletion has previously been shown to reduce dopamine neurotransmission in both animals and humans. In this study, we investigated the effects of brain dopamine depletion, through acute tyrosine and phenylalanine depletion, on plasma prolactin, mood and neuropsychological function in 12 normal subjects. In a randomized, double-blind, cross-over design, subjects received two amino-acid drinks separated by a week, a nutritionally balanced mixture (Bal) and on the other occasion a tyrosine and phenylalanine deficient mixture (TP-). The plasma ratio of tyrosine and phenylalanine to the other large neutral amino acids decreased significantly on the TP-occasion (-78.7%, p < 0.0001) and there was an increase in plasma prolactin concentration relative to the balanced drink in the seven subjects for whom results were available for both occasions (p < 0.02). Acute tyrosine depletion did not alter mood as measured by visual analogue scale ratings, and measures of memory, attention and behavioural inhibition were also unaffected. Our results are consistent with acute dietary tyrosine depletion causing a reduction in brain dopamine neurotransmission but raise questions about how robust or consistent the effects are on psychological function.

Key Words: dopamine • neuropsychology • prolactin • tyrosine depletion

Journal of Psychopharmacology, Vol. 19, No. 1, 5-11 (2005)
DOI: 10.1177/0269881105048886


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				A. A.-B. Badawy Acute tryptophan or tyrosine depletion test: time for reappraisal? J Psychopharmacol, July 1, 2005; 19(4): 429 - 430. [PDF]

				K. E. Lythe, I. M. Anderson, J. F. W. Deakin, R. Elliott, and P. L. Strickland Reply to Abdulla A.-B. Badawy - Acute tryptophan or tyrosine depletion test: time for reappraisal? J Psychopharmacol, July 1, 2005; 19(4): 431 - 431. [PDF]