GDNF levels in the serum have been reported to increase following ECT in TRD patients; this effect was described as attributable to responders, since no significant change was observed in non-responders, suggesting that successful ECT is associated with enhanced GDNF [67]; in another study on rats subjected to ECS, decreased GDNF concentrations were noted in the hippocampus and the striatum, accompanied by increased levels of NGF in the frontal cortex [68]. This evidence concerns the gene GDNF and treatment resistant depression.