Two variables that can be used as pain indices in experimental animal models of arthritis

Group III mGluR7 and mGluR8 in the amygdala differentially modulate nocifensive and affective pain behaviors

“…Supporting evidence comes from an increasing body of literature about pain-related vocalizations. Audible squeaks in response to noxious stimuli indicate a supraspinally organized nocifensive reflex response (Borszcz and Leaton, 2003;Calvino et al, 1996;Jourdan et al, 1995;Neugebauer et al, 2007;Yu et al, 2002). Ultrasonic vocalizations in the 22-25 kHz range are reliably emitted in aversive situations and are believed to reflect an unpleasant emotional-affective state such as fear and anxiety.…”

“…The total duration of vocalizations (arithmetic sum of the duration of individual events) was recorded for 1 min, starting with the onset of the mechanical stimulus. Audible and ultrasonic vocalizations reflect supraspinally organized nocifensive and affective responses to aversive stimuli (Borszcz and Leaton, 2003;Borta et al, 2006;Calvino et al, 1996;Hodgson et al, 2008;Jourdan et al, 1995;Knutson et al, 2002;Ko et al, 2005;Neugebauer et al, 2007;Oliveira and Barros, 2006;Yu et al, 2002).…”

Role of peripheral μ‐opioid receptors in arthritis: Are they potential targets for therapy?

“…The mechanism of joint inflammation in these 2 models involves a T cell-mediated immunologic response, and the histologic picture is very similar to that observed in rheumatoid arthritis (12)(13)(14). Finally, CFA can be given by intraarticular injection, after which it induces a direct, destructive monarthritis localized to the affected joint, with onset within 4-6 hours and increasing intensity over 1-2 weeks (9,14).…”

“…Because systemic (intravenous or intraperitoneal) or central nervous system administration of opioids can result in severe side effects such as disruption of cognitive and motor functions, confusion, hallucinations, or vomiting (10,14), peripheral administration of opioids during periods of inflammation has been proposed (3,4,6). Inflammation increases the number of sensory nerve terminals and disrupts the perineurium, the diffusion barrier for hydrophilic substances such as endogenous or exogenous opioids (15).…”

“…Throughout these experiments, inflammation remained confined to the soft tissue of the inoculated paw (19,21), and the contralateral side and the joints were not affected. Although intraplantar administration of the adjuvant causes inflammation of the unilateral tibiotarsal joint, a longer period of time (1-4 weeks) is required for the development of arthritis (12,14).…”