Ultrasound-Guided Inferior Alveolar Nerve Block in the Horse: Assessment of the Extraoral Approach in Cadavers.

Blinded techniques to desensitize the inferior alveolar nerve (IAN) include intraoral, angled, and vertical extraoral approaches with reported success rates of 100%, 73%, and 59%, respectively. It has not been determined whether an ultrasound-guided extraoral approach is feasible. Further, the fascicular nature of the inferior alveolar and lingual nerves of the horse has not been described. The objectives of this study were to describe a low-volume ultrasound-guided vertical extraoral inferior alveolar nerve block technique and to describe the fascicular nature of these nerves. An ultrasound-guided approach to the IAN was conducted with a microconvex transducer and an 18-G, 15-cm spinal needle using a solution containing iodinated-contrast and methylene blue dye. Accuracy was assessed by contrast visualized at the mandibular foramen on computed tomography (CT) and methylene blue dye staining of the nerves on gross dissection. Sections of inferior alveolar and lingual nerves were submitted for histological analysis. Assessment by CT and dissection determined success rates of 81.3% and 68.8%, respectively; 68.8% of injections had inadvertent methylene blue dye staining of the lingual nerve. Nerve histology revealed both the inferior alveolar and lingual nerves to be multifascicular in nature. Mean fascicle counts for the inferior alveolar and lingual nerves were 29 and 30.8, respectively. The technique is challenging and no more accurate than previously published blinded techniques. Any extraoral approach to the IAN is likely to also desensitize the lingual nerve.

Phenotypic change in trigeminal ganglion neurons associated with satellite cell activation via extracellular signal-regulated kinase phosphorylation is involved in lingual neuropathic pain.

Iatrogenic trigeminal nerve injuries remain a common and complex clinical problem. Satellite glial cell (SGC) activation, associated phosphorylation of extracellular signal-regulated kinase (ERK), and neuropeptide expression in the trigeminal ganglion (TG) are known to be involved in trigeminal neuropathic pain related to trigeminal nerve injury. However, the involvement of these molecules in orofacial neuropathic pain mechanisms is still unknown. Phosphorylation of ERK1/2 in lingual nerve crush (LNC) rats was observed in SGCs. To evaluate the role of neuron-SGC interactions under neuropathic pain, calcitonin gene-related peptide (CGRP)-immunoreactive (IR), phosphorylated ERK1/2 (pERK1/2)-IR and glial fibrillary acidic protein (GFAP)-IR cells in the TG were studied in LNC rats. The number of CGRP-IR neurons and neurons encircled with pERK1/2-IR SGCs was significantly larger in LNC rats compared with sham rats. The percentage of large-sized CGRP-IR neurons was significantly higher in LNC rats. The number of CGRP-IR neurons, neurons encircled with pERK1/2-IR SGCs, and neurons encircled with GFAP-IR SGCs was decreased following CGRP receptor blocker CGRP8-37 or mitogen-activated protein kinase/ERK kinase 1 inhibitor PD98059 administration into the TG after LNC. Reduced thresholds to mechanical and heat stimulation to the tongue in LNC rats were also significantly recovered following CGRP8-37 or PD98059 administration. The present findings suggest that CGRP released from TG neurons activates SGCs through ERK1/2 phosphorylation and TG neuronal activity is enhanced, resulting in the tongue hypersensitivity associated with lingual nerve injury. The phenotypic switching of large myelinated TG neurons expressing CGRP may account for the pathogenesis of tongue neuropathic pain.

Bilateral sensory deprivation of trigeminal afferent fibres on corticomotor control of human tongue musculature: a preliminary study.

Transcranial magnetic stimulation (TMS) has demonstrated changes in motor evoked potentials (MEPs) in human limb muscles following modulation of sensory afferent inputs. The aim of this study was to determine whether bilateral local anaesthesia (LA) of the lingual nerve affects the excitability of the tongue motor cortex (MI) as measured by TMS. The effect on MEPs after bilateral LA of the lingual nerve was studied, while the first dorsal interosseous (FDI) muscle served as a control in ten healthy participants. MEPs were measured on the right side of the tongue dorsum in four different conditions: (i) immediately prior to anaesthesia (baseline), (ii) during bilateral LA block of the lingual nerve, (iii) after anaesthesia had subjectively subsided (recovery) and (iv) 3 h after bilateral lingual block injection. MEPs were assessed using stimulus-response curves in steps of 10% of motor threshold (T). Eight stimuli were given at each stimulus level. The amplitudes of the tongue MEPs were significantly influenced by the stimulus intensity (P < 0·001) but not by condition (P = 0·186). However, post hoc tests showed that MEPS were statistically significantly higher during bilateral LA block condition compared with baseline at T + 40%, T + 50% and T + 60% (P < 0·028) and also compared with recovery at T + 60% (P = 0·010) as well as at 3 h after injection at T + 50% and T + 60% (P < 0·029). Bilateral LA block of the lingual nerve seems to be associated with a facilitation of the corticomotor pathways related to the tongue musculature.

Developmental time course of peripheral cross-modal sensory interaction of the trigeminal and gustatory systems.

Few sensory modalities appear to engage in cross-modal interactions within the peripheral nervous system, making the integrated relationship between the peripheral gustatory and trigeminal systems an ideal model for investigating cross-sensory support. The present study examined taste system anatomy following unilateral transection of the trigeminal lingual nerve (LX) while leaving the gustatory chorda tympani intact. At 10, 25, or 65 days of age, rats underwent LX with outcomes assessed following various survival times. Fungiform papillae were classified by morphological feature using surface analysis. Taste bud volumes were calculated from histological sections of the anterior tongue. Differences in papillae morphology were evident by 2 days post-transection of P10 rats and by 8 days post in P25 rats. When transected at P65, animals never exhibited statistically significant morphological changes. After LX at P10, fewer taste buds were present on the transected side following 16 and 24 days survival time and remaining taste buds were smaller than on the intact side. In P25 and P65 animals, taste bud volumes were reduced on the denervated side by 8 and 16 days postsurgery, respectively. By 50 days post-transection, taste buds of P10 animals had not recovered in size; however, all observed changes in papillae morphology and taste buds subsided in P25 and P65 rats. Results indicate that LX impacts taste receptor cells and alters epithelial morphology of fungiform papillae, particularly during early development. These findings highlight dual roles for the lingual nerve in the maintenance of both gustatory and non-gustatory tissues on the anterior tongue.

Differences in control of parasympathetic vasodilation between submandibular and sublingual glands in the rat.

We examined blood flow in the submandibular gland (SMGBF) and sublingual gland (SLGBF) during electrical stimulation of the central cut end of the lingual nerve (LN) in the urethane-anesthetized rats using a laser speckle imaging flow meter. LN stimulation elicited intensity- and frequency-dependent SMGBF and SLGBF increases, and the magnitude of the SMGBF increase was higher than that of the SLGBF increase. The increase in both glands was significantly inhibited by intravenous administration of the autonomic cholinergic ganglion blocker hexamethonium. The antimuscarinic agent atropine markedly inhibited the SMGBF increase and partly inhibited the SLGBF increase. The atropine-resistant SLGBF increase was significantly inhibited by infusion of vasoactive intestinal peptide (VIP) receptor antagonist, although administration of VIP receptor antagonist alone had no effect. The recovery time to the basal blood flow level was shorter after LN stimulation than after administration of VIP. However, the recovery time after LN stimulation was significantly delayed by administration of atropine in a dose-dependent manner to the same level as after administration of VIP. Our results indicate that 1) LN stimulation elicits both a parasympathetic SMGBF increase mainly evoked by cholinergic fibers and a parasympathetic SLGBF increase evoked by cholinergic and noncholinergic fibers, and 2) VIP-ergic mechanisms are involved in the noncholinergic SLGBF increase and are activated when muscarinic mechanisms are deactivated.

Nerve fiber analysis on the morphology of the lingual nerve.

The route of fine fascicles of nerve fibers in the lingual nerve was clarified. Contemporary anatomy textbooks describe the lingual nerve as supplying sensory innervation to the mucous membrane of the presulcal part of the tongue, the floor and side wall of the mouth, and the mandibular gums. In addition to receiving the chorda tympani and a branch of the inferior alveolar nerve, the lingual nerve is connected to the submandibular ganglion by a few branches. It carries preganglionic fibers from the chorda tympani and postganglionic fibers from the submandibular ganglion to the submandibular and sublingual glands. The branch from the mylohyoid nerve is described as a sensory nerve. However, we observed that this branch was directly connected to the submandibular ganglion. Furthermore, the branch from the submandibular ganglion innervated thin membranous tissue that originated in the petrous part of the temporal bone and inserted into the lateral surface of the superior constrictor. These branches have not been described in the anatomy textbooks and literature. Therefore, we studied the morphological features of the lingual nerve and discovered the route of fine fascicles of nerve fibers in the lingual nerve. These findings will likely improve the neurological and physiological understanding of the function of the lingual nerve.

Surgical neurolysis for the treatment of neuropathic pain in 2 postmenopausal women with mandibular necrosis resulting from oral bisphosphonates.

We analyze the use of surgical neurolysis for the treatment of neuropathic pain of the inferior alveolar nerve. For that, 3 surgical neurolysis were performed on 2 postmenopausal women experiencing neuropathic pain of the inferior alveolar nerve due to mandibular necrosis resulting from treatment with oral bisphosphonates. Both patients showed sensory impairment of the inferior alveolar nerve. We obtained complete control of neuropathic pain after 6 months of the patients' evolution, preserving the function of the lingual nerve in all 3 neurolysis, without causing any impact as regards to the sensitive situation before treatment. Surgical neurolysis of the inferior alveolar nerve may be considered as the choice therapeutic technique to treat neuropathic pain of this nerve when there is a sensory impairment in patients showing mandibular necrosis resulting from bisphosphonates.

Parasympathetic reflex vasodilation in the cerebral hemodynamics of rats.

We investigated the role of parasympathetic reflex vasodilation in the regulation of the cerebral hemodynamics, and whether GABAA receptors modulate the response. We examined the effects of activation of the parasympathetic fibers through trigeminal afferent inputs on blood flow in the internal carotid artery (ICABF) and the cerebral blood vessels (rCBF) in parietal cortex in urethane-anesthetized rats. Electrical stimulation of the central cut end of the lingual nerve (LN) elicited intensity- and frequency-dependent increases in ICABF that were independent of changes in external carotid artery blood flow. Increases in ICABF were elicited by LN stimulation regardless of the presence or absence of sympathetic innervation. The ICABF increases evoked by LN stimulation were almost abolished by the intravenous administration of hexamethonium (10 mg kg(-1)) and were reduced significantly by atropine administration (0.1 mg kg(-1)). Although the LN stimulation alone had no significant effect on rCBF, LN stimulation in combination with a blocker of the GABAA receptor pentylenetetrazole increased the rCBF markedly. This increase in rCBF was reduced significantly by the administration of hexamethonium and atropine. These observations indicate that the increases in both ICABF and rCBF are evoked by parasympathetic activation via the trigeminal-mediated reflex. The rCBF increase evoked by LN stimulation is thought to be limited by the GABAA receptors in the central nervous system. These results suggest that the parasympathetic reflex vasodilation and its modulation mediated by GABA receptors within synaptic transmission in the brainstem are involved in the regulation of the cerebral hemodynamics during trigeminal afferent inputs.

Restoration of quinine-stimulated Fos-immunoreactive neurons in the central nucleus of the amygdala and gustatory cortex following reinnervation or cross-reinnervation of the lingual taste nerves in rats.

Remarkably, when lingual gustatory nerves are surgically rerouted to inappropriate taste fields in the tongue, some taste functions recover. We previously demonstrated that quinine-stimulated oromotor rejection reflexes and neural activity (assessed by Fos immunoreactivity) in subregions of hindbrain gustatory nuclei were restored if the posterior tongue, which contains receptor cells that respond strongly to bitter compounds, was cross-reinnervated by the chorda tympani nerve. Such functional recovery was not seen if instead, the anterior tongue, where receptor cells are less responsive to bitter compounds, was cross-reinnervated by the glossopharyngeal nerve, even though this nerve typically responds robustly to bitter substances. Thus, recovery depended more on the taste field being reinnervated than on the nerve itself. Here, the distribution of quinine-stimulated Fos-immunoreactive neurons in two taste-associated forebrain areas was examined in these same rats. In the central nucleus of the amygdala (CeA), a rostrocaudal gradient characterized the normal quinine-stimulated Fos response, with the greatest number of labeled cells situated rostrally. Quinine-stimulated neurons were found throughout the gustatory cortex, but a "hot spot" was observed in its anterior-posterior center in subregions approximating the dysgranular/agranular layers. Fos neurons here and in the rostral CeA were highly correlated with quinine-elicited gapes. Denervation of the posterior tongue eliminated, and its reinnervation by either nerve restored, numbers of quinine-stimulated labeled cells in the rostralmost CeA and in the subregion approximating the dysgranular gustatory cortex. These results underscore the remarkable plasticity of the gustatory system and also help clarify the functional anatomy of neural circuits activated by bitter taste stimulation.

Intraoral electrostimulator for xerostomia relief: a long-term, multicenter, open-label, uncontrolled, clinical trial.

OBJECTIVE: A previous sham-controlled multinational study demonstrated the short-term efficacy and safety for xerostomia treatment of an intraoral device that delivers electrostimulation to the lingual nerve. The objective of this study was to test the hypothesis that those beneficial effects would be sustained over an 11-month period. STUDY DESIGN: The device was tested on a mixed sample of 94 patients with xerostomia in an open-label, uncontrolled, prospective multicenter trial. Statutory outcome assessments were done at 5th, 8th, and 11th months and analyzed by multiple comparisons. RESULTS: Improvements achieved at month 5 from baseline were sustained throughout the follow-up period for the primary outcome, xerostomia severity, and the secondary outcomes resting whole salivary flow rate, xerostomia frequency, oral discomfort, and difficulties in speech, swallowing, and sleeping. No significant side effects were detected. CONCLUSIONS: The beneficial effects of a removable intraoral electrostimulating device were sustained for an 11-month period.

What factors are associated with functional sensory recovery following lingual nerve repair?

PURPOSE: To identify factors associated with functional sensory recovery (FSR) after lingual nerve repair. MATERIALS AND METHODS: This retrospective cohort study was composed of subjects who underwent lingual nerve repair from 2004 through 2010. The predictor variables were demographic, anatomic, and operative measurements. The primary outcome measurement was FSR (ie, FSR achieved, yes or no). The secondary outcome measurements were time to FSR and an improvement of at least 2 levels on the British Medical Research Council scale of neurosensory function. Descriptive, bivariate, and multiple logistic regression statistics were computed to identify associations between the predictor variables and FSR. A Cox proportional hazards model was used to identify associations between the predictors and time to FSR. P ≤ .05 was considered statistically significant. RESULTS: The sample was composed of 55 subjects with a mean age of 30.7 ± 11.2 years. The mean duration from injury to repair was 151.6 days (range, 41 to 384 days). Most patients (74.5%) achieved FSR postoperatively, with a mean time to FSR of 262.8 days (median, 208 days). Eighty-six percent of subjects showed an improvement of at least 2 levels on the British Medical Research Council scale. In multiple regression models, younger subjects were more likely to achieve FSR (odds ratio, 1.10; 95% confidence interval, 1.01 to 1.18; P = .02); subjects with better preoperative neurosensory function achieved FSR faster (hazard ratio, 1.9; 95% confidence interval, 1.2 to 3.1; P = .01). CONCLUSION: Most patients undergoing lingual nerve repair achieved FSR. Younger subjects were more likely to achieve FSR. Subjects with better preoperative neurosensory function achieved FSR faster.

The rostral parvicellular reticular formation neurons mediate lingual nerve input to the rostral ventrolateral medulla.

In rats that had been anesthetized by urethane-chloralose, we investigated whether neurons in the rostral part of the parvicellular reticular formation (rRFp) mediate lingual nerve input to the rostral ventrolateral medulla (RVLM), which is involved in somato-visceral sensory integration and in controlling the cardiovascular system. We determined the effect of the lingual nerve stimulation on activity of the rRFp neurons that were activated antidromically by stimulation of the RVLM. Stimulation of the lingual trigeminal afferent gave rise to excitatory effects (10/26, 39%), inhibitory effects (6/26, 22%) and no effect (10/26, 39%) on the RVLM-projecting rRFp neurons. About two-thirds of RVLM-projecting rRFp neurons exhibited spontaneous activity; the remaining one-third did not. A half (13/26) of RVLM-projecting rRFp neurons exhibited a pulse-related activity, suggesting that they receive a variety of peripheral and CNS inputs involved in cardiovascular function. We conclude that the lingual trigeminal input exerts excitatory and/or inhibitory effects on a majority (61%) of the RVLM-projecting rRFp neurons, and their neuronal activity may be involved in the cardiovascular responses accompanied by the defense reaction.

Autonomic and cardiovascular effects of pentobarbital anesthesia during trigeminal stimulation in cats.

Stimulation of the trigeminal nerve can elicit various cardiovascular and autonomic responses; however, the effects of anesthesia with pentobarbital sodium on these responses are unclear. Pentobarbital sodium was infused intravenously at a nominal rate and the lingual nerve was electrically stimulated at each infusion rate. Increases in systolic blood pressure (SBP) and heart rate (HR) were evoked by lingual nerve stimulation at an infusion rate between 5 and 7 mg·kg(-1)·h(-1). This response was associated with an increase in the low-frequency band of SBP variability (SBP-LF). As the infusion rate increased to 10 mg·kg(-1)·h(-1) or more, decreases in SBP and HR were observed. This response was associated with the reduction of SBP-LF. In conclusion, lingual nerve stimulation has both sympathomimetic and sympathoinhibitory effects, depending on the depth of pentobarbital anesthesia. The reaction pattern seems to be closely related to the autonomic balance produced by pentobarbital anesthesia.

Role of medullary GABA signal transduction on parasympathetic reflex vasodilatation in the lower lip.

In the orofacial area, noxious stimulation of the orofacial structure in the trigeminal region evokes parasympathetic reflex vasodilatation, which occurs via the trigeminal spinal nucleus (Vsp) and the inferior/superior salivatory nucleus (ISN/SSN). However, the neurotransmitter involved in the inhibitory synaptic inputs within these nuclei has never been described. This parasympathetic reflex vasodilatation is suppressed by GABAergic action of volatile anesthetics, such as isoflurane, sevoflurane, and halothane, suggesting that medullary GABAergic mechanism exerts its inhibitory effect on the parasympathetic reflex via an activation of GABA receptors. The aim of the present study was to determine the role of GABA(A) and GABA(B) receptors in the Vsp and the ISN in regulating the lingual nerve (LN)-evoked parasympathetic reflex vasodilatation in the lower lip. Under urethane anesthesia (1g/kg), change in lower lip blood flow elicited by electrical stimulation of the LN was recorded in cervically vago-sympathectomized rats. Microinjection of GABA (10 µM; 0.3 µl/site) into the Vsp or the ISN significantly and reversibly attenuated the LN-evoked parasympathetic reflex vasodilatation. Microinjection of the GABA(A) receptor-selective agonist muscimol (100 µM; 0.3 µl/site) or the GABA(B) receptor-selective agonist baclofen (100 µM; 0.3 µl/site) into the Vsp or the ISN significantly and irreversibly reduced this reflex vasodilatation, and these effects were attenuated by pretreatment with microinjection of each receptor-selective antagonists [GABA(A) receptor selective antagonist bicuculline methiodide (1mM; 0.3 µl/site) or GABA(B) receptor selective antagonist CGP-35348 (1mM; 0.3 µl/site)] into the Vsp or the ISN. Microinjection of these antagonists alone into the Vsp or the ISN had no significant effect on this reflex vasodilatation. In addition, microinjection (0.3 µl/site) of the mixture of muscimol (100 µM) and baclofen (100 µM) into the Vsp or the ISN also significantly reduced this reflex vasodilatation. These results suggest that medullary GABA signal transduction inhibits the parasympathetic reflex vasodilatation in the rat lower lip via GABA(A) and GABA(B) receptors in the Vsp and the ISN.

A survey of oral cavity afferents to the rat nucleus tractus solitarii.

Visualization of myelinated fiber arrangements, cytoarchitecture, and projection fields of afferent fibers in tandem revealed input target selectivity in identified subdivisions of the nucleus tractus solitarii (NTS). The central fibers of the chorda tympani (CT), greater superficial petrosal nerve (GSP), and glossopharyngeal nerve (IX), three nerves that innervate taste buds in the oral cavity, prominently occupy the gustatory-sensitive rostrocentral subdivision. In addition, CT and IX innervate and overlap in the rostrolateral subdivision, which is primarily targeted by the lingual branch of the trigeminal nerve (LV). In the rostrocentral subdivision, compared with the CT terminal field, GSP appeared more rostral and medial, and IX was more dorsal and caudal. Whereas IX and LV filled the rostrolateral subdivision diffusely, CT projected only to the dorsal and medial portions. The intermediate lateral subdivision received input from IX and LV but not CT or GSP. In the caudal NTS, the ventrolateral subdivision received notable innervation from CT, GSP, and LV, but not IX. No caudal subnuclei medial to the solitary tract contained labeled afferent fibers. The data indicate selectivity of fiber populations within each nerve for functionally distinct subdivisions of the NTS, highlighting the possibility of equally distinct functions for CT in the rostrolateral NTS, and CT and GSP in the caudal NTS. Further, this provides a useful anatomical template to study the role of oral cavity afferents in the taste-responsive subdivision of the NTS as well as in subdivisions that regulate ingestion and other oromotor behaviors.

Response latency to lingual taste stimulation distinguishes neuron types within the geniculate ganglion.

The purpose of this study was to investigate the role of response latency in discrimination of chemical stimuli by geniculate ganglion neurons in the rat. Accordingly, we recorded single-cell 5-s responses from geniculate ganglion neurons (n = 47) simultaneously with stimulus-evoked summated potentials (electrogustogram; EGG) from the anterior tongue to signal when the stimulus contacted the lingual epithelium. Artificial saliva served as the rinse solution and solvent for all stimuli [(0.5 M sucrose, 0.03-0.5 M NaCl, 0.01 M citric acid, and 0.02 M quinine hydrochloride (QHCl)], 0.1 M KCl as well as for 0.1 M NaCl +1 µM benzamil. Cluster analysis separated neurons into four groups (sucrose specialists, NaCl specialists, NaCl/QHCl generalists and acid generalists). Artificial saliva elevated spontaneous firing rate and response frequency of all neurons. As a rule, geniculate ganglion neurons responded with the highest frequency and shortest latency to their best stimulus with acid generalist the only exception. For specialist neurons and NaCl/QHCl generalists, the average response latency to the best stimulus was two to four times shorter than the latency to secondary stimuli. For NaCl-specialist neurons, response frequency increased and response latency decreased systematically with increasing NaCl concentration; benzamil significantly decreased NaCl response frequency and increased response latency. Acid-generalist neurons had the highest spontaneous firing rate and were the only group that responded consistently to citric acid and KCl. For many acid generalists, a citric-acid-evoked inhibition preceded robust excitation. We conclude that response latency may be an informative coding signal for peripheral chemosensory neurons.

Implant-supported electrostimulating device to treat xerostomia: a preliminary study.

BACKGROUND: The full accomplishment of salivary function depends on proper salivary flow rate and composition. Salivary secretion is highly essential in the maintenance of health and integrity of oral hard and soft tissue. Xerostomia is a common symptom affecting between one-fifth and one-third of the adult population, more commonly women than men. Induction of salivary secretion exists in several pharmacological formulations per os. Electrostimulation to enhance salivary secretion has been used frequently as a research tool but only in limited extent as a clinical method to treat patients with xerostomia. PURPOSE: The aims of this preliminary study were to observe and evaluate the therapeutic effect on xerostomia of the Saliwell Crown (Saliwell Ltd., Harutzim, Israel), an innovative saliva electrostimulation device fixed on an implant, placed in the lower third molar area. MATERIALS AND METHODS: A Saliwell Crown was placed in the lower third molar area of an 81-year-old female patient with complaints of dry and burning mouth. Salivary secretion was measured, and the patient was asked to fill in written satisfaction questionnaires. The patient was monitored for a year, comparing her salivary secretion rates and the written questionnaires. RESULTS: The results showed a constant slight but significant increase in the salivary secretion and in the patient's personal feelings as presented in the questionnaires. CONCLUSIONS: The saliva stimulation device Saliwell Crown, placed on an implant in an 81-year-old patient with dry and burning mouth complaints, presented promising results when both the salivary secretion tests and the self-assessment questionnaires were examined and compared.

Role of the spinal trigeminal nucleus in the rat autonomic reflex.

The goal of the present study was to investigate the regional differences between the three subnuclei (oralis, interpolaris, and caudalis) of the spinal trigeminal nucleus (Vsp) in eliciting parasympathetic and sympathetic reflex autonomic responses. We evoked changes in lower lip blood flow (LBF) and systemic arterial blood pressure (SABP) by electrically stimulating these subnuclei in artificially ventilated, urethane-anaesthetised, cervically vago-sympathectomized rats. The LBF increases evoked by electrical stimulation of the Vsp at interpolaris were much larger than those at the sites of the oralis and caudalis. No significant difference in SABP increase was observed by Vsp stimulation between the interpolaris and caudalis, although the SABP increase evoked by electrical stimulation of the oralis was much smaller than in the interpolaris and caudalis. The present findings show that the Vsp at the interpolaris subnucleus of the Vsp participates as a relay in lingual nerve- and Vsp-evoked somato-autonomic reflex.

Trigeminal projections on gustatory neurons of the nucleus of the solitary tract: a double-label strategy using electrical stimulation of the chorda tympani and tracer injection in the lingual nerve.

Taste and sensory information are closely associated and our electrophysiological studies showed a trigeminal modulation of gustatory neurons in the nucleus of the solitary tract (NST). Chorda tympani (CT) and lingual nerves (LN) converge centrally in the rostral subdivision of the NST in hamsters and rats. However, no study has yet revealed the details of this overlap on a same section. We therefore used a double-label strategy to visualize neurons in the NST that receive both trigeminal and gustatory inputs. An anterograde tracer (BDA, Biotinylated Dextran Amine) was applied unilaterally to the cut central end of the LN in male Sprague-Dawley rats. One week later, the ipsilateral CT was electrically stimulated, after which animals were perfused and brainstem sections double-labelled for Fos immunoreactivity of activated NST neurons and BDA labelling of LN afferents. Our results permitted to circumscribe the regional overlap of the trigeminal and CT afferents mainly in the rostral central (RC) subdivision of the gustatory NST. Fos-immunoreactive neurons were observed to be closely apposed by BDA-labelled fibres and terminal boutons. Such varicosities mainly "en passant" were especially present in the RC zone of the nucleus. These observations provide an anatomical substrate for trigemino-gustatory interactions.