Behavioural responses of anxiety in aversive and non-aversive conditions between young and aged Sprague-Dawley rats

Abstract

Introduction: Measures of anxiety in behavioural tests remain largely unclear even decades after their establishment. Differences in the severity of anxiety measured by anxiety tests are an important issue that must be addressed. We hypothesized that the addition of light as an aversive stimulus to elicit a behavioural change could reflect different degrees of anxiety measured between such tests. Materials and Methods: The present study compared the responses of aged and young animals between the elevated plus maze (EPM) and the home cage emergence test (HCET) in high aversive bright light and low aversive dim light conditions. Results and Discussion: In the EPM, bright light conditions induced anxiogenic effects in both animal groups. However, in the HCET, bright light conditions affected only aged animals, who exhibited greater anxiety, increased escape latency, and reduced escape frequency. The correlation analysis showed the escape latency in the HCET was negatively correlated with the time spent and frequency of entry in the open arms of EPM in aged animals in the dim light condition. Interestingly, no correlation of HCET and EPM was found in aged animals in the bright light condition or in young animals in both bright and dim light conditions, which suggests HCET and EPM measure two different entities of anxiety. Conclusion: The specific behaviours of aged and young animals in the various tests indicate different levels of anxiety are measured by HCET and EPM in aversive and non-aversive environmental conditions.