BACKGROUND: Social defect and chronic pain are 2 major health problems and recent data has demonstrated that they generally exist concurrently. However, a powerful evaluation model on the behavioral change is lacking. This study was designed to evaluate the behavioral curves using a statistically modeled trajectory analysis in neuropathic animals with or without social defect exposure.

MATERIAL AND METHODS: After approval by the institutional animal care committee, Sprague-Dawley rats were randomized into different interventional groups with 15 animals each. Sprague-Dawley rats underwent spared nerve injury (SNI) to establish the neuropathic pain model, of which the mechanical withdrawal threshold was measured using von Frey filaments for a period of 105 days. Otherwise, a modified version of the resident (Long-Evans rats)-intruder paradigm was applied to produce a social defect animal model through the elevated plus maze (EPM). After raw data collection, we modeled them into a powerful statistical effects analysis to build up the behavioral change tendency in single SNI or in combined SNI and social defect animals.

RESULTS: The random and fixed effects analyses of the pain behavior after SNI were successfully modeled and demonstrated a gradient recovery tendency during the 15-week post-injury observational period. Correspondingly, SNI rats exhibited increased social defected symptoms, as indicated by the increased anxiety-like behavior in the EPM test. In addition, continuous social defect stress for 5 days or 10 days, respectively, partially attenuated and exacerbated SNI-induced allodynia in both random and fixed effects models. Five days but not 10 days social defect ameliorated SNI-associated anxiety-like behavior.

CONCLUSIONS: These data suggest that statistically powerful analysis of nerve injury-induced neuropathic pain is a highly sensitive model to determine the behavioral change tendency and distinguish them among behavior curves with or without social defect, and the combination of SNI with resident-intruder paradigm may be a suitable model for behavior evaluation of neuropathic pain with social defect.

Keywords: Behavior, Animal, Neuralgia - pathology, Rats, Long-Evans, Sciatic Nerve - pathology, Social Behavior