Effects of LTP-inducing tetanic stimulations of the perforant path on the commissural inhibition and facilitation of dentate granule cell discharge.
Effects of diazepam (1 mg/kg, i.p.) on the commissural influences on granule cells were first examined to further assess its GABAergic inhibitory mechanism. Whereas the commissural inhibition at an interval of 5-8 ms of the contralateral dentate-perforant path (CP) combined stimulus was not enhanced by diazepam, the commissural facilitation at a CP interval of 11-20 ms was reduced, suggesting that the GABAergic inhibition is involved in rather a part of the commissural facilitation at a CP interval of 11-20 msec than a part of the 'commissural' inhibition at a shorter CP interval. Based on the results of diazepam, effects of high-frequency stimulations of the perforant path on the commissural inhibition of dentate granule cells were then examined, in relation to their effects on the dentate paired-pulse depression. These stimulations produced the long-term potentiation of the perforant path-dentate excitatory synapse and significant reduction of the paired-pulse depression. The commissural inhibition at a CP interval of 5-8 ms remained unchanged following tetanization. The commissural facilitation at a CP interval of 11-20 ms was, however, slightly enhanced by tetanic stimulations and a statistical significance was obtained at a CP interval of 19 ms. These results imply that tetanic stimulations of the perforant path selectively reduce the GABAergic component of the commissural inhibition, as well as that of the paired-pulse depression.
Kanda
M
M
Department of Internal Medicine, National Defense Medical College, Saitama, Japan.
Maru
E
E
Ashida
H
H
Tatsuno
J
J
Takatani
O
O
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D003975:Diazepam / Q000494:pharmacology*; D004558:Electric Stimulation; D006624:Hippocampus / Q000187:drug effects / Q000502:physiology*; D008297:Male; D009433:Neural Inhibition / Q000187:drug effects*; D051381:Rats; D011919:Rats, Inbred Strains; D011930:Reaction Time / Q000187:drug effects / Q000502:physiology*; D005680:gamma-Aminobutyric Acid / Q000502:physiology*
D005680:gamma-Aminobutyric Acid; D003975:Diazepam