LTP-associated EPSP/spike dissociation in the dentate gyrus: GABAergic and non-GABAergic components.
The induction of long-term potentiation (LTP) in the dentate gyrus (DG) leads to a change in the firing characteristics of the dentate granule cells. This phenomenon, termed EPSP/spike dissociation, is seen in field potential studies as a shift to the left of the E-S curve, in which population spike amplitude is plotted against pEPSP slope at various stimulus intensities. It has been suggested that EPSP/spike dissociation reflects a decrease in feed-forward inhibition. To test this hypothesis, we blocked GABA-A neurotransmission in a circumscribed area of the DG in urethane-anaesthetized rats by inserting a micropipette filled with 8 mM bibuculline methiodide in saline. We then recorded E-S curves from 9 such electrodes and from 8 control electrodes before and after inducing LTP in the perforant path. Bicuculline prevented the LTP-associated leftward shift of the E-S curves. Instead, the E-S curve showed a consistent shift to the right at the bicuculline sites after LTP, reflecting potentiation of the pEPSP without corresponding increases in the population spike amplitude. The results indicate that the EPSP/spike relationship is controlled largely by GABAergic input, and that potentiation of the population spike in the DG depends largely on a change in the EPSP/spike relationship.
Tomasulo
R A
RA
Department of Neuroscience, University of Virginia School of Medicine, Charlottesville 22908.
Levy
W B
WB
Steward
O
O
D000200:Action Potentials / Q000502:physiology; D000818:Animals; D001640:Bicuculline / Q000031:analogs & derivatives / Q000494:pharmacology; D005071:Evoked Potentials / Q000502:physiology*; D006624:Hippocampus / Q000502:physiology*; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D013997:Time Factors; D005680:gamma-Aminobutyric Acid / Q000502:physiology*
C017069:bicuculline methiodide; D005680:gamma-Aminobutyric Acid; D001640:Bicuculline