Jean Azérad

Physiological properties of neurons in different parts of the cat trigeminal sensory complex

The following points emerge from a systematic investigation of the 4 divisions of the cat trigeminal sensory complex. (1) The subnucleus oralis receives a large representation from the oral cavity, a region also represented in the 3 other divisions of the trigeminal sensory complex. (2) Nucleus principalis cells project heavily to the contralateral and to the ipsilateral ventroposterior thalamus. Ipsilateral projections are only from the oral cavity representation. (3) Units responding to noxious mechanical stimulation have been found at two different loci: the subnucleus caudalis for the entire trigeminal area, and subnucleus oralis for the oral cavity alone. (4) The dental pulp projects to the 4 divisions of the trigeminal sensory complex, but the heaviest projection was found in the rostral part (nucleus principalis and subnucleus oralis). (5) Three distinct types of post-synaptic responses were found to be evoked by dental pulp stimulation: (a) short latency, consistent and synaptically secure, (b) strongly variable latency, inconstant and easily fatigued and (c) a class showing progressive enhancement by progressive increase in stimulus intensity and repetition.

Environmental effects on laser Doppler pulpal blood-flow measurements in man

The increasing number of experiments using laser Doppler flowmetry in man for pulpal blood-flow recordings leads to questioning of the experimental recording conditions. The present study focused on three points: the design of the laser probe holder, the isolation of the tooth, and the influence of the recording site. A rigid polyurethane splint used in addition to different isolation devices (cotton roll, metal shield, rubber dam) was compared with a silicone splint. The silicone resulted in significantly higher values (+341%) than the polyurethane splint. The combination of the polyurethane splint with isolation devices decreased, in all cases, the flux values. The polyurethane/rubber-dam combination was the most efficient in individualizing the pulpal blood flow (-69% decrease). Recordings on non-vital teeth confirmed the hypothesis that there was periodontal contamination of the recorded flow, as the signal was abolished when using the polyurethane/rubber-dam combination. Cervical recording sites gave significantly higher values than occlusal sites (+42%). It is concluded that, in man, the part played by the periodontium may have been underestimated in previous recordings of pulpal blood flow. The use of a rubber dam in combination with a rigid splint to enhance the validity of recordings is proposed.

Trigeminal modulation of gustatory neurons in the nucleus of the solitary tract

Electrophysiological methods were used to investigate the effects of trigeminal nerve stimulation or transection on responses of single gustatory neurons in the nucleus of the solitary tract (NTS) to tastants (NaCl, sucrose, citric acid, monosodium glutamate) in pentobarbital-anesthetized rats. Unilateral transection of the lingual nerve, or the mandibular branch of the trigeminal nerve, resulted in significant reductions (by 21 and 29%, respectively; P<0.01) in tastant-evoked responses, with no further effect following bilateral transection. Electrical stimulation of the central cut end of the mandibular nerve directly excited nine of 14 gustatory NTS units. For these units, central mandibular stimulation facilitated the tastant-evoked responses in six, depressed responses in three, and had no effect in five. Facilitation of tastant-evoked responses peaked 4 min after mandibular stimulation and recovered within 8 min. Electrical stimulation of the peripheral cut end of the mandibular nerve significantly reduced tastant-evoked responses in nine other NTS units, with a maximal reduction at 4 min post-stimulation followed by recovery. Stimulation of the superior cervical sympathetic ganglion did not affect NTS tastant-evoked responses. These results suggest the presence of complex central modulation of NTS neurons by trigeminal afferents, as well as a peripheral depressant effect on gustatory processing possibly mediated via neuropeptide release from trigeminal nerve endings in the tongue.

The properties of cells in the cat trigeminal main sensory and spinal subnuclei activated by mechanical stimulation of the periodontium

Neurophysiological exploration of the trigeminal sensory complex was done on 42 cats under ketamine anaesthesia, paying special attention to units receiving a periodontal input. Among 492 cells recorded in the trigeminal sensory complex, 73 responded to mechanical stimulation of the periodontium and were precisely localized histologically. Thalamic stimulation was also delivered to the ipsi and contralateral ventro-posterior nucleus to test for antidromic responses. Results of this systematic study were plotted on reference drawings of the full extent of the trigeminal sensory complex.

Use of a new retrograde filling material (Biodentine) for endodontic surgery: two case reports

Mineral trioxide aggregate (MTA) is considered at the present time as the gold standard for root-end filling in endodontic surgery. However, this biocompatible material presents several drawbacks such as a long setting time and handling difficulties. The aim of this article is to present a new commercialized calcium silicate-based material named Biodentine with physical improved properties compared to MTA in a clinical application. Two endodontic microsurgeries were performed by using specific armamentarium (microsurgical instrumentation, ultrasonic tips) under high-power magnification with an operatory microscope. Biodentine was used as a root-end filling in order to seal the root canal system. The two cases were considered completely healed at 1 year and were followed for one more year. The 2-year follow-up consolidated the previous observation with absence of clinical symptoms and radiographic evidence of regeneration of the periapical tissues.

Effects of Excitatory Amino Acid Receptor Antagonists on Pulpal Blood Flow of the Rat Mandibular Incisor

Pulpal blood flow (PBF) changes have been monitored by laser Doppler flowmetry on rat mandibular incisors. Electrical stimulation (10 sec, 50 μA, 2 ms, 20 Hz) of one incisor induced a blood flow decrease followed by a blood flow increase. The effect of intravenous administration of antagonists of ionotropic glutamate receptors (iGluRs) and antagonists of metabotropic glutamate receptors (mGluRs) was compared with that of those obtained from animals treated with the vehicle alone. No long-term effect on basal PBF was observed, except a remaining increase of 34.5% (p < 0.05, n = 5) for ketamine (10 mg/kg), an iGluR antagonist, and of 37% (p < 0.05, n = 5) for MCPG (7.5 mg/kg), an mGluR antagonist. In animals treated with iGluR antagonists, acute changes in PBF after stimulation were not significantly different from those observed with vehicle. In animals treated with mGluR antagonists, the blood flow decrease was significantly enhanced in amplitude and duration for MCPG (7.5 mg/kg), respectively, +73% and +92% (p < 0.05, n = 5). These results suggest that Group I mGluRs participate in the regulation of the immediate pulpal blood flow decrease induced by electrical stimulation of the lower incisor in the rat.

Superficial architecture of the jaw-closing muscles of the cat (Felis catus): the temporo-masseteric complex.

The muscle fiber fascicles of the temporo-masseter complex of the cat were minutely dissected. Some heads were embedded in paraffin while others were put into methyl-methacrylate resin and sections were made. The results of this anatomical study demonstrate that this complex consists of the masseter muscle, the temporal muscle and two well individualized transitional fascicles: the maxillomandibularis and zygomato-comandibularis muscles. The masseter and temporal muscles are composed of individualized compartments in which the orientation and aponeuroses of the fibers of which they are composed differ with regard to the centric occlusion plane. The masseter muscle consists of a superficial fascicle made up of two layers, an intermediate fascicle, and a deep fascicle composed of two layers. The temporal muscle consists of one anterior orbital part and one posterior temporal part. This structure is in accordance with the mammalian archetype described by Gaspard and Saban. These findings should lead towards a homology-based nomenclature founded on comparative anatomy studies of mammalian species. Such a classification would permit the comparison of results obtained from physiological and histochemical studies of these complex muscle fibers when they are published by different researchers.

Effects of RPR 100893, a potent NK1 antagonist, on the jaw-opening reflex in the guinea pig

RPR 100893 appears as a new potent NK1 selective non-peptide antagonist both in vitro and in vivo, and exhibits high affinity for guinea pig and human NK1 receptor [M. Tabart, J.-F. Peyronel, Synthesis of RPR 100893, prototype of a new series of potent and selective non-peptide NK1 antagonists: the triarylperhydroisoindolols, Bioorg. Med. Chem. Lett., 4 (1994) 673-676.]. Intra-oral administration of RPR 100893 (3, 15, 10, 30 mg/kg) was performed in freely moving guinea pigs during recording of the short- (6-10 ms) and long-latency (18-26 ms) jaw-opening reflex (JOR) elicited by electrical stimulation (0.5 Hz) of the lower incisor tooth pulp. RPR 100893 induced a noticeable and dose-dependent increase of the long-latency reflex thresholds (P<0. 001) but was ineffective on the short-latency responses (P=0.14). The results suggest that, in guinea pigs, the long-latency JOR requires activation of NK1 receptors, while the earlier reflex component, elicited by activation of periodontal afferents, does not. These NK1 receptors could be located either on JOR interneurons activated by tooth pulp afferents or on digastric motoneurons, receiving the tooth pulp input through a polysynaptic pathway.

Glutamate control of pulpal blood flow in the incisor dental pulp of the rat.

Glutamate is present in primary sensory afferents innervating the dental pulp and is known to exert vasoactive effects. The aims of this study were (i) to assess pulpal blood flow (PBF) after glutamate infusion in the dental pulp and (ii) to observe the distribution of glutamatergic nerve fibers expressing the vesicular transporters of glutamate (VGluT). The PBF was monitored with laser Doppler flowmetry before and after glutamate (0.5 M) infusion in the dental pulp vs. saline infusion. Immunochemistry for VGluT1, 2, and 3 was performed in addition to immunochemistry for the vascular and neuronal markers smooth-muscle actin (SMA), isolectin B4 (IB4), and calcitonin gene-related peptide (CGRP). Glutamate infusion resulted in a PBF increase that lasted for 60 s. Positive immunolabeling was observed for the three glutamate transporters, but was more pronounced for VGluT3. Moreover, VGluT3 immunoreactivity was observed within nerve fibers entering the dental pulp and terminating at the periphery and at the vicinity of odontoblasts. Also, VGluT3 was colocalized with the vascular marker SMA, and in some nerve fibers with IB4, but not with CGRP. This study provides support for a control of dental pulp microcirculation by neurons expressing VGluT3.

Effects of BP 2-94, a selective H3-receptor agonist, on blood flow and vascular permeability of the rat mandibular incisor pulp

Pulpal blood-flow changes were monitored by laser Doppler flowmetry after electrical stimulation of the mandibular incisor. Stimuli of 10 s (50 microA, 2 ms, 20 Hz) were applied to the incisors of untreated animals and longer stimulations (5 min) were applied in animals treated with the alpha-blocker phenoxybenzamine. Changes in vascular permeability in the dental pulp were measured by Evans blue extravasation following resection of the superior cervical ganglion. In these groups, a selective agonist of H(3) receptors, BP2-94 (1.5 and 15 mg/kg), and an H(3)-antagonist ciproxifan (1 mg/kg) were administered. The effects of these drugs were compared with those obtained from animals treated only with the vehicle (methylcellulose 1%). Basal pulpal blood-flow was not affected significantly by BP2-94 or ciproxifan. The vasoconstriction induced in the group of intact rats by electrical stimulation of 10 s is decreased in amplitude and duration at the higher dose of BP2-94 by 58 and 40%, respectively (P<0.05, n=5). In the sympathectomized animals, plasma extravasation was significantly increased at 15 mg/kg BP2-94 (+100%, P<0.01, n=5). These results suggest that H(3) receptors may participate in the regulation of changes in vessel contraction and permeability provoked by electrical stimulation of the dental pulp. However, the non-selective effects of the H(3) agonists reacting on adrenergic sites and H(1) receptors could explain a part of the results.