INHIBITORY CA1-CA3-HILAR REGION FEEDBACK IN THE HIPPOCAMPUS

The organization of the hippocampus is generally thought of as a serie s of cell groups that form a unidirectionally excited chain, regulated by localized inhibitory circuits. With the use of in vivo intracellul ar labeling, histochemical, and extracellular tracing methods, a longi tudinally widespread, inhibitory feedback in rat brain from the CA1 ar ea to the CA3 and hilar regions was observed. This long-range, cross-r egional inhibition may allow precise synchronization of population act ivity by timing the occurrence of action potentials in the principal c ells and may contribute to the coordinated induction of synaptic plast icity in distributed networks.