Distribution and morphology of vasoactive intestinal polypeptide-like immunoreactive neurons in regio superior of the rat hippocampal formation.

The distribution and morphology of vasoactive intestinal polypeptide-like (VIP-L) immunoreactive neurons were studied in thick (70-120 microns) sections from the rat hippocampal formation using VIP antibody in combination with immunohistochemistry. Analysis of serial sections cut through the regio superior revealed a relatively dense aggregation of cells in stratum lacunosum-moleculare. Classification of cells in these (and other) layers on the basis of their morphology and orientation showed that hippocampal VIP-positive cells, unlike cortical ones, constitute a remarkably heterogeneous population. Studies of axonal trajectories of individual VIP cells showed that while some have local terminal arbors within the stratum lacunosum-moleculare close to the parent soma, other VIP cells send longer projections to other layers and subfields of the hippocampal formation.