BrainResearchBulletin, Vol. 32, pp. 57-63, 1993 0361-9230/93 $6.00 + .00 Printedin the USA.All rightsreserved. Copyright© 1993Pergamon PressLtd. Hash and Pattern Reversal Visual Evoked Potentials in C57BL/6J and B6CBAF /J mice GEORGE M. STRAIN ~ AND BRUCE L. TEDFORD Veterinary Physiology, Pharmacology and Toxicology, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803-8420 Received 3 August 1992; Accepted 9 February 1993 STRAIN, G. M. AND B. L. TEDFORD. Flashand pattern reversal visualevokedpotentials in C57BL/6J and B6CBAFJJ mice. BRAIN RES BULL 32(1) 57-63, 1993.--Visual system responses(visual evoked potentials) to flash (FVEP) and pattern reversal (PRVEP) stimuli were recorded in mice. Two strains were used: black C57BL/6J mice and agouti B6CBAFdJ mice (first generation offspring of C57BL/6J females and CBA/J males.) Subjects were sedated with ketamine and xylazine. Flash rate (FVEP) and stimulus spatial frequency and pattern reversal rate (PRVEP) were varied to determine optimum stimulus parameters. Normative FVEP and PRVEP data were collected from mice of both strains after determination of optimum parameters. Five positive and four negative alternating peaks were routinely observed in the FVEP, while three positive and three negative alternating peaks were seen with the PRVEP. Varying the flash rate, the pattern reversal rate, and spatial frequency significantly affected nearly all amplitude and latency measures in the responses. Significantdifferences between strains were seen on some, but not all, latency and amplitude measures when the stimulus parameters were varied. Pattern reversal visual evoked potentials Flash visual evoked potentials B6CBAF~/J vs. C57BL/6J mice NONINVASIVE objective evaluation of visual pathway function is most often accomplished through the visual evoked potential (VEP), where scalp responses are recorded to appropriate visual stimuli, either flashes of white light or an alternating pattern of checks or bars. The VEP has been described for numerous spe- cies, including human (4,6,24), monkey (6,16), dog (26), cat (6), rat (3,6,19-21), guinea pig (6), cow (27), pig (18), and sheep (25), among others. Applications of flash VEPs in mice have been reported in drug (2) and senescence studies (1), but detailed characterizations of the responses to flash and pattern reversal stimuli in mice have not been reported. The characterizations reported here were performed to enable visual system studies of transgenic mice with disrupted myelinization of the optic nerves. Two related strains were compared to evaluate within-species variability. Methods were developed to enable recordings without implantation of chronic electrodes because of an anticipated low availability of transgenic subjects. METHOD Animals Young adult male mice (average weight 25 g) from two strains were used: black mice of the C57BL/6J strain (n = 15) and agouti mice (B6CBAF~/J, n = 14) which were first generation offspring of C57BL/6J females and CBA/J males (Jackson Lab- oratory, Bar Harbor, ME). Retina pigmentation is present in both mouse strains. Anesthesia Mice were lightly anesthetized with a combination of IP ket- amine and xylazine to avoid the cortical depressant effects of injectable barbiturate anesthetics; gas anesthetic use was pre- cluded by the need for unobstructed visual stimulation. The B6CBAF~/J mice required higher doses (130 and 26 mg/kg, re- spectively) than the C57BL/6J mice (80 and 16 mg/kg). When required, supplemental doses of 1/4 the initial dose were ad- ministered. No mydriatic drugs or dark adaptation were used, and refraction of the eye was not performed because of the con- siderable depth of field of rodent eyes (15). During recordings the mice were placed in a depression on an isothermal chemical heating pad (Deltaphase, Braintree Scientific, Braintree, MA) that maintained a constant 37°C temperature to counteract hy- pothermia effects of the anesthesia. Visual Stimulation Recordings were collected in a darkened room with a background illuminance of 0.25 lumens/ft 2. Stimuli were binocular, presented in front of the nose, and on a plane level with the mouse's head. Flash stimuli of 10 us duration from a photostimulator (Model PS22 photic stimulator, Grass In- struments Co., Quincy, MA) were presented at a distance of 15 cm from the eyes. A flash intensity setting of 16 was used, which represented an approximate peak intensity of 2 × 10 7 lumens. Flash rates of 1, 3, 5, and 7/s were evaluated in eight To whom requests for reprints should be addressed. 57