Restraint or immobilization: A comparison of methodologies for restricting free movement in rodents and their potential impact on physiology and behavior

Restriction of free movement has historically been used as a model for inducing acute and chronic stress in laboratory animals. This paradigm is one of the most widely employed experimental procedures for basic research studies of stress-related disorders. It is easy to implement, and it rarely involves any physical harm to the animal. Many different methods have been developed with variations in the apparatuses used and the degree of limitation of movement. Unfortunately, very few studies directly compare the differential impact of the distinct protocols. Additionally, restraint and immobilization terms are not differentiated and are sometimes used interchangeably in the literature. This review offers evidence of great physiological differences in the impact of distinct restraint and immobilization procedures in rats and mice and emphasizes the need for a standardized language on this topic. Moreover, it illustrates the necessity of additional systematic studies that compare the effects of the distinct methodologies, which would help to decide better which procedure should be used depending on the objectives of each particular study.