Hippocampo-prefrontal cortex pathway: Anatomical and electrophysiological characteristics

The hippocampus, the prefrontal cortex, and imterconnected neural circuits are implicated in several aspects of cognitive and memory processes. The pr esent review is dedicated to the description of the anatomo-functional char acteristics of the hippocampo-prefrontal pathway and related neuronal circu its in the rat. This pathway, which originates from the hippocampal CA1/sub iculum fields, innervates the prelimbic/medial orbital areas of the prefron tal cortex (PL/MO). Its synaptic influence on cortical pyramidal neurons co nsists in an early monosynaptic excitation followed by an inhibition and, i n some cases, a late excitation. These later effects are likely due to the subsequent activation of the local cortical network. PL/MO areas and the CA 1/subiculum both send projections to the nucleus accumbens, a region of the ventral striatum which is particularly implicated in goal-directed behavio r. Therefore, emphasis is placed on respective projections from PL/MO areas and from the CA1/subiculum on the "core" and the "shell" regions of the nu cleus accumbens, as well as on their interconnected circuits. Signals which are directed to the prefrontal cortex through these circuits might modulat e hippocampo-prefrontal inputs. Finally, the direct and/or indirect relatio nships of the hippocampus, prefrontal cortex, and nucleus accumbens with th e ventral tegmental area/substantia nigra pars compacta complex (VTA/SNC) ( where dopamine neurons are located) will also be described, because these n eurons are known to modulate synaptic transmission and plasticity in their target structures and to play a fundamental rose in motivational processes. (C) 2000 Wiley-Liss, Inc.