Local cerebral metabolic effects induced by nigral stimulation following ventromedial thalamic lesions. I: Basal ganglia and related motor structures.

The effects of unilateral electrical stimulation of the substantia nigra (SN) were mapped in the extrapyramidal system of conscious rats bearing ventromedial thalamic (VM) lesions, using the quantitative autoradiographic 14C-deoxyglucose method. SN-stimulation in VM-intact rats resulted in metabolic activation within the deep layer of superior colliculus, subthalamic nucleus, ventrolateral thalamus and sensory-motor cortex ipsilaterally, and bilaterally in the reticulata, compacta, centrolateral and ventromedial thalamus, striatum, globus pallidus and entopeduncular nucleus. SN-stimulation 8 days following ipsilateral VM-lesion, induced activation only within the ipsilateral compacta, subthalamic and entopeduncular nuclei and the globus pallidus and in addition, the reticulata bilaterally. However, SN-stimulation 30 days following VM-injury elicited bilateral metabolic activation in all the examined structures. It is concluded that the VM-thalamic nucleus mediates information from one SN to the ipsilateral motor cortex and striatum, as well as to the extrapyramidal components of the contralateral hemisphere. Moreover, due to the plasticity of the central nervous system, one month following the VM-lesion transmission of information from the SN to all the bilateral components of this network is reestablished.