NEURONS CO-LOCALIZING CALRETININ IMMUNOREACTIVITY AND REDUCED NICOTINAMIDE ADENINE-DINUCLEOTIDE PHOSPHATE DIAPHORASE (NADPH-D) ACTIVITY IN THE HIPPOCAMPUS AND DENTATE GYRUS OF THE RAT

Co-localization of calretinin immunoreactivity and nicotinamide adenin e dinucleotide phosphate diaphorase (NADPH-d) activity was studied in the rat hippocampus and dentate gyrus. Neurons co-expressing both mark ers (CR/NADPH-d) were observed throughout the hippocampus and dentate gyrus. However, they were more abundant in the stratum pyramidale and radiatum of CA3, stratum pyramidale of CA1, and in the juxtagranular z one of the hilus. The NADPH-d activity appeared in 37% of the calretin in immunoreactive neurons in CA3, 42% in CA1, and 36% in the dentate g yrus, whereas calretinin immunoreactivity occurred in 41% of the NADPH -d positive neurons in the hippocampus, and 16% in the dentate gyrus. The morphology and location of the double marked cells could not be us ed as a characteristic of the co-localizing neurons. The heavily stain ed NADPH-d neurons occurring mainly in CA1 do not show calretinin immu noreactivity. NADPH-d fiber swellings could be observed in close appos ition to calretinin immunoreactive neurons and dendrites, suggesting s ynaptic contacts. It has been reported that calretinin immunoreactivit y and NADPH-d activity co-localize infrequently in other areas such as the neocortex, striatum, hypothalamus and tegmental nucleus. The rela tively high proportion of double marked cells found in the hippocampus and dentate gyrus could be indicative of the importance of the CR/NAD PH-d interneurons in the circuitries of these areas.