Psychiatry - Theses

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Subject: catecholamine × Subject: acute tyrosine and phenylalanine depletion × Author: Letic, Tony Robert ×

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    The effects of catecholamine depletion and acute psychosocial stress on neurocognition
    Letic, Tony Robert ( 2012)
    Extensive research has clearly established that neurocognition is negatively impacted by various stressors. While the extant research has focused on the effects of cortisol on declarative memory, little attention has been given to the role of the catecholamines in the deterioration of neurocognitive performance following psychosocial stress. Forty healthy male (n = 21) and female (n = 19) volunteers aged between 18-47 years who had been screened for eligibility participated in the study. Heart rate, blood pressure and salivary cortisol were measured at baseline, pre-stress, post stress (immediate) and after one hour of rest (post stress recovery). Neurocognitive assessment included immediate and delayed verbal recall, spatial learning and strategy, attention and working memory (spatial and non-spatial) at the same four phases. Participants randomly received an L-tyrosine and L-phenylalanine depleted (DEP) or a nutritionally balanced (BAL) amino acid drink in a randomised, double blind, placebo-controlled parallel group design 5 hrs before exposure to the Trier Social Stress Test (TSST). The ratio of L-tyrosine and L-phenylalanine to the sum of other large neutral amino acids (ΣLNAAs) in plasma were both significantly reduced by -80% at the post-ingestion period (5 h) compared to baseline. Exposure to the TSST for both ATPD and balanced-treated participants resulted in the robust stimulation of the sympathomedullary (SAM) and hypothalamic-pituitary adrenocortical (HPA) axes. This was demonstrated by significant increases in heart rate and blood pressure immediately after stress exposure compared to baseline in both ATPD and balanced conditions. Salivary cortisol levels significantly increased immediately after the completion of the TSST compared to pre-stress levels. There were a limited number of effects of the TSST combined with ATPD on measures of neuropsychological performance. These outcomes suggest that neurocognition is not severely impacted by acute social stress under conditions of catecholamine depletion.