Responses to light after retinal degeneration

Transgenic rodless mice were given 1-h pulses of light of varying brightnes s at times of the night when they were normally active. The rodless mice sh owed decreases in locomotor activity during light pulses brighter than 2 lu x; these decreases were significantly greater than those in wildtypes (ANOV A, P < 0.01). However, with very dim light, rodless mice showed no changes in activity, whereas wildtype mice actually increased their activity. It is suggested that irradiance detection could be enhanced by absence of image- forming vision. Enhanced inhibition of activity around twilight may be adap tive for mice in some circumstances and so help maintain genes for retinal degeneration in natural populations. (C) 2000 Elsevier Science Ltd. All rig hts reserved.