Propofol enhances the field excitatory postsynaptic potentials in CA1 hippocampal slices of young and aged mice

Background Increasing age was shown to decrease the requirements for propfol.However,the mechanisms of ageing-induced potentiation of anesthetic actions have not been clearly explored.The aim of this study is to compare the effects of propofol on the field excitatory postsynaptic potentials （fEPSPs） in hippocampal slices of young and aging mice.Methods Brain slices were prepared from C57BL6 male young （2 months） and aging （＞12 months） mice.The dendritic field excitatory postsynaptic potential was recorded from the CA1 stratum radiatum using patch clamp electrophysiological methods.A bipolar concentric stimulating electrode was placed along the Schaffer collateral for othodromic stimulation.The effects of clinically-relevant concentrations of propofol were studied in the young and ageing mouse tissues.Results Propofol application increased the orthodromically evoked fEPSP produced in slices taken from young and older animals.A striking feature in the I/O relationship was the decreased enhancement of the fEPSPs by propofol in slices from older mice.A clinically relevant concentration of propofol,10 μmol/L,showed more significant enhancement in amplitude and area under the curve （AUC） of fEPSP in young compared to tissues from older mice （amplitude：young （24.9±3.4）％,old （4.6±1.6）％; AUC young （30.6±5.4）％,old （2.1±1.7）％）.There was no statistically significant difference between the paired-pulse facilitation （PPF） ratios calculated for the responses obtained in tissues from young mice.In slices from older mice,in the presence of 10 μmol/L propofol,PPF was decreased and returned to baseline after washout （baseline 1.21±0.01,propofol：1.16±0.01）.Bicuculline （15 μmol/L） blocked the enhancement of propofol on fEPSP in tissues from young and old mice.Conclusion The fEPSP of slices from aging mice demonstrates diminished sensitivity to the enhancing actions of propofol.

ZD7288, a selective hyperpolarization-activated cyclic nucleotide-gated channel blocker, inhibits hippocampal synaptic plasticity

The selective hyperpolarization-activated cyclic nucleotide-gated（HCN） channel blocker 4-（N-ethyl-N-phenylamino）-1,2-dimethyl-6-（methylamino） pyrimidinium chloride（ZD7288） blocks the induction of long-term potentiation in the perforant path-CA3 region in rat hippocampus in vivo. To explore the mechanisms underlying the action of ZD7288, we recorded excitatory postsynaptic potentials in perforant path-CA3 synapses in male Sprague-Dawley rats. We measured glutamate content in the hippocampus and in cultured hippocampal neurons using high performance liquid chromatography, and determined intracellular Ca2＋ concentration（[Ca2＋]i） using Fura-2. ZD7288 inhibited the induction and maintenance of long-term potentiation, and these effects were mirrored by the nonspecific HCN channel blocker cesium. ZD7288 also decreased glutamate release in hippocampal tissue and in cultured hippocampal neurons. Furthermore, ZD7288 attenuated glutamate-induced rises in [Ca2＋]i in a concentration-dependent manner and reversed 8-Br-c AMP-mediated facilitation of these glutamate-induced [Ca2＋]i rises. Our results suggest that ZD7288 inhibits hippocampal synaptic plasticity both glutamate release and resultant [Ca2＋]i increases in rat hippocampal neurons.