Effect Of ZD7288 On The Synaptic Transmission And Synaptic Plasticity In The Schaffer Collateral-CA1 Synapse Of Hippocampus In Normal And Ischemic Brain

PartⅠEffect of ZD7288 on the synaptic transmission and long-term potentiation in the Schaffer collateral-CA1 synapse of hippocampusBackground and purpose:Hyperpolarization-activated cyclic-nucleotide-gated (HCN) channels are expressed in a broad range of cells and suggested to play an important role in the control of membrane excitability and rhythmic neuronal activity. The evidence indicates that HCN channels may be involved in long-term potentiation (LTP) in the hippocampus and contributed to synaptic integration and plasticity. Our previous study showed that the selective HCN channels blocker, ZD7288 (4-(N-ethyl-N-phenylamino)-1,2-dimethyl-6-(methylamino) pyrimidinium chloride) can inhibit the amplitudes of population spikes (PS) and block the induction of LTP in perforant path-CA3 region in rat hippocampus in vivo. However, little is known about the effect of ZD7288 on the induction and maintenance of LTP at the Schaffer collateral-CA1 synapse in vivo. In the present study, we aim to investigate the effect of ZD7288 on synaptic transmission and high frequency stimulation (HFS)-induced LTP in the Schaffer collateral-CA1 synapse of hippocampus in vitro and in vivo, and identify whether the effect of ZD7288 on the induction of LTP can be reversed by direct activation of N-methyl-D-aspartate (NMDA) type of glutamate receptor.Methods:We have examined the effects ZD7288 on synaptic transmission and LTP in the Schaffer Collateral-CA1 synapse in mouse hippocampus slices in vitro and rat hippocampus in vivo, the field excitatory postsynaptic potentiation (fEPSP) and LTP were analyzed by extracellular electrophysiological recordings.Results:(1) Perfusion of 10μM ZD7288 had no effect on basal synaptic transmission, but prevented the induction of HFS-induced LTP at the Schaffer collateral-CA1 synapse in mouse hippocampal slices; perfusion of 50μM ZD7288 significantly depressed basal synaptic transmission. (2) Intracerebroventricular (i.c.v.) application of 0.5-10μg ZD7288 had no effect on the basal synaptic responses compared with normal saline-injected controls, while the higher dose of 25μg ZD7288 obviously decreased the amplitude of fEPSP at the Schaffer collateral-CA1 synapse in vivo; I.c.v. administration of 0.5,1,5 and 10μg ZD7288 significantly and dose dependently inhibited the induction of HFS-induced LTP; But 10μg ZD7288, when given 30 min after HFS, did not alter the expression and maintenance of LTP; In addition, application of 0.03μg NMDA for 5 min before administration of 5μg ZD7288 resulted in a significant suppression of the response to ZD7288, NMDA partially reversed the inhibition of ZD7288 on the LTP induction.Conclusions:The results suggest that ZD7288 has the ability to modulate synaptic transmission and prevent the induction of LTP at the Schaffer collateral-CA1 synapse of hippocampus, and that this inhibitory effect can be attenuated by direct activation of the NMDA receptor. In addition, ZD7288 has no effect on the expression and maintenance of the potentiated response once LTP has been established. Part II Effect of ZD7288 on the synaptic plasticity at hippocampal CA1 region after focal cerebral ischemia reperfusion injury in ratsBackground and purpose:Stroke is one of the commonest cause of death and the principal cause of disability in the world, which result in damage to neuronal networks and impairment of movement, sensation, cognition and learning. The CA1 hippocampal region is one of the most vulnerable areas to ischemia or anoxia in the brain, long-term potentiation (LTP) is one of the principal forms of activity-dependent synaptic plasticity that are regarded as cellular and molecular mechanisms of learning and memory. Synaptic transmission and brain plasticity, especially hippocampus region, have been suggested to play an important role in improving cognition, learning and memory during neurorehabilitation in the post-stroke recovery phase. Excitotoxicity is a critical mechanism contributed to neuronal damage or death after cerebral ischemia. The major step of excitotoxic cascade is overactivation of glutamate receptors and results in massive depolarization, abnormal Ca2+ entry and cytoplasmic Ca2+ overload, and subsequent causes pathological postischemic synaptic plasticity and impairs activity-dependent LTP. The aim of the present study was to investigate whether ZD7288 can rescue the impaired LTP and the physiological synaptic plasticity at hippocampal CA1 region after focal cerebral ischemia reperfusion injury in rats.Methods:Model of transient focal cerebral ischemia-reperfusion injury was induced by occlusion of the right middle cerebral artery for 2 hours and followed by 48 hours of reperfusion in male Sprague-Dawley rats. Animals were treated by i.c.v. injection of 0.25μg ZD7288 at 30 min and 3 hours after ischemia onset. At 48 hours after reperfusion, LTP induction in hippocampal CA1 region was analyzed by extracellular electrophysiological recordings in vivo, and the expression of NR2B and PSD-95 mRNA in this area was determined by real time PCR.Results:(1) The neurological deficit score of rats treated with ZD7288 was significantly reduced when evaluated at 24 hours and 48 hours after reperfusion compared with ischemia injury model group. (2) Ischemia2h/reperfusion48h injury resulted in an impairment of LTP induction in CA1 region of hippocampus in vivo, and the impairment could be attenuated by icv administration of ZD7288 at 30 min and 3 hours after the onset of ischemia. (3) The NR2B and PSD-95 mRNA level in hippocampal CA1 region was decreased after 48 hours reperfusion, i.c.v. application of ZD7288 partially rescued NR2B and PSD-95 mRNA downregulation induced by focal cerebral ischemia-reperfusion injury in rats.Conclusions:Our results suggest that ZD7288 can partially rescue the impaired LTP and preserve physiological plasticity in ischemic CA1 region of hippocampus after cerebral ischemia-reperfusion injury in the rat.