Figure 7

Potential neural pathways involved in motor behavior modulated by mGluR5. (A) Shows schematic representing CNS regions where MPEP injections were performed and the possible neural pathways involved in the behavioral findings following mGluR5 blockage. (1) MPEP injection on the main olfactory bulb (MOB) led to an increase in the distance traveled in the center of the arena and to decreased motor performance on the rotarod. (2) MPEP injection into the primary motor area (M1) led to a decrease in locomotion in the open field and to decreased rotarod performance. (3) The blockage of mGluR5 in the dorsolateral striatum (DLStr) led to increased locomotor activity. Inhibition of mGluR5 by MPEP in DLStr (Green lines) may disinhibit the globus pallidus externa (GPe), which can then inhibit the subthalamic nucleus (STN). STN inhibition will diminish activation of the substantia nigra pars reticulata (SNr)/ globus pallidus interna (GPi), with consequent disinhibition of the thalamus (Th) – cerebral cortical (Cx) circuit, resulting in increased locomotor activity. (4) The blockage of mGluR5 in the ventral striatum (VStr) by MPEP (pink lines) may disinhibit the SNr, which can inhibit Th-Cx projections, resulting in decreased locomotor activity. (5) mGluR5 inhibition in the dorsal hippocampus (dHPC) resulted in increased locomotor activity. The dHC projects to the VStr, which is involved in motor control (orange lines). Moreover, it has been shown that the dHPC has intrahippocampal projections connecting it to the ventral hippocampus (vHPC). (6) MPEP injections on the posterior parietal cortex (V2MM) elicited no alteration on behavioral tests. (B) Shows summary results of the behavioral findings for each neural substrate injected with MPEP. Blue circles indicate brain regions that highly express mGluR5 and that were injected with MPEP. Colorful lines (green, pink and orange) represent neural circuits. Filled lines indicate activated circuits and dotted lines indicate inhibited circuits. Excitatory pathways are depicted as arrows and inhibitory pathways as blocked lines.