Reduction of the extracellular level of glutamate in the median raphe nucleus associated with hippocampal theta activity in the anaesthetized rat
Section snippets
Animals
Sprague–Dawley rats (Labor Animal BT, Budapest, Hungary) of either sex weighing 250–400 g were used. Rats were allowed food and water ad libitum prior to the beginning of the experiments. The experiments were performed under urethane anaesthesia (i.p., 1.2–1.5 g/kg).
Electrophysiological recordings
Hippocampal field activity was recorded with bipolar electrodes positioned in the dorsal hippocampi on both sides. With the rats mounted in a David-Kopf stereotaxic frame, two pairs of twisted insulated stainless steel wires (125 μm)
Results
The location of the microdialysis probe was histologically verified in the MRN in eight out of 12 experiments. In the other four rats, the probe was found in the reticular formation lateral (n=3) or antero-lateral (n=1) to the MRN (Fig. 1).
In all experiments, two patterns of the electrical activity of the hippocampus, one characterized by regular rhythmic oscillations (theta) and the other by desynchronization of the extracellular field potentials (non-theta), changed spontaneously without any
Discussion
The present study demonstrates a significant relationship between spontaneous changes in the electrical activity of the hippocampus and the extracellular level of glutamate in the MRN of the urethane anaesthetized rat. The extracellular level of glutamate was elevated in the MRN during periods dominated by desynchronized hippocampal activity as compared with those mostly containing long and/or frequently-occurring theta segments. Similar to that found during spontaneous changes in the
Acknowledgements
This study was supported by OTKA Grants T17778 to B. Kocsis and T16552 to G. Juhasz.
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