The development of exploration and spontaneous alternation in hooded rat pups: effects of unusually early eyelid opening.

Changes in exploratory activity and spontaneous alternation were examined across postnatal Days 8-31 in Lister hooded rat pups whose eyelids were surgically opened at 6-8 postnatal days. Compared with controls, whose eyes open naturally at 14-16 days, the treated animals showed accelerated behavioral development. Open-field activity increased more rapidly in the week following surgery, but only when all pups in the litter had their eyelids opened, and not when only half of the litter was treated. Rearing on the hind paws emerged earlier in treated animals, but grooming was unaffected. Pups having unilateral early eyelid opening made pivotal circling movements contraversive to the opened eye in an open-field arena in the early neonatal period. When tested in a T-maze, treated pups showed earlier spontaneous alternation than controls. Possible physiological systems underlying such changes are discussed. Our results show that unusually early visual stimulation has behavioral consequences, producing a brief speeding of some attentional and investigatory behaviors, though such changes may also depend upon environmental factors.