Synaptic organization of the basal ganglia: an electroanatomical approach in the rat

The physiological processes by which basal ganglia participate in the elaboration of movement are still poorly understood. In particular, lack of information about the synaptic organization of the output pathways of the basal ganglia impedes functional analysis of this system. To bridge this gap electroanatomical studies have been undertaken of one of the major output systems of the basal ganglia: the substantia nigra pars reticulata (SNr). This paper reviews recent results and proposes functional perspectives. The findings reported clearly establish that SNr exerts a tonic inhibitory influence on its collicular and thalamic targets. It is suggested that the striatum may achieve a complex-spatial pattern of facilitation in a large spectrum of structures related to ocular and cephalic motor activity by inhibiting the inhibitory nigrothalamic and nigrocollicular branched neurons.