Battery of behavioral tests in mice to study postoperative delirium

Abstract

Postoperative delirium is associated with increased morbidity, mortality and cost. However, its neuropathogenesis remains largely unknown, partially owing to lack of animal model(s). We therefore set out to employ a battery of behavior tests, including natural and learned behavior, in mice to determine the effects of laparotomy under isoflurane anesthesia (Anesthesia/Surgery) on these behaviors. The mice were tested at 24 hours before and at 6, 9 and 24 hours after the Anesthesia/Surgery. Composite Z scores were calculated. Cyclosporine A, an inhibitor of mitochondria permeability transient pore, was used to determine potential mitochondria-associated mechanisms of these behavioral changes. Anesthesia/Surgery selectively impaired behaviors, including latency to eat food in buried food test, freezing time and time spent in the center in open field test, and entries and duration in the novel arm of Y maze test, with acute onset and various timecourse. The composite Z scores quantitatively demonstrated the Anesthesia/Surgery-induced behavior impairment in mice. Cyclosporine A selectively ameliorated the Anesthesia/Surgery-induced reduction in ATP levels, the increases in latency to eat food, and the decreases in entries in the novel arm. These findings suggest that we could use a battery of behavior tests to establish a mouse model to study postoperative delirium.

Figure 1. Diagram of the experimental design.

The mice received behavior tests at 24 hours (baseline) before the abdominal surgery under isoflurane anesthesia (Anesthesia/Surgery), and then at 6, 9 and 24 hours after the Anesthesia/Surgery.

Figure 2. Anesthesia/Surgery impairs the behavior of mice in buried food test in a time-dependent manner.

(A) Anesthesia/Surgery (black bar) does not significantly change the latency to eat food of the mice in the buried food test as compared to the control condition (white bar) at 6 hours after the Anesthesia/Surgery. (B) Anesthesia/Surgery (black bar) significantly increases the latency to eat food of the mice in the buried food test as compared to the control condition (white bar) at 9 hours after the Anesthesia/Surgery. (C) Anesthesia/Surgery (black bar) does not significantly change the latency to eat food of the mice in the buried food test as compared to the control condition (white bar) at 24 hours after the Anesthesia/Surgery. N = 14 in the control condition group and N = 14 in the Anesthesia/Surgery group.

Figure 3. Anesthesia/Surgery impairs the behavior of mice in open field test in a time-dependent manner.

(A) Anesthesia/Surgery (black bar) significantly decreases the time spent in the center of the open field as compared to the control condition (white bar) at 6 (A1), but neither 9 (A2) nor 24 (A3), hours after the Anesthesia/Surgery in the mice. (B) Anesthesia/Surgery (black bar) significantly decreases the freezing time in the open field test as compared to the control condition (white bar) at 6 (B1), but neither 9 (B2) nor 24 (B3), hours after the Anesthesia/Surgery in the mice. (C) Anesthesia/Surgery (black bar) does not significantly change the time to reach the center (latency to the center) in the open field test as compared to the control condition (white bar) at 6 (C1), 9 (C2) and 24 (C3) hours after the Anesthesia/Surgery in the mice. N = 14 in the control condition group and N = 14 in the Anesthesia/Surgery group.

Figure 4. Anesthesia/Surgery impairs the behavior of mice in Y maze test in a time-dependent manner.

(A) Anesthesia/Surgery (black bar) significantly decreases the number of entries in the novel arm in the Y maze test as compared to the control condition (white bar) at 6 (A1) and 9 (A2), but not 24 (A3), hours after the Anesthesia/Surgery in the mice. (B) Anesthesia/Surgery (black bar) significantly decreases the duration in the novel arm in the Y-maze test as compared to the control condition (white bar) at 6 (B1), but not 9 (B2) nor 24 (B3), hours after the Anesthesia/Surgery in the mice. N = 14 in the control condition group and N = 14 in the Anesthesia/Surgery group.

Figure 5. CsA mitigates the Anesthesia/Surgery-induced ATP reduction and behavior changes in buried food test and Y maze test.

(A) Anesthesia/Surgery (black bar) decreases the ATP level in mouse brain tissue as compared to the control condition (white bar) immediately after the Anesthesia/Surgery. Treatment with CsA alone (gray bar) does not significantly change the ATP level as compared to the control condition (white bar). However, there is a significant interaction of CsA and Anesthesia/Surgery on the ATP level, and treatment with CsA attenuates the Anesthesia/Surgery-induced reduction in ATP level. (B) Anesthesia/Surgery (black bar) increases the latency to eat food of the mice in the buried food test as compared to the control condition (white bar) at 9 hours after the Anesthesia/Surgery. Treatment with CsA alone (gray bar) does not significantly change the latency as compared to the control condition (white bar). However, there is a significant interaction of CsA and Anesthesia/Surgery on the latency, and treatment with CsA attenuates the Anesthesia/Surgery-induced increase in the latency. (C) Anesthesia/Surgery (black bar) decreases the number of entries in the novel arm of Y maze test as compared to the control condition (white bar) at 6 hours after the Anesthesia/Surgery. Treatment with CsA alone (gray bar) does not significantly change the number of entries as compared to the control condition (white bar). However, there is a significant interaction of CsA and Anesthesia/Surgery on the number of entries, and treatment with CsA attenuates the Anesthesia/Surgery-induced decrease in the number of entries. (D) Anesthesia/Surgery (black bar) decreases the number of entries in the novel arm of Y-maze test as compared to the control condition (white bar) at 9 hours after the Anesthesia/Surgery. Treatment with CsA alone (gray bar) does not significantly change the number of entries as compared to the control condition (white bar). However, there is a significant interaction of CsA and Anesthesia/Surgery on the number of entries, and treatment with CsA attenuates the Anesthesia/Surgery-induced decrease in the number of entries. CsA, cyclosporine A. ATP, adenosine triphosphate. N = 9 and 10 in each group of ATP studies and behavioral studies, respectively.