Primary Study In The Effects Of Tactile Experience On The Function And Plasticity Of Rat Barrel Cortex

ObjectiveNeural network plasticity is fundamental for learning and memory.Its abnormal change underlies some neural diseases.Measurement of the plasticity of cortex can help understand the mechanism of plasticity,and provide a quantitative way to observe the neural process of natural aging and neurodegenerative diseases,which may lead to a new approach for evaluation of anti-aging drugs and new medical treatments for neurodegenerative diseases.The rodent barrel cortex with its well-defined somatotopic map offers immense experimental potential for studying the structure and function of the neocortex integrated with quantitative behavioral analyses and defined molecular manipulations.Sensory input produced by deflection of the whiskers is conveyed to cortex,where contains discrete clusters of closely packed cells,termed barrels.There is one-to-one correspondence between each barrel and vibrissa.Each whisker in turn excites an entire cortical column.In view of the aforementioned content,as we all known,c-Fos is a cellular proto-oncogene belonging to the immediate early gene family of transcription factors.At the same time,BDNF is a member of the "neurotrophin" family of growth factorswhich are related to the canonical "Nerve Growth Factor",NGF.Neurotrophic factors are found in the brain and the periphery.Neuroscientists measure expression of c-fos and BDNF as an indirect marker of neuronal activity.So we choice c-fos protein and BDNF as two markers,when the whiskers of rodent are excited by motor activity, results in the ac cumulation of c-fos protein and BDNF in somatosensory cortex.Accordingly,morphological changes and changes in neural plasticity emerge.Methods1.Model.We demonstrate two new methods of stimulating whiskers that provide major sensory input to rat neocortex in this work.In the first model,animals were placed for a brief period of time into a new,wired cage resulting in vibrissae stimulation when they explored the new environment.In the second model,animals were placed on the top of a cylinder and their vibrissae were brushed by hand.2.Grouping.All of the rats in the experiments were divided randomly into two groups.3.Behavior monitoring.The animals were kept under natural light/dark cycle in Plexiglas cages(60×45×25 cm) with the cover made of 1.5-mm-thick iron wires,1.5 cm spaced,with water and food provided ad libitum.4.Histology and Staining.All rats were anesthetized with chloral hydrate and perfused with the modified procedure.Then,the brain was removed and postfixed overnight immersed in 30%sucrose at 4℃for 2-3 d.The hippocampus was cut in 50μm thick.The position of the regions and layers was determined by Nissl and cytochrome oxidase staining.Immunohistochemistry evaluate c-Fos protein expression in all levers of the barrel cortex.5.Statistical analysis.The number of c-Fos-stained nuclei was evaluated by an image analysis system.The SPSS13.0 software was performed in all statistical analyses and separate one-way ANOVAs were applied for each layer.Values were expressed as mean±SEM.Results1.Model 1.Immunocytochemistry staining shows an increase of c-los expression in the PMBSF of control group and experimental group.Contrasted with control group,our data show that the increased ratio of c-los expression in experimental group is biggest in layerⅣ(526.6%,89.6±18.2 vs 14.3±2.8),as well as layersⅡ/Ⅲ(243.7%,46.35±8.4 vs 13.5±2.3) andⅤ/Ⅵ(390.3%,105.9±22.1 vs 21.6±4.5),c-Fos activation was also significantly increase.One-way ANOVAs applied separately for each layer showed significant differences between control and experimental animals in layersⅡ/Ⅲ,Ⅳ,andⅤ/Ⅵ(P＜0.05).2.Model 2.Immunocytochemistry staining shows an increase of c-fos expression in the PMBSF of control group and experimental group.Contrasted with control group,our data show that the increased ratio of c-fos expression in experimental group is biggest in layerⅣ(352.3%,439.6±23.6 vs 97.2±19.6),as well as layersⅡ/Ⅲ(336.1%,119.5±20.4 vs 27.4±5.7) andⅤ/Ⅵ(159.5%,380.4±46.1 vs 146.6±21.6).One-way ANOVAs applied separately for each layer showed significant differences between control and experimental animals in layersⅡ/Ⅲ,Ⅳ,andⅤ/Ⅵ(P＜0.01).Contrasted with control group,our data show that the increased ratio of expression of BDNF was respectively 177.8%in layerⅣ(33.8±8.7 vs 1.8±0.4),as well as 281.5%in layersⅡ/Ⅲ(20.6±5.3 vs 5.4±1.1) and 319.4%inⅤ/Ⅵ(13.0±3.4 vs 3.1±0.8).One-way ANOVAs applied separately for each layer showed significant differences between control and experimental animals in layersⅡ/Ⅲ,Ⅳ,andⅤ/Ⅵ(P＜0.05).Conclusion1.Our test shows that it is not just the presence of new objects,but their nature (especially the presence of holes between bars).The experience-dependent plasticity can be expressed in primary signaling pathway from whisker to cortex by stimulating whisker.We surmised the tactile experiences of whiskers in rodent play an important role in receiving outside information.2.Both of model approaches to increase c-Fos expression in PMBSF after the whiskers stimulated.Those indicate that sensory experiments can induce gene expression and protein synthesis in the correlative cortex of whisker-cortex pathway,and result in neuronal plasticity.3.The primary signaling pathway from whisker to cortex in the rodent is an important model of plastic changes in the brain and it has a close relationship with the change of plasticity of neural network.It is emerging as a key system for such integrative studies.