Spreading depression of activity in amphibian retina.

GOURAS, PETER. Spreading depression of activity in amphibian retina. Am. J. Physiol. 195(1): 28-32. [email protected] studies on excised amphibian retina have uncovered a phenomenon of spreading retinal depression which in many respects resembles Leao’s spreading cortical depression. The phenomenon is characterized by a spontaneous ‘milky’ wave that periodically marches across the surface of the retina and lasts for 2-3 minutes at any one point. There is a concomitant and sudden negative shift in the resting retinal potential of 1-2 mv which gradually returns to its previous level in 3-6 minutes. As the wave front approaches a microelectrode recording ganglion cell activity, there is a marked increase in its spontaneous firing climaxing in an intense discharge as the wave engulfs the electrode. A profound depression follows so that even the most intense photic stimulation becomes unable to elicit a local response. As the color change disappears and the d.c. level returns, the local area of retina becomes reexcitable. Similar changes occur in the local electroretinogram, which always returns slightly before the ganglion cell activity. The process occurs spontaneously but can also be induced by trauma, electrical current, or the application of KCl. It happens less often in bright light or with oxygenation, although neither of these factors can prevent its occurrence. It appears to be entirely reversible. PREADING depression has C established phenomenon become a well of cortical elec0 trophysiology ever since its initial description by Leao in 1944 (I). The process is characterized by an expanding wave of depression of spontaneous electrical activity which travels across the cerebral cortex at the rate of 2-3 mm/min. and lasts for 2-6 minutes at any one point. There is a concomitant unresponsiveness to electrical stimulation and a marked shift in the resting cortical potential. Grafstein (2) has recently shown that the same phenomenon can occur in the isolated cerebral cortex of the cat and is frequently accompanied by increased unitary activity at the beginning of the wave of depression. The entire process is reversible. It occurs spontaneously but can be induced by either weak mechanical or electrical stimulation (I) or the application of KCl, CaC12 or strychnine (3, 4). Its spontaneous occurrence is facilitated by dehydraReceived for publication March 12, 1958. tion (s), cooling (6), or deterioration (7), suggesting that it is a pathologic condition. So far the description of this phenomenon has been confined to mammalian cerebral cortex, but the analogy between it and a process found in the excised retina suggests a common relationship. This report presents observations made on a spreading electrical depression, noticed during microelectrode studies of toad retina, and discusses imilarities between it and Leao’s phenomenon. Similar observations were made by Hartline during his original work on single optic nerve fiber preparations of frog retina (personal communication).