Low-frequency subthreshold sympathetic stimulation augments maximal reflex parasympathetic salivary secretion in cats

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.

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.

Nifedipine-induced inhibition of parasympathetic-mediated vasodilation in the orofacial areas of the cat

In anesthetized cats, we 1) compared the effects of antihypertensive agents (nifedipine, clonidine, phentolamine, propranolol, and nitroprusside) on the parasympathetic vasodilations elicited by lingual nerve (LN) stimulation in the lower lip and tongue and 2) investigated the mechanisms underlying the inhibitory effect of nifedipine on parasympathetic lower lip vasodilation. At the doses used, each antihypertensive agent reduced systemic arterial blood pressure by approximately 20 mmHg; however, the parasympathetic vasodilation elicited by LN stimulation was significantly reduced only by nifedipine. This inhibitory effect of nifedipine was not seen when LN was stimulated during ongoing repetitive stimulation of the superior cervical sympathetic trunk at 1-Hz frequency. This suggests that the ability of lip and tongue blood vessels to relax to parasympathetic stimulation is not directly impaired by this calcium channel blocker and that the inhibitory effects of nifedipine seen here probably resulted from an action on postsynaptic sites in vascular smooth muscle that caused a reduction in preexisting sympathetic vasoconstrictor tone (by inhibiting calcium influx into the vascular smooth muscle cell).

Sympathetic attenuation of parasympathetic vasodilatation in oro-facial areas in the cat

1. The present study was designed to examine the interaction between sympathetic and parasympathetic influences on blood flow in oro-facial areas such as lower lip, palate and submandibular gland (SMG) and in the common carotid artery (CCA) in anaesthetized cats. 2. Section of the ipsilateral superior cervical sympathetic trunk (CST) increased the basal CCA blood flow significantly. The control level with the nerve intact was comparable with that seen at 0.5-1 Hz CST stimulation, suggesting a spontaneous discharge of around 0. 5-1 Hz in the CST fibres innervating the beds supplied by the CCA. The basal blood flow at all sites examined was reduced by CST stimulation in a frequency-dependent manner. 3. Electrical stimulation of the central end of the lingual nerve (LN) evoked blood flow increases in the lower lip and palate. These blood flow increases were markedly reduced by concurrent CST stimulation in a manner that was frequency dependent, but not simply related to the vasoconstrictor effect of CST stimulation. This effect of CST stimulation was not observed in tongue or SMG, even though CST stimulation evoked vasoconstriction in these tissues. A significant reduction in the level of CCA blood flow attained during LN stimulation was observed on repetitive CST stimulation only at 10 Hz, indicating that this response behaved in a fashion different from that seen in the lower lip, palate, tongue and SMG. 4. The present study suggests that concurrent repetitive CST stimulation reduces parasympathetically mediated blood flow increases in certain oro-facial areas (such as the lower lip and palate), but not in the tongue and SMG. This inhibitory action was not a simple additive effect (between vasoconstriction and vasodilatation) and it disappeared rapidly after the cessation of CST stimulation.

Blood flow increases in common carotid artery, lower lip and palate elicited by lingual nerve stimulation in anesthetized cats

The purpose of the present study was to examine whether changes in blood flow in the common carotid artery (CCA) reflect those in individual extracranial tissues (lower lip and palate). Changes were evoked at the three sites simultaneously using a somato-parasympathetic reflex activation method in urethane-alpha-chloralose anesthetized, vago-sympathectomized cats. Somato-parasympathetic reflex activation was induced by electrical stimulation of the central cut end of the ipsilateral lingual nerve. The blood flow changes evoked in CCA, lower lip and palate changed in parallel when the stimulus to the blood vessels was changed (by changing the stimulus applied to the afferents or by blocking the efferent pathway). However, when drugs were given intravenously which would act directly on receptors in the blood vessels (including the endothelium) or alter the systemic blood pressure level, the evoked responses in CCA reacted in a quantitatively different manner from those evoked in lower lip and palate. These results suggest that evoked changes in CCA blood flow cannot be regarded as an accurate reflection of changes occurring simultaneously in individual extracranial tissues, at least when examining the effect of such drugs on parasympathetic mediated vasodilation.