HIPPOCAMPAL NPY NEURONS PROJECT TO THE FASCIA-DENTATA IN ORGANOTYPIC CULTURES

The distribution of neuropeptide Y immunoreactive (NPY-ir) neurons in organotypic cultures of hippocampi from neonates was compared to that seen in adult rats. In addition to the known NPY-ir neurons in the hip pocampus proper and in the hilus of the fascia dentata, isolated, larg e, multipolar, NPY-ir neurons were observed in the subiculum and in ar eas CA1 and CA3. Their axons projected into stratum radiatum of the hi ppocampus proper and into the molecular layers and hilus of the fascia dentata where they branched profusely. These NPY-ir neurons were regu larly distributed throughout the septo temporal extent of the hippocam pus and were present in both neonates and adult hippocampi. The hilar NPY-ir neurons have always been considered the source of the NPY-ir pl exus in the outer molecular layer of the dentate gyrus. However, our r esults show that there is also a contribution from the NPY-ir neurons in the hippocampus proper. (C) 1996 Wiley-Liss, Inc.