NPY and obesity due to melanocortin 4 receptor deficiency: Deletion of Mfn1 or Mfn2 in AgRP/NPY neurons prevents fusion and impairs neuronal firing frequency in diet-induced obesity (62), illustrating that the induction of mitochondrial fusion is required for the paradoxical neuronal activation of AgRP/NPY neurons following exposure to HFD (Figure 2Cii).