Identification Of Rat Hippocampal Liver Sensitive Neurons And Their Neural Pathways

Objective:To identify rat hippocampal liver sensitive neurons and explore their neural pathways,so as to provide experimental evidence for further study on the neuroregulatory mechanism of liver function.Methods : The experiment is divided into two parts.Firstly,the neural electrophysiological experiments,selection of SPF healthy adult SD(Sprague wrote-Dawley)rats,Referring to the stereotaxic map of the brain of the rats,the brain stereotaxic instrument is used to open a craniotomy window above the left hippocampal area of the rats.The hippocampal neurons are recorded with gold-plated tungsten electrode outside the cell.The screw is fixed on the skull to connect the silver wire to guide the grounding,and the vagus nerve electrical stimulator is made by ourselves,it is used to stimulate the hepatic branch of vagus nerve.Through the data acquisition and processing system of biological function,the changes of frequency and amplitude of hippocampal neurons before and after stimulation were observed and recorded,and the hippocampal liver sensitive neurons were identified.Secondly,different doses of FG were injected into hippocampal liver sensitive neurons and related brain areas in the retrograde tracing experiment of fluorogold(FG).The control group was injected with the same amount of normal saline.After 72 hours of survival,the rats were perfused with PBS and paraformaldehyde in the heart.The brain was taken and fixed in paraformaldehyde for 24 hours.The gradient sucrose dehydrated to the bottom completely,frozen sections were made in dark,floating patches were made,and observed under the fluorescence microscope.Results:(1)compared with the basal discharge frequency of 124.31 ± 16.31 Hz and the amplitude of 90.77 ±14.23?V,26 of the 30 rats showed significantly increased nerve discharge frequency and amplitude in the hippocampus CA3 area(AP:-4.9mm,ML:-5.1mm,DV:-5.0mm)after electrical stimulation of the hepatic branch of the vagus nerve.When the stimulation intensity was 3V,the frequency of neural discharge were 157.81 ± 16.94 Hz,the amplitude was 180.81 ± 10.50?V,when intensity was 6V,the frequency were 187.77 ± 10.66 Hz the discharge,the amplitude was 264.88 ± 10.94?V,and at 9V,the discharge frequency was 193.31± 13.08 Hz,the amplitude was 265.23 ± 12.91?V.When the hepatic branches of the vagus nerve were stimulated with the intensity of 3V,6V and 9V,the firing frequency and amplitude of neurons in the hippocampus CA3 region(AP:-4.9mm,ML:-5.1mm,DV:-5.0mm)were significantly increased(P<0.001)compared with the basal hippocampal nerve discharge before the stimulation.The time of recovery to the pre stimulation state also increased with the increase of stimulation intensity.(2)Different doses of fluorogold were injected into the left hippocampal liver sensitive neurons.Neuronal cell bodies and axons clear bright white fluorescent labeled cells were found in the contralateral hippocampus,ipsilateral piriform cortex(PC),locus coeruleus(LC)and bilateral lateral hypothalamic area(LHA).The number of labeled cells increased with the increase of the injection dose,suggesting that the hippocampal liver sensitive neurons may emit fibers to the same Side PC,LC and LHA,Bilateral projection can be seen at LHA,and the fluorescence of the ipsilateral LHA is stronger than that of the contralateral side,indicating that the ipsilateral projection is stronger than that of the contralateral side.FG was injected into the left LHA,PC and LC,and no fluorescent labeled cells were found in the left hippocampal CA3 area(AP:-4.9mm,ML:-5.1mm,DV:-5.0mm),and no fluorescent labeled cells were found in the control group.Conclusions: There may be hepatic sensitive neurons in CA3 area of rat hippocampus,which may play an important role in the regulation of liver function.The regulation of liver function by hepatic sensitive neurons in CA3 area of rat hippocampus may be related to the lateral area of hypothalamus,piriform cortex and locus coeruleus.