Early and late visual deprivation induce hypersensitivity to mechanical and thermal noxious stimuli in the ZRDBA...

Visual deprivation leads to behavioural adaptations. Early visual deprivation has greater effects on sensory systems compared with late visual deprivation. Although this has been well studied, the impact of visual deprivation on pain sensitivity has scarcely been investigated. In humans, one study indicates that pain sensitivity is increased in early, but not late-onset blindness. In animals, one study indicates that sensitivity to noxious stimulation is increased in anophthalmic mice, but the impact of late visual deprivation on sensitivity remains unknown. The aim of this behavioural study was to examine sensitivity to noxious stimulation in mice with early and late visual deprivation. We hypothesized that visual deprivation would have different effects on sensitivity to noxious stimulation depending on its onset.

In Experiment 1, mechanical and thermal sensitivity was examined in four ZRDBA mouse groups: sighted mice, anophthalmic mice, dark-reared sighted mice and adult sighted mice deprived of vision for one week. In Experiment 2, mechanical and thermal sensitivity was examined in adult sighted ZRDBA mice deprived of vision for two months.

Anophthalmic and dark-reared mice showed mechanical and thermal hypersensitivity, while the one-week visual deprivation did not alter sensitivity. The two-month deprivation also resulted in mechanical and thermal hypersensitivity.

These results indicate that early visual deprivation, regardless of the integrity of the visual system, induces hypersensitivity. Moreover, the present findings indicate that late visual deprivation may induce mechanical and thermal hypersensitivity, although this depends on visual deprivation duration. These results have implications for the biological significance of pain in the blind.

Sensory deprivation induces behavioural adaptions. For most sensory systems, the extent of these adaptations generally depends on the stage of cerebral development. In contrast, the present results indicate that for the nociceptive system, both early and late visual deprivation have similar effects. Anophthalmic, dark-reared mice and adult mice deprived of vision for two months showed thermal and mechanical hypersensitivity. This shows a clear interaction between visual and nociceptive systems and has implications for the biological significance of pain in the blind.