Low-intensity sciatic nerve-stretch injury increases nociception, anxiety-like behaviors, and astrocyte activity in male Wistar rats

The incidence of chronic pain in the general population is highly correlated to anxiety disorders, which promote negative effects on the quality of life. Stretch injury is the primary cause of nerve dysfunction and injury in the civilian population. Here, we characterized changes in nociception, anxiogenic-like behaviors, and astrocyte expression in the low-intensity sciatic nerve-stretch injury (NSI) model. Male Wistar rats were submitted to NSI, chronic constriction injury of the sciatic nerve (CCI), or sham surgery (SHAM). Animals were submitted to nociceptive tests (von Frey, acetone, and hot plate) before surgery and 6, 12, 18, and 24 days post-surgery. Anxiety-like behaviors were assessed in the open field test (OFT) 23 days after surgery. Immunofluorescence for astrocyte activity (glial fibrillary acidic protein (GFAP)) was performed in cortical, thalamic, and brainstem areas involved with pain and emotional processing. Animals submitted to NSI showed increased mechanical allodynia and thermal hyperalgesia, similar to those submitted to CCI. In the OFT, both NSI and CCI animals showed an increase in anxiety-like behaviors. Also, NSI animals presented an increased expression of GFAP in all analyzed areas, similar to CCI animals. In conclusion, the NSI model produced behavioral alterations comparable to those observed in the CCI model, including hypersensitivity to mechanical and thermal (heat) stimuli that lasted for more than three weeks. Additionally, both models induced a similar increase in GFAP expression in cortical, thalamic, and brainstem regions.