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

Measures of anxiety in behavioural tests remain largely unclear even decades after their establishment. Differences in the severity of anxiety measured by anxiety tests is an important issue that must be addressed. To test the hypothesis that the addition of light as an aversive stimulus will elicit a difference in behaviour between aged and young animals, we compared the responses of aged and young animals in the home cage emergence test (HCET) and elevated plus maze (EPM), in high aversive bright light and low aversive dim light conditions. In the HCET, our results demonstrated that young animals escaped with shorter latency and greater frequency than aged animals in both bright and dim light conditions, indicating that young animals display greater exploratory tendencies than aged animals. In the EPM, bright light conditions induced anxiogenic effects in both age groups. Interestingly, two-way ANOVA showed a significant interaction effect of age and light on the number of entries into the open arms of the EPM as well as frequency of escape in the HCET. These results show that the addition of light as an aversive stimulus in the EPM and HCET produced different responses in aged versus young animals in each test. In conclusion, significant interactions between age and light affected aged and young animals differently in the HCET and EPM, indicating that the two tests measure different aspects of anxiety.