INS and major depressive disorder: Appetite and satiety via GLP-1 and PYY release and direct hypothalamic actions; energy expenditure and thermogenesis (BAT activation, sympathetic outflow); glucose homeostasis (enhanced incretin effect, improved insulin sensitivity); neuroinflammation and neuroprotection (reduced microglial activation, improved synaptic plasticity; roles in neuropathic pain, depression and neurodegeneration) [68,116,118,119]