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

Abstract

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.

Figure 1. Schematic representation of the sites of electrical stimulation

Stimulation sites: central (a) and peripheral (b) cut ends of the lingual nerve, the central cut end of the inferior alveolar nerve (c) and the peripheral cut end of the superior cervical sympathetic trunk (d). The dashed lines indicate the parasympathetic vasodilator fibres from the superior and inferior salivatory nuclei. The continuous lines indicate trigeminal and facial sensory inputs to the brain stem. The sympathetic supply, via the superior cervical ganglion, and the common carotid artery are shown at the bottom. Abbreviations: CCA, common carotid artery; EMF, electromagnetic flowmeter; IAN, inferior alveolar nerve; ISN, inferior salivatory nucleus; LDF, laser-Doppler flowmeter; NST, nucleus of the solitary tract; OG, otic ganglion; PPG, pterygopalatine ganglion; CST, superior cervical sympathetic trunk; SCG, superior cervical ganglion; SMG, submandibular gland; SSN, superior salivatory nucleus; V, trigeminal nerve root; VII, facial nerve root; IX, glossopharyngeal nerve root.

Figure 2. Effects of section of the CST and of electrical stimulation of its peripheral cut end on the basal CCA blood flow level, and of electrical stimulation of the central cut end of the LN on CCA blood flow during a period of repetitive CST stimulation at each stimulation frequency

Parameters used are given in Methods. CCA blood flow levels are shown with intact CST (Control; open column, n = 7) and during repetitive stimulation of the CST (after its section) at various frequencies (0.5-10 Hz; filled columns, n = 7). The hatched portions of the columns indicate the increase in CCA blood flow evoked by LN stimulation during repetitive CST stimulation at various frequencies (0-10 Hz). The CCA blood flow levels are expressed on the ordinate in absolute terms (ml min⁻¹ kg⁻¹). Values shown are means ± s.e.m.*P < 0.01, **P < 0.001 vs. before section of the CST (Control; ANOVA followed by a contrast test); *P < 0.05, **P < 0.01 vs. 0 Hz CST stimulation (ANOVA followed by a contrast test). †P < 0.001, significant difference between the increase in blood flow recorded on LN stimulation during 0 Hz CST stimulation and that during repetitive CST stimulation (at 10 Hz) (ANOVA for repeated measurements followed by a contrast test). The bracket (P < 0.001) indicates a significant difference between the two columns (Student's paired t test).

Figure 3. Individual examples of the effects of electrical stimulation

A, effects of electrical stimulation of the central cut end of the LN on blood flow in lower lip (LBF), palate (PBF), CCA (CCABF) and SMG (SMGBF). B and C, effects of electrical stimulation of the peripheral cut end of the LN (B), and of the central cut end of the inferior alveolar nerve (C) on tongue blood flow (TBF). The above stimuli were delivered alone (Control) or during on-going repetitive CST stimulation in vago-sympathectomized cats. The LN was stimulated where indicated (•) for 20 s at a supramaximal voltage (30 V) at 10 Hz with pulses of 2 ms duration. The frequencies (0.5-10 Hz) of CST stimulation are shown at the top. ABP, systemic arterial blood pressure. a.u., arbitrary units.

Figure 4. Mean data (±s.e.m.) for effects of electrical stimulation

Effects of electrical stimulation of the central cut end of the LN on blood flow in lower lip (LBF, •, n = 11), palate (PBF, ^, n = 5), SMG (SMGBF, ▪, n = 4) and CCA (CCABF, □, n = 8), and of the peripheral cut end of the LN on tongue blood flow (TBF, ▴, n = 7). The above nerves were stimulated alone (Control) or during on-going repetitive CST stimulation in vago-sympathectomized cats. Experimental conditions were as in Fig. 3. The LN-stimulated blood flow increases during CST stimulation are expressed as a percentage of the response to LN stimulation in the absence of CST stimulation (Control). Statistical significance was calculated by means of ANOVA followed by a contrast test. *P < 0.01, **P < 0.001 vs. the response in the absence of CST stimulation (Control).