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. 1998 Mar 1;18(5):1806–1817. doi: 10.1523/JNEUROSCI.18-05-01806.1998

Fig. 8.

Fig. 8.

Schematic representation of a hypothetical model of the functional organization of the basal ganglia based on the results of cytochrome oxidase histochemistry (modified from Albin et al., 1989). Lesions of the nigrostriatal bundle can deprive DA innervation of not only the striatum (STR) but also the the subthalamic nucleus (STN) and cortex (Cx). The hyperactivity of the entopeduncular nucleus (EP) and substantia nigra pars reticulata (SNR) is attributable to the lesion-induced suppression of direct inhibitory inputs from the striatum (direct pathway). In this model, the striatopallido–subthalamic pathway (indirect pathway) does not play a major role in the increased activity of the STN. The DA denervation of the STN and cortex could contribute to the overactivity of the STN through direct and indirect mechanisms, respectively. The hyperactivity of the STN may result in the increased activity of the globus pallidus (GP). The graft-derived restoration of DA levels in the striatum can attenuate the increased activity of the EP and SNR by a trans-synaptic mechanism. On the other hand, the intrastriatal grafts fail to affect the increased activity in the GP or STN.