L-tyrosine improves neuroendocrine function in a mouse model of chronic stress

Abstract

Adult BALB/c mice, individually housed, were stimulated with nine different stressors, arranged randomly, for 4 continuous weeks to generate an animal model of chronic stress. In chronically stressed mice, spontaneous locomotor activity was significantly decreased, escape latency in the Morris water maze test was prolonged, serum levels of total thyrotropin and total triiodothyronine were significantly decreased, and dopamine and norepinephrine content in the pallium, hippocampus and hypothalamus were significantly reduced. All of these changes were suppressed, to varying degrees, by L-tyrosine supplementation. These findings indicate that the neuroendocrine network plays an important role in chronic stress, and that L-tyrosine supplementation has therapeutic effects.

Keywords: L-tyrosine; chronic unpredictable stress; dopamine; neural regeneration; neuroendocrine network; norepinephrine; total thyrotropin; total triiodothyronine.

Figure 1

Escape latency trends at 1–4 weeks in the Morris water maze test. Data are presented as mean ± SD. Differences between the control group and the other two groups were tested using analysis of variance and paired sample t-test. ^aP < 0.05, vs. CUS group. CUS: Chronic and unpredictable stress; CUS-L: CUS plus L-tyrosine interference.

Figure 2

Dopamine (A) and norepinephrine (B) content in the pallium, hippocampus and hypothalamus (ng/mg). Data are presented as mean ± SD. Differences between the control group and the other two groups were tested using analysis of variance and paired sample t-test. ^aP < 0.01 and ^bP < 0.05, vs. control group; ^cP < 0.05, vs. CUS group. CUS: Chronic and unpredictable stress; CUS-L: CUS plus L-tyrosine interference.