Exogenous carbon monoxide improves postoperative anxiety-like behaviors in elderly rats by inhibiting excessive autophagy of astrocytes

Abstract

Objective To investigate the role of exogenous carbon monoxide (CO) in improving anxiety-like behaviors in elderly rats under perioperative stress by inhibiting excessive autophagy of astrocytes. Methods Thirty-six clean healthy male SD rats (aged 18~20 months) were randomly divided into 3 groups (n=12): sham-operation group (Group S), peritoneal surgery group (Group P), and peritoneal surgery+carbon monoxide-releasing molecule 3 (CORM-3) group (Group PC). The rats in Group PC were injected with exogenous CORM-3 (4 mg/kg) via caudal vein immediately, and in 24 and 48 h after surgery. Open field test and elevated plus maze test were performed to evaluate the anxiety-like behaviors on the 7th day after surgery. The neuronal amount in the amygdala, the expression of Bcl-2 interacting protein 1 (Beclin 1) and ubiquitin (Ub) in the astrocytes, microglia and neurons were assessed by immunofluorescence assay. The expression levels of microtubule associated protein 1 light chain 3 (LC3) was detected by Western blotting. The number of autophagosomes in the amygdala were observed with transmission electron microscopy. Results The results of open field test and elevated plus maze test showed that, as compared with Group S, the percentage of staying time in the central area was significantly decreased in Group P and Group PC (P < 0.05), so were the percentages of open arm stay duration and entry times (P < 0.05), indicating increased anxiety-like behaviors in the rats from these 2 groups. The histopathological and Western blotting results suggested declined number of NeuN positive cells in the amygdala, up-regulated expression of Beclin 1 and Ub in the astrocytes, and elevated ratio of LC3Ⅱ/Ⅰ were observed in Group P and PC (P < 0.05). Under transmission electron microscope, no autophagosomes were found in the astrocytes of Group S, while they were observed in Group P and PC. However, the above indexes of Group PC were all remarkably improved in comparison with those of Group P (P < 0.05). Conclusion Exogenous CO can improve the anxiety-like behaviors in aged rats under perioperative stress, and the mechanism may be associated with its inhibition on excessive autophagy of astrocytes in the amygdala.

Keywords

• perioperative period
• carbon monoxide
• astrocyte
• amygdala
• autophagy