EFFECTS OF SOCIAL-ISOLATION REARING ON LEARNING IN THE MORRIS WATER MAZE

Impaired learning has been shown as a consequence of isolation-rearing in a variety of paradigms. However, there are situations in which lea rning in isolation-reared rats is enhanced or unimpaired compared to s ocially reared rats. The present experiments investigated the effects of isolation rearing on place navigation in the Morris water maze. Two complementary paradigms were studied: isolation and socially reared r ats were exposed to the water maze either without drug pretreatment or following systemic administration of scopolamine. Two conditions were examined: place learning and reversal learning. Male Lister hooded ra ts were either housed singly (isolation reared) or in groups of four ( social reared) from weaning at 21 days of age. Six weeks later place l earning and reversal learning were determined using the Morris water m aze. The time taken to locate the submerged island (escape latency) wa s used as the measure of learning ability. The results showed that pla ce learning, and reversal learning were enhanced in isolation reared r ats compared to socially reared controls. Pretreatment with scopolamin e (0.3 and 0.5 mg/kg, i.p.) produced a dose-related cognitive deficit as shown by an increase in the escape latency. Scopolamine (0.3 mg/kg) impaired both place and reversal learning but this was less pronounce d in isolation compared to socially-reared rats. These results suggest that rearing in isolation may enhance spatial learning though central cholinergic mechanisms.