Studies of NPY/AgRP and POMC neurons from ob/ob mice as well as DIO guinea pigs and NR5A1-cre mice reveal that they undergo extensive synaptic plasticity under conditions of obesity; with the former getting more excitatory glutamatergic inputs and fewer inhibitory GABAergic inputs, and the latter receiving large number of GABAergic inputs and less glutamatergic input (49) (117); however, fasting can diminish the strength of the excitatory inputs onto POMC neurons (48). Here, NPY is linked to obesity due to melanocortin 4 receptor deficiency.