Facultative control of avian unihemispheric sleep under the risk of predation

Lewis (LEW) is an inbred strain of rats frequently used as an animal model of autoimmune diseases. However, there is evidence that some lines of LEW rats develop autoimmune diseases more readily than do other LEW rat lines. Because the hypothalamus-pituitary-adrenal system is involved in the pathophysiology of these diseases, we compared two LEW lines (SsNHsd and HANRijHsd) in their behavioural and neuroendocrine response to stress. In addition, we studied the psychostimulant effects of acute and repeated amphetamine in these two LEW rat lines. HAN rats were less active in the open field test and showed faster habituation of novelty-induced locomotion. The acoustic startle response was lower in HAN than in SSN rats, whereas prepulse inhibition of the startle response was greater in the HAN than in the SSN LEW subline. Moreover, HAN rats showed impaired acquisition of the two-way active avoidance response relative to SSN rats. The psychostimulant effects of acute amphetamine were smaller in HAN rats. Following repeated injections of amphetamine, behavioural sensitization to the psychostimulant effects of amphetamine was more pronounced in HAN than in SSN rats. Basal concentrations of serum corticosterone did not differ between the two rat lines. Following stress, however, HAN rats showed slightly higher corticosterone secretion than SSN rats. Our results show that two sublines of the LEW inbred strain of rats show profound behavioural differences which are only marginally paralleled by differences at the level of the HPA system.