HTR3A and obesity due to melanocortin 4 receptor deficiency: Studies have suggested that 5-HT3 receptor expression is downregulated following short term exposure to a high fat diet (Nefti et al., 2009) and 5-HT3-dependent activation of vagal afferent neurons is attenuated in diet-induced obese mice (Daly et al., 2011) but it is unclear whether this reflects the obesity-induced generalized decrease in vagal afferent excitability or a more specific decline in 5-HT3 function.