CALCIUM-BINDING PROTEIN IMMUNOREACTIVITY IN THE PIRIFORM CORTEX OF THE GUINEA-PIG - SELECTIVE STAINING OF SUBSETS OF NON-GABAERGIC NEURONS BY CALRETININ

Selective immunostaining for calcium-binding proteins identifies subpo pulations of neurons with hypothetical distinct functional roles. The neuronal localization of calcium-binding proteins calretinin, parvalbu min and calbindin is here correlated to GABA and glutamate immunoreact ivity in the guinea-pig piriform cortex. In the external border of the molecular layer, neurons positive for calretinin with morphological f eatures of Cajal-Retzius cells were found. Rare GABA immunoreactive ce lls were observed in the same subpial region, whereas neurons containi ng GABA were abundant within layers Ia and Ib. Aspartate-and glutamate -immunoreactive cells were also found in the outer Ia layer. A distinc t band of calretinin-immunoreactive fibres and terminals localized in layer Ia, where the afferent fibres originating from the olfactory bul b are segregated. In layer II the number of cells containing calretini n exceeded the number of neurons positive for the anti-GABA antibody. Part of the layer II calretinin-positive neurons with pyramidal shape and large apical dendrites directed toward the surface were found to b e immunoreactive for the anti-glutamate antibody on adjacent sections. Neurons in layer II immunoreactive for either parvalbumin or calbindi n showed morphological features of interneurons, and their number matc hed the count of GABA containing cells. Calretinin-positive neurons wi th the general morphological features of interneurons were scarcely re presented in the deep piriform cortical layers, where large multipolar and small bipolar calbindin-positive cells prevailed. The present dat a show that in the piriform cortex of the guinea-pig calretinin, altho ugh expressed in Cajal-Retzius-like cells as in other cortical areas, also marks a subpopulation of glutamate containing pyramidal-like neur ons in layer II. (C) 1997 IBRO. Published by Elsevier Science Ltd.