Dentate hilar mossy cells and somatostatin-containing neurons are immunoreactive for the alpha 8 integrin subunit: Characterization in normal and kainic acid-treated rats

Integrins are heterodimeric cell surface receptors composed of different al pha and beta subunits that mediate cell-cell and cell-extracellular matrix interactions. They have been implicated in the regulation of neuronal migra tion, differentiation process outgrowth, and plasticity. The alpha8 integri n subunit associates exclusively with the beta1 subunit to form a receptor (alpha8 beta1) for fibronectin, vitronectin, tenascin and osteopontin. In a previous study, we demonstrated that hippocampal dentate hilar neurons are immunoreactive for alpha8. The present study identifies the major types of alpha8-immunoreactive hilar neurons and characterizes the effects of kaini c acid-induced seizures on alpha8-immunoreactivity in these cells. Examinat ion of the hilus in normal rats revealed alpha8-immunoreactivity in the som atodendritic compartments of large hilar neurons identified as mossy cells, including a subset of dendritic thorny excrescences that were contacted by large mossy fiber terminals. alpha8-immunoreactivity also was found in app roximately 71% of somatostatin-containing hilar cells. Kainic acid-induced seizures dramatically and rapidly altered the levels and distribution of al pha8-immunoreactivity in hilar neurons. After 1.5 h of seizures, alpha8-imm unoreactivity in their dendrites was reduced greatly. One day after kainic acid treatment, labeling was diminished throughout the somatodendritic comp artments of most hilar cells. This decrease appeared to be transient since alpha8 labeling returned to normal levels in surviving hilar neurons within 2 weeks of treatment. In addition, many alpha8-immunoreactive hilar neuron s, particularly in caudal dentate regions, were lost 3-5 weeks after kainic acid treatment. Our findings suggest that alpha8 beta1 may mediate adhesive interactions of the dendritic processes of mossy cells and somatostatin-containing hilar n eurons with other cellular elements or with extracellular matrix components . They also suggest that alpha8 may be susceptible to activity-dependent pr oteolysis that could modulate its function in the somatodendritic compartme nt of these cells. (C) 2001 IBRO. Published by Elsevier Science Ltd. All ri ghts reserved.