MPTP susceptibility in the mouse: behavioral, neurochemical, and histological analysis of gender and strain differences

To investigate the impact of strain and sex in the l-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) animal model of Parkinson's disease, C57BL/6 and BALB/c mice were treated with either systemic MPTP-HCl (4 x 15 mg/kg) or saline and were examined in a number of behavioral tests. Furthermore, neostriatal and ventral striatal monoamine contents were determined, and the numbers of tyrosine hydroxylase-immunostained cells were counted in the substantia nigra and ventral tegmental area. Open-field testing showed that locomotor activity was drastically reduced as an acute effect of MPTP in both strains; however, subsequent recovery to control levels was faster in BALB/c mice than in C57BL/6. Nest building also indicated strain-dependent effects, since it was delayed only in C57BL/6 mice treated with MPTP. The other tests (grip test, pole test, rotarod, elevated plus-maze), although partly sensitive for over-all strain or gender differences, turned out not to be useful to compare MPTP effects in these two strains. Neurochemically, MPTP led to more severe neostriatal dopamine depletions in C57BL/6 (-85%) than in BALB/c mice (-58%). Histologically, a loss of tyrosine hydroxylase immunoreactivity (-25%) was observed only in the substantia nigra of C57BL/6 animals. Thus, our analysis consistently showed that the C57BL/6 mouse strain is more susceptible to MPTP than the BALB/c strain. Sex differences in MPTP sensitivity were not observed in our mice. The implications of these findings for the search for genes related to susceptibility to neurodegeneration are discussed.