Localisation of parvalbumin‐immunoreactive structures in primate caudate‐putamen

To investigate the morphology, distribution, and connections of parvalbumin‐containing neurones in the caudate‐putamen of primates, perfuse‐fixed sections were stained to reveal parvalbumin immunoroactivity. In agreement with previous observations, the caudate‐putamen was rich in parvalbumin‐positive neurones and neuropil. The neuropil staining was uneven such that the dense background staining was interspersed with zones of relatively weak staining. The distribution corresponded to the striosome/matrix system as defined by substance P or met‐enkephalin immunostaining in adjacent sections. Because parvalbumin‐positive neurones are present in regions known to project to the caudate‐putamen and the majority of parvalbumin‐positive terminals in the matrix formed asymmetric synapses, it is concluded that the uneven staining is probably due to afferents of the neostriatum. The morphology of the parvalbumin‐immunoreactive neurones varied between the striosomes and matrix; those in the matrix were smaller and possessed dendritic arborisations that were relatively uniform, whereas those in the striosomes were generally more extensively stained and possessed a greater variation in their dendritic branching patterns. The dendrites frequently crossed the boundary between the striosomes and matrix. A population of giant parvalbumin‐immunoreactive neurones was also observed in the putamen. Electron microscopic analysis revealed that, in addition to terminals forming asymmetric synapses, a smaller population formed symmetric synaptic specialisations and are presumed to be derived from the local parvalbumin‐immunoreactive neurones. Terminals of the latter group formed synapses with medium‐sized spiny neurones. Because parvalbumin‐positive neurones receive input from the cortex, they may transmit cortical information to spiny neurones. © 1994 Wiley‐Liss, Inc.