SOD1 and Huntington disease: Sigma-1 agonists, which activate TrkB receptors, have been shown to increase BDNF levels in the rat hippocampus [21] and demonstrate neuroprotective effects [22, 23] in a non-SOD1 motor neuron disease model, Huntington's disease model, and an SOD1 ALS model through the ERK and Akt pathways downstream of TrkB [24–26].