IRS1 and major depressive disorder: The study also found that Neuron-EVPs have a higher concentration of insulin receptor substrate-1 (IRS-1) associated with suicidality and anhedonia, confirming previous research linking MDD to insulin resistance, which also impacts glutamate levels (Grillo et al., 2011; Al-Hakeim et al., 2018; Hamer et al., 2019; Nasca et al., 2021).