SP-like immunoreactivity in the primary trigeminal neurons projecting to the nucleus tractus solitarii

Inhibition of Water-Evoked Swallowing During Noxious Mechanical Stimulation of Tongue in Anesthetized Rats

Dysphagia is sometimes accompanied by pain. Because orofacial structures subserve mastication and swallowing, orofacial pain might impair both functions. Tongue biting can occur not only accidentally while eating but also in some pathological conditions. However, it remains unclear whether noxious mechanical stimulation of the tongue affects swallowing. To explore this question, we evaluated the effects of lingual pinch stimulation on the initiation of swallowing evoked by distilled water (DW) infusion with a flow rate of 5.0 µL/s for 20 s into the pharyngolaryngeal region in anesthetized rats. The swallowing reflex was identified by electromyographic (EMG) bursts in the suprahyoid muscles which include the anterior belly of the digastric muscle, mylohyoid and geniohyoid muscles, and laryngeal elevation by visual inspection. The number of DW-evoked swallows during pinch stimulation was significantly smaller than that in a control condition or during pressure stimulation. The onset latency of the first swallow during pinch stimulation was significantly longer than that in the control condition. DW-evoked swallowing was almost abolished following bilateral transection of the superior laryngeal nerve (SLN) compared with the control condition, suggesting that the SLN plays a crucial role in the initiation of DW-evoked swallowing. Finally, electrophysiological data indicated that some SLN-responsive neurons in the nucleus tractus solitarii (nTS) exhibited delayed latency from a single SLN stimulation during lingual pinch stimulation. These results suggest that noxious mechanical stimulation of the tongue inhibits the initiation of swallowing and modulates neuronal activity in the nTS.

Changes in the frequency of swallowing during electrical stimulation of superior laryngeal nerve in rats

The aim of the present study was to investigate the adaptation of the swallowing reflex in terms of reduced swallowing reflex initiation following continuous superior laryngeal nerve stimulation. Forty-four male Sprague Dawley rats were anesthetized with urethane. To identify swallowing, electromyographic activity of the left mylohyoid and thyrohyoid muscles was recorded. To evoke the swallowing response, the superior laryngeal nerve (SLN), recurrent laryngeal nerve, or cortical swallowing area was electrically stimulated. Repetitive swallowing evoked by continuous SLN stimulation was gradually reduced, and this reduction was dependent on the resting time duration between stimulations. Prior SLN stimulation also suppressed subsequent swallowing initiation. The reduction in evoked swallows induced by recurrent laryngeal nerve or cortical swallowing area stimulation was less than that following superior laryngeal nerve stimulation. Decerebration had no effect on the reduction in evoked swallows. Prior subthreshold stimulation reduced subsequent initiation of swallowing, suggesting that there was no relationship between swallowing movement evoked by prior stimulation and the subsequent reduction in swallowing initiation. Overall, these data suggest that reduced sensory afferent nerve firing and/or trans-synaptic responses, as well as part of the brainstem central pattern generator, are involved in adaptation of the swallowing reflex following continuous stimulation of swallow-inducing peripheral nerves and cortical areas.

Prenatal exposure to nicotine affects substance p and preprotachykinin-A mRNA levels in newborn rat

Prenatal nicotine exposure influences neuronal development including effects on several neurotransmitter systems. It also attenuates the ventilatory response to hypoxia, known to require a functional substance P-ergic system. Previous studies have shown that nicotine increases the risk for sudden infant death syndrome (SIDS) by 4-fold, and that SIDS-victims have elevated brainstem levels of substance P. We, therefore, studied the effect of prenatal nicotine exposure on the levels of substance P-like immunoreactivity by RIA in the brain in newborn rat pups. The expression of the substance P precursor preprotachykinin A mRNA was also determined by real-time reverse transcriptase-polymerase chain reaction in carotid body, in petrosal/jugular and trigeminal ganglia, in cervical and lumbar dorsal root ganglia, and in the brainstem. We found that prenatal nicotine exposure increased levels of substance P-like immunoreactivity in the brainstem without changing levels in other parts of the brain or in the adrenals. Furthermore, mRNA levels were increased in the carotid bodies and in the petrosal ganglia, in contrast to the decreased levels in the cervical dorsal root ganglia. We conclude that nicotine causes alterations in the substance P-ergic system in the brainstem, possibly linked to the increased risk for SIDS after prenatal nicotine exposure.

Cardiovascular responses to substance P in the nucleus tractus solitarii: microinjection study in conscious rats

The cardiovascular effects of substance P (SP) microinjections in the nucleus tractus solitarii (NTS) were evaluated in conscious rats. We chose this model because it is an effective way to access some of the cardiovascular effects of neurotransmitters in the NTS without the inconvenience of blunting pathways with anesthetic agents or removing forebrain projections by decerebration. The cardiovascular responses to SP injections were also evaluated after chronic nodose ganglionectomy. We found that, in conscious rats, SP microinjections into the NTS induced hypertension and tachycardia. Unilateral and bilateral SP injections into the NTS caused a slow increase in blood pressure and heart rate that peaked 1.5-5 min after injection and lasted for 20-30 min. Nodose ganglionectomy increased the duration of the pressor and tachycardic effects of SP and enhanced the pressor response. These data show that SP in the NTS is involved in pressor pathways. The supersensitivity to SP seen after nodose ganglionectomy suggests that vagal afferent projections are involved in those pressor pathways activated by SP in the NTS.

Integration of cornea and cardiorespiratory afferents in the nucleus of the solitary tract of the rat

We determined the activity of neurons within the nucleus of the solitary tract (NTS) after stimulation of the cornea and assessed whether this input affected the processing of baroreceptor and peripheral chemoreceptor inputs. In an in situ, unanesthetized decerebrate working heart-brain stem preparation of the rat, noxious mechanical or electrical stimulation was applied to the cornea, and extracellular single unit recordings were made from NTS neurons. Cornea nociceptor stimulation evoked bradycardia and an increase in the cycle length of the phrenic nerve discharge. Of 90 NTS neurons with ongoing activity, corneal stimulation excited 51 and depressed 39. There was a high degree of convergence to these NTS neurons from either baroreceptors or chemoreceptors. The excitatory synaptic response in 12 of 19 baroreceptive and 10 of 15 chemoreceptive neurons was attenuated significantly during concomitant electrical stimulation of the cornea. This inhibition was GABA(A) receptor mediated, being blocked by pressure ejection of bicuculline. Thus the NTS integrates information from corneal receptors, some of which converges onto neurons mediating reflexes from baroreceptors and chemoreceptors to inhibit these inputs.

Horner's syndrome revisited: with an update of the central pathway

A brief summary is presented of the life of Johann Friedrich Horner, the eminent Swiss ophthalmologist, renowned for describing the effects of paralysis of the human cervical sympathetic nerves. His early education, the quality of his professional training, and the influence of his mentors, notably Carl Ludwig and Albrecht von Graefe, contributed to his discovery of the syndrome. The full text of Horner's original work (translated by J. F. Fulton, 1929a, Arch. Surg. 18:2025-2039) is cited. The history of clinical and experimental work carried out on the autonomic nervous system prior to Horner's discovery is reviewed, including the studies of Pourfour du Petit (cited in Fulton, 1929a and Singer and Underwood, 1962, Clarendon); Hare, 1838, Lond. Med. Gaz. 23:16-18; Bernard (cited by Singer and Underwood); Budge (1853, Acad. de Sci., p.377-378); Mitchell et al. (1864, Lippincott). Hare and Mitchell et al. came close to making the discovery but were apparently hindered by their inability to interpret the signs they elicited in their patients. The experiments of Claude Bernard gave succinct accounts of the effects of damage to the cervical sympathetic nerves in animals, although there appears to be no evidence that he made similar observations in humans. Horner was the first to give a detailed, scientifically supported account and accurately interpret the signs of cervical sympathetic nerve damage in a human subject. The anatomy of the pathway is reviewed and the detailed structure of its central part updated. Evidence from computerized tomography (CT), magnetic resonance imaging (MRI), positron emission tomography (PET), and single-photon-emission computerized tomography (SPECT) studies have confirmed that reciprocally connected centers in the insular cortex, central nucleus of amygdala, hypothalamus, mesencephalic and pontine tegmentum, nucleus of tractus solitarius, and the ventrolateral medulla form the central pathway. The nucleus of tractus solitarius is probably the main reflex center for the sympathetic system, whereas the ventrolateral medulla serves as the pathway through which the central neurons influence the preganglionic neurons of the thoracolumbar outflow. Emotional and sensory inputs from the frontal and somatosensory cortices provide the inputs needed by the insula to drive the sympathetic nervous system to produce appropriate responses.

Calbindin-D28k-immunoreactivity in the trigeminal ganglion neurons and molar tooth pulp of the rat

The cell body size and coexpression of carbonic anhydrase (CA), calretinin (CR) and calcitonin gene-related peptide (CGRP) of primary neurons with calbindin-D28k (CB) was examined in the trigeminal ganglion (TG) of the rat. CB-immunoreactive (-ir) cells were mostly large and preferentially distributed in the maxillary and mandibular divisions of the TG. 48% of CB-ir TG cells exhibited enzyme CA activity. 10% of CB-ir TG cells contained CR-ir. Most TG cells coexpressing CB- and CR-irs were localized to the maxillary and mandibular divisions and exhibited CA activity. 6.5% of CB-ir TG cells coexisted with CGRP-ir. 46% of TG cells coexpressing CB and CGRP exhibited CA activity. The innervation of the molar tooth pulp by CB-ir TG primary neurons was also examined. CB-ir thick and smooth nerve fibers projected from the root pulp to the pulp horn and the roof of the pulp chamber, where they became thinner and rarely entered the subodontoblastic layer. However, they could not be traced to the odontoblastic layer, predentin or dentine. The distribution pattern of CB-ir pulpal fibers was different from that of CR-ir ones. The trigeminal neurons cells retrogradely labeled with fast blue (FB) from the maxillary molar tooth pulp contained CB- and CR-irs. 23% and 1% of the labeled cells were immunoreactive for CB and CR, respectively. The coexpression of CB- and CR-immunoreactivities (-irs) in FB-labeled cells was negligible. An immunoelectron microscopic method revealed that 21% of pulpal nerve fibers were immunoreactive for CB, and that all CB-ir nerve fibers in the root pulp were myelinated. The present study indicated that the tooth pulp primary neurons contained CB-ir but did not coexpress CB- and CR-irs and that these neurons projected their myelinated axons to the pulp.

Parvalbumin- and calretinin-immunoreactive trigeminal neurons innervating the rat molar tooth pulp

Calcium-binding proteins and neuropeptides were examined in trigeminal neuronal cell bodies retrogradely labeled with Fast blue (FB) from the maxillary molar tooth pulp of the rat. FB-labeled cells were located in the maxillary division of the trigeminal ganglion. Approximately 30 and 50% of the labeled cells were immunoreactive for parvalbumin and calcitonin gene-related peptide (CGRP), respectively. The coexpression of these substances was observed in 9.5% of FB-labeled cells. On the other hand, 2.4% of FB-labeled cells exhibited calretinin-immunoreactivity (CR-ir) and 20% tachykinin (TK)-ir. The coexpression of CR and TK was observed in 1.9% of FB-labeled cells, i.e., most of CR-ir FB-labeled neurons coexpressed TK-ir. An immuno-EM method revealed that all parvalbumin-ir nerve fibers in the root pulp were myelinated and that CGRP-ir nerve fibers were both myelinated (15%) and unmyelinated (85%). The present study indicated that primary nociceptors innervating the rat molar tooth pulp contained parvalbumin and CR and coexpressed these calcium-binding proteins and neuropeptides. It was suggested that peripheral axons of parvalbumin-ir tooth pulp primary neurons are all myelinated. Most peripheral CR-ir axons are probably unmyelinated because TK-ir myelinated axons have never been demonstrated in any peripheral organ.

Neural parvalbumin and calretinin in the tooth pulp

Parvalbumin- and calretinin-immunoreactivities (CR-irs) were examined in the molar tooth pulp of the rat using immunohistochemical methods. CR-ir fibers were further classified based on the tachykinin-ir revealed by a double immunofluorescence method. The rat root pulp contained three types of nerve fibers; parvalbumin-ir smooth fibers, CR-ir (TK-negative) smooth fibers and CR-ir (TK-ir) varicose fibers. These fibers projected toward the roof of the pulp chamber and pulp horn without marked ramification. In the subodontoblastic layer at the roof of the pulp chamber and pulp horn, parvalbumin-ir smooth fibers repeatedly ramified and extended varicose terminals into the odontoblastic layer. CR-ir (TK-negative) smooth fibers reached the subodontoblastic layer without marked ramification and gave rise to varicose terminals that appeared to terminate within the subodontoblastic layer. On the other hand, CR-ir (TK-ir) varicose fibers proceeded to the subodontoblastic layer at the roof of the pulp chamber and pulp horn, where they ramified and penetrated the odontoblastic layer. The present study indicates that the rat tooth pulp contains myelinated parvalbumin-ir and CR-ir (TK-negative) fibers, and unmyelinated CR-ir (TK-ir) fibers, and that they project varicose terminals to the subodontoblastic and odontoblastic layers. The central projection sites of these sensory fibers have yet to be revealed.

Nucleus of the solitary tract and dorsal motor nucleus of the vagus nerve of the pigeon: localization of peptide and 5-hydroxytryptamine immunoreactive fibers

The distribution of peptide and serotonin fibers in the nucleus of the solitary tract (NTS) and the dorsal motor nucleus of the vagus nerve (DMNX) in the pigeon (Columba livia) was investigated immunocytochemically. This information was correlated with the viscerotopic organization of the nuclei and with central NTS circuitry to suggest the role of the neurochemical containing fibers in the regulation of organ function. The distribution of fibers containing cholecystokinin (CCK), calcitonin gene-related peptide (CGRP), enkephalin (ENK), neuropeptide Y (NPY), neurotensin (NT), substance P (SP), somatostatin (SS), vasoactive intestinal peptide (VIP), and 5-hydroxytryptamine (5-HT) was determined. Each substance had a distinct distribution within the subnuclei of NTS-DMNX, but certain generalities can be deduced. In the DMNX, fibers immunoreactive for ENK, NT, and SP were found in greatest concentration, while CGRP and 5-HT immunoreactive fibers were the least dense. This suggests that ENK, NT, and SP may have a significant modulatory effect on gastrointestinal functions. In the NTS overall, ENK, NT, SP, and VIP fibers were found in high density, CCK, NPY, SS, and 5-HT fibers were found in moderate density, and CGRP fibers were found in low density. However, some individual NTS subnuclei were found to contain moderate to high concentrations of each of the substances, including CGRP. Fibers containing CCK, ENK, NT, SP, SS, and VIP in the medial dorsal NTS subnuclei may regulate gastroesophageal functions. The caudal part of subnucleus lateralis parasolitarius did not contain most of the substances, which suggests that pulmonary function is not modulated by these neurochemicals. The boundaries of a subnucleus could sometimes be demarcated by a change in density of immunoreactive fibers between adjacent subnuclei. This was particularly evident in NTS subnuclei medialis dorsalis anterior centralis and lateralis parasolitarius, and in DMNX subnucleus posterior dorsalis magnocellularis. The selective distribution of peptide and serotonin immunoreactive fibers in various subnuclei of NTS-DMNX suggests that these substances may be differentially involved in neural circuits that mediate cardiovascular and gastrointestinal functions.