Hippocampal neurochemical and electrophysiological measures from freely moving rats

This paper describes surgical and recording procedures that have been developed which permit the simultaneous monitoring of levels of select neurochemicals (via microdialysis) and measures of dentate-evoked field potentials within the hippocampal formation of freely moving adult rats. To test and evaluate these procedures, they were employed to examine changes in hippocampal neurochemistry and neuronal excitability associated with the establishment and maintenance of hippocampal long-term potentiation (LTP). Measures of hippocampal norepinephrine (NE) and glutamate levels along with measures of the dentate granule cell population spike amplitude (PSA) were obtained before, during, and after tetanization of the medial perforant path using two separate tetanization paradigms. Results obtained using these new procedures in several animals indicated that changes in NE and glutamate levels were strongly correlated with increases in the dentate granule cell PSA measure obtained following tetanization. The results indicate that this newly developed procedure can be effectively used to directly examine the relationship between neurochemical and neurophysiological changes associated with hippocampal neuroplasticity.