Evaluation of Lewis and SHR rat strains as a genetic model for the study of anxiety and pain.

The study of inbred strains of rodents that differ for specific behaviours can help us to understand the biological mechanisms underlying complex psychological traits. Lewis (LEW) and SHR inbred rat strains, for example, have been recently proposed as a genetic model for the study of anxiety. Our goal was to characterise two Brazilian substrains of LEW and SHR rats, that have never been compared before, behaviourally and/or pharmacologically, in order to evaluate their potential contribution to studies on anxiety and pain. Male and female LEW and SHR rats were submitted after 8 weeks of age to five anxiety/emotionality tests: the open field (7 or 260 lux), the elevated plus-maze, the elevated T-maze and the black/white box. Rats of all groups were also submitted to the formalin test of nociception and measurement of blood pressure. Significant strain differences (P<0.05) were observed in both sexes for all indices of anxiety and also for measures of pain and blood pressure. SHRs, compared with LEWs, explored more the aversive environments of all anxiety tests, showed less nociceptive responses and were hypertensive. All differences in experimental anxiety parameters agree with previous differences reported between two French LEW and SHR substrains, suggesting that LEWs are more anxious than SHRs, thus consolidating these strains as a useful genetic model for the study of anxiety and pain. The possible involvement of tachykinergic mechanisms is discussed.