Generation and phenotypic characterization of a sigma-1 receptor knockout rat.

The sigma-1 receptor (σ1R) is a chaperone involved in multiple physiological and pathological processes, including pain modulation, neuroprotection, and neurodegenerative diseases. Despite its functional significance, its precise roles remain unclear due to the lack of suitable models for detailed mechanistic studies. In this work, we describe the generation and phenotypic characterization of a novel σ1R knockout (σ1R KO) rat model. Using CRISPR/Cas9 technology, we introduced a specific 218-base-pair deletion into the σ1R gene, resulting in a complete loss of receptor expression, as confirmed by Western blot, immunohistochemistry, and binding assays. Comprehensive phenotypic analyses revealed no major developmental or behavioral abnormalities in σ1R KO rats under baseline conditions, suggesting that σ1R is not essential for development or survival. Additionally, no genotype-related differences were observed in cellular or biochemical blood parameters. Motor function tests (rotarod, grip strength, and wheel running) showed no deficits; however, σ1R KO rats displayed reduced exploratory behavior in actimetry and markedly diminished burrowing behavior. By contrast, no anxiodepressive-like behaviors were observed in the open field, startle, or forced swim tests. Sensory testing of naive rats revealed no significant genotype-related differences in responses to mechanical, heat, or cold stimuli, or in the formalin test (chemical-induced pain). However, σ1R KO rats displayed attenuated neuropathic pain after traumatic nerve injury (spared nerve injury), highlighting the role of σ1R in pain sensitization pathways. This study establishes the σ1R KO rat as a valuable tool for investigating σ1R-mediated mechanisms and for developing therapeutic strategies targeting σ1R for chronic pain, neurodegeneration, and psychiatric disorders.