Neuropeptide Y innervation of the hippocampal region in the rat and monkey brain

Using antibodies to neuropeptide Y (NPY) in combination with immunohistochemical techniques we have studied the distribution of cell bodies and nerve terminals containing NPY immunoreactivity (‐i) in the hippocampal region of rats and monkeys (cynomolgus). In colchicine‐pretreated rats a large number of NPY‐positive cells are present in all areas of the hippocampal region. The NPY‐i cells range in size from small (diameter across soma: 10–15 μm) to large (approximately 20 μm). Most of the NPY‐i cells are situated in the hilus, in the subgranular zone of the area dentata, and in the stratum oriens of Ammon's horn. A majority of these are polymorphic cells but cells of different morphology are present in these layers as well. These include small spheroid cells and dentate pyramidal basket cells that are distinct from the polymorphic cells in the subgranular zone. The subicular complex (e.g., the subiculum, pre‐, and parasubiculum) and the entorhinal area contain fewer NPY‐i cells than the rest of the hippocampal region. In the dorsal parts of the pre‐ and parasubiculuin numerous small cells are scattered throughout all layers, while in the entorhinal area the NPY‐stained cells are situated primarily in the deep layers (V and VI). In the ventral part of the lateral entorhinal area large multipolar and bitufted cells are found in layers II‐VI. In the untreated monkey brain NPY‐positive cells are found in the hilus of the area dentata and in the deep (IV through VI) layers of both the medial and lateral entorhinal area. Fewer NPY‐stained cells are present in the subicular complex and in the entorhinal area. In the monkey as well as in the rat, NPY‐stained cells are present in the angular bundle and in the alveus.