MPTP treatment impairs tyrosine hydroxylase immunopositive fibers not only in the striatum, but also in the amygdala.

Parkinson's disease (PD) is characterized by a triad of symptoms (tremor, rigidity, and bradykinesia). Aside from this, emotional deficits are known to be associated with PD. A key structure of emotional processing is the amygdala. Emotional deficits seen in PD might be due to alterations in the catecholaminergic innervation of this limbic structure. We therefore examined whether 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) applied to C57/BL6 mice (an animal model of PD) affects the density of tyrosine hydroxylase (TH) immunoreactive fibers in the amygdala as it does in the striatum. MPTP treatment caused a prominent reduction in dopamine levels (about -70%) in the striatum (determined by high-performance liquid chromatography and electrochemical detection), accompanied by massive losses of TH-positive fibers in the striatum (-48.3%). Moreover, MPTP treatment caused prominent reductions of TH-positive fiber densities in the basolateral, lateral and central nucleus of the amygdala (about -20%). These results may provide the morphological basis for behavioral studies analyzing altered emotional responses in animal models of PD.