| In this thesis, the hippocampal theta rhythm EEG pattern is examined in the context of its functional significance as described by the Sensorimotor Integration Model, with an emphasis on the antagonistic role played by the median raphe nucleus in desynchronizing this rhythm. To provide background, the gross, functional, and cellular anatomy of the hippocampus and connected structures associated with the modulation of the hippocampal EEG theta rhythm are introduced. As the major focus of this thesis, the median raphe nucleus is examined in detail. Three studies are presented that investigated the relationship of the MR to the hippocampal theta rhythm. The first study used simultaneous drug infusions to antagonize MR and the medial septum (MS) and determined that the medial septum manipulation had a dominant effect on the hippocampal theta rhythm. Using triple-label immunohistochemistry, the second study determined that the MR's glutamatergic projection expressed the 5-HT1A receptor and was therefore affected by drug infusions targeting that receptor, in parallel with the MR's serotonergic projection, as established by the literature surveyed in this thesis. The third study recorded signals from single neurons in the hippocampus during functional inactivation of the MR 5-HT1A receptor population, finding that they maintained their theta-related firing patterns in this condition. |
