To facilitate the study of pain transmission and the characterization of novel analgesic compounds, an array of experimental animal pain models has been developed mainly in rodents, reflecting all types of pain, from acute to chronic, somatic to visceral, and nociceptive to neuropathic and cancer-related pain. Depending on the model, pain measurements can encompass spontaneous pain behaviors as well as pain evoked by various sensory modalities. It is important to note that in rodents, measuring spontaneous pain is very difficult and is generally limited to the observation of quantifiable nocifensive (pain-escape) behaviors such as hind paw lifting or altered grooming. However, experimental measures of evoked pain are well characterized and are analogous to clinical diagnostic methods. In the following overview, acute pain refers to pain that lasts from seconds to a day while chronic pain typically refers to experimental pain manipulations that persist for at least several days. In addition, this section will focus on the most-widely used preclinical pain models.
The majority of these animal models of pain were originally developed in rats. Except as noted below, essentially all have also been successfully carried out using various mouse strains including gene-disrupted (knockout) mice.25 However, significant differences in the basal nociceptive sensitivity and analgesic response have been noted for different mouse strains serving to further complicate the interpretation of the knockout phenotype.26
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