This article presents a method for recording theta oscillations in the hippocampus of mice using local field potential (LFP) electrodes. The study highlights the synchronization of neuronal network activity across different layers of the hippocampus.
Begin with an isolated mouse hippocampus in a recording setup.
Lower the local field potential or LFP electrode to the surface of the hippocampus. This electrode can detect extracellular voltage changes indicative of neuronal network activity.
Insert the electrode and observe the voltage changes.
Insert further into the lower layer and observe the rhythmic neuronal network activity, known as theta oscillations.
Position a second electrode at a distance from the first within the same layer to record theta oscillations across a broader region.
Monitor the synchronization of theta oscillations over considerable distances. This shows the connectivity of the neuronal network.
To record theta oscillations through different hippocampal layers, begin by placing the second electrode in the upper layer.
Gradually lower the electrode through different layers.
Record and observe the inversion of the oscillation pattern, which reflects the unique neuronal composition and function of each layer of the hippocampus.
In this procedure, lower the LFP electrode to the surface of the hippocampus. Advance the LFP electrode through the pyramidal layer, and observe the increase in extracellular spiking activity. A single unit discharge from individual neurons is detected.
Lower the electrode further and note that spiking begins to fade again as the tip crosses into the radiatum. Observe that a clearly visible network oscillation in the theta frequency range becomes apparent, and reaches maximum amplitude as the recording location is lowered through the radiatum.
To test the spatial properties of spontaneous theta oscillations across the CA1 region, place a second LFP electrode into a CA1 site and observe that CA1 theta oscillations synchronize over large distances.
To test the properties of theta oscillations across hippocampal layers, leave a reference electrode in a CA1 radiatum site. Starting from just above the stratum oriens, lower a second electrode into the pyramidal cell layer and through the radiatum. Observe a gradual inversion of the LFP signal across the pyramidal layer.
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