Microelectrode study of spreading depression (SD) in frog retina--general observations of field potential associated with SD.

Using microelectrodes, the field potential change associated with SD (SDP) was recorded from frog retinas conditioned with Cl-free Ringer's. In such retinas, SDP was induced by light or chemical agents such as glutamate, aspartate and K+. The chemicals, when applied iontophoretically, produced a local graded response which eventually triggered SDP. A potential similar to the local response to chemicals was often discerned on the rising phase of SDPs produced by light or occurring spontaneously. The SDP was maximal across an innermost retinal layer 50 mum or less in thickness with the intraretinal polarity predominantly negative, indicating that the major sink of SDP is in the inner plexiform layer. The influence of SDP on the receptor potential was relatively small, but the other components completely disappeared at the beginning of SDP, recovering gradually thereafter. Concomitantly, a strong depolarization occurred in the ganglion cells. Stimulation of the optic nerve could induce SDP, but nerve impulse activity is not important for SDP because tetrodotoxin was unable to prevent SDP due to light or chemical agents.