Calretinin-immunoreactivity in trigeminal neurons innervating the nasal mucosa of the rat

[WITHDRAWN] Neuron-dependent tuft cell expansion initiates sinonasal allergic Type 2 inflammation

The authors have withdrawn this manuscript owing to inaccuracies in the calculation of tuft cell numbers and errors in the selection of immunofluorescence images used to support our claims. Therefore, the authors do not wish this work to be cited as reference for the project. If you have any questions, please contact the corresponding author.

The Mammalian Diving Response: Inroads to Its Neural Control

The mammalian diving response (DR) is a remarkable behavior that was first formally studied by Laurence Irving and Per Scholander in the late 1930s. The DR is called such because it is most prominent in marine mammals such as seals, whales, and dolphins, but nevertheless is found in all mammals studied. It consists generally of breathing cessation (apnea), a dramatic slowing of heart rate (bradycardia), and an increase in peripheral vasoconstriction. The DR is thought to conserve vital oxygen stores and thus maintain life by directing perfusion to the two organs most essential for life-the heart and the brain. The DR is important, not only for its dramatic power over autonomic function, but also because it alters normal homeostatic reflexes such as the baroreceptor reflex and respiratory chemoreceptor reflex. The neurons driving the reflex circuits for the DR are contained within the medulla and spinal cord since the response remains after the brainstem transection at the pontomedullary junction. Neuroanatomical and physiological data suggesting brainstem areas important for the apnea, bradycardia, and peripheral vasoconstriction induced by underwater submersion are reviewed. Defining the brainstem circuit for the DR may open broad avenues for understanding the mechanisms of suprabulbar control of autonomic function in general, as well as implicate its role in some clinical states. Knowledge of the proposed diving circuit should facilitate studies on elite human divers performing breath-holding dives as well as investigations on sudden infant death syndrome (SIDS), stroke, migraine headache, and arrhythmias. We have speculated that the DR is the most powerful autonomic reflex known.

Direct reticular projections of trigeminal sensory fibers immunoreactive to CGRP: potential monosynaptic somatoautonomic projections

Few trigeminal sensory fibers project centrally beyond the trigeminal sensory complex, with only projections of fibers carried in its sensory anterior ethmoidal (AEN) and intraoral nerves described. Fibers of the AEN project into the brainstem reticular formation where immunoreactivity against substance P and CGRP are found. We investigated whether the source of these peptides could be from trigeminal ganglion neurons by performing unilateral rhizotomies of the trigeminal root and looking for absence of label. After an 8–14 days survival, substance P immunoreactivity in the trigeminal sensory complex was diminished, but we could not conclude that the sole source of this peptide in the lateral parabrachial area and lateral reticular formation arises from primary afferent fibers. Immunoreactivity to CGRP after rhizotomy however was greatly diminished in the trigeminal sensory complex, confirming the observations of others. Moreover, CGRP immunoreactivity was nearly eliminated in fibers in the lateral parabrachial area, the caudal ventrolateral medulla, both the peri-ambiguus and ventral parts of the rostral ventrolateral medulla, in the external formation of the nucleus ambiguus, and diminished in the caudal pressor area. The nearly complete elimination of CGRP in the lateral reticular formation after rhizotomy suggests this peptide is carried in primary afferent fibers. Moreover, the arborization of CGRP immunoreactive fibers in these areas mimics that of direct projections from the AEN. Since electrical stimulation of the AEN induces cardiorespiratory adjustments including an apnea, peripheral vasoconstriction, and bradycardia similar to those seen in the mammalian diving response, we suggest these perturbations of autonomic behavior are enhanced by direct somatic primary afferent projections to these reticular neurons. We believe this to be first description of potential direct somatoautonomic projections to brainstem neurons regulating autonomic activity.

The mammalian diving response: an enigmatic reflex to preserve life?

The mammalian diving response is a remarkable behavior that overrides basic homeostatic reflexes. It is most studied in large aquatic mammals but is seen in all vertebrates. Pelagic mammals have developed several physiological adaptations to conserve intrinsic oxygen stores, but the apnea, bradycardia, and vasoconstriction is shared with those terrestrial and is neurally mediated. The adaptations of aquatic mammals are reviewed here as well as the neural control of cardiorespiratory physiology during diving in rodents.

Mechanism of capsaicin receptor TRPV1-mediated toxicity in pain-sensing neurons focusing on the effects of Na(+)/Ca(2+) fluxes and the Ca(2+)-binding protein calretinin

Transient receptor potential vanilloid subtype 1 (TRPV1) receptor is a pain-sensing, ligand-gated, non-selective cation channel expressed in peripheral sensory neurons. Prolonged activation of TRPV1 by capsaicin leads to cell swelling and formation of membrane blebs in rat dorsal root ganglion (DRG) neurons. Similar results were obtained in NIH3T3 fibroblast cells stably expressing TRPV1. Here, we assessed the contribution of Ca(2+) and Na(+) ions to TRPV1-mediated changes. Cell swelling was caused by a substantial influx of extracellular Na(+) via TRPV1 channels, causing concomitant transport of water. In the absence of extracellular Na(+), the membrane blebbing was completely inhibited, but Ca(2+) influx did not change under these conditions. Na(+) influx was modulated by the intracellular Ca(2+) concentration ([Ca(2+)]i). Elevation of [Ca(2+)]i by ionomycin sensitized/activated TRPV1 channels causing cell swelling in TRPV1-positive cells. In the absence of extracellular Ca(2+), capsaicin caused only little increase in [Ca(2+)]i indicating that the increase in [Ca(2+)]i observed after capsaicin application is derived essentially from extracellular Ca(2+) and not from internal Ca(2+) stores. In the absence of extracellular Ca(2+) also the process of cell swelling was considerably slower. Calretinin is a Ca(2+) buffer protein, which is expressed in a subset of TRPV1-positive neurons. Calretinin decreased the amplitude, but slowed down the decay of Ca(2+) signals evoked by ionomycin. Cells co-expressing TRPV1 and calretinin were less sensitive to TRPV1-mediated, capsaicin-induced volume increases. In TRPV1-expressing NIH3T3 cells, calretinin decreased the capsaicin-induced Ca(2+) and Na(+) influx. Swelling and formation of membrane blebs resulted in impaired plasma membrane integrity finally leading to cell death. Our results hint towards a mechanistic explanation for the apoptosis-independent capsaicin-evoked neuronal loss and additionally reveal a protective effect of calretinin; we propose that the Ca(2+)-buffering capacity of calretinin reduces the susceptibility of calretinin-expressing DRG neurons against cell swelling/death caused by overstimulation of TRPV1 channels. This article is part of a Special Issue entitled:12th European Symposium on Calcium.

Electrical stimulation of the anterior ethmoidal nerve produces the diving response

Stimulation of the upper respiratory tract usually produces apnea, but it can also produce a vagally mediated bradycardia and a sympathetically mediated increase in peripheral vascular resistance. This cardiorespiratory response, often called the diving response, is usually initiated by nasal stimulation. The purpose of this research was to investigate the anterior ethmoidal nerve (AEN) that innervates the nasal mucosa of muskrats (Ondatra zibethicus). Electrical stimulation of the AEN (typically 50 Hz, 100 micros and 500 microA) produced immediate and sustained bradycardia and cessation of respiration similar to that of the diving response. Heart rate (HR) significantly decreased from 264+/-18 to 121+/-8 bpm, with a concurrent 4.2+/-0.9 s apnea, during the 5 s stimulation period. BP decreased from 97.9+/-4.8 to 91.2+/-6.4 mmHg. Using estimations from (1) cross-sectional areas of AEN trigeminal ganglion cells labeled with WGA-HRP, and (2) electron microscopic analysis of the AEN, we found that approximately 65% of the AEN is composed of unmyelinated C-fibers. In addition, 72.4% of myelinated fibers from the nerves that innervate the nasal passages were of small diameter (<6 microm, presumably Adelta fibers). Thus, the AEN of the muskrat contains a high concentration of small diameter fibers (89.8%). We conclude that electrical stimulation of small diameter fibers within the AEN of muskrats can produce the cardiovascular and respiratory responses similar to that of the diving response.

Coexpression of calretinin and parvalbumin in Ruffini-like endings in the rat incisor periodontal ligament

The coexpression of calretinin- (CR) and parvalbumin-immunoreactivities (irs) was examined in oro-facial tissues of the rat. Nerve fibers coexpressing these calcium-binding proteins (CaBPs) were observed in the lingual periodontal ligament of incisors but not other tissues. In the part of periodontal ligament adjacent to the alveolar bone, such nerve fibers left nerve bundles and formed bush-like endings, i.e., they ramified repeatedly and terminated with one to four twigs. An immunoelectron microscopic method indicated that these endings were identical to Ruffini-like endings, 4% of trigeminal neurons retrogradely labeled from the inferior alveolar nerve coexpressed CR- and parvalbumin-irs. The present observations suggest that the coexpression of these CaBPs may be a specific marker for low-threshold mechanoreceptors in the trigeminal ganglion.

Fos immunohistochemical determination of brainstem neuronal activation in the muskrat after nasal stimulation

Stimulation of the nasal passages of muskrats with either ammonia vapours or retrogradely-flowing water produced cardiorespiratory responses (an immediate 62% decrease in heart rate, 29% increase in mean arterial blood pressure, and sustained expiratory apnoea). We used the immunohistological detection of Fos, the protein product of the c-fos gene, as a marker of neuronal activation to help elucidate the brainstem circuitry of this cardiorespiratory response. After repeated ammonia stimulation of the nasal passages, increased Fos expression was detected within the spinal trigeminal nucleus (ventral laminae I and II of the medullary dorsal horn, ventral paratrigeminal nucleus, and spinal trigeminal nucleus interpolaris), an area just ventromedial to the medullary dorsal horn, the caudal dorsal reticular formation and the area of the A5 catecholamine group compared to control animals. Repeated water stimulation of the nasal passages produced increased Fos expression only in the A5 catecholamine group. There was an increase in the number of Fos-positive cells in the ammonia group in the ventral laminae I and II of the medullary dorsal horn and the ventral paratrigeminal nuclei compared with the water group. We conclude that ammonia stimulation of the nasal passages produces a different pattern of neuronal activation within the brainstem compared with water stimulation. We also conclude that Fos immunohistochemistry is a good technique to determine functional afferent somatotopy, but that immunohistochemical detection of Fos is not a good technique to identify the medullary neurons responsible for the efferent aspects of an intermittently produced cardiorespiratory reflex.

S100 protein-immunoreactive primary sensory neurons in the trigeminal and dorsal root ganglia of the rat

The cell body size (cross-sectional area) of S100-immunoreactive (-ir) primary neurons was measured in the trigeminal (TG) and lumbar dorsal root ganglia (DRG). About a half of neurons exhibited S100-immunoreactivity (-ir) in the DRG (44.0%) and TG (59.0%). DRG neurons with cell bodies > 1200 microm2 mostly exhibited S100-ir (96.5%), whereas S100-ir DRG neurons < 600 microm2 were rare (8.0%). 36.6% of DRG neurons in the cell size range 600-1200 microm2 showed the ir. TG neurons > 800 microm2 mostly exhibited S100-ir (93.1%), whereas those < 400 microm2 were devoid of it (positive cells 10.5%). 58.3% of TG cells in the range 400-800 microm2 contained S100-ir. Double-immunofluorescence method revealed the co-expression of S100 and other calcium-binding proteins. Parvalbumin-ir neurons mostly exhibited S100-ir in the DRG (97.4%) and TG (97.0%). The co-expression of S100 and calbindin D-28k was very rare in the DRG, because the DRG contained few calbindin D-28k-ir neurons. Unlike in the DRG, numerous neurons co-expressed S100- and calbindin D-28k-ir in the TG. Most calbindin D-28k-ir TG neurons were also immunoreactive for S100 (90.7%). Sub-populations of calretinin (CR)-ir neurons co-expressed S100-ir in both the DRG (68%) and TG (50.0%). Virtually all CR-ir neurons > 1400 microm2 co-expressed S100-ir in the DRG (100%) and TG (95.9%). CR-ir neurons < 800 microm2 were rarely exhibited S100-ir (DRG 18.0%, TG 21.9%). 71.3 and 60.5% of CR-ir neurons in the range 800-1400 microm2 co-expressed S100-ir in the DRG and TG, respectively. The present study indicates that S100 is closely correlated to the primary neuronal cell size in the DRG and TG.

Trigeminally-mediated alteration of cardiorespiratory rhythms during nasal application of carbon dioxide in the rat

Stimulation of the upper respiratory tract with air-borne irritants can result in dramatic alterations of cardiorespiratory rhythms that include apnea, bradycardia and selective peripheral vasoconstriction. Since carbon dioxide can stimulate receptors in the nasal passages, we wanted to determine if this odorless gas can induce the same autonomic changes as air-borne irritants. Passing 100% carbon dioxide through the nasal passages of rats anesthetized with chloralose-urethane produced apnea, a vagally-mediated bradycardia and a sympathetically-mediated increase in mean arterial blood pressure. Application of atropine blocked the bradycardia without affecting respiratory or blood pressure changes, while injection of prazosin eliminated blood pressure responses but did not affect heart rate or apnea. There were no significant autonomic responses to nasal application of 10, 25 or 50% carbon dioxide. The responses were mediated through the trigeminal innervation of the nasal mucosa since they could be blocked when the anesthetic procaine was applied to the nasal cavity. We conclude that these cardiorespiratory responses are due to stimulation of trigeminal nociceptors located within the nasal mucosa.

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.

Parvalbumin, calretinin and carbonic anhydrase in the trigeminal and spinal primary neurons of the rat

The cell-body size of parvalbumin-immunoreactive (-ir) primary neurons was measured in the trigeminal (TG) and lumber dorsal root ganglia (DRG). In the DRG, parvalbumin-ir was mostly detected in large cells (94% in the range of 600-2800 microns2). Parvalbumin-ir TG cells were smaller than similar DRG cells and yet parvalbumin-ir TG cells of < 400 microns2 (2.86%) were rare. Trichrome stains for parvalbumin, calretinin (CR) and carbonic anhydrase (CA), and for parvalbumin, calcitonin gene-related peptide (CGRP) and CA were performed to estimate possible overlap of these substances. Virtually all parvalbumin-ir DRG cells contained CA activity while a small subpopulation (28.5%) of CR-ir DRG cells lacked CA activity. All the CR-ir DRG cells that exhibited CA were also ir for parvalbumin. 31.1% of parvalbumin-ir DRG cells exhibited CR-ir while 71.5% of CR-ir DRG cells showed parvalbumin-ir. All the CR-ir DRG cells of < 400 microns2 lacked CA activity and parvalbumin-ir while all those of > 800 microns2 exhibited both activities. Approximately 30% of CR-ir DRG cells in the size range of 400-800 microns2 co-expressed CA. DRG cells co-expressing parvalbumin and CGRP were rare (approximately 1%). As was the case for the DRG, most of parvalbumin-ir TG cells exhibited CA activity (89.24%) and lacked CGRP-ir (96.6%). CR-ir TG cells were also subdivided into two groups; one with and the other without co-expression of CA. Unlike in the DRG, however, co-expression of parvalbumin and CR could never be detected in the TG.