Separation-induced body weight loss, impairment in alternation behavior, and autonomic tone: effects of tyrosine.
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.
Hao
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Department of Human Nutrition and Metabolism, Hadassah Medical School, Hebrew University, Jerusalem, Israel.
Avraham
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Y
Bonne
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Berry
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EM
D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects* / Q000502:physiology; D002352:Carrier Proteins / Q000187:drug effects / Q000378:metabolism; D004298:Dopamine / Q000378:metabolism*; D005260:Female; D006624:Hippocampus / Q000187:drug effects / Q000378:metabolism; D008734:Methoxyhydroxyphenylglycol / Q000378:metabolism; D051379:Mice; D009638:Norepinephrine / Q000378:metabolism*; D043643:Receptor, Muscarinic M1; D018341:Receptors, Adrenergic, alpha-2 / Q000187:drug effects / Q000378:metabolism; D011943:Receptors, Adrenergic, beta / Q000187:drug effects / Q000378:metabolism; D011976:Receptors, Muscarinic / Q000187:drug effects / Q000378:metabolism; D013315:Stress, Psychological / Q000378:metabolism* / Q000523:psychology; D014443:Tyrosine / Q000494:pharmacology*; D015431:Weight Loss / Q000187:drug effects / Q000502:physiology
D002352:Carrier Proteins; D043643:Receptor, Muscarinic M1; D018341:Receptors, Adrenergic, alpha-2; D011943:Receptors, Adrenergic, beta; D011976:Receptors, Muscarinic; D014443:Tyrosine; D008734:Methoxyhydroxyphenylglycol; D004298:Dopamine; D009638:Norepinephrine