| 其他摘要 | The conduction of somatosensory information and the formation of perception are processed by the spinal cord and the brain collaboratively. Simultaneous recording the interactions between the brain and spinal cord is important to reveal the functional connectivity within the entire central nervous system. The biggest challenge during this process is from spinal cord, because unlike brain, the spinal cord flexes with the body during movement. Animal research plays an important role in overcoming the limitations of human study, especially in the mechanism research. The vivo multi- channel recording method has a high temporal and spatial resolution, and can be easily used in animals. Besides, most previous studies have been carried out under anesthesia, and the neuronal activity is significant different between awake and anesthetized states. Therefore, it is necessary to carry out further studies in freely moving animals.
In recent years, the soft carbon nanotube fiber (CNTF) electrodes have been developed, showing great advantages over traditional rigid electrodes in mechanical compliance, biocompatibility and long-term stability. Therefore, we developed a new method with CNTF electrodes, to record the stimulus-related-signals in spinal cord and brain simultaneously in freely moving rats. The spinal dorsal horn is the first integrated site of somatosensory peripheral input. The primary somatosensory cortex (S1) is the key brain region for sensory consciousness, which receives a large number of projections from spinal cord, brainstem and thalamus. Thus, we set spinal dorsal horn and S1 as target sites and validated this synchronous recording methods using laser and electrical stimulus.
Our present study has a higher signal-to-noise ratio (SNR), compared with previous spinal cord related studies. In the time interval 250~350ms after laser stimulus onset, there is a negative component in spinal cord field potential, the amplitude of this component is regulated by stimulus intensity and location significantly. The amplitude increases with stimulus intensity, and the amplitude on the ipsilateral side is significantly higher than the contralateral side. The S1-N1 appears about 270~350ms after the onset of laser stimulus, and both the latency and amplitude of S1-N1 are regulated by stimulus intensity. Besides, both the γ-oscillations (gamma-band oscillations, GBOs) and the neuron firing rate in spinal cord and S1 are regulated by the stimulus intensity significantly. The correlation analysis shows a high correlation between spinal cord and S1. In addition, the spinal cord response characteristics evoked by laser are highly correlated with pain score, which is consistent with the relationship in S1. This indicates that spinal cord electrophysiological signals may also represent pain intensity. In the end, we further applied normalized partial directed coherence (nPDC) analysis to the electrophysiological signal in spinal cord and S1, and find an increased information flow from spinal cord to S1 during laser stimulus presentation in 0-300Hz band, and the information flow increases with stimulus intensity. In short, although there are some differences between spinal cord and S1 in pain processing, they show high consistency in demonstrating stimulus physical characteristics and representing pain intensity.
In the time interval between 20 and 30ms after electrical stimulus onset, there is a negative component in the spinal cord field potential, which is not regulated significantly by electrical stimulus intensity and location. In addition, at the time interval of 20~30ms and 40~60ms after electrical stimulus onset, there is a negative component in the S1 field potential respectively, both of them are regulated by stimulus intensity. Besides, the spike firing rate in the spinal cord is regulated by stimulus intensity and location, which increases with stimulus intensity, and the firing rate on the ipsilateral side is higher than the contralateral side. While the spike firing rate in S1 neither regulated by stimulus intensity, nor by stimulus location. Collectively, different from the high consistency in laser stimulus modality, there are more difference in electrical modality. The further nPDC analysis shows there is no significant information flow between spinal cord and S1.
In conclusion, we developed a novel experimental method for synchronous recording of spinal cord and cortex in freely moving rats, and verified the validity of this method with laser and electrical stimulus. And some of our present results are consistent with previous researches, the new findings are also reasonable in anatomy. Besides, the neural mechanism of spinal cord and S1 in pain and touch modulation and processing, as well as the functional connection between spinal cord and S1 are also explored. And this method can be widely used in future research to explore the underlying neural mechanisms of sensation and motion. |
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