Effects of Long-Term and Acute Hindlimb Unloading Model on Neuroelectrophysiological Signals of Hippocampal Interneurons and Pyramidal Cells Using Microelectrode Arrays

Microgravity is the key environment of weightlessness experienced by all astronauts during spaceflights that cause severe physiological alterations in the human body. The effect of microgravity on the nervous system has not been elucidated. In this study, hindlimb unloading rats were used as the simulated microgravity model, and self-designed novel microelectrode arrays were used as the essential tools. The special arrangement of detection sites and platinum nanoparticles modification made the electrodes have excellent performance at the neuron level. By comparing the changes of the neuroelectrophysiological signals in the CA1 regions of rats in different periods of long-term and short-term modeling, the following results were obtained. In the long-term model, the firing rates reached a peak after about seven days of modeling, and then kept decreasing till 28 days. The average firing rates and individual single cell firing rates of the acute model rose immediately after modeling. Analysis of power spectral density signals showed that the signals shifted to the low frequency band after both long-term and acute modeling. The neurons in the CA1 were classified into pyramidal cells and interneurons. The continuous observation of neurons under the acute modeling showed that the firing rates and amplitude of pyramidal cells have a greater increase than interneurons. The self-designed novel implantable microelectrode arrays provide an advanced tool for the detection of neurons in hindlimb unloading rats. The hippocampal nerve cells were impaired after modulation, and that pyramidal cells were more susceptible than interneurons.