Morphological features of neurons containing calcium-binding proteins in the human striatum

An immunohistochemical approach was used to characterize the morphological phenotype of neurons containing the calcium-binding proteins calretinin (CR), parvalbumin (PV), or calbindin-D28k (CB) in the normal human striatum. The protein CR occurs in at least four morphologically distinct types of neurons. Apart from the numerous medium-sized aspiny interneurons and the less abundant giant aspiny interneurons, CR also labels some medium-sized spiny neurons morphologically identical to striatal projection neurons. This finding indicates that CR is not only confined to striatal interneurons but also may be involved in the function of certain projection neurons. Some small and peculiar bushy-like aspiny neurons also are enriched with CR. These neurons could correspond to the dwarf or neurogliform neurons first described by Ramón y Cajal (1911). Three types of PV-immunoreactive striatal neurons can be visualized in the human striatum: 1) the common medium-sized aspiny leptodendritic neurons, 2) some smaller and profusely arborized aspiny neurons, and 3) a few large and intensely stained neurons with conspicuously beaded and poorly branched dendrites. The protein CB labels virtually all medium-sized spiny projection neurons located in the striatal matrix but also identifies a small subset of large and more intensely immunostained aspiny neurons. The latter finding indicates that CB is not entirely confined to striatal projection neurons but also may play a role in local circuit neurons. These normative data should help our understanding of the chemical anatomy of the human striatum in both health and disease.