Non-associative learning (habituation) in normotensive and hypertensive rats and the effects of social isolation

Social isolation is a mild stressor and prolonged exposure to this stressor leads to the development of mental disorders and an increase in mortality from various causes, especially in the group of older people. In animals, social isolation also has a stressful effect. In the present study we investigated the effect of long-term isolation on non-associative learning in outbred Wistar rats and genetically related normotensive rats of the WKY strain and spontaneously hypertensive rats of the SHR strain. Nine-ten-month-old male rats were used for the study. Some animals were placed in individual cages, and the other part was left in home cages under group maintenance. Non-associative learning (habituation) was studied in the “open field” test. Short-term habituation was assessed using indices of locomotor activity and the number of rearing during the first session. Long-term habituation was assessed after a repeated test performed 96 h later on. It was found that in Wistar rats, isolation disrupted both short-term and long-term habituation. In WKY rats, short-term habituation was observed, and long-term habituation was impaired. In SHR rats, non-associative learning was completely disrupted. Prolonged isolation did not have a significant effect on the behavioral indices studied in WKY and SHR rats. Thus, hypertension in SHR rats was accompanied by an impairment of non-associative learning. Isolation caused disruption of non-associative learning in Wistar control rats, but did not affect this type of learning in rats of genetically related WKY and SHR strains.