Control of eye movements while recording from single units in the pigmented rat.

Many investigators report recording from single units in the rodent visual pathway without neuromu~uIar relaxants to immobilize the eye. This is in contrast to the situation in the cat where it has been shown that neuromuscular blocking agents are required to reduce eye movements to a tolerable level (Cleland and Enroth-CugelI, 1966; Rod&k, Pettigrew, Nikara and Bishop, 1967). Attempts at controlling rodent eye movements without paralyzing agents have been varied. Brown and Rojas (1965), Partridge and Brown (1970) and Hughes (1971) report no eye stabilization methods. Siminoff, Schwas&man and Kruger (1966) used no eye stabilization techniques, but remapped receptive fields to assure that the eye had not moved. Montero and his colleagues (1968, 1973) used a disc pressed against the eye to m~hani~lly stabilize the eye and report no eye movements. Shaw, Yinon and Auerbach (1975) state that eye movements were rarely encountered using deep urethane anesthesia. In order to prevent eye movements in cases with lighter anesthesia, a ring was sewn or firmly pressed around the eye and securely fixed to the apparatus. Wiesen-feld and Kornel (1975) pressed an eye ring against the eye and by projecting the optic disc once an hour over 6 hr. report finding only 1' movement. Unlike the previous investigators who used deep urethane anesthesia (IP dose of 1200-17OOmg/kg), Driger (197.5) working on the mouse rather than the rat. used light pentobarbital anesthesia exclusively (60 mg/kg initially and 0.2 mg as needed, IP) and no mechanical stabilization. She tried carefully to assess the extent of eye movements. By tracking light reflected from a small mirror placed on the cornea1 surface, she found slow drifts of up to 15' in 3 hr; but by locating the projection of the optic disc, she finds slow drifts of no more than 2 to 3 degihr which were within the tolerance necessary for her experiments. Driiger thus speculates that large slow drifts may be an arti-fact caused by glue irritation or the weight of the mirror. However, Drfiger and Hubel (1976) report that if tectal coordinates were remapped 3-5 hr after the original mapping, a general shift of the projection of up to 15' in one direction was found. Atthough Drager and Hubel believe swelling of tissue is the most likely cause for the shift, as they also point out, eye movements can well account for the observation. DrPger also attempted the use of Flaxedil, a neuro-muscular blocking …