After being severed, optic axons in goldfish regenerate
and eventually restore the retinotectal map; refinement
of the map depends upon impulse activity generated by the
ganglion cells. Because little is known about the changes
in activity and receptive-field properties of ganglion
cells during regeneration, we made extracellular recordings
from them 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 antidromic
activation. The rate of encountering single units dropped
drastically at 4–8 days postsection when only a few
OFF-center units could be recorded, recovering to normal
between 42 and 63 days. Receptive-field 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 responses in OFF-center units were
subnormal at 4–8 days, becoming supernormal at 16
days and normal thereafter. ON–OFF- and ON-center
units started to regain responsiveness at 16 days, and
became supernormal at 42 days, before returning to normal.
Conduction velocities of all fiber groups dropped to a
minimum at 8 days, the fastest being affected most. There
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 ganglion cell responsiveness correlates
with functional recovery in the retinotectal system: OFF-center
units recover light-evoked responses at about the time
OFF activity first reappears in the tectum. ON- and ON–OFF-center
units recover later, exhibiting supernormal spiking activity
around the time that ON responses reappear in the tectum.