Investigating Consistency and Stability of Temperament in Two Strains of Rattus Norvegicus

Open Access
Wang, Kayllie
Area of Honors:
Bachelor of Science
Document Type:
Thesis Supervisors:
  • Victoria Anne Braithwaite Read, Thesis Supervisor
  • Dr. James Harold Marden, Honors Advisor
  • temperament
  • personality
  • behavior
  • Long-Evans
  • Sprague-Dawley
  • enrichment
  • chronic mild stress
  • open field
  • novel object
Personality (consistency of temperament across conditions) was once thought to be exclusive to humans. It is now, however, recognized in a wide range of non-human animals and is measured using assays of activity and response to novelty. We measured the utility of such temperament assays in Rattus norvegicus; the Long-Evans and Sprague-Dawley strain, specifically addressing the effects of enrichment loss and exposure to chronic mild stress. As temperament is, by definition, stable over time and context, we hypothesized that the removal of enrichment and exposure to chronic mild stress (CMS) would not significantly change temperament measures. We used open field and novel object tests, and evaluated three cohorts of rats. Measures from the open field indicating boldness were: high locomotion and time spent in the middle of an arena. Novel object measures reflecting a bold phenotype were: high activity, short latency to reach novel objects, and high proportion of time around novel objects. Each cohort was measured for: baseline scores, after a manipulation to cage enrichment, and the third cohort of rats also experienced CMS (both social and physical stressors) before a further set of assays. Surprisingly, we found a considerable lack of consistency across the three cohorts studied for both the open field and the novel object assays. Such a lack of predictive value of these tests across time questions the utility of these methods. We therefore suggest that the open field and novel object tasks should be avoided in future rat temperament studies.