Hippocampo-prefrontal cortex pathway: anatomical and electrophysiological characteristics

The hippocampus, the prefrontal cortex, and interconnected neural circuits are implicated in several aspects of cognitive and memory processes. The present review is dedicated to the description of the anatomo-functional characteristics of the hippocampo-prefrontal pathway and related neuronal circuits in the rat. This pathway, which originates from the hippocampal CA1/subiculum fields, innervates the prelimbic/medial orbital areas of the prefrontal cortex (PL/MO). Its synaptic influence on cortical pyramidal neurons consists in an early monosynaptic excitation followed by an inhibition and, in 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 CA1/subiculum both send projections to the nucleus accumbens, a region of the ventral striatum which is particularly implicated in goal-directed behavior. 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 nucleus accumbens, as well as on their interconnected circuits. Signals which are directed to the prefrontal cortex through these circuits might modulate hippocampo-prefrontal inputs. Finally, the direct and/or indirect relationships of the hippocampus, prefrontal cortex, and nucleus accumbens with the ventral tegmental area/substantia nigra pars compacta complex (VTA/SNC) (where dopamine neurons are located) will also be described, because these neurons are known to modulate synaptic transmission and plasticity in their target structures and to play a fundamental role in motivational processes.