Some non-fluorescent connections of the nigro-neostriatal dopamine neurones.

This study of the relationships between cells identified by their catecholamine fluorescence and their less fortunate neighbours became possible with the advent of autoradiographic tracing methods. A major output from the neostriatum returns to the substantia nigra where it fills the pars reticulata. Outputs from this area of substantia nigra are present on both sides of the brain in the thalamus, in parts of parafascicular, intralaminar, and mediodorsal nuclei, and the superior colliculi in the deeper layers. Mainly unilateral pathways reach the ventromedial nucleus of thalamus and also pass under the lateral part of the colliculus to reach the region of the nucleus pendunculo-pontinus among the fibres of the brachium conjunctivum. The roles of those areas in the transmission of the output of the basal ganglia to the motor system of the animal, however, remain obscure.