Chronic Exposure Of Streptavidin-coated Quantum Dots On Hippocampal Synaptic Plasticity

Quantum dot has prominent physicochemical property, such as small size effect, surface effect, quantum size effect, macroscopic quantum tunneling effect and etc. Due to the above features, it has been widely used in various fields like electronics, optics, magnetics, energy chemical industry, biomedical science, environmental protection and micromachining etc al. With the industrialization course of the quantum dot, it will be put on production in a large scale and wide application in the near future. Meanwhile, it will stand a good chance of bringing people into contact with quantum dots. Obviously, there will be a great need to develop a research on the biological security and the potential hazard of quantum dot.Hippocampus plays a critical role in spatial learning and memory, and synaptic plasticity is regarded as cell and molecular basis of learning and memory. Therefore, we choose the rat hippocampus as the point of penetration to research on the effect of the chronic exposure of quantum dots coated with Streptavidin on I/O curve, PPF and LTP.1. I/O curves of fEPSP and PS indicates that 0.5 nM strep-CdSe/ZnS QD has no significant difference with control group; 10 nM strep-CdSe/ZnS QD chronic exposure can significantly increased the fEPSP slope and the PS amplitude in the rat hippocampus's DG area, so that the basic synaptic transmission in the rat hippocampus's DG area has been reinforced. Our previous study has proved that the application of high concentration of QD resulted in the significant elevation of calcium ion, which can further enhance the release of certain neurotransmitter and promote the response of the postsynapse. This may be the reason that chronic exposure of high concentration of QD can lead to the strength of basic synaptic transmission.2. Paired-pulse facilitation (PPF) is a facilitation of a second response when a synapse is stimulated twice with a short interstimulus interval, and it is regarded as a short-term synaptic plasticity. This phenomenon partly attributes to the increased neurotransmitter in the second stimulation, and furthermore, the postsynaptic adjustment rather than the presynaptic adjustment is much more important for PPF of PS in the DG area. Our study indicated that both 0.5nM and 10nM chronic QD exposure significantly reduce the peak value of PPF, which suggests that the chronic exposure of quantum dots can damage the short-term synaptic plasticity of the rat hippocampus's DG area. 3. LTP is an activity-dependent synaptic plasticity, and is regarded as the neurobiological basis of learning and memory. Our research suggested that the chronic exposure of quantum dots of 0.5 nM strep-CdSe/ZnS QD can significantly reduce the LTP amplitudes of EPSP and PS. Compared with the exposure of quantum dots of 0.5 nM strep-CdSe/ZnS QD exposure group, 10 nM strep-CdSe/ZnS QD decreases the LTP amplitudes of EPSE and PS to a further step. The above results suggested that the chronic exposure of quantum dots can damage the long-term synaptic plasticity of the rat hippocampus's DG area. The release of Cd2+, Oxidative Stress may account for the impaired-synaptic plasticity, however, the further studies are needed to clarify the detailed mechanism.