CALBINDIN-D28K IMMUNOREACTIVITY IN THE RAT AMYGDALA

Calbindin-D28k (CB) is a calcium-binding protein whose exact function has yet to be elucidated. Because CB is contained in distinct cell typ es in the nervous system, it is a valuable marker for distinguishing s pecific nuclear subdivisions and neuronal populations. In the present study, immunohistochemical methods were used to localize CB in the rat amygdala. A subpopulation of nonpyramidal neurons in all nuclei of th e basolateral amygdala (ABL) exhibited intense CB immunoreactivity (CB -ir). CB-positive puncta resembling axon terminals were observed surro unding pyramidal perikarya in the ABL. Pyramidal neurons in caudal and lateral portions of the ABL exhibited moderate CB-ir. Intensely stain ed nonpyramidal neurons resembling those of the ABL were also seen in the cortical nuclei, periamygdaloid cortex, and nucleus of the lateral olfactory tract; these nuclei also contained variable numbers of mode rately stained pyramidal cells. Numerous CB-positive neurons were obse rved in all subdivisions of the medial nucleus. The posterodorsal subd ivision of the medial nucleus exhibited a centrally located island of small CB-negative neurons and three cell-dense clusters of CB-positive neurons. The distribution of CB-ir in the central nuclear complex was very heterogeneous. The intermediate subdivision of the central nucle ar complex exhibited the most robust staining, whereas the lateral sub division contained relatively few CB-positive cells. Dorsal and ventra l portions of the lateral capsular subdivision of the central nuclear complex could be readily distinguished on the basis of differing level s of CB-ir. These results indicate that CB is localized in discrete ce ll types and nuclear subdivisions in the rat amygdala and suggest that CB immunohistochemistry is a useful technique for identifying specifi c structural components in this brain region. (C) 1997 Wiley-Liss, Inc .