Vasoactive intestinal polypeptide in neuroglia? Immunoelectron microscopiclocalization in astrocytes of the rat mesencephalon

The dorsal region of the rat interpeduncular nucleus (IPN) was found highly immunoreactive for vasoactive intestinal polypeptide (VIP). This area appe ared as a cap-like structure at the midcaudal level of the nucleus. Unlike other brain areas, however, VIP immunoreactivity within the "cap" appeared vaguely punctuate with no light microscopically identifiable cell structure s. Ultrastructurally, a dense meshwork of VIP-immunopositive bouton-laden a xons was revealed. Labeled neuronal perikarya were not encountered. Some li ghtly immunoreactive dendrites were observed. In addition, immunopositive g lial profiles were frequently seen. Perikarya and numerous fine processes, occasionally perivascular, identified as astroglia by established ultrastru ctural criteria, exhibited VIP immunoreactivity. Constant feature of the pe ptide immunolocalization was the predilection for the intermediate filament bundles of astrocytic perikarya and processes. This was usually accompanie d by a thick coating of the inner aspect of glial plasmalemma and, in perik arya, by highly reactive vesicular profiles. Glial immunopositive elements were never seen beyond the boundaries of the diffuse "cap." In view of the repertoire of metabolic, neurotrophic, and neuroprotective mechanisms in wh ich VIP neurons are involved in conjunction with astroglia, the presence of VIP-immunoreactive astrocytes in a circumscribed area, confirms the hetero geneity bf astrocyte populations. GLIA 34:229-233, 2001. (C) zool Wiley-Lis s, Inc.