The hippocampal lamella hypothesis revisited

We have re-examined the hippocampal lamellar organization of the CA3-to-CA1 connection. Based on a new technique with electrophysiological quantificat ion of Schaffer collateral density, and a review of recent literature, we c onclude that the lamellar organization remains a useful concept for underst anding hippocampal connectivity. Using a sheet-like hippocampal preparation . containing the whole CA1 region, we mapped the distribution of Schaffer c ollaterals by two procedures. First. we recorded the amplitude of the Schaf fer compound action potential in various parts of CA1 after stimulation of a point in CA3. Second, we charted the CA1 positions from which we could an tidromically excite individual CA3 neurones. Although the Schaffer collater als radiated from their CA3 cells of origin within a wide, fan-shaped area. covering a large part of the septo-temporal extent of CA1. the amplitude o f the compound action potential was largest in a slightly oblique, transver se band across the CA1 towards the subicular region. (C) 2000 Elsevier Scie nce B.V. All rights reserved.