In addition, ectopic expression of the neuron survival factor, glial cell line-derived neurotrophic factor, by way of adeno-associated virus, reduced food intake and decreased aging-related obesity in adult rats, associated with activation of corticotropin-releasing factor neurons in the paraventricular nucleus [36], consistent with increased melanocortin tone. Here, GDNF is linked to obesity due to melanocortin 4 receptor deficiency.