Change Of Neural Axons, Dendrites And Synapses Of Rat Somatosensory Cortex Following Neonatal Posthaemorrhagic Hydrocephalus And Impact On The Change Of TGF-β 1/Smad2/3 Passway

The motor, cognitive and sphincteral dysfunctions that can occur during hydrocephalus following aneurismal subarachnoid hemorrhage seriously threaten the patient's quality of life and the prognosis. Even when the hydrocephalus is relieved by surgery and dehydration, residual motor, cognitive and sphincteral neurological dysfunctions may persist in some patients. The deleterious effect of hydrocephalus to brain is dependent on magnitude and duration of ventriculomegaly, also modified by the age of onset. Rapid increase in head circumference is often as a symptom of hydrocephalus in children but not adult patients. Symptoms of hydrocephalus patients varied significantly from individual to individual, but the patients always associated with memory loss and dementia.Higher neurological functions depend on the construction of large numbers of neural circuits and projections. Neurotransmitter delivery across synapses is the basis of all neural circuits. Neural function depends on neurotransmission. Any change in cortical neural structures, especially degeneration of dendrites and a decrease in the number of synapse, alters the formation of neural circuits and projections and, thus affects cortical movement, sensation and other higher neurological functions. Leggio et al. has demonstrated that there is a clear correlation between dementia and a decreased number of cortical synapses. Using immunohistochemistry, Li et al. have found the presence of degeneration of cortical and hippocampal neurons in their animal model of brain trauma. Swann et al. have also found degeneration of cortical neurons and decrease in the number of synapses after epilepsy.Hydrocephalus after subarachnoid hemorrhage can induce cognitive and motor dysfunctions. However, the neuropathological changes underlying these dysfunctions are still unknown.TGF-β1/Smad2/3 plays an important role on the pathophysiology of hydrocephalus following subarachnoid hemorrhage. We also studied the passway through inhibiting smad2 and smad3 respectively.Part One:Change of Neural axons, Dendrites and Synapses of Rat Somatosensory Cortex Following Neonatal Posthaemorrhagic HydrocephalusObjective To construct a model of hydrocephalus after subarachnoid hemorrhage and to observe pathologic changes of neuron morphology in somoto-sensory cortex.MehhodsNeurons of somoto-sensory cortex were labeled by EGFP using the in utero electroporation technique. We used the method described by Cherian et al. to construct a model of hydrocephalus after subarachnoid hemorrhage and then observed the subsequent pathological changes in the morphology of neurons labeled by enhanced green fluorescent Proteins (EGFP) using the in utero electroporation technique.ResultsInjection of venous blood into the lateral ventricles of 7-day-old rats in the operation group caused marked enlargement of the ventricles in 60%(9/15) of the rats after 2 weeks and in 53.3%(8/15) of the rats after 3 weeks. Compared with the control group, the length of the neural axons and dendrites in the somatosensory cortex was shortened and the number of both neuron dendrite branches and synapses was significantly decreased. There was no evidence of cerebral cortical neuron death as shown by positive EGFP cell countingConclusionNeurological dysfunction after subarachnoid hemorrhage-induced hydrocephalus may be related to the shortening of neural dendrites and the decreased number of synapses in somatosensory cortex, thus providing possible neurological cause for hydrocephalus-induced cognation and motor dysfunction.Part Two:Impact of TGF-β1/Smad2/3 Passway on the Change of Neural axons, Dendrites and Synapses of Rat Somatosensory Cortex Following Neonatal Posthaemorrhagic HydrocephalusObjectiveTo investigate the role of TGF-β1/Smad2/3 Passway on the pathophysiology of hydrocephalus following subarachnoid hemorrhage.MehhodsNeurons of somoto-sensory cortex were labeled by EGFP using the in utero electroporation technique. We used the method described by Cherian et al. to construct a model of hydrocephalus after subarachnoid hemorrhage and then observed the subsequent pathological changes in the morphology of neurons labeled by enhanced green fluorescent Proteins (EGFP) using the in utero electroporation technique. Inhibitor of smad2 and smad3 were injected respectively to the lateral ventricle together with injection of venous blood. TGF-β1, Smad2, smad3 and fibronectin were detected with Western Blot.ResultsWith decrease expression of smad2 and smad3, there was no difference in the enlargement of ventricle. With injection of inhibitor of smad3, the expression of fibronectin was decreased together with increased number of synapses in somatosensory cortex compared with control group (inject blood only).ConclusionTGF-β1/Smad2/3 passway should play an important role in pathological changes of hydrocephalus following subarachnoid hemorrhage through increasing the expression of the ECM protain fibronectin. Inhibitor of smad3 could partly reverse these pathological changes.Total ConclusionThe results obtained from our study showed that the length of dendrite and axon was shortened and the number of dendrite branches and synapses in the somatosensory cortex was decreased in hydrocephalus after subarachnoid hemorrhage. TGF-β1/Smad2/3 passway should play an important role in theses pathological changes through increasing the expression of the ECM protain fibronectin. Inhibitor of smad3 could partly reverse these pathological changes.