Effect of adenosine on bicuculline-resistant paired-pulse inhibition in the rat hippocampal slice.
This study extends previous investigations into the effect of adenosine on bicuculline-resistant paired-pulse inhibition between field potentials evoked 300 ms apart in the CA1 area of the rat hippocampal slice. A direct assessment of the effect of adenosine on paired-pulse inhibition is complicated by the facts that adenosine directly depresses evoked potentials and bicuculline-resistant paired-pulse inhibition is greater between pairs of small potentials than between pairs of larger potentials. Adenosine increased bicuculline-resistant paired-pulse inhibition when stimulus strength was constant between adenosine and control but paired-pulse inhibition of responses in adenosine was markedly less than paired-pulse inhibition of control responses of the same size. Furthermore, adenosine decreased the size of conditioned potentials to a significantly lesser extent than unpaired potentials of the same initial size. Taken together the results indicate that adenosine can decrease bicuculline-resistant paired-pulse inhibition in the hippocampus. A possible mechanism for this effect is that adenosine is suppressing transmission at excitatory terminals onto interneurones which would suggest that these receptors are more sensitive to adenosine than those on the Schaffer collateral/CA1 pyramidal cell synapses. In this case adenosine should reduce paired-pulse inhibition at lower concentrations than are required for depression of single evoked potentials. A comparison of the concentration-response relationships for the effects of adenosine on paired-pulse inhibition and on single evoked potentials ruled out greater sensitivity of adenosine receptors at excitatory terminals onto interneurones as an explanation for adenosine's action on bicuculline-resistant paired-pulse inhibition.(ABSTRACT TRUNCATED AT 250 WORDS)
Higgins
M J
MJ
Pharmacology Laboratories, Institute of Biomedical and Life Sciences, University of Glasgow, United Kingdom.
Stone
T W
TW
D000241:Adenosine / Q000494:pharmacology*; D000818:Animals; D001418:Baclofen / Q000494:pharmacology; D001640:Bicuculline / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004351:Drug Resistance; D004558:Electric Stimulation / Q000379:methods; D006624:Hippocampus / Q000187:drug effects*; D066298:In Vitro Techniques; D008297:Male; D009433:Neural Inhibition / Q000187:drug effects*; D009994:Osmolar Concentration; D051381:Rats; D017208:Rats, Wistar
D001418:Baclofen; D000241:Adenosine; D001640:Bicuculline