animal experiment nonhuman 63 controlled study 61 Article 59 Animals 55 metabolism 55 animal 54 animal model 49 animal tissue 41 mouse 40 male 38 animal cell 32 genetics 32 human 31 unclassified drug 30 Humans 27 gene expression 26 protein expression 25 Mice 24 female 24 in vivo study 24 upregulation 22 Male 21 human cell 21 pathology 21 rat 21 down regulation 20 gene expression regulation 20 in vitro study 20 Rats 17