Multiple forms of feedback inhibition by str. oriens inhibitory interneurons?

In the CA1 region of the hippocampus pyramidal neuron basilar dendrites extend into the stratum oriens-alveus while the apical dendrites project deep into the stratum lacunosum-moleculare, a distance several hundred micrometres in extent. This extended dendritic arbor provides a large surface area for afferent input. For example, the axons of CA3 pyramidal neurons synapse onto pyramidal cell dendritic spines across approximately 2/3 of the apical dendritic tree. In contrast a diverse population of local-circuit GABAergic inhibitory interneurons selectively innervate specific postsynaptic domains of principal cells (for review see Freund & Buzsaki, 1996). These cells target their axons either to the axon initial segment, somata, or proximal and distal dendrites, with each cell type implicated in a particular operational role. However, rigid classification of the numerous subpopulations has been problematic (see Parra et al. 1998 for further discussion).