Lip Blood Flow Research Articles

Role of medullary GABA signal transduction on parasympathetic reflex vasodilatation in the lower lip

In the orofacial area, noxious stimulation of the orofacial structure in the trigeminal region evokes parasympathetic reflex vasodilatation, which occurs via the trigeminal spinal nucleus (Vsp) and the inferior/superior salivatory nucleus (ISN/SSN). However, the neurotransmitter involved in the inhibitory synaptic inputs within these nuclei has never been described. This parasympathetic reflex vasodilatation is suppressed by GABAergic action of volatile anesthetics, such as isoflurane, sevoflurane, and halothane, suggesting that medullary GABAergic mechanism exerts its inhibitory effect on the parasympathetic reflex via an activation of GABA receptors. The aim of the present study was to determine the role of GABAA and GABAB receptors in the Vsp and the ISN in regulating the lingual nerve (LN)-evoked parasympathetic reflex vasodilatation in the lower lip. Under urethane anesthesia (1g/kg), change in lower lip blood flow elicited by electrical stimulation of the LN was recorded in cervically vago-sympathectomized rats. Microinjection of GABA (10μM; 0.3μl/site) into the Vsp or the ISN significantly and reversibly attenuated the LN-evoked parasympathetic reflex vasodilatation. Microinjection of the GABAA receptor-selective agonist muscimol (100μM; 0.3μl/site) or the GABAB receptor-selective agonist baclofen (100μM; 0.3μl/site) into the Vsp or the ISN significantly and irreversibly reduced this reflex vasodilatation, and these effects were attenuated by pretreatment with microinjection of each receptor-selective antagonists [GABAA receptor selective antagonist bicuculline methiodide (1mM; 0.3μl/site) or GABAB receptor selective antagonist CGP-35348 (1mM; 0.3μl/site)] into the Vsp or the ISN. Microinjection of these antagonists alone into the Vsp or the ISN had no significant effect on this reflex vasodilatation. In addition, microinjection (0.3μl/site) of the mixture of muscimol (100μM) and baclofen (100μM) into the Vsp or the ISN also significantly reduced this reflex vasodilatation. These results suggest that medullary GABA signal transduction inhibits the parasympathetic reflex vasodilatation in the rat lower lip via GABAA and GABAB receptors in the Vsp and the ISN.

Role of the spinal trigeminal nucleus in the rat autonomic reflex

The goal of the present study was to investigate the regional differences between the three subnuclei (oralis, interpolaris, and caudalis) of the spinal trigeminal nucleus (Vsp) in eliciting parasympathetic and sympathetic reflex autonomic responses. We evoked changes in lower lip blood flow (LBF) and systemic arterial blood pressure (SABP) by electrically stimulating these subnuclei in artificially ventilated, urethane-anaesthetised, cervically vago-sympathectomized rats. The LBF increases evoked by electrical stimulation of the Vsp at interpolaris were much larger than those at the sites of the oralis and caudalis. No significant difference in SABP increase was observed by Vsp stimulation between the interpolaris and caudalis, although the SABP increase evoked by electrical stimulation of the oralis was much smaller than in the interpolaris and caudalis. The present findings show that the Vsp at the interpolaris subnucleus of the Vsp participates as a relay in lingual nerve- and Vsp-evoked somato-autonomic reflex.

Occurrence of parasympathetic vasodilator fibers in the lower lip of the guinea-pig

The present study was designed to examine whether there are parasympathetic vasodilator fibers in the lower lip of the guinea-pig. Electrical stimulation of the central cut end of the lingual nerve of guinea-pigs evoked intensity- and frequency-dependent decreases in lower lip blood flow and systemic arterial blood pressure (SABP). Pretreatment with guanethidine, a postganglionic sympathetic nerve blocker and antihypertensive drug (30 mg kg(-1), s.c., 24 h prior to experiments), reduced the magnitude of the decrease in SABP while the intensity- and frequency-dependent increases of the lip blood flow occurred by the lingual nerve stimulation only on the side ipsilateral to stimulation. Increases in the lip blood flow evoked by lingual nerve stimulation in guanethidine pretreated guinea-pigs were reduced by hexamethonium (an autonomic ganglion cholinergic blocker) in a dose-dependent manner. When fluoro-gold (a retrograde neural tracer) was injected into the lower lip, labeled neurons were observed in the ipsilateral otic ganglion. The present study indicates the presence of parasympathetic vasodilator fibers originating from the otic parasympathetic ganglion in the guinea-pig lower lip, similar to those reported previously in rats, cats, rabbits and humans.

Suppression of inferior alveolar nerve-induced vasoconstrictor response by ongoing cervical sympathetic nerve activity in cat

We examined the effects of ongoing cervical sympathetic trunk (CST) stimulation on the vasoconstrictor responses in the lower lip elicited by electrical stimulation (ES) of the inferior alveolar nerve (IAN) or CST in anaesthetised cats to determine whether (i) the previously reported suppressive effect of ongoing CST activity on IAN-induced vasoconstriction occurs during not only ipsilateral, but also contralateral CST stimulation; and (ii) a vasoconstriction can be elicited by brief CST stimulation during ongoing stimulation of the contralateral CST. The central lower lip blood vessels are innervated by both left and right CST. The fall in central lip blood flow (LBF) elicited by IAN stimulation alone was reduced in a frequency-dependent manner during concurrent CST stimulation at 0.2-2 Hz, and at the high end of this frequency range was transformed to a rise regardless of whether the CST stimulation was ipsilateral or contralateral to the IAN stimulation. The fall in central LBF elicited by stimulation of one CST was not transformed to a rise by ongoing stimulation of the contralateral CST. Possibly, IAN-evoked orofacial vasoconstriction does not occur under physiological conditions (unlike IAN-evoked vasodilatation) because it is suppressed by the spontaneous sympathetic discharge in CST.

Trigeminal nerve-mediated reflex arterial blood pressure decrease and vasodilatation in lower lip of the rabbit

We measured the effects of electrical stimulation of the central cut end of the lingual nerve on lower lip blood flow (LBF) and on arterial blood pressure in urethane-anesthetized, artificially ventilated, cervically vagosympathectomized rabbits. Different effects were observed depending on the stimulus frequency. Increasing the stimulus frequency above 5 Hz produced progressively larger ipsilateral LBF increases until the optimal frequency was reached at 20 Hz. In contrast, stimulation at above 0.5 Hz evoked progressively larger decreases in both contralateral LBF and arterial blood pressure until the optimal frequency was reached at around 10 and 2 Hz, respectively. Thus, the optimal stimulus frequencies for the ipsilateral LBF increase and the arterial blood pressure decrease were widely different. The lingual nerve-evoked change (i.e., fall) in arterial blood pressure showed a significant correlation with the contralateral LBF decrease, but not with the ipsilateral LBF increase. Prior administration of hexamethonium at 10 mg/kg markedly reduced both the ipsilateral LBF increase and arterial blood pressure decrease, although it was more effective against the former than against the latter. Pretreatment with scopolamine (muscarinic-receptor antagonist, 0.1 mg/kg), phentolamine (α-adrenoceptor antagonist, 0.1 mg/kg), or propranolol (β-adrenoceptor antagonist, 0.1 mg/kg) failed to affect either response. However, 1.0 mg/kg phentolamine significantly reduced both responses ( P<0.05). These results indicate that, in the rabbit, the LN-evoked reflex increase in ipsilateral LBF is (a) largely independent of any concomitant arterial blood pressure change and (b) probably due to active vasodilatation mediated via parasympathetic mechanisms. In contrast, the evoked decrease in contralateral LBF was proportional to the decrease in arterial blood pressure, suggesting that the former was secondary to the latter.

Reduction in parasympathetic reflex vasodilatation following stereotaxic ear-bar insertion: importance of reduced afferent input

As in our previous report, when cats were fitted with stereotaxic ear-bars ‘type A’ animals (26 out of 41) still exhibited a parasympathetic reflex lip blood flow (LBF) increase in response to lingual nerve stimulation, while in ‘type B’ animals (the remaining 15) it was greatly reduced or abolished. We compared (in both magnitude and in their sensitivity to hexamethonium, 10 mg/kg, i.v.) the LBF responses evoked by electrical stimulation of various sites within the reflex arc (lingual nerve, trigeminal ganglion, spinal trigeminal nucleus (Vsp)) in type A and type B animals to examine where the suppressive effect of ear-bar insertion might be exerted (using artificially ventilated, cervically vago-sympathectomized cats deeply anesthetized with α-chloralose and urethane). After ear-bar insertion: (a) in type A animals, stimulation of both lingual nerve and Vsp evoked a similar, hexamethonium-sensitive LBF increase; (b) in type B animals (in which lingual-nerve stimulation evoked no LBF increase), Vsp stimulation evoked a hexamethonium-sensitive LBF increase; (c) in both type A and type B animals, trigeminal ganglion stimulation consistently elicited an LBF increase (abolished by hexamethonium in type A, but reduced by only 50% in type B). These results suggest (i) that abolition of the lingual nerve-induced parasympathetic reflex vasodilatation by ear-bar insertion is due to reduced afferent traffic (in peripheral trigeminal or facial nerves) rather than to a damaged efferent output, and (ii) this effect in type B animals seems somehow to allow an antidromic (hexamethonium-insensitive) vasodilatation to occur on trigeminal ganglion stimulation.

Simultaneous measurement of parasympathetic reflex vasodilator and arterial blood pressure responses in the cat

We measured the changes in lower lip blood flow and systemic arterial blood pressure evoked by lingual nerve or trigeminal spinal nucleus (Vsp) stimulation to gain an insight into the brainstem integration of sympathetic and parasympathetic responses to nociceptive stimulation. We used artificially ventilated, cervically vago-sympathectomized cats deeply anesthetized with α-chloralose and urethane. A lip blood flow increase occurred in an intensity- and frequency-dependent manner following electrical stimulation of Vsp or lingual nerve regardless of whether systemic arterial blood pressure increased or decreased. In contrast, there was no apparent optimal frequency for the changes in systemic arterial blood pressure elicited by electrical stimulation of Vsp or lingual nerve. No relationship was found between the amplitude of the lip blood flow increase and that of the systemic arterial blood pressure change. Microinjection of lidocaine or kainic acid into the Vsp evoked, respectively, reversible and irreversible inhibition of the lip blood flow increase and systemic arterial blood pressure change evoked by lingual nerve stimulation. When microinjected unilaterally directly into the ipsilateral Vsp, the GABA agonist muscimol abolished both lingual nerve-evoked effects (increase in lip blood flow and changes in systemic arterial blood pressure) without changing basal systemic arterial blood pressure, suggesting the presence in the Vsp of GABA receptors serving to modulate both the parasympathetically mediated lip blood flow increase and the sympathetically mediated systemic arterial blood pressure change. Lidocaine microinjection into the salivatory nucleus caused a significant attenuation of the lingual nerve-induced blood flow increase, but had no effect on the lingual nerve-induced systemic arterial blood pressure change. Thus, the neural pathway mediating the lingual nerve-induced lip blood flow increase seems to be simple, requiring a minimum of four neurons: trigeminal afferent–Vsp–parasympathetic pre-ganglionic neurons with cell body located in the inferior salivatory nucleus–otic postganglionic neuron. On the other hand, the pathway underlying the evoked systemic arterial blood pressure changes, presumably mediated via altered sympathetic activity, seems to be more complicated and could be affected by more numerous factors.

Parasympathetic reflex vasodilatation in rat submandibular gland.

The present study was designed to investigate 1) whether parasympathetic reflex vasodilatation occurs in the submandibular gland (SMG) in deeply urethan-anesthetized, cervically vagotomized, and sympathectomized rats when the central cut end of the lingual nerve (LN) is electrically stimulated and 2) to what extent the neural mechanisms underlying such responses are the same as those involved in the response to direct stimulation of the chorda-LN (CLN). Stimulation of each nerve separately elicited a marked blood flow increase in SMG. Section of the chorda tympani abolished the SMG blood flow response but had no effect on the lip blood flow increase evoked by LN stimulation. Section of the CLN abolished the SMG blood flow increases evoked by stimulation of either nerve. The SMG blood flow increases (regardless of whether they were evoked by LN or CLN stimulation) were markedly reduced by the autonomic cholinergic ganglion blocker hexamethonium. The present study demonstrates that a parasympathetic reflex vasodilator mechanism is present in the rat SMG and that it can express its effects under deep general anesthesia.

Involvement of two different mechanisms in trigeminal ganglion-evoked vasodilatation in the cat lower lip: role of experimental conditions

The present study was designed to examine the vasodilator mechanisms elicited by electrical stimulation of trigeminal ganglion (TG) in cat lower lip of the cats. When vago-sympathectomized cats were fixed into a stereotaxic frame by means of ear-bars, etc., the lip blood flow (LBF) increase evoked by lingual nerve (LN) stimulation (parasympathetic reflex response) was almost abolished in 15 out of 34 animals, but unaffected in the other 19. With the animal in the stereotaxic frame, electrical stimulation at sites within the TG evoked an LBF increase whether or not the LN stimulation-induced reflex response was intact. However, hexamethonium abolished the TG stimulation-induced LBF increase in animals whose brainstem parasympathetic reflex was intact, but reduced it by only 50% in animals whose reflex was impaired. This difference was seen in all experiments in which the electrode site was within the TG proper, regardless of its exact position. Although the underlying mechanism is unclear, these data suggest that when the TG is stimulated the LBF increase is entirely mediated via the parasympathetic reflex mechanism in animals whose brainstem reflex is intact, and that an antidromic vasodilatation occurs only in animals whose brainstem parasympathetic reflex is impaired.

Involvement of Nitric Oxide in Parasympathetic and Antidromic Vasodilatations in Cat Lower Lip

The involvement of nitric oxide (NO) in the lower lip vasodilatations mediated via parasympathetic and antidromic mechanisms was examined in alpha-chloralose/urethane-anesthetized cats, with the two types of blood flow responses being recorded separately (by laser Doppler flowmeter) from the two sides of the lower lip. The central cut end of the lingual nerve (LN) or the peripheral cut end of the inferior alveolar nerve (IAN) was electrically stimulated to elicit parasympathetic or antidromic vasodilatation, respectively, in the lower lip. N(G)-nitro-L-arginine methyl ester (L-NAME), but not N(G)-nitro-D-arginine methyl ester (D-NAME) (each at 30 mg/kg), markedly reduced the increases in lip blood flow evoked by stimulation, the reduction being to a similar degree irrespective of whether LN or IAN was stimulated. Pretreatment with L-arginine did not prevent the L-NAME-induced attenuation of either type of vasodilatation. In conclusion, these results suggest that synthesized NO may have a common site of action in antidromic and parasympathetic vasodilator pathways to the cat lower lip.

Innervation of the cat lip by two groups of parasympathetic vasodilator fibres.

1. Electrical stimulation of the peripheral cut ends of the chorda tympani nerve proper (CTNP) and the chorda-lingual nerve (CLN) elicited a blood flow increase in the ipsilateral lower lip, tongue and submandibular gland in a stimulus intensity-dependent manner in anaesthetized cats. 2. Pretreatment with hexamethonium (1.0 mg kg-1, i.v.), an autonomic ganglionic blocker, significantly reduced the CTNP-induced blood flow increases in all of the above three sites as well as the CLN-induced blood flow in the lower lip, but it had no effects on the CLN-induced blood flow increases in the tongue and submandibular gland. 3. The CTNP stimulation-induced lower lip blood flow was not influenced by sectioning the lingual nerve proper, but it was abolished by section of either the CLN or the inferior alveolar nerve (IAN) in the mandibular canal. 4. The lip blood flow increases elicited reflexly by electrical stimulation of the upper gingiva, the central cut ends of the mylohyoid nerve and CLN were not affected by cutting of the CTNP, but were markedly reduced by pretreatment with hexamethonium and abolished by the section of the inferior alveolar nerve just distal to the mylohyoid nerve. These observations imply that the parasympathetic vasodilator fibres involved in trigeminally induced reflex vasodilatation responses do not travel with the CTNP. 5. These results suggest that there is a dual innervation of the cat lower lip by two groups of parasympathetic vasodilator fibres; in one case fibres originating from the facial nerve root are distributed to the lower lip via the CTNP, CLN and IAN and in the other fibres emanating from the glossopharyngeal nerve root project to the lower lip via the mandibular nerve and the IAN.

Somatosensory afferents in the parasympathetic vasodilator reflex in cat lip

Somato-parasympathetic reflexive vasodilatation elicited by activation of the nociceptors in the oro-facial areas of the cat was investigated. Changes in lower lip blood flow monitored by a laser Doppler flowmeter took place in pentobarbital-anesthetized and artificially respirated cats. Pinch and heat stimulation of the oro-facial areas evoked a blood flow increase similar to that of electrically induced vasodilatation. Sustained increased responses in blood flow were obtained when a 1% capsaicin solution was applied to the tongue. These results show that the C-polymodal nociceptor is a strong candidate for a receptor that provokes somato-parasympathetic vasodilatation. Capsaicin-insensitive nerve fibers, however, also participate because electrical stimulation of the capsaicin-treated tongue evoked vasodilatation. The correlation between noxious stimulation-induced vasodilatation and systemic blood pressure change also is discussed.

Somatosensory stimulation causes autonomic vasodilatation in cat lip.

1. Electrical stimulation of the infra-orbital nerve and the maxillary buccal gingiva caused an increase in ipsilateral lip blood flow in a stimulus intensity-dependent manner in anaesthetized cats. 2. The reflex vasodilator response was resistant to blockade by antimuscarinic (atropine), antiadrenergic (phentolamine and propranolol) and antihistaminergic (tripelennamine) but sensitive to ganglionic blocking agent (hexamethonium). 3. The reflex vasodilator response was unaffected by section of the ipsilateral cervical sympathetic trunk and facial nerve root, but was completely abolished by ipsilateral section of the glossopharyngeal nerve root. 4. The vasodilator response elicited by stimulation of the facial and glosso-pharyngeal nerves was never affected by lesion of the ipsilateral pterygopalatine ganglion. 5. Local anaesthesia or section of the inferior alveolar nerve abolished the vasodilator effects of stimulation of the facial and the glossopharyngeal nerves. 6. These results suggest that there is a somato-autonomic reflex vasodilator system mediated via final neurons that are not cholinergic, and that the parasympathetic vasodilator fibres emerge from the brain stem with the glossopharyngeal nerve and reach the blood vessels via the otic ganglion and the inferior alveolar nerve in the cat mandibular lip.

The jaw opening reflex evoked by toothpulp stimulation in anaesthetized cats: Habituation and the effects of surgical trauma

The goal of the present study was to investigate the regional differences between the three subnuclei (oralis, interpolaris, and caudalis) of the spinal trigeminal nucleus (Vsp) in eliciting parasympathetic and sympathetic reflex autonomic responses. We evoked changes in lower lip blood flow (LBF) and systemic arterial blood pressure (SABP) by electrically stimulating these subnuclei in artificially ventilated, urethane-anaesthetised, cervically vago-sympathectomized rats. The LBF increases evoked by electrical stimulation of the Vsp at interpolaris were much larger than those at the sites of the oralis and caudalis. No significant difference in SABP increase was observed by Vsp stimulation between the interpolaris and caudalis, although the SABP increase evoked by electrical stimulation of the oralis was much smaller than in the interpolaris and caudalis. The present findings show that the Vsp at the interpolaris subnucleus of the Vsp participates as a relay in lingual nerve- and Vsp-evoked somato-autonomic reflex.