Keishiro Karita

Vasodilator responses following intracranial stimulation of the trigeminal, facial and glossopharyngeal nerves in the cat gingiva

The effects of electrical stimulation of the trigeminal, facial and glossopharyngeal nerves on gingival blood flow in the cat were studied. The intracranial part of these nerves was stimulated electrically, and gingival blood flow was measured by the laser Doppler technique. Electrical stimulation of the trigeminal, facial and glossopharyngeal nerves caused blood flow to increase in the ipsilateral gingiva both with the cranial nerve intact and after cutting it to the medulla. Stimulation of the distal cut ends of the facial and glossopharyngeal nerves elicited an increase in blood flow but no increase in systemic blood pressure. Pretreatment with hexamethonium reduced the increase in blood flow elicited by electrical stimulation of the facial and glossopharyngeal nerves, but had no effect on that elicited by stimulation of the trigeminal nerve. In contrast, pretreatment with tripelennamine attenuated the trigeminal nerve-stimulated blood flow increase, but not that elicited by stimulation of the facial and glossopharyngeal nerves. Atropine, propranolol and phentolamine had no effect on these responses. These results suggest that the autonomic nervous system, particularly the parasympathetic nervous system, is responsible for the blood flow increase elicited by facial and glossopharyngeal nerve stimulation, and that the trigeminal nerve-stimulated blood flow increase is induced by antidromic vasodilatation of the trigeminal sensory nerve.

Selective excitation of parasympathetic nerve fibers to elicit the vasodilatation in cat lip

Electrical stimulation of the tongue and the proximal cut end of the lingual nerve caused a blood flow to increase in a stimulus-intensity dependent manner in the ipsilateral lower lip of the cats. Pretreatment with hexamethonium (an autonomic ganglionic blocker, 1.0 mg/kg) abolished the vasodilator response, while atropine, phentolamine, propranolol and tripelennamine had no effect on these vasoresponses. Ipsilateral sections of either the glossopharyngeal nerve root, inferior alveolar nerve or mental nerve at the main mental foramen, but not at the posterior mental foramen, abolished the vasodilator response caused by electrical stimulation of the tongue and the lingual nerve. Electrical stimulation of the distal cut ends of the glossopharyngeal nerve root and inferior alveolar nerve caused the vasodilator and vasoconstrictor responses, whereas stimulation of the tongue and the proximal cut ends of the lingual nerve did not elicit the vasoconstrictor response. These results suggest that reflex vasodilatation in the cat mandibular division is exclusively mediated via activation of the parasympathetic nerve fibers, and that selective excitation of the parasympathetic nerve fibers in the oral area is possible.

Response fields of the periodontal mechanosensitive units in the superior alveolar nerve of the cat

Response properties of periodontal mechanoreceptor primary afferent fibers recorded from the superior alveolar nerve were studied in the cat. The left maxillary canine tooth was stimulated manually in 8 directions and/or in 24 directions in the horizontal plane by a specially designed stimulator. The responses of 328 slowly adapting units observed were affected by the direction of stimulus. These units were classified into three groups according to the shape of the response field: a broad type (more than 180 degrees), a medium type (90 degrees to 180 degrees), and a narrow type (less than 90 degrees). The groups contained 27 units (8.2%), 284 units (86.6%), and 17 units (5.2%), respectively, and the remaining 10 units (10.0%) were unclassified. The shape of each response field was little changed by changes in the stimulus intensity. Every response field investigated showed a unimodal distribution. These results were different from those of Mei et al. (1975) who reported that the response fields of units recorded from a Gasserian ganglion had generally consisted of two parts.

The nervous control of gingival blood flow in cats

The purpose of the present study was to investigate the nervous control of gingival blood flow in cats. Gingival blood flow was measured by laser Doppler flowmeter in 75 cats during electrical stimulation and cutting or ligation of the inferior alveolar nerve and cervical sympathetic nerve without sympathectomy or pretreatment with adrenoceptor blocking agents. Three different patterns of responses in gingival blood flow were observed following electrical stimulation of the inferior alveolar nerve in cats. In 45 cats there was an increase in blood flow, in 4 cats a decrease in blood flow, and in 7 cats a biphasic change consisting of an initial decrease and a successive increase in blood flow. The vasodilator effect was significantly reduced by pretreatment with (D-Pro2, D-Trp7.9)-substance P. tripelennamine, and methysergide. Pretreatment with cimetidine, atropine, hexamethonium, phentolamine, or propranolol had no effect on vasodilatation. The vasoconstrictor response was completely inhibited by pretreatment with phentolamine; in this case the vasodilator response appeared after stimulation of the inferior alveolar nerve. Ligation or cutting of the inferior alveolar nerve always elicited an increase in gingival blood flow. Cutting the cervical sympathetic nerve had no effect on gingival blood flow in 8 of 10 cats and caused an increase in gingival blood flow in 2 cats; however, electrical stimulation of the cervical sympathetic nerve always caused a decrease in gingival blood flow in the cats investigated. The present results suggest that cat gingival blood flow is controlled by sympathetic alpha-adrenergic fibers for vasoconstriction and by sensory fibers and mast cells for vasodilatation.

Response properties of periodontal mechanosensitive fibers in the superior dental nerve of the cat

Periodontal mechanosensitive units were detected as single nerve fibers from the anterior branches of five cats, and their receptive fields and optimal stimulus directions were examined. Of 801 units detected, 759 units (95%) responded to movement of only one tooth (single-tooth unit), and 42 units (5%) responded to movement of two or three teeth (multitooth unit). Eighty percent of the single-tooth units were of the sustained type which discharged during more than 1 s to a long-lasting pressure applied to the tooth, and 20% were of the transient type which adapted in less than 1 s to the pressure. The majority (93%) of the sustained type exhibited directional selectivity to stimulation, but only 35% of the transient type showed it. More than half of the single-tooth units had their receptive fields in the canine tooth, stimulation of which produced the largest mass discharge in the nerve bundle. The optimal stimulus direction for many single-tooth units was the same as that for the mass discharge in the nerve bundle. The receptive fields of the multitooth units were observed mainly in the incisor teeth adjacent to each other.

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.

Origins of parasympathetic postganglionic vasodilator fibers supplying the lips and gingivae; an WGA-HRP study in the cat

Application of WGA-HRP to the mandibular lip and buccal gingiva of the cat resulted in retrograde labeling in the ipsilateral otic ganglion (OG), whereas labeled neurons appeared in the pterygopalatine ganglion (PPG) as well as in the OG when the tracer was injected into the maxillary lip and buccal gingiva. The results suggest that both the facial and the glossopharyngeal preganglionic vasodilator fibers supplying the mandibular lip and buccal gingiva mediated in the OG, and those innervating the maxillary lip and buccal gingiva are mediated in the PPG and the OG.

The effects of capsaicin applied topically to inferior alveolar nerve on antidromic vasodilatation in cat gingiva

Electrical stimulation of the cut inferior alveolar nerve caused 3 different patterns of vasoresponses in the cat gingiva: vasodilatation, vasoconstriction, and biphasic response consisting of vasoconstriction and vasodilatation. Topical capsaicin application onto the inferior alveolar nerve produced a vasodilatation in all of cats tested. After the repeated application of capsaicin, the vasodilator response was no more elicited by electrical stimulation of the inferior alveolar nerve, while the vasoconstrictor response was observed in every preparation. The vasoconstrictor response caused by electrical stimulation of the inferior alveolar nerve was not affected by the capsaicin application, but was completely inhibited by phentolamine, sympathetic alpha-adrenergic receptor antagonist. The present results suggest that vasodilatation induced by electrical stimulation of the inferior alveolar nerve occurs via the sensory nerve, and vasoconstriction via the sympathetic nerve.

Axon Reflex Vasodilatation in Cat Dental Pulp Elicited by Noxious Stimulation of the Gingiva

Antidromic stimulation of sensory nerves has been shown to increase blood flow in the tissue they innervate. This study was designed to determine if antidromic vasomotor responses occur in feline dental pulp and if they are mediated by branched axons supplying both tooth pulp and gingiva. Dynamic changes in pulpal blood flow (PBF) elicited by electrical stimulation, pinching, heating, and capsaicin application to the gingivae were investigated in cat mandibular canine teeth by means of Laser Doppler Velocimetry. All inferior alveolar nerve bundles and the cervical sympathetic trunk had been previously sectioned to avoid the occurrence of brainstem reflexes, e.g., somato-autonomic vasomotor reflexes. Increases in PBF were observed in seven out of 12 cats when a restricted gingival area adjacent to the canine teeth was stimulated as described, but the increases were abolished after the sensitive gingival area was painted with lidocaine jelly, a surface anesthetic. These vasodilator responses, remarkably reduced following repeated application of 30 mM of capsaicin, are considered to be induced via antidromic activation of capsaicin-sensitive nociceptive nerve fibers, presumably by axon reflex mechanisms, suggesting that nerve terminals supplying the gingiva originate from parent axons which have collaterals that innervate the canine tooth pulp.

Investigation of mechanisms of the flare and wheal reactions in human skin by band method

Following intradermal injection of histamine, substance P or neurotensin into the normal human forearm skin at the site 0.5 cm proximal to the band, the flare response developed as quickly on the distal side as on the proximal side of the band, whereas the wheal reaction was localized on the proximal side. Pretreatment of skin with capsaicin dramatically inhibited the histamine-induced flare response but had no effect on nicotine-induced axon reflex sweating. The usefulness of the band method is discussed.