The Neuron Loss And The Activation Of Neuroglial Cells In Hypoglossal Nucleus After Hypoglossal Nerve Injury

Objective: In this study, a peripheral nerve injury model was established by cutting the left hypoglossal nerve. Using this model the relationship between the neuron loss and the functions of neuroglial cells were studied by observe the changes in the amount and the morphology of astrocytes and microglia in hypoglossal nuclei after hypoglossal nerve injury in adult mouse at different time points.Methods: A total of 30 adult Kunming mice which bodyweight was 30±5g were used in this study. The left hypoglossal nerve of the mouse was cut under 4% chloral hydrate anesthesia, and then the skin was sutured. For Day 7 or day 35 after the injury, Mice were anesthetized with diethylether and were perfused with 4% paraformaldehyde solution (PFA). Brains were removed and stored in the same fixative overnight. Then, the brains were cryoprotected in PBS containing 20% sucrose overnight, embedded in OCT compound, and were cut in 18μm slices for immunohistochemistry(IHC) and thionine staining. The number and morphology of neuroglial cells at different time points were studied by IHC using GFAP and Iba1 antibody which is the marker of astrocytes and microglia,respectively. Neurons were labeled by thionine then be counted. The data statistics was analyzed by using spss11.5 software.Results: On the 7th day after hypoglossal nerve injury, neurons in injured side appeared soma swell, nuclear deviation and nissl body margination, but the amount (8.00±1.35/14400μm2) has no significant difference(P>0.05) compared with that in non-injury side (8.51±1.30/14400μm2). On the 35th day after injury, the shape of neurons in injured side reached normal, however the amount of neurons in injured side (6.70±1.22/14400μm2) was significantly decreased compared with that in non-injury side (8.41±0.61/ 14400μm2) (P<0.05).On the 7th day after injury, the GFAP IHC signals of astrocytes in injured side were lightly stronger than that in non-injury side. However, there is no significant difference(P > 0.05) between the amount of astrocyte in non-injury side (5.33±0.62/14400μm2) and that in injured side (6.67±0.73/ 14400μm2 ). On the 35th day after injury, the amount of astrocytes in injured side (7.85±0.42 /14400μm2) was significantly incresed compared with that in non-injury side (5.41±0.3314400μm2,P<0.05).On the 7th day after injury, activated microglia accumulated in injured side, their thickening and retractive branches wrapped around the neurons, and their amount (9.59±0.80/14400μm2) was significantly increased compared with that in non-injury side (2.52±1.17/14400μm2)(P<0.05)On the 35th day after injury, the morphology of microglia returned to ramified which had long and thin branches. However,the amount of microglia in injured side(5.40±0.95/14400μm2) still significantly more than that in non-injury side (2.18±0.28/14400μm2,P<0.05).Conclusions:1.The neuron loss happened on the 35th day after hypoglossal nerve injury in adult mice.2.Neuroglial cells were in different active state coincide with the neuron loss, indicates neuroglia may be involved in the process of neuron loss.