MPTP causes Parkinsonism in primates including humans. Rodents are much less susceptible. Rats are almost immune to the adverse effects of MPTP. Mice were thought to only suffer from cell death in the substantia nigra (to differing degree according to the strain of mice used) but do not show Parkinsonian symptoms; however, most of the recent studies indicate that MPTP can result in Parkinsonism-like syndromes in mice (especially chronic syndromes). It is believed that the lower levels of MAO-B in the rodent brain's capillaries may be responsible for this.