title: The catecholamine neurotransmitter precursor tyrosine increases anger during exposure to severe psychological stress.
abstract: BACKGROUND
  Acute stress produces behavioral and physiological changes modulated by central catecholamines (CA). Stress increases CA activity, and depletion of CA stores reduces responses to stress. Increasing CA activity by administration of the dietary amino acid CA precursor tyrosine may increase responsiveness to stress. This study determined whether tyrosine enhances the ability of humans to respond to severe stress.
  
  
  METHODS
  Severe psychological stress was generated during training at Survival, Evasion, Resistance, and Escape (SERE) School. The acute stressor consisted of two mock interrogations conducted during several days of simulated captivity. Seventy-eight healthy male and female military personnel participated in this double-blind, between-subjects study, in which they received either tyrosine (300 mg/kg, N = 36) or placebo (N = 36). Tyrosine (or placebo) was administered in food bars in two doses of 150 mg/kg each approximately 60 min before each mock interrogation. Mood (Profile of Mood States), saliva cortisol, and heart rate (HR) were assessed prior to stress exposure during a week of academic training preceding mock captivity and immediately following the mock interrogations.
  
  
  RESULTS
  The severe stress produced robust effects on mood (i.e., increased tension, depression, anger, fatigue, vigor, and confusion; p < .001), cortisol, and HR (p < .001). Tyrosine increased anger (p = .002, ANOVA treatment condition by test session interaction) during stress but had no other effects.
  
  
  CONCLUSIONS
  Tyrosine did not alter most subjective or physiological responses to severe acute stress, but it increased ratings of anger. The modest increase in anger may be an adaptive emotional response in stressful environments.
authors.affiliation: Military Nutrition Division, US Army Research Institute of Environmental Medicine, Kansas Street, Natick, MA, 01760, USA, harris.lieberman@us.army.mil.
authors.forename: Harris R
authors.initials: HR
authors.lastname: Lieberman
authors.forename: Lauren A
authors.initials: LA
authors.lastname: Thompson
authors.forename: Christina M
authors.initials: CM
authors.lastname: Caruso
authors.forename: Philip J
authors.initials: PJ
authors.lastname: Niro
authors.forename: Caroline R
authors.initials: CR
authors.lastname: Mahoney
authors.forename: James P
authors.initials: JP
authors.lastname: McClung
authors.forename: Gregory R
authors.initials: GR
authors.lastname: Caron
mesh_terms: D000328:Adult; D000339:Affect / Q000187:drug effects*; D000786:Anger / Q000187:drug effects*; D004311:Double-Blind Method; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D006801:Humans; D006854:Hydrocortisone / Q000032:analysis; D008297:Male; D012463:Saliva / Q000737:chemistry; D013315:Stress, Psychological / Q000523:psychology*; D014443:Tyrosine / Q000494:pharmacology*; D055815:Young Adult
chemical_list: D014443:Tyrosine; D006854:Hydrocortisone