Juan-Carlos Toledo-Salas, Ph.D.
Long Term Potentiation in Hippocampus
After Long Term Potentiation an excitatory postsinaptic potential (EPSP) responds more, with a larger amplitude to the same stimulus. This increase of response to the same stimulus is considered to be involved in the generation of memory and learning. Here it is shown how to get good EPSP in the hippocampus, from CA3-CA1 areas, to get good LTP. Changes in the stimulation frequency from high to low frequency can generate the opposite effect, Long Term Depression.
1. Insert the stimulation electrode (4.2mm, 3.8mm) and the recording electrode at (3.4mm, 2.5mm). Lower them about 1.5mm.
2. Lower the stimulation electrode slowly until a positive EPSP is obtained.
3. After a maximum positive EPSP is obtained, lower the recording electrode to get a negative EPSP.
4. Lower slowly the recording electrode to get a good negative EPSP. A curve with a latency of around 12 ms to its minimum point should be obtained.
5. Once you get a good negative EPSP with good latency, apply a double stimulation withe the same intensity.
6. The double stimulation intensity should produce 2 EPSP, the second one with a larger negative EPSP than the first one. Then stimulate with single pulse, increasing the stimulus intensity, to create a curve of intensity vs amplitude. ONLY here you can use dental cement ti fix electrodes.
7. Make a high frequency stimulus with the intensity that gave 50% of maximum amplitude from the intensity vs amplitude curve. This shows the EPSP with high frequency stimulation.
8. EPSP amplitude before high frequency stimulation. Amplitude of EPSP is around -2mV.
9. EPSP after high frequency stimulation. The amplitude increased 50% from -2mV to -3 mV. If maintained after hours it would be Long Term Potentiation.
After high frequency stimulation the excitatory postsynaptic potential will have a larger amplitude for the same stimulus during hours
Here the electrodes should be in CA1 the and CA3 areas of the hippocampus so they can be fixed using dental cement. This technique for insertion of electrodes can also be used for electrophysiological experiments when animals will move freely, recording single unit activity or local field potentials.
 1.Clean skull, drill holes and insert screws for reference, earth and for holding the electrodes. |  2. Insert recording electrodes and seal them with dental cement. |  3. Use dental cement to keep the electrodes in place. |
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