| Resting-state functional connectivity(RSFC)refers to the functional connectivity between brain regions characterized by the spatio-temporal correlation of spontaneous neural activity signals in the brain without external stimulation,and is one of the important ways to cognize brain function and understand brain diseases.The widely used magnetic resonance imaging RSFC studies rely on the neurovascular coupling mechanism,which can only reflect neural activity indirectly through hemodynamic signals and cannot construct functional connections based on neural electrical activity patterns.There lacks intensive studies on the functional connections of specific types of neuronal activity.With the development of neuronal labeling technology,the genetically encoded calcium indicator GCa MP can specifically label single types of neurons.Combined with fluorescent calcium imaging technology,it can detect and track of specific types of neuronal activity,effectively solving the problem of signal sources in RSFC studies.In this paper,GCa MP6 s fluorescent probe was used to separately label excitatory neuron: Vesicular glutamate transporter 2(VGLUT2)neuron,and three kinds of inhibitory interneurons: Parvalbumin(PV),Somatostatin(SOM),Vasoactive intestinal polypeptide(VIP)neurons,and wide-field calcium imaging technology was used to explore the RSFC of specific types of neurons on the cerebral cortex during adulthood,development,and under anesthesia.The main contents of the research include:(1)A wide-field fluorescence calcium imaging system was built to study the RSFC of four specific types of neurons on the adult mouse cerebral cortex under awake states.The main RSFC patterns of various neuron activities were divided by the fast clustering method based on density centers,and the RSFC characteristics of different types of neurons were compared and analyzed.It was found that the RSFC spatial distribution of low-frequency spontaneous activity of VGLUT2 neurons was similar to that of other inhibitory neurons in most of the observed brain regions,but the strength of their RSFC connections and the range of brain regions involved in the connections were larger than the RSFC of inhibitory neurons.The differences between the RSFC patterns of different types of neurons were mainly manifested in the middle and posterior parts of the following brain regions: motor cortex,somatosensory cortex and barrel cortex.In particular,the low-frequency spontaneous neural activity of VGLUT2 neurons on the middle,mid-posterior,and caudal sides of the unilateral barrel cortex had a high correlation with that on the middle,mid-posterior,and caudal sides of the motor cortex,respectively,whereas no such corresponding features were found in the functional connectivity patterns of PV,SOM,and VIP neurons.(2)Based on a chronic cranial imaging window model,wide-field calcium imaging was used to explore RSFC changes in specific types of neurons during mouse brain development.The strength of functional connections between low-frequency spontaneous activity in various brain regions of specific types of neurons on the cortex was found to vary dynamically during brain development,with the strength of functional connections between some brain regions showing an inverse variation during the two developmental stages.VGLUT2 neurons had established a relatively well-established functional connectivity pattern in early brain development(Postnatal day 10～14).With the development of the brain,the RSFC of inhibitory neurons was gradually established,the strength and the range of brain areas involved in the connections gradually increased,and functional connections between the bilateral hemispheres were established.In addition,none of the three inhibitory neurons showed functional connectivity patterns between barrel cortex and motor cortex in early development.PV neurons showed this functional connectivity pattern in the first stage of development(postnatal day 14～28),while SOM and VIP neurons showed this functional connectivity pattern in the second stage(postnatal day 28～56).(3)Burst suppression(BS)is an electroencephalogram(EEG)pattern that occurs when the brain is under deep anesthesia.The characteristics of RSFC under deep anesthesia were explored using a combination of wide-field calcium imaging and EEG recordings.VGLUT2 neuronal activity was found to be suppressed in observed brain regions when the EEG showed inhibitory features.When the EEG showed burst waveforms,the spontaneous activity of VGLUT2 neurons in the occipital-parietal lobe near the midline cortex(secondary motor cortex,retrosplenial area)was highly time correlated.Under the BS states induced by sevoflurane and isoflurane,the peak amplitude of the calcium signal "burst" and the range of brain areas where the "burst" occurred were larger than those under the propofol induced BS.In addition,the correlation between EEG signals in frontal cortex and calcium signals in occipital-parietal cortex was compared.It was found that the fluorescence signal in the medial occipital-parietal cortex was more correlated with the EEG signal.The results suggested that cortical VGLUT2 neuronal activity under the BS state exhibited new spatial patterns. |
