Differential immunoreactivity for alpha-actinin-2, an N-methyl-D-aspartate-receptor/actin binding protein, in hippocampal interneurons

Recent studies have demonstrated that hippocampal interneurons possess dist inct cytoskeletal and cell-signaling proteins in comparison to hippocampal principal cells; however, little is known about the differences in the acti n cytoskeleton between these two populations. This study examined the immun oreactivity of alpha -actinin-2, an actin binding/N-methyl-D-aspartate-rece ptor linking protein, in the rat hippocampal formation using double-labelli ng immunofluorescence. Alpha-actinin-2 immunoreactivity is seen throughout the hippocampus with heavy labeling observed in the dendrites of granule ce lls, in CA2 pyramidal cells and in presumed interneuronal somata throughout the dentate gyrus and CA1. All the cells with heavy somatic a-actinin-2 im munoreactivity in the dentate gyrus and CA1 were GABAergic interneurons lab eled by glutamate decarboxylase (99%). Examination of the neurochemical mar ker content of the alpha -actinin-2 immunoreactive interneurons revealed th at the majority of this population was neuropeptide-Y-positive and a minori ty was positive for calretinin. Fluid percussion head trauma did not result in significant alterations of alpha -actinin-2 immunoreactivity in hippoca mpal interneurons. The developmental profile of alpha -actinin-2 immunoreac tivity showed the presence of alpha -actinin-2 in the hippocampus at P1, la beling of interneurons by P7 and the adult staining pattern seen by P21. This study demonstrates that principal cells and interneurons are different ially immunoreactive for alpha -actinin-2, and that alpha -actinin-2 staini ng is restricted to a subpopulation of interneurons. Each of the three clas ses of cytoskeletal elements have been shown to be differentially expressed in hippocampal interneurons and principal cells, suggesting that the cytos keleton is a defining feature of neuronal populations. Additionally, the li mited expression of alpha -actinin-2 could have important functional implic ations in N-methyl-D-aspartate receptor localization and modulation. (C) 20 01 IBRO. Published by Elsevier Science Ltd. All rights reserved.