Exogenous L-lactate promotes astrocyte plasticity but is not sufficient for enhancing striatal synaptogenesis or motor learning in mice
L-lactate is an energetic and signaling molecule that is key to the metabolic and neuroplastic connection between astrocytes and neurons and may be involved in exercise-induced neuroplasticity. This study sought to explore the role of L-lactate in astrocyte reactivity and neuroplasticity. Using in vitro cultures of primary astrocytes, we show L-lactate increased expression of plasticity-related genes, including neurotrophic factors, Bdnf, Gdnf, Cntf and the immediate early gene cFos. L-lactates promotion of neurotrophic factor expression may be mediated in part by the lactate receptor HCAR1 since application of the HCAR1 agonist 3,5-DHBA also increased expression of Bdnf in primary astrocytes. In vivo L-lactate administration to healthy mice caused a similar increase in the expression of plasticity-related genes as well as increased astrocyte morphological complexity in a region-specific manner, with increased astrocytic response found in the striatum but not the ectorhinal cortex, regions of the brain where increases in regional cerebral blood flow are increased or unaltered, respectively, with motor behavior. Additionally, L-lactate administration did not cause synaptogenesis or improve motor behavior based on the latency to fall on the accelerating rotarod, suggesting that L-lactate administration can initiate astrocyte-specific gene expression, but the activation of motor circuits is necessary to initiate striatal neuroplasticity. These results suggest that peripheral L-lactate is likely an important molecular component of exercise-induced neuroplasticity by acting in an astrocyte-specific manner to prime the brain for neuroplasticity.