Neuroscience 2000 Abstract
| Presentation Number: | 69.4 |
|---|---|
| Abstract Title: | Electrical stimulation of CA3 evokes a short latency population EPSP from CA1 interneurons in freely moving rats. |
| Authors: |
Muller, R. U.*1
; Fox, S. E.1
; Hargreaves, E. L.1
1Dept of Physiology, SUNY-Brooklyn, Brooklyn, NY |
| Primary Theme and Topics |
H. Other Systems of the CNS - 98. Limbic system and hypothalamus |
| Secondary Theme and Topics | I. Neural Basis of Behavior<br />- 108. Learning and memory: physiology |
| Session: |
69. Limbic system and hypothalamus I Poster |
| Presentation Time: | Sunday, November 5, 2000 11:00 AM-12:00 PM |
| Location: | Hall G-J |
| Keywords: | Hippocampus, Evoked Potentials, Single Units, Paired Pulse |
To a very good first approximation, CA1 field potentials (1Hz -10KHz; X1,000) evoked in freely moving rats by microstimulation of CA3 conform closely to expectations from hippocampal slices and from the hippocampus of anesthetized rats (Hargreaves & Muller, SFN 2000). Thus, in CA1 str. oriens we saw a positive going 3 msec event corresponding to the population EPSP from pyramidal cells. The amplitude of this event grew with increasing stimulus intensity; at higher intensities a biphasic, initially negative pyramidal cell population spike was superimposed on the field EPSP. With electrodes in and deep to str. pyramidale the sign of the population EPSP but not the population spike was inverted. In addition to the usual evoked field potential we saw in some rats a short latency (1 - 1.5 msec) negativity whose sign did not reverse as the electrodes were driven into str. radiatum. This early event occurred at lower stimulus intensities than later pyramidal cell population events. We suggest that the early event is a monosynaptic population EPSP from CA1 str. oriens interneurons. In this hypothesis, the early event polarity in str. oriens and below is negative because the electrodes are deeper than the generating cells. The low threshold and brief latency may indicate that the neural elements directly activated by stimuli are larger than most CA3 Schaffer collaterals. We also note that evoked spike latencies in interneurons tend to be at and after the peak of the early event. Moreover, in some cases high frequency noise starting at the peak of the early event was evoked by stimuli too weak to generate any later events; this noise may reflect multi-unit activity in interneurons. Finally, the early event caused by a second shock at the peak of the early negativity from a first shock is reduced in amplitude, perhaps due to inhibition of inhibitory cells whereas the late event from the second shock is enhanced, as if due to disinhibition of pyramidal cells. The early field potential event may reveal a subtlety of the CA3 → CA1 pathway not previously seen because of stimulating electrode location or because we explored a regime of very weak stimulation.
Supported by R01-NS37510
Sample Citation:
[Authors]. [Abstract Title]. Program No. XXX.XX. 2000 Neuroscience Meeting Planner. New Orleans, LA: Society for Neuroscience, 2000. Online.
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