Second messenger modulation of electrotonic coupling between region CA3 pyramidal cell axons in the rat hippocampus.

Gap junction coupling between hippocampal cell axons has been implicated in high frequency oscillations. We used antidromic activation of region CA3 from the fimbria to test the hypothesis that, if gap junctions exist between CA3 pyramidal cell axons, they should cause cross-talk between cells. Agents known to open gap junctions, including 8-Br-cAMP and forskolin (analogue and activator of the cAMP 2nd messenger system respectively) augmented the antidromic population spike and uncovered fast oscillations in the extracellular field. Increasing 2nd messenger concentration reduced the threshold stimulation for antidromic triggering of action potentials, suggesting an improved capability to conduct the electrical impulse retrogradely to the soma. Our studies support the existence of gap junction coupling between CA3 pyramidal cell axons in the fimbria that can be acutely modulated by 2nd messengers.