Many patients with chronic pain can suffer with anxiety and depression as well as learning and memory impairments. The hippocampus is a brain area that has been suggested to play a role in these affective and cognitive impairments. Romero-Grimaldi and colleagues examined the consequences of adding a chronic stress to the effects of a nerve injury on hippocampal neurogenesis in 6 – 8 week old rats.1 Researchers administered a chronic nerve constriction injury (NCI) to the sciatic nerve in one group of rats while performed a sham operation without constricting the nerve in a second group. To induce stress, sub-groups of NCI and sham rats were immobilized in restriction bags for 45 minutes/day for 7 and 28 days.
NCI animals exhibited allodynia and hyperalgesia. Eight days after surgery, a significant increase in plasma corticosterone was detected in the stressed animals compared to the unstressed animals.
One week after surgery, a significant decrease in cell proliferation in the hippocampal dentate gyrus of NCI animals was observed compared to the sham surgery group. This reduction in NCI rats was exacerbated by stress and statistically significant compare to other groups. Four weeks after the injury, the NCI animals exhibited a reduction in the number of neuroblasts and reduced survival of new neurons in the hippocampal dentate gyrus compared to the sham operated animals. Again, this decrease was exacerbated by stress.
Authors concluded that neuropathic pain negatively influences neurogenesis in the hippocampus and this effect is exacerbated by a daily stressor. This research, suggesting that a stressor, independent of the stress of an injury, can amplify maladaptive neurogenesis in the hippocampus, provides further evidence for the potential importance of including stress management strategies in the treatment of patients experiencing pain. Mindfulness training enables patients to calmly observe physical, cognitive and emotional reactions to daily stressors. This stable, open and compassionate observation can facilitate patients’ insights into the automatic reactions that exacerbate distress and pain and those conscious alternatives that de-escalate distress and pain. With practice, patients grow increasingly skillful self-regulating their responses to daily stressors and often, can reduce their stress and pain.
1Romero-Grimaldi C, Berrocoso E, Alba-Delgado C, et al. Stress increases the negative effects of chronic pain on hippocampal neurogenesis. Anesth Analg. 2015;121(4):1078-88.