BDNF and obesity due to melanocortin 4 receptor deficiency: The implications of regulatory mechanisms on reduced SERT expression in obesity is indirectly supported by studies conducted on double knockout SERT(−/−)/brain derived neurotrophic factor (BDNF) (+/−) mice [56,57] revealing the regulatory role of either other monoamine protein markers or trophic factors on 5-HT physiology and activity on body weight balance.