Examining the Impact of Housing Conditions on Depression-Like Responses in Rats

Abstract

Part of the increasing attention to improving animal welfare includes the shift to individually-ventilated cages (IVCs). There is some evidence that housing animals in IVCs is inherently stressful, which could impact the outcome of preclinical research and would therefore benefit from more in-depth study. Consequently, the purpose of my thesis is to determine if extended housing of rats in IVCs influences the development of depression-like outcomes to a greater extent than conventional, open-top cages (OTCs) and to determine if these outcomes are impacted by social housing. My hypotheses were: that IVC rats would show more depression-like responses than OTC rats and that single-housed rats would show more depression-like responses than pair-housed rats. I also expected a cage type by social housing interaction such that the differences in depression-like responding between single and pair-housed animals would be reduced in the IVC condition relative to the OTC condition. To test the rats’ depression-like behaviours, I used the forced swim test and the splash test. To test for changes in physiology related to depression, I weighed each animal’s adrenal glands post-mortem. In the splash test, as expected, I found that IVC rats took longer to begin grooming than OTC rats, and that IVC rats showed fewer grooming bouts than OTC rats. However, unexpectedly, single-housed rats showed more grooming bouts and longer grooming time than pair-housed rats. In the forced swim test, the results did not follow my predictions. Instead, IVC and single-housed rats spent less time immobile than OTC animals and pair-housed animals, respectively. However, the decreases in immobility appeared to be secondary to increases in escape-like behaviour (i.e., climbing and diving). My results indicate that IVC-housed rats did not show more depression-like outcomes than OTC rats. However, the behaviour shown may be explained by increased anxiety-like responses in the IVC rats. Overall, it appeared that the behavioural profiles displayed by IVC-housed rats and single-housed rats were indicative of greater anxiety-like behaviour as opposed to depression-like behaviour.