The Effects of Essential Amino Acid Supplementation on Hippocampal Neurotrophin, Dopaminergic and Serotonergic Changes in an Overtraining Mouse Model

<b>Background/Objectives</b>: This study examined the efficacy of essential amino acid (EAA) supplementation on changes in behavior and hippocampal neurotrophin, dopaminergic and serotonergic markers to a volume overload stress resembling an overtraining syndrome. <b>Methods</b>: Thirty-two 3-month-old male C57Bl/6J mice were randomized into four groups: Resistance training (RT), resistance training with overtraining (RTO), resistance training with overtraining and EAA (RTOEAA), or control. Mice in RTOEAA received EAA supplementation (1.5 g·kg·day^-1), while the other groups received a sham treatment. A 5-week resistance training protocol was employed. Training volume was increased two-fold during the final two weeks for RTO and RTOEAA to cause the OTS. EAA intervention for RTOEAA occurred during the OTS. <b>Results</b>: A significant decline in the maximum resistance carrying load in RTO compared to RT (<i>p</i> = 0.002) and RTOEAA (<i>p</i> = 0.029) confirmed that the animals in that group were overtrained. Significantly greater average latency times for RTO compared to RT (<i>p</i> = 0.009) and C (<i>p</i> = 0.05) indicated that the OTS caused spatial memory deficits in animals that were not supplemented. These latter changes may have been related to the significant declines in brain derived neurotrophic (BDNF) expression and elevations in dopamine 1 receptor (D1R) expressions. Increased resiliency for RTOEAA may have been related to the effect of EAA on stimulating significant increases in the expression of hippocampal tyrosine receptor kinase B (TrkB) and serotonin receptors (5-HT1A). <b>Conclusions</b>: EAA supplementation during a resistance model of overtraining appeared to provide increased resiliency to OTS by maintaining neurotrophin expression and enhancing serotonergic adaptation.