The Effects Of Neuropeptide Y(NPY) On Neurorepair Of Spinal Cord Injured Zebrafish

Following spinal cord injury(SCI),the spinal cord of adult zebrafish is capable of regeneration,which is in stark contrast to the limited repair within the mammalian central nervous system.Therefore,exploring the mechanism of repairment in spinal cord injuried adult zebrafish will be conducive to the treatment of human spinal cord injury,and provide a new perspective for human spinal cord injury therapy.It had been proposed that axotomy induced transient upregulation of NPY synthesis and gene expression in the rat.However,the function of NPY during neuroinjury and regeneration remains unknown.In particular,NPY exhibited neuroprotective proprieties via activation of the Y1 receptor subtype.In the present study,we evaluated the effects of neuropeptide Y(NPY)on adult zebrafish SCI by swimming ability,axon regrowth and motor neuron proliferation.We found that NPY was expressed in both control and injured zebrafish spinal cord,as judged by quantitative real-time polymerase chain reaction(qRT-PCR)and in situ hybridization(ISH).And qRT-PCR showed that compared to the sham group,expression of NPY mRNA in the spinal cord was significantly decreased at 12 h,6 d,11 d and 21 d.The qPCR results were confirmed by in situ hybridization.Immunofluorescence analysis of NPY protein level was in further support of our qPCR and ISH results and NPY-positive cells were located predominantly in the cytoplasm in the area surrounding the central canal.NPY morpholino(MO)treatment resulted in retarding of both axon regrowth(25.3% decreased compared to the control MO group)and locomotor recovery(68% decreased at 2 w,57.8% decreased at 3 w,48.5% decreased at 4 w and 36.6% decreased at 6 w,compared to control)in the injured zebrafish spinal cord.Immunofluorescence staining of NPY and motoneuron demonstrated that NPY expressed in the cytoplasm of spinal cord motoneurons,moreover,immunostaining of PCNA and motoneuron showed motoneuron proliferation after SCI.Inhibition of NPY expression after SCI prevented proliferation of motoneurons.In addition,the qPCR results showed that the Y1 receptor was activated in spinal cord injured adult zebrafish,and the expression of Y1 mRNA in the spinal cord injured-zebrafish was significantly decreased at 12 h,6 d,11 d and 21 d.The co-localization of Y1,NPY and motoneurons results showed that Y1 overlapped with NPY and expressed in spinal cord motoneurons after spinal cord injury.Our data favor the possibility that NPY may promote motor neuron and axon growth by activating the Y1 receptor.Collectively,our data suggest that NPY promotes locomotor recovery and axon regrowth by regulating motoneuron proliferation through activation of the Y1 receptor.