P-VEP Recording With Implanted Electrode In Guinea Pig

Examination of visual electro-physiology is an objective and noninvade evaluation method of vision function, especially for infants, aged people, mental retardation, loners and simulated blindness. Visual evoked potential is one method of the frequently used in clinical examinations. Visual evoked potential is a bunch of electrical signals from cerebral cortex which react to visual stimulus. The type commonly used in clinic consists of P-VEP and F-VEP. P-VEP correlates closely with pictorial recognition of retina, and visual acuity. And the P-VEP form is stable, so the clinical application of P-VEP is commonly in diagnosis of visual pathway diseases, such as diagnosis of optic neuritis, macula flava diseases, glaucomatous and judicial identification. F-VEP is generally used in the condition that P-VEP can not record or record incompletely because of the great variation of F-VEP. The amplitude of P-VEP is very small and it is easily interfered by electrocardio and myoelectric. So it is very important to explore a new P-VEP recording method for increase P-VEP stability and decrease interference in order to study P-VEP deeply, especially for animal experiment.Guinea pigs belong to rodents, and they are altricial animals. They have much more cones in retina than other rodents and they have semblable cone and rod proportion with mankind. The anatomic structure, organism construction and physiological function of crystalline lens and retina of guinea pigs are similar to mankind and primate. So guinea pigs are good models for vision research. Meanwhile guinea pigs are widespreadly used in basic research of various subjects. So they play influential role in research. But there are few reports of guinea pigs'electrophysiology research. It is very important to study the examination and evaluation of vision function of guinea pigs. And what we have done is important for future research work of guinea pig or P-VEP.Laser is different to common light source because of monochromaticity, coherence and directionality. When it comes out, it is utilized in various scopes, including military and aerospace territory. The energy of laser is highly concentrated in time and space. Different energy of laser has different effect on body. High-energy laser is detrimental to body and its bad effects on body are related to power, wave length, exposure time and light spot. But how to evaluate animal visual function especially form sense function of animals in the condition of laser or other factors remains a tough problem in the vision science currently. We explore a recording method of P-VEP of guinea pig, which is correlated closely to vision form sense function of guinea pigs and then explore the application effect in the condition of 680nm laser .The experiment concludes two parts: 1, To establish a new method to record pattern visual evoked potential (P-VEP) of guinea pigs. 2, To observe the effect of 680nm-laser on P-VEP.Methods and materialsRandom coloured mature male guinea pigs which had no opacity observed by ophthalmoscope were provided by animal experiment center of the Fourth Military Medical University. Anesthesia drugs: Sumianxin, which was made by military veterinary laboratory in military medical science academy in Changchun, code: (2004)005013. All guinea pigs were treated with anesthesia drugs and vehicled by intraperitoneal injection(ip). When cornea reflection vanished which was checked by cotton swab, the animals were considered getting in the anesthesia condition. After anesthesia, the guinea pigs ' scalp surface was exposed and three stainless screws were implanted as recording electrode, ground electrode and reference electrode. 3 days later, the awaked guinea pig was fixed in multifunctional head-body apparatus. Stainless screws and RETI-port system (Roland Consult, Germany) were connected with Ag-AgCl electrode to record P-VEP in different conditions. Semiconductor laser, made in north electronic equipment research institute, was used. And its wavelength is 680nm, width was 10μs, frequency was 20Hz, mean power was 1.4mW. The distance between laser and eyes of guinea pigs was 1.3 meters. The angle between laser beam and right eye was 45 degrees, and the time was 30s. We recorded PVEP simultaneously. We changed the laser energy to 0.3, 0.5, 0.8, 1.1 and 1.4mW in the experiment and observed the effect on visual acuity of the guinea pig. Visual acuity of the guinea pig was defined as the smallest checkerboard at which P wave could just be indentified. We used cpd as its visual acuity. The span time between each animal experiment was 5 to 10mins according to the different energy.Results1.The characteristic of P-VEP in awaked guinea pigsWe could record steady P-VEP, and the typical wave form was NPN. The spatial frequency had an evident influence on P-VEP. With the spatial frequency increased, implicit time of N1 and P1 was delayed, especially beyond 0.5cpd, and amplitude of P1 decreased, too. Oppositely, implicit time was shorten and amplitude was augmented with contrast increased. The difference of amplitude between either was significant (P<0.05). But difference of implicit time of P wave between 97% and 60% was not significant (P>0.05). The amplitudes of B-W and R-G were separately higher than R-B and B-G (P<0.01). P-VEP wave form was more stable in the bandpass of 5-50Hz than the other. P-VEP was not recorded in the condition of anaesthesia, and F-VEP was not influenced significantly in the condition of anaesthesia.2. The effect on P-VEP of 680nm laserThe latency of P wave of experiment group was increased significantly (P<0.05) compared with control group when the spatial frequency was in 0.1and 0.3cpd, but nonsignificant in other spatial frequencies. The amplitude of P wave of experiment group was decreased significantly (P<0.05) compared with control group when the spatial frequency was beyond 0.5cpd. 680-nm laser has an obvious effect on visual acuity. The visual acuity decreased quickly with the laser energy increased.Conclusions1. Established a method of recording P-VEP of awaked guinea pigs with implanted electrode. P-VEP has an close correlation with recording parameters, and can be stably recorded in the condition of high contrast(97%) ,narrow low bandpass(5-50Hz) and proper spatial frequency(below 0.5 cpd) .2. The 680nm-laser has an evident effect on P-VEP. The latency of P wave is delayed and amplitude of P wave is decreased. The effect on visual acuity is also significant. Visual acuity is decreased quickly with the energy increasing. But whether the low-energy 680nm-laser has damage to body or not is worth researching deeply.