DISTRIBUTION OF PARVALBUMIN-D28K-IMMUNOREACTIVE, CALRETININ-D28K-IMMUNOREACTIVE, AND CALBINDIN-D28K-IMMUNOREACTIVE NEURONS AND FIBERS IN THE HUMAN ENTORHINAL CORTEX

Parvalbumin, calretinin, and calbindin-D28k are calcium-binding protei ns that are located in largely nonoverlapping neuronal populations in the brain. The authors studied the distribution of parvalbumin-, calre tinin-, and calbindin-D28k-immunoreactive (ir) cells, fibers, terminal s, and neuropil in the eight subfields of the human entorhinal cortex. The distribution of each of the three calcium-binding proteins largel y followed the cytoarchitectonic borders of the eight entorhinal subfi elds, although the regional and laminar distributions of the three pro teins were segregated rather than overlapping. The highest density of parvalbumin-ir neurons and terminals was found in the caudal and later al subfields of the entorhinal cortex. Calretinin and calbindin-D28k i mmunoreactivities were high rostromedially, although a large number of calretinin and calbindin-D28k neurons were also found in the caudal s ubfields. All parvalbumin-ir cells had a morphological appearance of n onpyramidal neurons. Parvalbumin-ir terminals formed basket-like forma tions around unstained somata and cartridges, suggesting that parvalbu min neurons compose a subpopulation of gamma-aminobutyric acid (GABA)e rgic basket cells and chandelier cells, respectively. Although calreti nin and calbindin-D28k were also found in numerous nonpyramidal neuron s, both were also located in pyramidal-shaped neurons in layers V and VI (calretinin) and in layers II and III (calbindin) of the entorhinal cortex, suggesting that they play roles in projection neurons as well . Moreover, the high density of nonpyramidal neurons containing calciu m-binding proteins in layers II and III of the entorhinal cortex sugge sts that they form an integral component of a network that controls th e entorhinal outputs to the hippocampus. Furthermore, the largely nono verlapping distributions of the parvalbumin-, calretinin-, and calbind in-ir neuronal populations in the entorhinal cortex indicate that each of them may modulate a different subset of topographically organized entorhinal outputs. (C) 1997 Wiley-Liss, Inc.