Amelioration of pain and anxiety in sleep-deprived rats by intra-amygdala injection of cinnamaldehyde

Background

Sleep disorders are accompanied by increased anxiety and somatic pain. In addition, it has been observed that anxiety and pain have a boosting effect on each other, resulting in continued sleep disturbances. Amygdala's (CeA) central nucleus plays a crucial role in these processes. Cinnamaldehyde (Cinn) is an aromatic compound with anti-anxiety, antioxidant, and sleep-promoting properties. The present study uses sleep-deprived rats to examine the effects of an intra-CeA injection of Cinn on pain and anxiety.

Methods

Sleep deprivation (SD) was induced using the platform technique. 35 male Wistar rats were divided into five groups. Anxiety state and nociception were evaluated among groups using formalin test (F.T.), open field test (OFT), and elevated plus maze (EPM). Anxiety tests (OFT and EPM) were conducted in all groups. The first group was undergone FT without induction of SD (SD⁻FT⁺). The second group received SD without FT(SD⁺FT⁻). The third group received both SD and FT(SD⁺FT⁺). The treatment and vehicle groups have undergone both SD and FT in addition to the respectively intra-CeA injection of Cinn (SD⁺FT⁺ Cinn) and Cinn vehicle (SD⁺FT⁺ VC). The recorded behaviors were analyzed between groups using IBM SPSS 24th version.

Results

SD did not lead to any significant difference in nociceptive behaviors in FT between groups SD⁻FT⁺ and SD⁺FT⁺ (P ≥ 0.05). At the same time, there was a considerable discrepancy in rearing behaviors (P < 0.006) and the number of fecal boli (P < 0.004) recorded in OFM between these groups. Treatment with Cinn led to decreased nociception (P < 0.038), decreased rearing behaviors (P < 0.01), and reduced defecation (P < 0.004) in group SD + FT+ Cinn in comparison to the group SD⁺FT⁺. There were no differences in anxiety test results between the first and second groups (P ≥ 0.05).

Conclusion

SD can lead to elevated anxiety, while intra-CeA injection of Cinn ameliorated both perceptions of acute pain and anxiety. Besides, the conduction of FT before the anxiety test led to no disturbance in the results of anxiety tests.