Here, using complementary molecular techniques, we demonstrated the conservation of the coding region of BDNF and Ntrk2 across several mammalian species, the mRNA expression of both genes within the uterus, and the uterine localization of both proteins in two species that menstruate, and four that do not. Additionally, we have shown that several protein isoforms of each gene were present in the human uterus, and that the antibodies employed in this study were specific to BDNF and Ntrk2 respectively. BDNF and Ntrk2 are part of the complex messenger system that is the neurotrophins, which regulate several physiological pathways, and thus we suggest are potentially important to uterine function. Our results show that both BDNF and Ntrk2 are highly conserved across the mammalian species studied, with protein sequences having greater homology than mRNA sequences. This was not entirely unexpected, as in some cases multiple codons exist for a single amino acid, and thus a base-pair substitution in the mRNA sequence might not alter the protein. Over time, as each of the species studied evolved, silent mutations in the genes likely arose. During evolution, Gotz et al., suggest that BDNF was more highly conserved than NGF across vertebrates. In our study the PCR primer pairs designed to isolate BDNF and Ntrk2 were capable of doing so in the uterus of all animals, and both antibodies employed in this study demonstrated specific uterine immunoreactivity for BDNF and Ntrk2 in each of the six mammals examined, supporting high sequence homology amongst orthologs over evolution. Doxorubicin Antibody specificity in the current study was ascertained in two ways. Firstly, by ensuring bands of the appropriate size were seen when Western blot was performed with human recombinant BDNF and Ntrk2. Secondly, mouse brain sections were stained for BDNF and Ntrk2 with primary antibodies which had been pre-absorbed with BDNF and Ntrk2, respectively. In sections incubated with pre-absorbed BDNF primary antibodies the staining was less intense than the positive control, which had been stained with anti-BDNF, but more intense than the negative control. Ideally pre-absorption obliterates all staining as the antibody should be completely bound by the excess protein. In the case of pre-absorbed BDNF, some of the BDNF bound to the antiBDNF antibody may have bound to endogenous Ntrk2 receptors, and thus given a faint signal when the secondary antibody was applied. Ntrk2 staining in the mouse brain was obliterated by preabsorption. The results of the antibody specificity tests indicated that the antibodies used for immunohistochemistry and Western blot were specific and capable of detecting BDNF and Ntrk2 within the mammalian uterus. While there are a few studies demonstrating the independent expression of BDNF and Ntrk2 in the uterus, the results of the present 
study are the first to show that both ligand and receptor are co-expressed, and co-localized in the uterus of several mammalian species. Our results show BDNF and Ntrk2 expression in the glandular epithelium, luminal epithelium, vascular smooth muscle, and myometrium of the human, mouse, rat, pig, and bat uterus. A GW786034 similar pattern of expression was also observed in the uterus of the pregnant mare. This is the first comprehensive and cross-species comparison of BDNF and Ntrk2 mRNA, and protein in the mammalian uterus.