A profile of the insulin receptor in cultured hippocampal slices.

Objectives: Insulin receptors (IRs) are distributed in a region-specific fashion throughout the brain, and may play a role in processes related to learning and memory. The hippocampus, which participates in spatial memory formation, is one region in which the IR is abundantly expressed. Organotypic hippocampal slice cultures (OHSCs) are an in vitro model that permits the easy manipulation of growth conditions, yet retains much of the source structure's cytoarchitecture. To assess OHSCs as a model for the study of hippocampal IRs, ligand-binding and the expression and cellular distribution of the β-subunit (which transduces the insulin signal) were examined over time in culture. Design & Results: Fluorescently conjugated insulin was used to assess neural insulin receptor binding, and revealed that labelling remained similar over three weeks in culture (a typical length of OHSC maintenance). Cross-linking of surface proteins helped to show that approximately half of β-subunits were found at the cell surface, and that this relative proportion remained stable over several weeks. In contrast, expression of the β-subunit protein progressively declined to a plateau approximately 60% less than that seen when the cultures were prepared.

Conclusions: Our results provide a foundation for subsequent studies to employ OHSCs to explore neural IRs; for instance, the dissonance between the progressive decline in expression of the IR β-subunit and the relative stability of receptor-mediated binding suggests the presence of an active process to hold steady the ability of cells to respond to insulin stimulation.