2010). Importantly, the intramuscular injection of acidic saline, a manipulation which induces mechanical hyperalgesia in the spinal regions (Sluka et al. 2001) does not result in any marked hyperalgesia in the orofacial region, further highlighting differences between the trigeminal region and the rest of the body (Ambalavanar et al. 2007). Of the above models, the one involving the stretching of the masseter muscle may be the most akin to the human conditions as it involves the natural contractility and movement of muscle and shows a similar pathophysiology (Dessem et al. 2010). Animals other than rats and mice are rarely used in orofacial inflammatory pain models, however,
some studies Inhibitors,research,lifescience,medical have been performed in rabbits (TMJ inflammation; Swift et al. 1998; Stoustrup et al. 2009) and guinea pigs (skin inflammation; Neubert et al. 2000). Neuropathic pain models Rats and mice have been the animals of choice wherein most, if not all, neuropathic pain models have been developed. And, in general, rats preceded mice as models where most neuropathy-inducing maneuvers Inhibitors,research,lifescience,medical have Inhibitors,research,lifescience,medical been tried. The direct damage to a nerve (cutting, ligating, or crushing) results in prominent changes in the expression of various molecules in the dorsal rot ganglias (DRGs) or trigeminal ganglions (TGs) of the affected nerves, leading to the emergence of neuropathic
pain. The neuropathic pain models involve ligating and cutting a whole Inhibitors,research,lifescience,medical nerve or parts of a nerve, or placing several loose ligatures around a nerve. Of the various nerve injury models used in the sciatic region, the most applicable to the facial region has selleck chemical proven to be the chronic constriction injury (CCI) model, which involves tying loose ligatures around the nerve (Vos et al. 1994; Khan and Hargreaves 2010). The infraorbital nerve (IoN; Inhibitors,research,lifescience,medical maxillary branch of the trigeminal nerve) branches peripherally in a fan-like fashion distal to the infraorbital foramen, and this is where the surgical
manipulations are most easily executed. Due to its branching, a wide ligature is necessary over the entire width of the nerve in order to “bunch up” all the branches of the IoN. The tightness of the ligature is important: too loose produces no pain behavior while too tight SB-3CT produces anesthesia (Martin et al. 2010; Krzyzanowska et al. 2011). Such manipulation of the IoN in rats results in behavioral abnormalities which can be compared with some of the symptoms observed in TN such as mechanical hyperalgesia, air-puff allodynia, and paraesthesias/dysaesthesias (Vos et al. 1994, and personal observations). An alternative way of accessing the IoN is from inside of the mouth (Imamura et al. 1997). The advantage of this last approach would be the avoidance of a skin incision and thus sensitization of the “testing area,” but it is likely to hamper feeding. This and the relative difficulty of surgery in this model are probably responsible for its not having been more generally adapted.