Electrophysiological Evaluation of Synaptic Plasticity in Injured CNS - Animal Models of Acute Neurological Injuries: Injury and Mechanistic Assessments - page 122

a b

Stimulating
Electrode

Recording
Electrode

CA1

SC

II/III
V

DG

CA1

PF

CA3

MF

WM CA3

DG

c

3

2

1

0.5 mV

20 ms

↑ ↑

Fig. 4. Field potential recording in neocortical and hippocampal slices. ( a ) An oblique cut brain slice showing both the barrel
cortex and hippocampus. Individual barrels in layer IV of cortex are discernible while major structures of the hippocampus,
including dentate gyrus (DG) and CA3 and CA1 regions, can be easily identifi ed in this slice. For neocortical FPR, a stimulating
electrode (in red ) is placed in white matter and a recording pipette (in blue ) in layer V directly above the stimulating
electrode. ( b ) A schematic drawing shows the structure of synaptic pathway in hippocampus. The arrangement of stimulat-
ing ( red ) and recording ( blue ) electrodes for recording CA1 fi eld potentials is also demonstrated. PF perforant pathway,
MF mossy fi bers, SC schaeffer collaterals. ( c ) Averaged fi eld potential responses from layer V evoked by a paired-pulse
stimulation of white matter of a cortical slice in rat. Following the stimulation artifact ( arrow ) is a two-component negative
potential. The fi rst one (1) is a population spike corresponding to compound action potentials activated by antidromic
stimulation of axons of layer V neurons. The second (2) is the glutamatergic fEPSP that is generated from synaptic activity
in layer V, which is evoked by stimulation of presynaptic fi bers in white matter. Additionally, a positive potential (3) following
these two components is a fi eld IPSP, which has low amplitude but lasts for long time.

3.3. FPR in
Hippocampal Slices:
Evaluation of
Long-Term Synaptic
Plasticity

1. Hippocampus slices are placed in an interface chamber, perfused
with oxygenated ACSF (95% O 2 /5% CO 2 ) preheated to ~32°C
at a rate of 2-3 ml/min.
2. To record CA3-CA1 fi eld potentials, Schaffer collateral axon
fi bers are stimulated with a bipolar tungsten electrode placed
in the stratum radiatum at the CA3 and CA1 border of the
hippocampus. The recording electrode is placed in the stratum
radiatum of the CA1 region; the distance between the recording
and stimulating electrode is about 300-500 m (Fig. 4b ).

3. To record mossy fi ber-CA3 fi eld potentials, the stimulating
electrode is placed next to the granule cell layer. The recording
pipette is placed in the stratum lucidum of the CA3 region.
4. Stimulus-response curves should be performed at the begin-
ning of each experiment. Stimulation pulses (100

μ

μ s, every

20 s) of increasing intensity (between 10 and 200 A

steps) are delivered to evoke fi eld excitatory postsynaptic
potentials (fEPSPs) until maximum amplitude is recorded.

μ A in 20 μ