Tyrosine prevents behavioral and neurochemical correlates of an acute stress in rats.
Exposure of rats to an acute, uncontrollable stressor can increase brain norepinephrine (NE) turnover and decrease locomotor and exploratory behavior. We examined the ability of exogenous tyrosine, NE's amino acid precursor, to protect rats from developing these neurochemical and behavioral changes when stressed. Animals pretreated with saline or tyrosine (200 mg/kg, i.p.) were subjected to tail shock (15 v, 2 mA, 5 sec/30 sec) or to no shock during a 60-min period. Exposure to shock depleted NE and increased its turnover [as indicated by altered NE and 3-methoxy-4-hydroxy-phenylene-glycol sulfate levels (MHPG-SO4)] within the locus coeruleus, the hippocampus and the hypothalamus. Behavioral deficits were observed using measures of locomotion, standing on hind legs, and hole-poking in an open-field apparatus. Animals given tyrosine before shock displayed neither shock-induced NE depletion nor the deficits in locomotion and hole-poking; brain MHPG-SO4 levels tended to be greater than after shock alone. These observations suggest that the stress caused NE to be released from some neurons more rapidly than it could be restored by synthesis or reuptake, thereby impairing noradrenergic transmission and NE-dependent exploratory behaviors. Tyrosine administration presumably enhanced the transmitter's synthesis in stressed animals, thereby preventing both the neurochemical and the behavioral deficits.
D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects*; D001923:Brain Chemistry / Q000187:drug effects*; D008297:Male; D008734:Methoxyhydroxyphenylglycol / Q000031:analogs & derivatives / Q000032:analysis; D009043:Motor Activity / Q000187:drug effects; D009638:Norepinephrine / Q000032:analysis; D051381:Rats; D011919:Rats, Inbred Strains; D013312:Stress, Physiological / Q000378:metabolism* / Q000523:psychology; D014443:Tyrosine / Q000494:pharmacology*
C030284:3-methoxy-4-hydroxyphenylglycol sulfate; D014443:Tyrosine; D008734:Methoxyhydroxyphenylglycol; D009638:Norepinephrine