Differential expression of calbindin and calretinin in the human fetal amygdala

The distribution patterns of the calcium-binding proteins calbindin and cal retinin, both expressed early during development within the various amygdal oid nuclei and areas, have been investigated. Anti-calbindin as well as ant i-calretinin mark immature, partly migrating neurons in the 5th gestational month; the number of calretinin-immunoreactive neurons is distinctly highe r. In the 8th month, calbindin and calretinin are found in a small proporti on of presumed pyramidal cells and in various types of non-pyramidal neuron s. Small and large bipolar and small and large multipolar neurons are shown to express calbindin and calretinin. Double-labellings show that calbindin and calretinin are largely contained in different subsets of these neurona l types, which are considered to represent interneurons. These nerve cell c lasses are widespread within the amygdala with mainly moderate to high pack ing densities. Diffuse immunoreactive structures, which are found in differ ent intensities in the various amygdaloid nuclei, display distinct redistri bution during fetal development. The results show that during early fetal d evelopment calbindin and particularly calretinin may be involved in the reg ulation of neuronal migration. In later development, definite subsets of in terneurons, which are likely to be functionally different, are marked by an ti-calbindin and -calretinin. Different diffuse immunolabelling at various developmental stages probably indicates the sequential arrival of afferent input from brain areas containing calbindin- or calretinin-immunoreactive n erve cells. With the exception that calretinin may be transiently expressed in pyramidal neurons, the distribution of calbindin- and calretinin-immuno reactive structures to a large degree corresponds to that in the adult. Thu s, little reorganisation is to be expected during proceeding development, M icrosc. Res. Tech. 46:1-17, 1999. (C) 1999 Wiley-Liss, Inc.