Stable bellows cup electrode demonstrates low-frequency properties of long-term electroretinographic recordings in the Limulus lateral eye

Conventional methods have long been used to record electroretinograms (ERGs) from the surface of the lateral eye of Limulus, the horseshoe crab. But, using these methods, the convexity of this eye has sometimes led to electrode problems that deterred acceptance of the validity of unexpected and unfamiliar phenomena. To deal with the electrode problem, a new gel/bellows cup electrode has been devised which was created from a small bellows suction cup. Coated with a recording gel and positioned by a massive apparatus arrangement, it maintains a secure connection to the convexity of the lateral eye for many days without requiring any attention after its placement. This new electrode has now been used for thousands of hours of ERG research during which crabs have often been left undisturbed in the apparatus for many days. This new method has revealed the existence of a novel low-frequency phenomenon demonstrated by the occurrence of noise-like fluctuations in successive ERGs. The frequency of these fluctuations is low relative to the properties of the ERG itself. Several converging tests of this new electrode system indicated that this new phenomenon is not an artifact but rather a genuine expression of endogenous bioelectric events. (c) 2006 Elsevier B.V. All rights reserved.