Evidence for parasympathetic vasodilator fibres in the rat masseter muscle

Abstract

The present study was designed to examine (1) whether there are vasodilator fibres in the masseter muscle, and (2) if there are, to establish the neural pathways mediating these responses in urethane-anaesthetized rats. Electrical stimulation of the central cut end of the lingual nerve (LN) elicited intensity-and frequency-dependent increases of the blood flow in the masseter muscle (MBF) and lower lip (LBF). Increases in both the MBF and LBF evoked by the LN stimulation were reduced by hexamethonium in a dose-dependent manner (1-10 mg kg −1 ). Pretreatment with phentolamine or propranolol at a dose of 100 µg kg −1 had no effect on the increases in either MBF or LBF evoked by LN stimulation. Pretreatment with atropine (100 µg kg −1 ) significantly reduced the MBF increase induced by LN stimulation, but not that in the LBF. The sectioning of the superior cervical sympathetic trunk did not affect the responses. MBF increases occurred with electrical stimulation of the trigeminal ganglion, and these increases were significantly reduced by the administration of hexamethonium and atropine. Lidocaine microinjection into the trigeminal spinal nucleus or salivatory nuclei caused a significant attenuation of the LN-induced MBF increases. When wheat germ agglutinin-horseradish peroxidase (WGA-HRP) was injected into the masseter muscle, labelled neurones were abundantly observed in the otic ganglion. The present study indicates that there are parasympathetic cholinergic and noncholinergic vasodilator fibres originating from cell bodies in the otic ganglion in the rat masseter muscle. The MBF increase evoked by activation of the parasympathetic fibres occurred via the trigeminal mediated reflex, suggesting that the novel parasympathetic vasodilator response may play an important role in the regulation of the haemodynamics of jaw muscles.

GABAB receptors in the NTS mediate the inhibitory effect of trigeminal nociceptive inputs on parasympathetic reflex vasodilation in the rat masseter muscle

“…These observations suggest that the evoked MBF increases as a result of "vasodilation." Although blood vessels in the masseter muscle are innervated with sympathetic postganglionic neurons derived from the superior cervical ganglion, these neurons did not contribute to the observed MBF increases evoked by cVN stimulation, since bilateral sectioning of the CST in the present study cuts the preganglionic inputs to the superior cervical ganglion, which projects postganglionic fibers to the cranial circulation (see MATERIALS AND METHODS), and electrical stimulation of the CST consistently reduced MBF, as reported by our previous reports (14,15). Therefore, we hypothesize that the cVN stimulationinduced vasodilation in the masseter muscle is mediated by a mechanism involving a parasympathetic reflex.…”

“…Anesthetized animals were intubated, paralyzed by intravenous injection of pancuronium bromide (Mioblock; Organon, Teknika, The Netherlands; 0.6 mg/kg initially, supplemented with 0.4 mg/kg every hour or so after testing the level of anesthesia; see below), and artificially ventilated with a mixture of 50% air-50% O2 via a tracheal cannula. A ventilator (model SN-480 -7; Shinano, Tokyo, Japan) was set to deliver a tidal volume of 8.5-10 cm 3 /kg at a rate of 20 -23 breaths/min, and the end-tidal concentration of CO2 was determined by means of an infrared analyzer (Capnomac Ultima; Datex, Helsinki, Finland), as reported elsewhere (14). Rectal temperature was maintained at 37-38°C with the use of a heating pad.…”

“…capsaicin; cervical vagus nerve; baclofen; bicuculline; CGP-35348 THE PRESENCE OF PARASYMPATHETIC vasodilator fibers innervating the blood vessels in the jaw muscles has been established both physiologically and histochemically (14,25,36), as in the case of other orofacial tissues, such as the lower lip (14, 16 -18, 43, 47) and the submandibular gland (16,24). Recently, we (12) reported that parasympathetic vasodilation in the masseter muscle, evoked by activation of cervical vagal afferents passing to the nucleus of the solitary tract (NTS), a primary target of the central projections of cervical vagal afferents (1,28), is involved in the increase of blood flow, not only in the masseter muscle, but also in the common carotid artery during the vagal-mediated depressor response.…”

Intermittent arm ischemia induces vasodilatation of the contralateral upper limb

“…Recently, Gourine et al reported that RIPC might be associated with the nerve reflex, which is the sensory afferent pathway from the peripheral organ (limbs) and parasympathetic vagal efferent outflow to the heart in rats [20]. Previous studies showed that there is evidence of parasympathetic vasodilator in the masseter muscle [21], lower lip [22] and brain vessels [23] in animals. Those findings indicated that vasodilatation is a result of reflex via increasing parasympathetic activity.…”

Differences in control of parasympathetic vasodilation between submandibular and sublingual glands in the rat

“…Rats were intubated, paralyzed by an intravenous injection of pancuronium bromide (Mioblock; Organon Teknika, Netherlands; 0.6 mg/kg initially, supplemented with 0.4 mg/kg every hour), and artificially ventilated with a 50:50 mixture of air and O 2 via a tracheal cannula. The ventilator (model SN-480-7; Shinano, Tokyo, Japan) was set with a tidal volume of 5.0 -7.5 cm 3 /kg at a rate of 18 -20 breaths/min, and the end-tidal concentration of CO 2 was determined by an infrared analyzer (Capnomac Ultima; Datex, Helsinki, Finland), as previously described (7). Rectal temperature was maintained at 37°C with a heating pad.…”