Role Of Hippocampal PSD-95PDZ In Long-term Cognitive Dysfunction Induced By Isoflurane Early Exposure

Currently around1.5million of individuals in the early postnatal period experience anesthetic exposure every year. Previous studies have demonstrated that early exposure to anesthetics is a dangerous factor that causes later development of learning disabilities and produces cognitive deficits during brain development period. Anesthetic isoflurane exposure markedly causes long-term neuropathic alterations in the new born rodents that even last into adulthood. But few study focus on acute effect of isoflurane on neurogenesis in the developing brain. In addition, the underlying mechanisms of isoflurane exposure resulting in synaptogenesis and neuroapoptosis remain to be illustrated. Based on this, more and more investigators begin to re-survey the application and security of these anesthetics including isoflurane in pediatrics, and to explore more studies on brain development after anesthetic exposure.Previous studies have shown that hippocampal neurons are involved in the synaptic mechanism of learning and memory. Neurogeneis and synaptogenesis during rapid formation period are very sensitive to be impaired in the developing nervous system. Several lines of evidence have shown that this long-term cognitive impairment can be attributed to neurogenesis suppression after anesthetic isoflurane exposure in the early postnatal period.Activities ofN-methyl-D-aspartate (NMDA) receptor subunits(NRs) and glutamate release are involved in the regulation of hippocampal neuron development. Hippocampal postsynaptic protein NRs are involved in the synaptic mechanism of learning and memory, and the degenerative alterations occur after knocking down the protein NRs. The functional activities of NRs are regulated by postsynaptic density-95(PSD-95) family proteins, which contain three PDZ domains in their N-terminus. Through the first two PDZ domains (mainly PDZ2), PSD-95interacts with NMDA receptor NR2subunits and regulate synaptic plasticity mediated by NRs. Therefore, we hypothesize that PSD-95PDZ-mediated protein interactions (PSD-95PDZ MPI) may be involved in the effect of early anesthetic exposure on long-term cognitive impairment.To determine whether PSD-95PDZ contribute to long-term cognitive impairment after early anesthetic isoflurane exposure, we will investigate four lines of the underlying mechanisms for this issue.1) The effect of isoflurane on the disrupting PSD-95PDZ.To determine the effect of isoflurane on the disrupting and interfering of PSD-95PDZ, we will observe the effect of isoflurane on PND7rats by co-immunoprecipitation.2) The effect of PSD-95PDZ on hippocampal LTP. To address this, we will observe the suppressive effect of isoflurane on hippocampal LTP by application of antagonists of PSD-95PDZ.3) The role of PSD-95PDZ in the long-term cognitive impairment after early anesthetic isoflurane exposure. We will explore the mechanism of isoflurane on cognitive impairment by up-regulating PSD-95and using antagonists of PSD-95PDZ.4) The role of PSD-95PDZ in the hippocampal neurogenesis and synaptogenesis after isoflurane exposure. By up-regulating PSD-95and using antagonists of PSD-95PDZ, we will determine the influence of isoflurane on hippocampal neurogenesis and synaptogenesis in rats.Our data have demonstrated the results as follows.1. Isoflurane dose-dependently inhibited the interactions of PSD-95and NR2in PND7and PND60rats.2.1soflurane exposure (1.5%) andTat-PSD-95, which is an antagonist of PSD95PDZ-mediated protein interactions, could remarkably inhibit fEPSP LTP in hippocampal slices. No significant effect of isoflurane (1.5%) on hippocampal fEPSP LTP was shown in PND60rats.3. Isoflurane exposure may cause short-term cognitive impairment dependent on hippocampus in PND60rats. Tat-PSD-95showed the similar effect with isoflurane on long-term hippocampal cognitive impairment in PND7rats. Up-regulating hippocampal PSD-95reduced the cognitive impairment induced by isoflurane in PND7rats.4. Both isoflurane exposure and Tat-PSD-95may inhibit hippocampal neurogenesis and synaptogenesis and promote neuroapoptosis in PND7rats. Up-regulating hippocampal PSD-95may reduce cognitive impairment induced by isoflurane exposure in PND7rats.Conclusions:Isoflurane exposure markedly affects protein interactions mediated by PSD-95by interfering and disrupting hippocampal postsynaptic PSD-95PDZ such as PSD-95-NR2and thus causes subsequent long-term neurocognitive impairment dependent on hippocampus. The underlying mechanisms are attributed to hippocampal LTP suppression, neurogenesis, synaptic proteins and synaptic formation inhibition and neuroapoptosis promotion.