Suppression of pair-pulse depression of the population spike in the dentate gyrus during carbachol-induced theta-like activity in guinea pig hippocampal slices.
In pair-pulse stimulation experiments, pair-pulse depression (PPD) of the population spike (PS) occurred at intervals shorter than 20 ms in the dentate gyrus in guinea pig hippocampal slices. Application of 50 microM carbachol resulted in an increase in the test PS amplitude and caused suppression of PPD. This suppression was antagonized by atropine sulfate, a muscarinic receptor antagonist. Carbachol at 50 microM induced intermittent bursts of theta-like activity (TLA). We compared the pair-pulse index (PPI) during TLA with that in a rest period between bursts of TLA. The PPI was defined as the ratio of the amplitude of the test PS to that of the conditioning PS. The PPI during TLA were significantly larger than that during the rest period, although there were no significant differences in the conditioning PS amplitude and the test pEPSP slope. When TLA was induced, the PPI during the rest period was increased by bicuculline. The PPI during TLA did not change significantly with the drug. The increase by bicuculline in the PPI during the rest period was caused by increase in the test PS amplitude. PPD can occur due to inhibition of granule cell activity by inhibitory neurons. Our findings suggest that the action of inhibitory neurons on granule cell activity is suppressed by activation of muscarinic receptors, with stronger suppression during TLA than during the rest period between bursts of TLA.
Natsume
K
K
Department of Biochemical Engineering and Science, Faculty of Computer Science and Systems Engineering, Kyushu Institute of Technology, Iizuka, Fukuoka, Japan.
Kometani
K
K
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D002217:Carbachol / Q000494:pharmacology*; D018891:Dentate Gyrus / Q000187:drug effects* / Q000502:physiology*; D006168:Guinea Pigs; D006624:Hippocampus / Q000187:drug effects* / Q000502:physiology*; D066298:In Vitro Techniques; D008297:Male; D012146:Rest; D013826:Theta Rhythm
D002217:Carbachol