| Summary: | 博士 === 國立陽明大學 === 生理學研究所 === 95 === Abstract
The effect of adenosine on the fEPSP was examined in lateral olfactory tract (Ia input) and associative tract (Ib input) in rat piriform cortex. The fEPSP evoked in Ia input showed paired-pulse (PP) facilitation, and in Ib input it showed PP depression, suggesting a lower resting release probability in the Ia input. This was supported by results showing that MK801 blocked the NMDA-receptor fEPSP at a faster rate in the Ib input. Adenosine caused a dose-dependent inhibition of the fEPSP in both inputs, the sensitivity being higher in the Ib input. This effect was mimicked by the A1 receptor agonist, CHA, and antagonized by co-application of the antagonist, DPCPX, showing that adenosine was acting at A1 receptors. Application of DPCPX alone increased the fEPSP, the increase being larger in the Ia input. DPCPX also caused PP depression in both inputs, and the PP ratios measured in its presence were very similar in both inputs. These results suggest a lower endogenous concentration of adenosine in the Ib sublayer than the Ia sublayer, which might account for the native difference in the resting release probability of the two inputs. The inhibition of the fEPSP in both inputs by adenosine was associated with an increase in the PP ratio and with significant lowering of the MK801 blocking rate of the NMDA-receptor fEPSP, suggesting a presynaptic location of the A1 receptors. Blocking of N-, P/Q-type calcium channels occluded the inhibition by adenosine, indicating a downregulation of presynaptic calcium channels by A1 receptors.
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