However, considering our finding of a lack of decrease in the number of 5-HT neurons in the MRN and DRN of VGLUT3 KO mice, as determined by unbiased stereological counting and fluorescent in situ hybridization, our in vitro observations suggest the possibility that although basal survival may be unchanged in VGLUT3 KO mice, 5-HT neurons in these animals may be more vulnerable to cellular stress, such as in the context of Parkinson’s disease, a pathology in which a subset of 5-HT neurons are lost in addition to DA neurons. This evidence concerns the gene SLC17A8 and Parkinson disease.