The Role of Norepinephrine in Long-Term Potentiation at Mossy-Fiber Synapses in the Hippocampus

Publisher Summary This chapter focuses on neurons in the regio inferior of the hippocampus and on the mossy fiber synapses that arise from dentate granule cells and terminate on the CA3 pyramidal neurons. The chapter reviews the results of experiments that have demonstrated that norepinephrine (NE) can enhance the magnitude, duration, and probability of induction of long-term potentiation (LTP) at the mossy fiber synapses. These experiments have suggested that under normal conditions, the release of NE may play a required role in the induction of LTP at these synapses. In the experiments described in the chapter, both intracellular and extracellular recordings from CA3 pyramidal neurons were used to measure the synaptic responses to stimulation of the dentate granule cells. The mossy fiber synapses are relatively unique. They are large, contain zinc and dynorphin, and they are ultrastructurally identifiable with both light and electron microscopes. In the experiments, an extensive anatomic, physiologic, and electrotonic analysis of the synaptic input was performed. It was found that the maximum electrotonic distance of the mossy fiber synapses from the cell bodies of the CA3 pyramidal neurons was approximately 0.06% or 6% of a length constant.