Separation-induced body weight loss, impairment in alternation behavior, and autonomic tone: effects of tyrosine

Pharmacol Biochem Behav. 2001 Feb;68(2):273-81. doi: 10.1016/s0091-3057(00)00448-2.

Abstract

We have investigated the effects of tyrosine on alternation behavior and hippocampal adrenergic and cholinergic tone in a model of self-induced weight loss caused by separation stress. Separation decreased body weight in mice (P < .001) and spontaneous alternations in the T-maze (P < .001). This impairment was associated with depletion of both norepinephrine (NE, P < .001) and dopamine (P < .01) while increasing MHPG (P < .05) and the ratio of MHPG/NE (P < .05). Increasing tyrosine availability restored performance to control levels (P < .001) and repleted dopamine (P < .05) and presumably also NE (indicated by increases in both MHPG, P < .001, and MHPG/NE, P < .05). Stress increased adrenergic alpha(2)-receptor density (P < .001) without changing its K(d) and the B(max) and K(d) of beta-receptors, suggesting that it decreased NE transmission through action on alpha(2)-receptors. The balance between beta- and alpha(2)-receptors appeared to be related to alternation behavior as shown by the decrease (P < .01) and increase (P < .05) in their ratios induced by stress and tyrosine, respectively. With regard to cholinergic tone, separation stress increased M1 receptor density (P < .05) and its mRNA signal (P < .001). Tyrosine further increased M1 receptor density of stressed mice (P < .05). Tyrosine might be a potential therapy for cognitive and mood problems associated with the maintenance of a reduced body weight in the treatment of obesity and in the extreme case of anorexia nervosa.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Behavior, Animal / drug effects*
  • Behavior, Animal / physiology
  • Carrier Proteins / drug effects
  • Carrier Proteins / metabolism
  • Dopamine / metabolism*
  • Female
  • Hippocampus / drug effects
  • Hippocampus / metabolism
  • Methoxyhydroxyphenylglycol / metabolism
  • Mice
  • Norepinephrine / metabolism*
  • Receptor, Muscarinic M1
  • Receptors, Adrenergic, alpha-2 / drug effects
  • Receptors, Adrenergic, alpha-2 / metabolism
  • Receptors, Adrenergic, beta / drug effects
  • Receptors, Adrenergic, beta / metabolism
  • Receptors, Muscarinic / drug effects
  • Receptors, Muscarinic / metabolism
  • Stress, Psychological / metabolism*
  • Stress, Psychological / psychology
  • Tyrosine / pharmacology*
  • Weight Loss* / drug effects
  • Weight Loss* / physiology

Substances

  • Carrier Proteins
  • Receptor, Muscarinic M1
  • Receptors, Adrenergic, alpha-2
  • Receptors, Adrenergic, beta
  • Receptors, Muscarinic
  • Tyrosine
  • Methoxyhydroxyphenylglycol
  • Dopamine
  • Norepinephrine