title: Inhibitory effects of excess sympathetic activity on parasympathetic vasodilation in the rat masseter muscle.
abstract: The present study was designed to examine the effect of sympathetic tonic activity on parasympathetic vasodilation evoked by the trigeminal-mediated reflex in the masseter muscle in urethane-anesthetized rats. Sectioning of the superior cervical sympathetic trunk (CST) ipsilaterally increased the basal level of blood flow in the masseter muscle (MBF). Electrical stimulation of the peripheral cut end of the CST for 2 min using 2-ms pulses ipsilaterally decreased in a dependent manner the intensity (0.5-10 V) and frequency (0.1-5 Hz) of the MBF. The CST stimulation for 2 min at <0.5 Hz with 5 V using 2-ms pulses seems to be comparable with the spontaneous activity in the CST fibers innervating the masseter vasculature, because this stimulation restored the basal level of the MBF to the presectioned values. Parasympathetic vasodilation evoked by electrical stimulation of the central cut end of the lingual nerve in the masseter muscle was markedly reduced by CST stimulation for 2 min with 5 V using 2-ms pulses in a frequency-dependent manner (0.5-5 Hz). Intravenous administration of phentolamine significantly reduced the vasoconstriction induced by CST stimulation in a dose-dependent manner (0.1-1 mg/kg), but pretreatment with either phentolamine or propranolol failed to affect the sympathetic inhibition of the parasympathetic vasodilation. Our results suggest that 1) excess sympathetic activity inhibits parasympathetic vasodilation in the masseter muscle, and 2) alpha- and beta-adrenoceptors do not contribute to sympathetic inhibition of parasympathetic vasodilation, and thus some other types of receptors must be involved in this response.
authors.affiliation: Department of Oral Physiology, Health Sciences University of Hokkaido, 1757 Kanazawa, Ishikari-Tobetsu, Hokkaido 061-0293, Japan.
authors.forename: Hisayoshi
authors.initials: H
authors.lastname: Ishii
authors.forename: Takeharu
authors.initials: T
authors.lastname: Niioka
authors.forename: Hidekazu
authors.initials: H
authors.lastname: Watanabe
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Izumi
mesh_terms: D018686:Anesthetics, Intravenous; D000818:Animals; D004558:Electric Stimulation; D008297:Male; D008406:Masseter Muscle / Q000098:blood supply* / Q000294:innervation*; D009433:Neural Inhibition / Q000502:physiology; D010275:Parasympathetic Nervous System / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D012018:Reflex / Q000502:physiology; D012121:Respiration, Artificial; D013564:Sympathetic Nervous System / Q000503:physiopathology*; D014276:Trigeminal Nerve / Q000502:physiology; D014520:Urethane; D014661:Vasoconstriction / Q000502:physiology; D014664:Vasodilation / Q000502:physiology*
chemical_list: D018686:Anesthetics, Intravenous; D014520:Urethane