Study Of Evoked Visual Cortex Potential Based On Rats Flashing

Background and Objective:Visual cortex is an essential center of vision. All sorts of visual information which transmit through visual path to visual cortex, causing the variation of potential in the neurons of the visual cortex, eventually makes visual sense. The visual signals could be integrated in primary visual cortex (V1 area) where is also the most able to reflect the feature information of the visual signal under different visual stimulation mode.Visual evoked potential (VEP) displaies the electrical activity of neuron in the cerebral cortex response to visual stimulation, and is convenient to record in the scalp.According to the different visual stimulating patterns, VEP could be roughly divided into figure stimulation and flash stimulation visual evoked potential(FVEP). Flash stimulation is a diffuse, and the contrast of light and shade is intense. Flashing made by some colors influences on nervous potential in the rats' visual cortex. According to the present research, except for the insensitivity for red color, the rats' visual cortex can react to flashing, such as white or other monochromatic ligh and makes the field potential of the neurons. Also some studies have indicated that the some colored sensitive nervous cells exist in the rats' visual cortex using functional magnetic resonance technology. We have confirmed that these cells have the ability to distinguish between the different colored stimulation. Central acetylcholine (Ach) is the important neurotransmitter both in the central and periphery nervous systems. The blocker of cholinergic muscarinic (M) receptor, scopolamine, decreases the leveal of cerebrum acetylcholine, and cause disorders. Carbachol (CCH), a muscarinic agonist enhances expression of neuron acetylcholineIn the present study, we detecte the visual evoked potentials in the rats'visual cortex in response to the flashing of red,green and white light and determine the functional role of acetylcholinic system in the FVEP profile in the primary visual cortex with cholinergic receptor agonist and anagonist based on the method of immunohistochemistry. At same time we have established a theoretical foundation for brain cognition.Methods:1.Animals 30 healthy adult SD rats, weighing 220g～280g, either male or female were used in all the experiments. The rats were divided into three groups. They are control, scopolamin (antagonist of M receptor) and CCH groups.2. Electrophysiology Animals were anaesthetized with intraperitoneal injection of 10% chloral hydrate, and surgically implanted with the screw electrodes binded with Agcl. For FVEP recording,2 of those ecletrodes were implanted on the skull according to stereotaxic coordinates of rat primary visual cortex (7 mm posterior,2 mm lateral).Another 2 electrodes (2.0 mm anterior to bregma,2.0 mm left lateral) serve as the reference. Recording sessions only begun after the animal had fully recovered, usually after five days.3. ImmunohistochemistryThe control and scopolamin groups were perfenned on the expression of cholinergic neurons of the primary visual cortex using immunohistochemistry. Rats were anesthetized, and then brains were removed. The paraffin brain slices contained the visual cortex were prepared. The brain slices were dewaxing, block and antigen reparing.Then the slices were incubated with the first antibodies Goat-anti-ChAT (1:100) or Rabbit-anti-C-fos (1:100), in 4℃overnight, respectively. After that the slices were treatd with, rabbit anti goat IgG (1:250) antibody. The secondary antibody only was used as the control. 3. Results:3.1 Flashing evoked VEP from the rat VI regionBoth white and green flashing evoked FVEP from the rat primary visual cortex.However, the red couldn't incite FVEP. There are no more different in the latent period and the amplitude of the FVEP between administrations of the white and the green stimulation.3.2 Cholinergic M receptor influenced the FVEP in the VI regionCampared with the control, injection of carbacl, an agonist of the cholinergic receptor, increased the amplitude of the FVEP after white and green flashing.Whereas administration of scopolamin, an anagonist of the M receptor, the amplitude of the FVEP was lower. The groups were treated by drugs, but the value of P2 wave amplitude, which the red light stimulation caused, were not seen the significant difference. The latent periods of the rat FVEP in the groups treated by drugs were not seen the significant difference.3.3 Flashing evoked expression of ChAT and c-Fos proteins in the VI regionA lot of c-Fos positive neurons in the primary visual cortex and the hippocampus while white flashing were observed using immunohistochemistry. Compared with the control, the white flashing depressed expression of ChAT in the neurons of the primary visual cortex after block cholinergic M receptor.Summary:1. Both white and green flashing inicite the evoked cortex potential from, whilist the red flashing might not evoked VEP from the rats'primary visual cortex.2. The agonist of cholinergic M receptor increases the amplitude of the FVEP in the rat primary visual cortex, and the antagonist of M receptor decreases the VEP amplotude.3. The flashing of white inicites expression of c-Fos protein in the rat primary visual cortex. Compared with the control, the white flashing depresses expression of ChAT in the neuron of the primary visual cortex after block cholinergic M receptor.4. Take together, flashing could inicite the evoked cortex potential, and the cholinergic transimitter system may be associated with the VEP profile of the rat primary visual cortex.