118. The interplay between psychological well-being, pain and inflammation in a rat model of spinal cord injury

We hypothesize that inflammation, inherent to spinal cord injury (SCI), contributes to decreased psychological well-being. To test this, male Sprague–Dawley rats ( N  = 47) received a mild, moderate, or severe contusion or were intact controls. Behavioral measures of anxiety, depression and pain were collected prior to injury, and on days 10 and 21 post injury. Behavioral tests assessed anhedonia (sucrose preference), anxiety (center activity and shock probe burying), psychomotor activity (open field activity) and social interest (social exploration). Pain tests assessed mechanical allodynia (tactile reactivity) and thermal hyperalgesia (tail-flick). Serum alpha-2 macroglobulin levels were also measured on Days 1, 10 and 21, and thymus weight was recorded on Day 25. First, subjects’ average scores (Days 10 and 21) on behavioral measures of depression and anxiety were subjected to principal components and hierarchical cluster analyses. The analyses derived three subject clusters, identified via ANOVAs as: “Depression/Anxiety” ( n  = 15), “Depression” ( n  = 12) and “Healthy” ( n  = 20). The “Depression/Anxiety” cluster showed increased mechanical allodynia, anxiety, and peripheral inflammation relative to the “Healthy” cluster. The “Depression” cluster also showed mechanical allodynia, increased alpha-2 macroglobulin levels and decreased thymus weight relative to the ”Healthy” cluster. These data provide preliminary support for a role of inflammation in decreasing psychological well-being after SCI. Overall, we demonstrate, post SCI, an interplay between decreased psychological well-being, increased peripheral inflammation and increased pain reactivity.