Electrode Placement

A depiction of the general placement of the stimulating and recording electrodes on the slices in the recording chamber is shown in Figure 10.4. Stimulating electrodes are typically placed on the Schaeffer collaterals (SC) to the pyramidal cell layer (Figure 10.5) in order to study area CA1 of the slice. The cell layer is quite visible by naked eye or with low-power (dissecting microscope) magnification. In slices taken from the middle third of the hippocampus as described above, the pyramidal cell layer appears as a translucent line a few millimeters below the cortical surface. The tips of the stimulating electrodes are generally placed close to the pyramidal cell layer, usually perpendicular to the orientation of it.

FIGURE 10.4

General placement of electrodes during an experiment on the hippocampal slice.

FIGURE 10.4

General placement of electrodes during an experiment on the hippocampal slice.

The recording electrode placement for studying population spikes elicited by SC stimulation also works well if it is placed near the pyramidal cell layer rather than too near the cortical surface (Figure 10.5). Studies of extracellular excitatory postsynaptic potentials (EPSPs)13 and stimulus input to the slice require placement just below the visible layer. While EPSPs are recorded typically from the stratum radiatum, population spikes (PS)13 are most easily examined by recording from the stratum pyramidale. Representative potentials recorded from these two locations are

STR. PYRAMIDALE (POPULATION SPIKE)

STR. PYRAMIDALE (POPULATION SPIKE)

FIGURE 10.5

Top view of a hippocampal slice illustrating the relative locations of cell populations studied in slice experiments. Stimuli delivered to the Schaffer collaterals (SC) evoke excitatory postsynaptic potentials (EPSPs) from the apical dendrites of pyramidal cells in the stratum radiatum while population spikes are evoked in the stratum pyramidale. Typical waveforms are illustrated.

FIGURE 10.5

Top view of a hippocampal slice illustrating the relative locations of cell populations studied in slice experiments. Stimuli delivered to the Schaffer collaterals (SC) evoke excitatory postsynaptic potentials (EPSPs) from the apical dendrites of pyramidal cells in the stratum radiatum while population spikes are evoked in the stratum pyramidale. Typical waveforms are illustrated.

also shown in Figure 10.5. A general reference13 for explanations of these potentials and the associated terminology may be useful for anyone unfamiliar with the basic neurophysiology.

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