Verhaltensrelevanz neurochemischer Interaktionen zwischen dem pedunculopontinen tegmentalen Nucleus und den ventralen Basalganglien

The pedunculopontine tegmental nucleus (PPTg) has an important anatomical position connecting basal ganglia and limbic systems with motor execution structures in the pons and spinal cord. It receives glutamatergic and GABAergic input and has additional reciprocal connections with mesencephalic dopaminergic neurons, suggesting that the PPTg plays a key role in fronto-striatal information processing. In vivo microdialysis in freely moving rats, in combination with behavioral analysis, was used in this study to investigate whether the dopaminergic input can be modulated at the level of the PPTg via N-methyl-D-aspartate (NMDA), α-amino-3-hydroxy-5-methyl-isoxazole-4-prpionic acid (AMPA) or GABAB receptors. Stimulation of the GABAB receptor decreased dopamine release in the PPTg while that of the AMPA and NMDA receptors increased it. A time-related comparison of the effects of NMDA (0.75 and 1 mM) and AMPA (50 and 25 μM) revealed a more long-lasting effect after AMPA stimulation than after NMDA. However, only the infusion of the GABAB receptor agonist baclofen (100 and 200 μM) stimulated stereotyped behavior (e.g. sniffing, digging or head movements) and contra lateral circling. This study clearly demonstrates that GABAergic as well as glutamatergic terminals in the PPTg are critically involved in the modulation of the dopamine system. Moreover, a decrease in PPTg dopamine via GABAB receptor stimulation seems to be behaviorally relevant.