FUNCTIONAL-PROPERTIES OF RETINAL GANGLION-CELLS DURING OPTIC-NERVE REGENERATION IN THE GOLDFISH

After being severed, optic axons in goldfish regenerate and eventually restore the retinotectal map; refinement of the map depends upon impu lse activity generated by the ganglion cells. Because little is known about the changes in activity and receptive-field properties of gangli on cells during regeneration, we made extracellular recordings from th em in the intact eye up to 95 days after sectioning their axons in the optic tract. Their receptive fields were classified as OFF-, ON-OFF-, or ON-centers, and their axonal conduction velocities measured by ant idromic activation. The rate of encountering single units dropped dras tically at 4-8 days postsection when only a few OFF-center units could be recorded, recovering to normal between 42 and 63 days. Receptive-f ield centers were normal in size, except for the few OFF-centers at 4- 8 days which were abnormally large. Maintained discharge rates of all types were depressed up to 42 days, but ON-OFF-center units were more spontaneously active than normal around 42 days. Light-evoked response s in OFF-center units were subnormal at 4-8 days, becoming supernormal at 16 days and normal thereafter. ON-OFF- and ION-center units starte d to regain responsiveness at 16 days, and became supernormal at 42 da ys, before returning to normal. Conduction velocities of all fiber gro ups dropped to a minimum at 8 days, the fastest being affected most. T here was a gradual recovery to normal conduction velocity by 63 days. The conduction latencies of OFF- and ON-OFF-center units recovered to normal by 42 days, and ON-center units by 63 days. Recovery of ganglio n cell responsiveness correlates with functional recovery in the retin otectal system: OFF-center units recover light-evoked responses at abo ut the time OFF activity first reappears in the tectum. ON- and ON-OFF -center units recover later, exhibiting supernormal spiking activity a round the time that ON responses reappear in the tectum.