Abstract
The prefrontal cortex (PFC) is an important structure for working memory. However, it is not the only brain structure responsible for working memory. Other brain areas, including the mediodorsal nucleus (MD) of the thalamus and the hippocampus (HP) have also been found to play significant roles in working memory, and both areas send monosynaptic projections to the medial prefrontal cortex (mPFC) in rats. To gain an understanding of the neural mechanisms of working memory, it is necessary to examine the functional interactions between the PFC and other brain structures. As we have observed that both HP-mPFC and MD-mPFC pathways express long-term potentiation (LTP), thought to be a model for learning and memory processes, this study focuses on interactions of synaptic plasticity in the MD-mPFC and HP-mPFC projections in an evoked potential level. Under the condition that recording either the MD or HP stimulation evoked field potential in the mPFC, twenty or fifty 100 µs-pulses at 250 Hz were applied 12 times at 10 s intervals to induce weak LTP in the MD-mPFC or strong LTP in the HP-mPFC pathway, respectively. When the weak LTP induction of the MD-mPFC was synchronized with strong LTP induction of the HP-PFC, the MD-mPFC revealed the cooperative effect of the LTP (about +10%). Our results suggest that the mPFC allows MD information to be positively associated with that of the HP. [Jpn J Physiol 55 Suppl:S182 (2005)]
