Electrophysiological properties of hippocampal-cortical neural networks, role in the processes of learning and memory in rats.

The recording of hippocampal and cortical long-term potentiation (LTP) in rats in vivo is an appropriate and commonly used method to describe changes in cellular mechanisms underlying synaptic plasticity. Recently, we introduced a method for the simultaneous recording of LTP in bilateral CA1 regions and parietal association cortex (PtA), and observed differences between the Schaffer collateral-CA1 pathway (SC), Schaffer collateral/associational commissural pathway (SAC) and Schaffer collateral/associational commissural-cortex pathway (SACC). In this study, we found that (1) synaptic transmission of the SAC and SACC pathways depended on hippocampal commissural fibers [dorsal and ventral hippocampal commissural fibers, the medial septum (MS) and hippocampal CA3 commissural fibers], (2) nerve conduction velocity of the SACC pathway might be higher than that of the SAC pathway, (3) the input/output (I/O) curve of the SC pathway was shifted to the left side, compared to that of the SAC and SACC pathways, (4) all three pathways could induce stable LTP; however, LTP of the SAC and SACC pathways was much stronger than that of the SC pathway, (5) the degree of paired-pulse facilitation (PPF) was weaker in the SC pathway than that in the SAC and SACC pathways, (6) after cutting off the corpus callosum and commissural fibers, spatial learning and memory were impaired, and the ability to explore the novel environment and spontaneous locomotor activity were weakened. Taken together, our results suggested that hippocampal commissural fibers were very important for exchanging information between hemispheres, and basic differences in electrophysiological properties of hippocampal-cortical neural networks play a vital role in the processes of learning and memory.