Distribution of parvalbumin, calretinin, and calbindin-D-28k immunoreactivity in the rat amygdaloid complex and colocalization with gamma-aminobutyric acid

To understand the organization of inhibitory circuitries in the rat amygdal a, the distribution of parvalbumin, calretinin, and calbindin immunoreactiv ity was investigated in the rat amygdaloid complex. Colocalization of vario us calcium-binding proteins with the inhibitory transmitter gamma-aminobuty ric acid (GABA) was studied by using the mirror technique. Parvalbumin-immu noreactive (-ir) elements were located mostly in the deep amygdaloid nuclei , whereas the calretinin-ir and calbindin-ir staining were most intense in the cortical nuclei as well as in the central nucleus and the amygdalohippo campal area. Second, the distribution of immunopositive neurons largely par allelled the distribution of terminal and neuropil labeling. Third, immunos tained neurons could be divided into four major morphologic types (types 1- 4) based on the characteristics of the somata and the dendritic trees. The fourth lightly stained neuronal type that had a pyramidal GABA-negative som a was observed only in calretinin and calbindin preparations. Fourth, parva lbumin-ir terminals formed basket-like plexus and cartridges, which suggest s that parvalbumin labels GABAergic inhibitory basket cells and axo-axonic chandelier cells, respectively. Colocalization studies indicated that 521 o f 553 (94%) of parvalbumin-ir, 419 of 557 (75%) of calbindin-ir, and 158 of 657 (24%) of calretinin-ir neurons were GABA-positive in the deep amygdalo id nuclei. A high density of large GABA-negative calbindin-ir neurons was o bserved caudally in the medial division of the lateral nucleus and GABA-neg ative calretinin-ir neurons were observed in the magnocellular division of the accessory basal nucleus as well as in the intermediate and parvicellula r divisions of the basal nucleus. These data suggest that in various amygda loid areas, neuronal excitability is controlled by GABAergic neurons that c ontain different calcium-binding proteins. The appearance of basket-like pl exus and cartridges in the parvalbumin preparations, but not in calretinin preparations, suggests that like in the hippocampus, the distribution of in hibitory terminals in the dendritic and perisomatic regions of postsynaptic neurons in the rat amygdala is organized in a topographic manner. J. Comp. Neurol. (C) 2000 Wiley-Liss, Inc.