GHRL and obesity due to melanocortin 4 receptor deficiency: Furthermore, in vivo fiber photometry recordings reveal obesity-driven reductions in intragastric nutrient- or hormone-induced modulation of AgRP neurons, which may either promote or reduce food intake (e.g., via desensitization of AgRP responses to intragastric infusion of fat or blunting of ghrelin-induced AgRP neuron activation, respectively)25,43.