Innocuous jaw movements increase c-fos expression in trigeminal sensory nuclei produced by masseter muscle inflammation

Abstract

Muscle tenderness and pain during movements are prominent symptoms associated with persistent jaw muscle pain. However, there is virtually no information on how trigeminal neurons respond to jaw movements (JM) or muscle palpation in the presence of muscle tissue injury or myositis. In this study, we investigated the effects of innocuous JM in the presence of acute masseteric inflammation on postsynaptic responses in the trigeminal brainstem nuclei by examining the expression of c-fos. In one group of rats, unilateral injections of an inflammatory substance, mustard oil (MO: 20%, 25 microl) were made into a masseter muscle. In another group, controlled and systematic JM were provided following MO injection. Three additional groups of rats were used to control for anesthetic, JM, and injection procedure. MO injected in the masseter muscle induced a high level of Fos protein expression in four principal trigeminal regions: the subnucleus caudalis (Vc), the ventral and dorsal regions of the Vc/Vi (subnucleus interpolaris) transition zone, and the paratrigeminal nucleus (PTN). Movements following MO injection consistently produced a significantly greater level of Fos expression in all these areas, especially in the Vc/Vi transition region and caudal Vc on the ipsilateral side. Importantly, movements also induced a significantly greater level of Fos expression in the caudal Vc on the contralateral side. The present results provide the first documentation that innocuous JM in the presence of muscle inflammation significantly increase the MO-induced c-fos expression in the trigeminal brainstem nuclei, which may explain the greater pain experienced during movement of inflamed or injured muscles.

Selective local PMN recruitment by CXCL1 or CXCL2/3 injection does not cause inflammatory pain

“…Despite these limitations, c-Fos is the most extensively studied marker available. In line with previous studies [33,85,86], we ob- served that inflammation induces hyperalgesia as well as c-Fos transcription and increases in the number of c-Fos immunoreactive cells in Laminae I and II in the dorsal horn (Fig. 6), and these changes were also detectable following PMN depletion.…”

Peripheral AMPA receptors contribute to muscle nociception and c-fos activation

“…The group of animals pretreated with PBS in the masseter followed by MO injection exhibited a pattern of behavioral responses similar to that described for injection of MO alone (Ro et al, 2003; Fig. 3A).…”

“…We have previously shown that algesic stimulation of the masseter muscle evokes ipsilateral hind-paw shaking responses in lightly anesthetized rats (Ro et al, 2003). Using the same behavioral paradigm we quantified the MO-induced hindpaw shaking responses in NBQX or vehicle treated rats by counting the number of shakes in 30-sec intervals.…”

The Role Of Trigeminal Interpolaris-Caudalis Transition Zone In Persistent Orofacial Pain

“…1999), and masseter muscle inflammation (Imbe et al ., 1999; Ro et al ., 2003). These studies reveal an interesting pattern of trigeminal nociceptive neuronal activation (Fig.…”