THRESHOLD AND CHROMATIC SENSITIVITY CHANGES IN FISH CONE HORIZONTAL CELLS FOLLOWING PROLONGED DARKNESS

The light-evoked responses of L-type cone horizontal cells in the tele ost retina were studied following a prolonged period of complete darkn ess. Intact, isolated white perch retinas were superfused in complete darkness for more than 90 min, following which horizontal cells were i mpaled without the aid of any light flashes. Following this prolonged darkness, L-type cone horizontal cell light responses to dim and brigh t full-field stimuli were slow and small in amplitude and response dur ation to bright stimuli was considerably longer than stimulus duration . In addition, absolute threshold was 2 log units lower than typical f or cone horizontal cells and spectral sensitivity to shorter wavelengt hs was increased. Following bright light stimulation, light responses became more transient and increased in amplitude, reaching 40-50 mV to bright flashes. Moreover, absolute threshold increased and responses to spectral stimuli were similar to those observed typically for L-typ e cone horizontal cells after light-sensitization. These results sugge st that following prolonged darkness, cone input to cone horizontal ce lls is reduced and rod input is present.