Mouse Cat Research Articles

Does Toxoplasma infection increase sexual masochism and submissiveness? Yes and no

ABSTRACTThe parasite Toxoplasma needs to get from its intermediate hosts, e.g. rodents, to its definitive hosts, cats, by predation. To increase the probability of this occurrence, Toxoplasma manipulates the behavior of its hosts, for example, by the demethylation of promoters of certain genes in the host's amygdala. After this modification, the stimuli that normally activate fear-related circuits, e.g., the smell of a cat in mice, or smell of leopards in chimpanzees, start to additionally co-activate sexual arousal-related circuits in the infected animals. In humans, the increased attraction to masochistic sexual practices was recently observed in a study performed on 36,564 subjects. Here I show that lower rather than higher attraction to sexual masochism and submissiveness among infected subjects is detected if simple univariate tests instead of multivariate tests are applied to the same data. I show and discuss that when analyzing multiple effects of complex stimuli on complex biological systems we need to use multivariate techniques and very large data sets. We must also accept the fact that any single factor usually explains only a small fraction of variability in the focal variable.

Limited proteolytic processing of the mature form of cathepsin D in human and mouse brain: Postmortem stability of enzyme structure and activity

The mature form of cathepsin D (Cat D), purified to homogeneity from postmortem human brain or mouse brain, behaved as a 42-kDa protein in its native state but revealed additional proteolytic processing under denaturing conditions. Human brain Cat D was composed of a 30–32 kDa heavy chain and a protein doublet consisting of 14 and 15 kDa light chains. Mouse Cat D, which closely resembled the human enzyme in amino acid composition, existed mainly as the uncleaved 42-kDa protein, but up to 40% existed as a complex of 30–32 kDa and 12–14 kDa chains. The 3 : 1 ratio of light to heavy (30–32 kDa) chains suggested processing of some 30-kDa chains. Cleavage of the 42-kDa chain could not be induced autolytically. Human brain Cat D had a 2–3-fold higher specific activity than the mouse enzyme but shared other properties, including similar biphasic pH optima (peaks at pH 3.0 and 4.2), K values for methemoglobin and inhibitor profiles. Human Cat D displayed the same polypeptide chain composition when purified from brains differing in postmortem interval (3–28 h). Fresh SH-SY5Y human neuroblastoma cells analyzed on Western blots with anti-Cat D antibodies also displayed only cleaved forms of mature Cat D. Furthermore, brain Cat D isolated from mice stored after death for 5, 15 or 30 h at 25°C contained the same molar ratios of cleaved and uncleaved enzyme found in fresh mouse brain. Cat D activity was stable in human brains with postmortem intervals up to 27 h and stored frozen for up to 3 years. Similarly, total Cat D activity was essentially unchanged in brains of mice subjected to simulated postmortem conditions for 0.5–42 h, although 20% of the total soluble brain protein became insoluble during this postmortem interval. These results demonstrate a remarkable postmortem stability of Cat D and strongly suggest that limited proteolytic cleavage of mature brain Cat D is an in vivo event, the extent of which varies markedly in different species.