Inhibitory Effects of Talipexole and Pramipexole on MPTP-Induced Dopamine Reduction in the Striatum of C57BL/6N Mice

Neurobiological and Pharmacological Perspectives of D3 Receptors in Parkinson’s Disease

The discovery of the D3 receptor (D3R) subtypes of dopamine (DA) has generated an understandable increase in interest in the field of neurological diseases, especially Parkinson’s disease (PD). Indeed, although DA replacement therapy with l-DOPA has provided an effective treatment for patients with PD, it is responsible for invalidating abnormal involuntary movements, known as L-DOPA-induced dyskinesia, which constitutes a serious limitation of the use of this therapy. Of particular interest is the finding that chronic l-DOPA treatment can trigger the expression of D1R–D3R heteromeric interactions in the dorsal striatum. The D3R is expressed in various tissues of the central nervous system, including the striatum. Compelling research has focused on striatal D3Rs in the context of PD and motor side effects, including dyskinesia, occurring with DA replacement therapy. Therefore, this review will briefly describe the basal ganglia (BG) and the DA transmission within these brain regions, before going into more detail with regard to the role of D3Rs in PD and their participation in the current treatments. Numerous studies have also highlighted specific interactions between D1Rs and D3Rs that could promote dyskinesia. Finally, this review will also address the possibility that D3Rs located outside of the BG may mediate some of the effects of DA replacement therapy.

Release and aggregation of cytochrome c and alpha-synuclein are inhibited by the antiparkinsonian drugs, talipexole and pramipexole

Recently, it has been shown that release of cytochrome c from the mitochondria to the cytosol is required for activation of the caspase-3-dependent cascade in apoptosis, and also for alpha-synuclein aggregation. In the present study, we examined the effects of talipexole and pramipexole on the release of cytochrome c and alpha-synuclein, their aggregations, and activation of caspases. Treatment of human neuroblastoma SH-SY5Y cells with 1-methyl-4-phenylpyridinium (MPP(+), 1 mM) induced the first event, which was the release of cytochrome c from the organellar fraction to the cytosolic fraction, then came the DNA fragmentation, and caused the last event, which was the accumulation of alpha-synuclein protein in the cytosolic fraction. Talipexole and pramipexole at low concentration (0.1-1 mM) significantly inhibited the accumulation of cytochrome c or alpha-synuclein in the cytosolic fraction. These drugs at high concentration (3-10 mM) inhibited in vitro aggregation of cytochrome c by hydrogen peroxide or that of alpha-synuclein by cytochrome c and hydrogen peroxide. In addition, in vitro activation of caspase-3 induced by cytochrome c and/or dATP was also inhibited by drugs at high concentration (5-10 mM). These results suggest that talipexole and pramipexole may have protective effects against the neurodegeneration, which is induced by intracellular accumulation of cytochrome c and alpha-synuclein.

Increase of bcl-2 protein in neuronal dendritic processes of cerebral cortex and hippocampus by the antiparkinsonian drugs, talipexole and pramipexole

Treatment of rats for 4 days with the antiparkinsonian drugs, talipexole and pramipexole, markedly increased Bcl-2 immunoreactivity in neuronal dendritic processes in both cerebral cortex and hippocampus, but treatment for 1 day with either of these drugs did not. Repeated administration of talipexole or pramipexole may have neuroprotective effect in neurodegenerative disorders.