Identification of different subpopulations of neostriatal neurones projecting to globus pallidus or substantia nigra in the monkey: a retrograde fluorescence double-labelling study.

Fluorescent tracers (Nuclear Yellow, True Blue, Fast Blue) were injected, in various combinations, into the globus pallidus and substantia nigra in three marmosets. Examination of perikarya in the ipsilateral neostriatum, well removed from pallidal injection sites, revealed that the predominant pattern was of single-labelled cells, retrogradely labelled from either the globus pallidus or substantia nigra. It is suggested, on the basis of this evidence and data previously available, that the striatum contains at least three types of efferent neurones, one projecting exclusively to the globus pallidus, one projecting exclusively to the substantia nigra, and another projecting to both structures.