New Methods Of Brain Structural And Functional Network Analysis Based On Small Animals Magnetic Resonance Imaging

Functional magnetic resonance imaging(f MRI)technology is still in preclinical research stage due to its unsatisfied stability and unclear signal mechanism,and small animal f MRI technology can provide interpretation of the f MRI results in combination with invasive detection methods such as electrophysiology and virus tracing.However,unclear mechanism of anesthetic,insufficient neuronal structure foundation,and unsatisfied image resolution limit the explanatory power of small animal f MRI.Therefore,the thesis focused on the three aspects including the effects of anesthetics on f MRI network,the neural circuits basis of f MRI network and the method for improving f MRI resolution.The main research contents are as follows:First,the thesis has studied the effect of the anesthetic isoflurane on brain f MRI network.Small animal f MRI is usually performed under anesthesia.Studies have shown that the use of anesthetic isoflurane may lead to abnormally increased resting-state functional connectivity strength,but some studies have shown that isoflurane inhibits animal brain activity.This study intended to explore the effects of isoflurane on brain f MRI network by comparing the task-state and resting-state functional networks of isoflurane and non-isoflurane induced animals.An awake animal experimental system was constructed.Then the light induced task-state and the resting-state f MRI were performed under isoflurane and non-isoflurane condition.Results showed that the task-state and resting-state f MRI networks in isoflurane induced state were similar to those in non-isoflurane induced state,while the signal intensities were lower.Thus,isoflurane could be used in f MRI experiments on the premise that enough animal quantities were fulfilled to obtain significant results.Second,the thesis has studied the characteristics and neural circuits of f MRI network in animal hyperalgesia model.Both chronic pathological pain and long-term use of opioids can induce hyperalgesia,but the mechanism of hyperalgesia in central nervous system remains unknown.This chapter intended to explore the relationship between the two hyperalgesia models by comparing the f MRI network in sciatic nerve injury(SNI)model and opioids-induced hyperalgesia(OIH)model.The experiment compared the task-state and resting-state f MRI networks in SNI model and OIH model.Different response patterns were shown in SNI model and OIH model with task-state and resting-state f MRI.Among them,the task-state response areas of SNI model were concentrated on pain-related regions,such as primary sensory cortex,secondary sensory cortex and insular cortex,and few changes occurred in functional connectivity strength of resting-state f MRI.In OIH model,the task-state response areas were concentrated on sensory regulation-related areas,such as primary sensory cortex,thalamus,and retrosplenial granular cortex,and the functional connectivity strength of multiple brain regions in resting-state f MRI changed a lot.The results indicated that the hyperalgesia behavior of SNI model might derive from the enhancement of peripheral afferent signals,while in OIH model the hyperalgesia behavior was related to the sensory heterization of central nervous system.The experiment further explored the neural circuits of the parietal lobe(MPt A)and the ventrolateral thalamus nucleus(VP),which both showed significant changes in resting-state f MRI of OIH model.Results demonstrated that there were direct synaptic connection and increased local field potential synchronization between MPt A and VP in both OIH and SNI models.Thus,changes in functional networks of resting-state f MRI in hyperalgesia models had their corresponding neural circuits.And MPt A and VP should be considered as research targets for hyperalgesia.Third,the thesis has studied the application of MRI reporter gene in the analysis of brain structural and functional networks.Brain functional network displayed by f MRI can only reflect the brain activity in a macroscopic and indirect way,which is limited by resolution and principle of f MRI.The development and application of MRI reporter genes may improve the sensitivity and credibility of f MRI.This thesis intended to dissect the neuronal structural network in living animal by expressing MRI reporter gene ferritin with the assistance of virus vector.The recombinant viral vector r AAV2-retro-CAG-Ferritin was constructed and then injected into the mouse striatum.Changes in MRI signals were observed in multiple brain regions,which were consistent with the ferritin expression areas.Thus,this method could be used to illustrate the neuron structural network in vivo.The experiment further compared the in vivo neuron structural network and the resting-state f MRI network.Results showed that there was significant ipsilateral preference in striatumrelated structural network,while more balance in functional network between two cerebral hemispheres,indicating that the striatum-related neuronal structural network and MRI functional network were different.The application of MRI reporter gene improved the analytical ability of MRI brain structural network and provided a new insight for the analysis of functional network.In summary,the thesis optimized the current methods and developed new methods for analyzing brain structural and functional network based on animal MRI,which improved the stability and interpretability of small animal MRI technology and expanded the application of small animal MRI in neuroscience research.