3.1 CUMS increased anxiety- and depression-related behaviour
Mice display distinct behavioural changes, suggesting an anxiety or depression response after exposure to chronic stress. Therefore, the behavioural response of control and CUMS mice in an anxiogenic environment was investigated using EPM and OFT and were compared with control mice. In EPM test, CUMS mice exhibited a significant (P<0.05; Student’s t test) reduction in both percentage time in open-arm (Control: 21.6 + 3.1%, n=10; CUMS: 12.2 + 3.3%, n=10; Fig. 2A) and percentage open-arm entries (Control: 40.9 + 3.5 %, n=10; CUMS: 24.6 + 4.2%, n=10; Fig. 2B). Thus, the CUMS mice made fewer entries and spent less time in open arms of the maze than control mice, indicating an enhanced anxiety response. Similar to the results in EPM, we observed increased anxiety response in OFT (Fig. 2C). In addition to measuring the number of entries in the central zone, we also analysed changes in the number of leaning, rearing, grooming and defecation of CUMS mice as compared to control. We observed a significant reduction in the number of entries in the central zone of the open-field (Control: 15.8 + 1.8, n=10; CUMS: 9.1 + 2.2, n=10) and rearing behaviour (Control: 9.6 + 0.9, n=10; CUMS: 6.3 + 1.5, n=10). Furthermore, as compared to control mice, CUMS exposure significantly increased grooming (Control: 2.3 + 1.3, n=10; CUMS: 4.8 + 0.7, n=10) and defecation (Control: 1.3 + 0.4, n=10; CUMS: 3.6 + 0.5, n=10) in young male mice. There were no overall significant differences between the control and CUMS mice with regard to leaning behaviour.
The behavioural effects of CUMS were further analysed by FST and sucrose preference test. When tested in FST (Fig. 2D), CUMS mice showed significant increase in the immobility time (Control: 74.8 + 16 s, n=10; CUMS: 136.2 + 24.7 s, n=10) and subsequent reduction in the swimming time (Control: 134.4 + 23.9 s, n=10; CUMS: 94.8 + 11.2 s, n=10). There were no significant differences in the climbing time between control and CUMS mice (Control: 88 + 30.2 s, n=10; CUMS: 61 + 33 s, n=10; P=0.07). Similarly, we assessed depression-like behaviour through sucrose preference test that is known to indicate anhedonia, also interpreted as behavioural despair, in stressed mice. As shown in Fig. 2E, 2-week CUMS exposure significantly reduced the percentage of sucrose consumption in the stressed mice in comparison to control mice (Control: 86.2 + 9.1 %, n=10; CUMS: 63.2 + 7.6 %, n=10; P<0.05). Thus, CUMS was found to elicit anxiety as well as depression-like behaviour in these tests, an interesting finding in the light of the fact that a sizeable subpopulation of depressed human subjects exhibit hyper anxiety .
3.2 CUMS changed ERα and ERβ mRNA expression in opposite manner
CUMS significantly increased the expression of ERα in prefrontal cortex (Control: 1.5 + 0.2, n=3; CUMS: 2.6 + 0.2, n=3; P<0.05; Fig. 3A) as well as hippocampus (Control: 1.4 + 0.4, n=3; CUMS: 2.5 + 0.1, n=3;...