Calcium-binding proteins show a heterogeneous distribution in the mammalian central nervous system and are useful markers for identifying neuronal populations. The distribution of the three major calcium-binding proteins - calbindin-D28k (calbindin), calretinin and parvalbumin - has been investigated in eight neurologically normal human thalami using standard immunohistochemical techniques. Most thalamic nuclei show immunoreactive cell bodies for at least two of the three calcium-binding proteins; the only nucleus showing immunoreactivity for one calcium-binding protein is the centre médian nucleus (CM) which is parvalbumin-positive. Overall, the calcium-binding proteins show a complementary staining pattern in the human thalamus. In general terms, the highest density of parvalbumin staining is in the component nuclei of the ventral nuclear group (i.e. in the ventral anterior, ventral lateral and ventral posterior nuclear complexes) and in the medial and lateral geniculate nuclear groups. Moderate densities of parvalbumin staining are also present in regions of the mediodorsal nucleus (MD). By contrast, calbindin and calretinin immunoreactivity both show a similar distribution of dense staining in the thalamus which appears to complement the pattern of intense parvalbumin staining. That is, calbindin and calretinin staining is most dense in the rostral intralaminar nuclear group and in the patchy regions of the MD which show very low levels of parvalbumin staining. However, calbindin and calretinin also show low levels of staining in the ventral nuclear complex and in the medial and lateral geniculate bodies which overlaps with the intense parvalbumin staining in these regions. These results show that the calcium-binding proteins are heterogeneously distributed in a complementary fashion within the nuclei of the human thalamus. They provide further support for the concept recently proposed by Jones (Jones, E.G., 1998.
Viewpoint: the core and matrix of thalamic organization. Neuroscience 85, 331-345) that the primate thalamus comprises of a matrix of calbindin immunoreactive cells and a superimposed core of parvalbumin immunoreactive cells which may have differential patterns of cortical projections.