Category
Applied
Description
Neuropathic pain is a chronic condition resulting from nervous system injury or disease, commonly associated with multiple sclerosis, spinal cord injury and diabetes. Current mouse models rely on invasive surgical techniques such as spinal nerve ligation (SNL) or chronic constriction injury (CCI), which require specialized training, increase variability, and reduced accessibility. Previous studies in rats have shown that formalin injections can induce a persistent pain state and spinal molecular changes comparable to those observed in surgical models. This study investigated whether a single subcutaneous injection of 5% formalin is sufficient to produce neuropathic pain behaviors and nervous tissue changes CCI and SNL.
Mice were injected with 20 µl of 5% formalin in the dorsal surface of the right hind paw and pain behavior assessed at different time points over the course of two weeks using both Hargreaves test for thermal sensitivity and von Frey filaments test for mechanical sensitivity. Compared to vehicle controls, formalin-injected mice exhibited significantly reduced pain thresholds, with peak hypersensitivity observed on day 10 post-injection. Brain and lumbar spinal cord tissues were collected for histology on day 14 post-injection. Hematoxylin and eosin staining suggested gliosis and demyelination consistent with central changes associated with neuropathic pain.
These findings suggest that a single subcutaneous formalin injection can induce both mechanical and thermal hypersensitivity and cellular alterations characteristic of neuropathic pain. Additional experiments are currently underway to further characterize the molecular and cellular changes underlying this model, and evaluate the utility in therapeutic screening.
We propose a streamlined, efficient, reproducible and less invasive alternative for investigating key mechanisms and potential treatments of neuropathic pain.
Hargreaves Test on Formalin Injected Mice: A Neuropathic Pain Model
Applied
Neuropathic pain is a chronic condition resulting from nervous system injury or disease, commonly associated with multiple sclerosis, spinal cord injury and diabetes. Current mouse models rely on invasive surgical techniques such as spinal nerve ligation (SNL) or chronic constriction injury (CCI), which require specialized training, increase variability, and reduced accessibility. Previous studies in rats have shown that formalin injections can induce a persistent pain state and spinal molecular changes comparable to those observed in surgical models. This study investigated whether a single subcutaneous injection of 5% formalin is sufficient to produce neuropathic pain behaviors and nervous tissue changes CCI and SNL.
Mice were injected with 20 µl of 5% formalin in the dorsal surface of the right hind paw and pain behavior assessed at different time points over the course of two weeks using both Hargreaves test for thermal sensitivity and von Frey filaments test for mechanical sensitivity. Compared to vehicle controls, formalin-injected mice exhibited significantly reduced pain thresholds, with peak hypersensitivity observed on day 10 post-injection. Brain and lumbar spinal cord tissues were collected for histology on day 14 post-injection. Hematoxylin and eosin staining suggested gliosis and demyelination consistent with central changes associated with neuropathic pain.
These findings suggest that a single subcutaneous formalin injection can induce both mechanical and thermal hypersensitivity and cellular alterations characteristic of neuropathic pain. Additional experiments are currently underway to further characterize the molecular and cellular changes underlying this model, and evaluate the utility in therapeutic screening.
We propose a streamlined, efficient, reproducible and less invasive alternative for investigating key mechanisms and potential treatments of neuropathic pain.
