Parvalbumin- and calbindin D-28k-immunoreactive innervation of orofacial tissues in the rat

Sensory neurons in the human jugular ganglion

The jugular ganglion (JG) contains sensory neurons of the vagus nerve which innervate somatic and visceral structures in cranial and cervical regions. In this study, the number of sensory neurons in the human JG was investigated. And, the morphology of sensory neurons in the human JG and nodose ganglion (NG) was compared. The estimated number of JG neurons was 2721.8-9301.1 (average number of sensory neurons ± S.D. = 7975.1 ± 3312.8). There was no significant difference in sizes of the neuronal cell body and nucleus within the JG (cell body, 1128.8 ± 99.7 μ m²; nucleus, 127.7 ± 20.8 μ m²) and NG (cell body, 963.8 ± 225.7 μ m²; nucleus, 123.2 ± 32.3 μ m²). These findings indicate that most of sensory neurons show the similar morphology in the JG and NG. Our immunohistochemical method also demonstrated the distribution of ion channels, neurotransmitter agents and calcium-binding proteins in the human JG. Numerous JG neurons were immunoreactive for transient receptor potential cation channel subfamily V member 1 (TRPV1, mean ± SD = 19.9 ± 11.5 %) and calcitonin gene-related peptide (CGRP, 28.4 ± 6.7 %). A moderate number of JG neurons contained TRPV2 (12.0 ± 4.7 %), substance P (SP, 15.7 ± 6.9 %) and secreted protein, acidic and rich in cysteine-like 1 (SPARCL1, 14.6 ± 7.4 %). A few JG neurons had vesicular glutamate transporter 2 (VGLUT2, 5.6 ± 2.9 %) and parvalbumin (PV, 2.3 ± 1.4 %). SP- and TRPV2-containing JG neurons had mainly small and medium-sized cell bodies, respectively. TRPV1- and VGLUT2- containing JG neurons were small to medium-sized. CGRP- and SPARCL1-containing JG neurons were of various cell body sizes. Sensory neurons in the human JG were mostly free of vasoactive intestinal polypeptide (VIP), tyrosine hydroxylase (TH) and neuropeptide Y (NPY). In the external auditory canal skin, subepithelial nerve fibers contained TRPV1, TRPV2, SP, CGRP and VGLUT2. Perivascular nerve fibers also had TRPV1, TRPV2, SP, CGRP, VIP, NPY and TH. However, PV- and SPARCL1-containing nerve endings could not be seen in the external auditory canal. It is likely that sensory neurons in the human JG can transduce nociceptive and mechanoreceptive information from the external auditory canal. Theses neurons may be also associated with neurogenic inflammation in the external auditory canal and ear-cough reflex through the vagus nerve.

Nerve Injury Increases the Expression of Alpha-2/Delta-1 Subunit of L-Type Calcium Channel in Sensory Neurons of Rat Spinal and Trigeminal Nerves

By immunohistochemistry, an effect of nerve injury on distribution of alpha-2/delta-1 subunit of L-type calcium channel was investigated in rat's 4th and 5th lumbar dorsal root ganglia (DRGs), trigeminal ganglion (TG), and mesencephalic trigeminal nucleus (Mes5). The immunoreactivity was expressed by 52.2% of DRG neurons and 31.4% of TG neurons in intact animals. These neurons mostly had small-to-medium-sized cell bodies. In the DRG and TG, alpha-2/delta-1 subunit-positive neurons were lightly or moderately stained. However, the number of alpha-2/delta-1 subunit-immunoreactive (-IR) neurons dramatically increased in the ipsilateral DRG at 3-28 days after sciatic nerve transection (75.3-79.5%) and in the ipsilateral TG at 7 days after infraorbital nerve transection (66.3%). The IR density of alpha-2/delta-1 subunit in DRG and TG neurons was also elevated by the transection. In the injured DRG and TG, many sensory neurons with small-to-medium-sized cell bodies were strongly stained. Some large DRG and TG neurons showing strong staining intensity also appeared after the treatment. In the intact Mes5, sensory neurons were mostly devoid of alpha-2/delta-1 subunit-immunoreactivity (0.4%). However, alpha-2/delta-1-IR sensory neurons on the ipsilateral side of the Mes5 dramatically increased at 7 days after masseteric nerve transection (31.3%). A double immunofluorescence method also demonstrated that c-Jun activating transcription factor 3 (ATF3)-positive DRG (98.3-99.9%) and Mes5 (81.8%) neurons mostly co-expressed alpha-2/delta-1 subunit after the nerve injuries. However, alpha-2/delta-1 subunit immunoreactivity was relatively infrequent among ATF3-immunonegative DRG neurons (51.6-74.1%) and Mes5 neurons (<1%). The present study indicates that the nerve injury increases the protein level of alpha-2/delta-1 subunit among several types of axotomized sensory neurons in the spinal and trigeminal nervous systems.

SCN2B in the Rat Trigeminal Ganglion and Trigeminal Sensory Nuclei

The beta-2 subunit of the mammalian brain voltage-gated sodium channel (SCN2B) was examined in the rat trigeminal ganglion (TG) and trigeminal sensory nuclei. In the TG, 42.6 % of sensory neurons were immunoreactive (IR) for SCN2B. These neurons had various cell body sizes. In facial skins and oral mucosae, corpuscular nerve endings contained SCN2B-immunoreactivity. SCN2B-IR nerve fibers formed nerve plexuses beneath taste buds in the tongue and incisive papilla. However, SCN2B-IR free nerve endings were rare in cutaneous and mucosal epithelia. Tooth pulps, muscle spindles and major salivary glands were also innervated by SCN2B-IR nerve fibers. A double immunofluorescence method revealed that about 40 % of SCN2B-IR neurons exhibited calcitonin gene-related peptide (CGRP)-immunoreactivity. However, distributions of SCN2B- and CGRP-IR nerve fibers were mostly different in facial, oral and cranial structures. By retrograde tracing method, 60.4 and 85.3 % of TG neurons innervating the facial skin and tooth pulp, respectively, showed SCN2B-immunoreactivity. CGRP-immunoreactivity was co-localized by about 40 % of SCN2B-IR cutaneous and tooth pulp TG neurons. In trigeminal sensory nuclei of the brainstem, SCN2B-IR neuronal cell bodies were common in deep laminae of the subnucleus caudalis, and the subnuclei interpolaris and oralis. In the mesencephalic trigeminal tract nucleus, primary sensory neurons also exhibited SCN2B-immunoreactivity. In other regions of trigeminal sensory nuclei, SCN2B-IR cells were very infrequent. SCN2B-IR neuropil was detected in deep laminae of the subnucleus caudalis as well as in the subnuclei interpolaris, oralis and principalis. These findings suggest that SCN2B is expressed by various types of sensory neurons in the TG. There appears to be SCN2B-containing pathway in the TG and trigeminal sensory nuclei.

Distribution of TRPVs, P2X3, and parvalbumin in the human nodose ganglion

Immunohistochemistry for several neurochemical substances, the transient receptor potential cation channel subfamily V member 1 (TRPV1) and 2 (TRPV2), P2X3 receptor, and parvalbumin (PV), was performed on the nodose ganglion, pharynx, and epiglottis in human cadavers. The nodose ganglion was situated beneath the jugular foramen, and had a spindle shape with the long rostrocaudal axis. The pharyngeal branch (PB) issued from a rostral quarter of the nodose ganglion, whereas the superior laryngeal nerve (SLN) usually originated from a caudal half of the ganglion. In the nodose ganglion, sensory neurons were mostly immunoreactive for TRPV1 (89 %) or P2X3 (93.9 %). About 30 % of nodose neurons contained TRPV2 (35.7 %)-or PV (29.9 %)-immunoreactivity (-IR). These neurons mainly had small to medium-sized cell bodies, and were distributed throughout the ganglion. Neurodegenerative profiles such as shrinkage or pyknosis could not be detected in the examined ganglion. Occasionally, TRPV2-IR nerve fibers surrounded blood vessels in the epiglottis as well as in the nasal and oral parts of the pharynx. Isolated TRPV2-IR nerve fibers were also located beneath the epithelium. TRPV1-, P2X3-, or PV-IR nerve endings could not be detected in the pharynx or epiglottis. In the PB and SLN, however, numerous nerve fibers contained TRPV1-, TRPV2-, P2X3-, and PV-IR. The present study suggests that TRPV1-, TRPV2-, P2X3-, and PV-IR neurons in the human nodose ganglion innervate the pharynx and epiglottis through the PB and SLN. These neurons may respond to chemical, thermal, and mechanical stimuli during respiration and swallowing.

Peptide 19-containing neurons in the medullary dorsal horn, subnuclei interpolaris and oralis, and nucleus principalis of the rat

Peptide 19 (PEP 19) is a 7.6 kDa polypeptide which can bind to calmodulin and inhibit calcium-calmodulin signaling. In this study, PEP 19-immunoreactivity (ir) was examined in the rat trigeminal sensory nuclei. Numerous PEP 19-immunoreactive (ir) neurons were detected in the medullary dorsal horn (MDH) and rostral parts of the trigeminal sensory nuclei (subnuclei interpolaris and oralis, and nucleus principalis). The mean numbers ± S.D. per section of PEP 19-ir neurons were 104.2 ± 30.4 in the MDH, 137.8 ± 39.5 in the subnucleus interpolaris, 129.2 ± 46.9 in the subnucleus oralis and 157.2 ± 34.1 in the nucleus principalis. In the MDH, small to medium-sized PEP 19-ir neurons were abundant within superficial laminae. PEP 19-ir neurons with various cell body sizes were also distributed in the rostral parts of the trigeminal sensory nuclei. A double immunofluorescence analysis also demonstrated that many PEP 19-ir neurons co-expressed parvalbumin (PV)-ir in the MDH (9.0%), subnucleus oralis (7.7%) and nucleus principalis (19.7%). In the subnucleus interpolaris, such neurons were relatively rare (1.7%). PEP 19-ir neurons were mostly devoid of calbindin D-28k. In addition, a retrograde tracing method revealed that a substantial number of PEP 19-ir neurons projected to the thalamus. PV-ir was common in thalamus-projecting PEP 19-ir neurons. These findings suggest that PEP 19-ir neurons in the MDH may have a function in modulation of nociceptive and thermo-receptive signaling. It is also likely that PEP 19-ir neurons in rostral parts of the trigeminal sensory nuclei are related to transduction of mechano-receptive information from facial regions to the thalamus.

Runx3 is required for the specification of TrkC-expressing mechanoreceptive trigeminal ganglion neurons

Sensory neurons project axons to specific peripheral and central targets according to their sensory modality. Runx3 is crucially involved in proprioceptive dorsal root ganglion neuron development. Runx3 is also expressed in trigeminal ganglion (TG) neurons. The role of Runx3 in the TG, however, is largely unknown because the TG does not contain proprioceptive neurons. In Runx3-deficient (Runx3(-/-)) mice, TrkB-expressing TG neurons were increased, whereas TrkC-expressing TG neurons were decreased during TG neuron development. In Runx3(-/-) neonatal mice, TrkC-expressing TG neurons did not project to the Merkel cells in the outer root sheath (ORS) of whisker vibrissae peripherally and the spinal trigeminal nucleus pars interpolaris (Sp5I) centrally. These findings suggest that Runx3 is required for the specification of TrkC-expressing TG neurons, conveying mechanoreceptive signals from the Merkel cells in the ORS of the whisker vibrissae to the Sp5I.

Characterization of a thy1.2 GFP transgenic mouse reveals a tissue-specific organization of the spinal dorsal horn

In this study, transgenic mice in which membrane-linked enhanced green fluorescent protein (mGFP) is expressed from the Thy1.2 promoter were used. In these mice, a subpopulation of small to medium sized DRG neurons double stained for IB4 but not for CGRP. Most of the peripheral terminals traversed the dermis and ramify within the epidermis and form superficial terminals. Within the spinal cord, these afferents terminated exclusively within the substantia gelatinosa (SG). A second fibre type in the skin also expressed mGFP, and formed club-shaped endings towards the bases of hairs. Injury to the sciatic nerve resulted in mGFP loss from the SG ipsilateral to the nerve injury, but also in the corresponding region contralaterally. Together, these findings reveal the specificity of connectivity of a defined subpopulation of DRG sensory neurons innervating the epidermis and this will facilitate analysis of their physiological functions.

The reduction of proprioceptors in the mesencephalic trigeminal tract nucleus after neonatal masseteric nerve transection; effect of brain-derived neurotrophic factor

The effect of neonatal masseteric nerve transection on primary proprioceptors was examined in the mesencephalic trigeminal tract nucleus (Mes5) of the rat. At 72 h to 21 days after the injury, the number of Mes5 neurons decreased on the side ipsilateral to the transection. The means+/-SD of percentage proportion of ipsilateral/contralateral neurons at 72 h and 21 days were 69.9+/-7.5% and 58.2+/-14.6%, respectively. The application of brain-derived neurotrophic factor to the proximal stump of the masseteric nerve delayed the loss of Mes5 neurons at 72 h after the injury; the mean numbers+/-SD of ipsilateral and contralateral Mes5 neurons in injured animals with BDNF application was 553.6+/-61.9 and 558.4+/-55.3, respectively. Saline application had no effect on the injury-induced loss of Mes5 neurons; i.e., the mean numbers+/-SD of ipsilateral and contralateral Mes5 neurons were 367.3+/-72.5 and 543+/-33.5, respectively. These findings indicate that trigeminal primary proprioceptors are sensitive to the neonatal injury. The survival of proprioceptors during early postnatal period is probably dependent upon brain-derived neurotrophic factor in the trigeminal nervous system.

ASIC3-immunoreactive neurons in the rat vagal and glossopharyngeal sensory ganglia

ASIC3-immunoreactivity (ir) was examined in the rat vagal and glossopharyngeal sensory ganglia. In the jugular, petrosal and nodose ganglia, 24.8%, 30.8% and 20.6% of sensory neurons, respectively, were immunoreactive for ASIC3. These neurons were observed throughout the ganglia. A double immunofluorescence method demonstrated that many ASIC3-immunoreactive (ir) neurons co-expressed calcitonin gene-related peptide (CGRP)- or vanilloid receptor subtype 1 (VRL-1)-ir in the jugular (CGRP, 77.8%; VRL-1, 28.0%) and petrosal ganglia (CGRP, 61.7%; VRL-1, 21.5%). In the nodose ganglion, however, such neurons were relatively rare (CGRP, 6.3%; VRL-1, 0.4%). ASIC3-ir neurons were mostly devoid of tyrosine hydroxylase in these ganglia. However, some ASIC3-ir neurons co-expressed calbindin D-28k in the petrosal (5.5%) and nodose ganglia (3.8%). These findings may suggest that ASIC3-containing neurons have a wide variety of sensory modalities in the vagal and glossopharyngeal sensory ganglia.

Aspartate-immunoreactive primary sensory neurons in the mouse trigeminal ganglion

Aspartate-immunoreactivity (ir) was examined in the mouse trigeminal ganglion (TG). The ir was detected in 34% of TG neurons and their cell bodies were of various sizes (mean +/- S.D. = 1,234 +/- 543 microm(2)). A triple immunofluorescence method revealed the co-expression of aspartate with calcitonin gene-related peptide (CGRP) and parvalbumin; 22% and 14% of aspartate-immunoreactive (ir) neurons were also immunoreactive for CGRP and parvalbumin, respectively. The co-expression of aspartate with both CGRP and parvalbumin was very rare in the TG. By retrograde tracing method, half and 66% of TG neurons which innervate the vibrissa and palate, respectively, contained aspartate-ir. The co-expression of aspartate with CGRP was more common among palatal neurons (36%) compared to vibrissal neurons (22%). Aspartate-ir neurons which co-expressed parvalbumin-ir were numerous in the vibrissa (17%) but not in the palate (4%). These findings may suggest that the function of aspartate-containing TG neurons is correlated with their peripheral receptive fields.

Calretinin-containing neurons which co-express parvalbumin and calbindin D-28k in the rat spinal and cranial sensory ganglia; triple immunofluorescence study

The co-expression of calretinin with parvalbumin and calbindin D-28k was examined in the rat cranial and spinal sensory ganglia by triple immunofluorescence method. In the trigeminal and nodose ganglia, 9% and 5% of calretinin-immunoreactive neurons, respectively, also contained both parvalbumin- and calbindin D-28k immunoreactivity. These neurons had large cell bodies. In the trigeminal ganglion, they were restricted to the caudal portion. Such neurons were evenly distributed throughout the nodose ganglion. The co-expression could not be detected in the dorsal root, jugular or petrosal ganglia. Nerve fibers which co-expressed all the three calcium-binding proteins were observed in the inferior alveolar nerve but not the infraorbital nerve or palate. In the periodontal ligament, these nerve fibers formed Ruffini-like endings. These findings suggest that (1) the co-expression in trigeminal neurons is intimately related to their peripheral receptive fields; (2) the three calcium-binding proteins (calretinin, parvalbumin, calbindin D-28k) co-expressed in the trigeminal neurons may have mechanoreceptive function in the periodontal ligament.

Peptide 19 in the rat vagal and glossopharyngeal sensory ganglia

Peptide 19 (PEP 19) is a 7.6-kDa polypeptide which binds to calmodulin and inhibits calcium-calmodulin signaling. In this study, PEP 19-immunoreactivity (PEP 19-IR) was examined in the rat vagal and glossopharyngeal sensory ganglia. Twenty-nine percent, 59%, and 41% of sensory neurons contained PEP 19-IR in the jugular, petrosal, and nodose ganglia, respectively. These neurons were of various sizes (jugular, mean +/- SD = 635.8 +/- 392.6 microm2, range = 105.9-1695.9 microm2; petrosal, mean +/- SD = 370.9 +/- 228.5 microm2, range = 57.7-1662.7 microm2; nodose, mean +/- SD = 380.5 +/- 157 microm2, range = 87.5-950.4 microm2) and scattered throughout these ganglia. Double immunofluorescence method revealed that PEP 19-IR neurons which had parvalbumin-IR were rare in the ganglia (jugular, 4%; petrosal, 10%; nodose, 8%). PEP 19-IR neurons which contained calbindin D-28k were abundant in the petrosal (20%) and nodose (22%) ganglia but not in the jugular ganglion (8%). Retrograde tracing method indicated that many PEP 19-IR neurons projected to the circumvallate papilla and soft palate. In the soft palate, taste buds were innervated by PEP 19-IR nerve fibers. The present study suggests that PEP 19-IR neurons include chemoreceptors in the vagal and glossopharyngeal sensory ganglia.

Osteocalcin-immunoreactive neurons in the vagal and glossopharyngeal sensory ganglia of the rat

Immunohistochemistry for osteocalcin (OC) was performed on the rat vagal and glossopharyngeal sensory ganglia. OC-immunoreactive (IR) neurons were detected in the jugular (10%), petrosal (11%) and nodose ganglia (6%). The cell size analysis demonstrated that OC-IR neurons were predominantly small to medium-sized in the jugular ganglion (mean+/-S.D.=356.3+/-192.2 microm(2), range=86.5-831.5 microm(2)). On the other hand, such neurons were medium-sized to large in the petrosal (mean+/-S.D.=725.6+/-280.7 microm(2), range=124.7-1540.4 microm(2)) and nodose ganglia (mean+/-S.D.=857.5+/-330.2 microm(2), range=367.1-1608.0 microm(2)). In the circumvallate papilla, OC-IR nerve fibers were located in the vicinity of taste buds. Some taste bud cells were also immunoreactive for the calcium-binding protein (CaBP). In the carotid body, however, OC-IR nerve fibers could not be detected. Retrograde tracing with fluorogold revealed that OC-IR nerve fibers in the circumvallate papilla mainly originated from the petrosal ganglion. These findings may suggest that OC-IR petrosal neurons have chemoreceptive function in the tongue.

Kv1.2-immunoreactive primary sensory neurons in the rat trigeminal ganglion

Immunohistochemistry for Kv1.2, a subunit of voltage-gated K(+) channels, was performed on the trigeminal ganglion (TG). Immunoreactivity (ir) was detected in half (48%) the TG neurons. These neurons were mostly medium-sized to large (range 137.6-2664.8 microm(2), mean+/-S.D. 892.6+/-413.3 microm(2)). A double immunofluorescence method also revealed co-expression of Kv1.2 and parvalbumin. Half (54%) the Kv1.2-immunoreactive (ir) neurons exhibited parvalbumin-ir, and parvalbumin-ir neurons mostly showed Kv1.2-ir (95%). Kv1.2-ir neurons which co-expressed CGRP-ir were rare in this ganglion. Some 40% of TG neurons retrogradely labeled from the facial skin exhibited Kv1.2-ir, whereas ir was detected in 16% of those labeled from the tooth pulp. The present study indicates that Kv1.2-ir TG neurons include low-threshold mechanoreceptors and nociceptors which innervate the facial skin and tooth pulp, respectively.

Calcium-binding protein-immunoreactive innervation of the rat vibrissa

Immunohistochemistry detected calcium-binding proteins (CaBPs) in corpuscular and Merkel nerve endings of the rat vibrissa. CaBP-immunoreactive (ir) corpuscular endings were divided into two types: ramified and unramified endings. Ramified endings were subdivided into reticular and Ruffini endings. Unramified endings were identical to longitudinal lanceolate endings which have been described previously. Reticular and unramified endings as well as Merkel endings co-expressed neurocalcin (NC)- and parvalbumin (PV)-immunoreactivity (ir). However, such endings were devoid of peptide 19 (PEP19)-ir. PV-ir Ruffini endings were immunoreactive for PEP19 but not NC. The retrograde tracing method revealed that 34, 21 and 18% of trigeminal neurons which project to the infraorbital nerve exhibited NC-, PEP19- and PV-ir, respectively. In addition, 73 and 36% of the PV-ir neurons showed NC- and PEP19-ir, respectively. The content and co-expression of CaBPs in vibrissal low-threshold mechanoreceptors may depend on their terminal morphology.

The neuronal distribution of cannabinoid receptor type 1 in the trigeminal ganglion of the rat

Cannabinoid compounds have been shown to produce antinociception and antihyperalgesia by acting upon cannabinoid receptors located in both the CNS and the periphery. A potential mechanism by which cannabinoids could inhibit nociception in the periphery is the activation of cannabinoid receptors located on one or more classes of primary nociceptive neurons. To address this hypothesis, we evaluated the neuronal distribution of cannabinoid receptor type 1 (CB1) in the trigeminal ganglion (TG) of the adult rat through combined in situ hybridization (ISH) and immunohistochemistry (IHC). CB1 receptor mRNA was localized mainly to medium and large diameter neurons of the maxillary and mandibular branches of the TG. Consistent with this distribution, in a de facto nociceptive sensory neuron population that exhibited vanilloid receptor type 1 immunoreactivity, colocalization with CB1 mRNA was also sparse (<5%). Furthermore, very few neurons (approximately 5%) in the peptidergic (defined as calcitonin gene-related peptide- or substance P-immunoreactive) or the isolectin B4-binding sensory neuron populations contained CB1 mRNA. In contrast, and consistent with the neuron-size distribution for CB1, nearly 75% of CB1-positive neurons exhibited N52-immunoreactivity, a marker of myelinated axons. These results indicate that in the rat TG, CB1 receptors are expressed predominantly in neurons that are not thought to subserve nociceptive neurotransmission in the noninjured animal. Taken together with the absence of an above background in situ signal for CB2 mRNA in TG neurons, these findings suggest that the peripherally mediated antinociceptive effects of cannabinoids may involve either as yet unidentified receptors or interaction with afferent neuron populations that normally subserve non-nociceptive functions.

Effect of Brn-3a deficiency on parvalbumin-, calbindin D-28k-, calretinin- and calcitonin gene-related peptide-immunoreactive primary sensory neurons in the trigeminal ganglion

Immunohistochemistry for parvalbumin, calbindin D-28k, calretinin and calcitonin gene-related peptide (CGRP) was performed on the trigeminal ganglion and oro-facial tissues in Brn-3a wildtype and knockout mice at embryonic day 18.5 and postnatal day 0. In wildtype mice, the trigeminal ganglion contained abundant parvalbumin-, calbindin D-28k- and CGRP-immunoreactive neurons while the ganglion was almost devoid of calretinin-immunoreactive neurons. In Brn-3a knockout mice, a 63% decrease of parvalbumin-immunoreactive neurons was detected. In contrast, the absence of Brn-3a dramatically increased the number of calbindin D-28k-immunoreactive (3.5-fold increase) and calretinin-immunoreactive neurons (91-fold increase). The number of CGRP-immunoreactive neurons, however, was not altered by the Brn-3a deficiency. Cell size analysis indicated that loss of Brn-3a increased the proportions of small (<100 microm (2)) parvalbumin-, calbindin D-28k- and CGRP-immunoreactive neurons while it decreased those of large (>200 microm(2)) immunoreactive cells. Calretinin-immunoreactive neurons were either small or medium (100-200 microm (2)) in mutant mice. The oro-facial tissues contained parvalbumin-, calbindin D-28k- and CGRP-immunoreactive fibers, but not calretinin-immunoreactive ones in wildtype mice. In Brn-3a knockout mice, the number of parvalbumin-immunoreactive fibers markedly decreased in the infraorbital nerve and parvalbumin-immunoreactive endings disappeared in the vibrissa. In contrast, the number of calbindin D-28k-immunoreactive fibers increased significantly in the infraorbital and mental nerves. In addition, calbindin D-28k-immunoreactive endings appeared in the vibrissa. As well, some fibers showed calretinin-immunoreactivity in the infraorbital nerve of the mutant. However, no obvious change of CGRP-immunoreactive fibers was observed in the oro-facial region of knockout mice. Taken together, our data suggest that Brn-3a deficiency has effects on the expression of neurochemical substances in the trigeminal ganglion.

Effect of Brn-3a deficiency on nociceptors and low-threshold mechanoreceptors in the trigeminal ganglion

Immunohistochemistry for protein gene product 9.5 (PGP 9.5, a neuron specific protein) and vanilloid receptor 1-like receptor (VRL-1, a marker for medium-sized to large primary nociceptors) were used to assess the effects of Brn-3a deficiency on neuronal innervation of oral tissues and neurons of the trigeminal ganglion (TG). In the knockout mouse, the number of PGP 9.5-immunoreactive (-ir) nerve fibers decreased in the facial cutaneous and oral mucous epithelia, as well as the incisor and molar tooth germs. The reduction of PGP 9.5-ir Merkel endings was also observed in some vibrissae. No obvious change was detected in other tissues. Cell size analysis demonstrated that the proportion of small neurons markedly increased while that of medium-sized and large neurons significantly decreased in the TG of the mutant. Moreover, Brn-3a deficiency caused the disappearance of TG neurons which were immunoreactive for VRL-1. Together, our data suggest that nociceptors and low-threshold mechanoreceptors with medium-sized to large cell bodies may be sensitive to the loss of Brn-3a.

The co-expression of ASIC3 with calcitonin gene-related peptide and parvalbumin in the rat trigeminal ganglion

The co-expression of ASIC3 with calcitonin gene-related peptide (CGRP) or parvalbumin (PV) was examined in the trigeminal ganglion (TG) by a double immunofluorescence method. ASIC3-immunoreactivity (IR) was detected in 23% of TG neurons. These neurons were of various sizes (range= 43-1768 microm(2), mean+/-S.D.=651+/-356 microm(2)); 26% and 14% of ASIC3-immunoreactive (IR) neurons co-expressed CGRP- and PV-immunoreactivity (IR), respectively; 33% and 13% of the TG neurons retrogradely labeled from the tooth pulp and facial skin, respectively, exhibited ASIC3-IR; 36% of CGRP-IR TG neurons which innervate these tissues co-expressed ASIC3-IR. Only 4% of ASIC3-IR cutaneous TG neurons showed PV-IR, while 25% of ASIC3-IR tooth pulp neurons were also immunoreactive for PV. The present study suggests that ASIC3-IR TG neurons supply the tooth pulp and facial skin with unmyelinated or finely myelinated axons. ASIC3-IR neurons which have large myelinated axons may be common in the tooth pulp but not the facial skin. The axonal morphology of ASIC3-IR TG neurons may depend on the variety of their receptive fields.

Co-expression of VRL-1 and calbindin D-28k in the rat sensory ganglia

The co-expression of vanilloid receptor 1-like receptor (VRL-1), a newly cloned capsaicin-receptor homologue, with calbindin D-28k was examined in the rat sensory ganglia. The co-expression was rare in the dorsal root, trigeminal and jugular ganglia and abundant in the petrosal and nodose ganglia. In the dorsal root ganglion, none of VRL-1-immunoreactive (ir) neuron co-expressed calbindin D-28k-immunoreactivity (ir). Of the VRL-1-ir neurons, 9 and 5% showed calbindin D-28k ir in the trigeminal and jugular ganglia, respectively. On the other hand, 35 and 63% of VRL-1-ir neurons in the petrosal and nodose ganglia, respectively, co-expressed these substances. The retrograde tracing method indicated that petrosal neurons which co-expressed VRL-1-and calbindin D-28k-ir innervated taste buds in the circumvallate papilla. The present findings may suggest that VRL-1 is associated with chemosensory functions in visceral sensory neurons.

Comparative analysis of the chemical neuroanatomy of the mammalian trigeminal ganglion and mesencephalic trigeminal nucleus

A characteristic peculiarity of the trigeminal sensory system is the presence of two distinct populations of primary afferent neurons. Most of their cell bodies are located in the trigeminal ganglion (TG) but part of them lie in the mesencephalic trigeminal nucleus (MTN). This review compares the neurochemical content of central versus peripheral trigeminal primary afferent neurons. In the TG, two subpopulations of primary sensory neurons, containing immunoreactive (IR) material, are identified: a number of glutamate (Glu)-, substance P (SP)-, neurokinin A (NKA)-, calcitonin gene-related peptide (CGRP)-, cholecystokinin (CCK)-, somatostatin (SOM)-, vasoactive intestinal polypeptide (VIP)- and galanin (GAL)-IR ganglion cells with small and medium-sized somata, and relatively less numerous larger-sized neuropeptide Y (NPY)- and peptide 19 (PEP 19)-IR trigeminal neurons. In addition, many nitric oxide synthase (NOS)- and parvalbumin (PV)-IR cells of all sizes as well as fewer, mostly large, calbindin D-28k (CB)-containing neurons are seen. The majority of the large ganglion cells are surrounded by SP-, CGRP-, SOM-, CCK-, VIP-, NOS- and serotonin (SER)-IR perisomatic networks. In the MTN, the main subpopulation of large-sized neurons display Glu-immunoreactivity. Additionally, numerous large MTN neurons exhibit PV- and CB-immunostaining. On the other hand, certain small MTN neurons, most likely interneurons, are found to be GABAergic. Furthermore, NOS-containing neurons can be detected in the caudal and the mesencephalic-pontine junction portions of the nucleus. Conversely, no immunoreactivity to any of the examined neuropeptides is observed in the cell bodies of MTN neurons but these are encircled by peptidergic, catecholaminergic, serotonergic and nitrergic perineuronal arborizations in a basket-like manner. Such a discrepancy in the neurochemical features suggests that the differently fated embryonic migration, synaptogenesis, and peripheral and central target field innervation can possibly affect the individual neurochemical phenotypes of trigeminal primary afferent neurons.

Osteopontin-immunoreactivity in the rat trigeminal ganglion and trigeminal sensory nuclei

Osteopontin-immunoreactivity (OPN-ir) was examined in the oro-facial tissues and trigeminal sensory nuclei (principal sensory nucleus and spinal trigeminal nucleus) to ascertain the peripheral ending and central projection of OPN-containing primary sensory neurons in the trigeminal ganglion (TG). No staining was observed using mouse monoclonal anti-OPN antibody preabsorbed with recombinant mature OPN. OPN-immunoreactive (ir) peripheral endings were classified into two types: encapsulated and unencapsulated types. Unencapsulated endings were subdivided into two types: simple and complex types. Simple endings were characterized by the thin neurite that was usually devoid of ramification. These endings were seen in the hard plate and gingiva. The complex type was characterized by the thick ramified neurite, and observed in the vibrissa, hard palate, and molar periodontal ligament. Encapsulated endings were found only in the hard palate. The trigeminal sensory nuclei contained OPN-ir cell bodies and neuropil. The neuropil was devoid of ir in laminae I and II of the medullary dorsal horn (MDH), and had various staining intensities in other regions of the trigeminal sensory nuclei. Transection of the infraorbital and inferior alveolar nerves caused an increase of OPN-ir intensity in ipsilateral TG neurons. The staining intensity of the neuropil also increased in the trigeminal sensory nuclei ipsilateral to the neurotomy excepting laminae I and II of the MDH. The present study indicates that OPN-ir primary sensory neurons in the TG innervate encapsulated and unencapsulated corpuscular endings. Such neurons probably project their central terminals to the trigeminal sensory nuclei except for the superficial laminae of the MDH.

Immunohistochemical demonstration of nerve terminals in the whole hard palate of rats by use of an antiserum against protein gene product 9.5 (PGP 9.5)

Sensory innervation of the entire hard palate was investigated in the rat using serial sections immunostained for protein gene product 9.5 (PGP 9.5), a neuronal marker. PGP 9.5-immunoreactive nerve endings were widely distributed in the hard palate, but the innervation pattern and density differed among portions. They were numerous at papillary protrusions including the incisal papilla, antemolar/intermolar rugae, and postrugal filiform papillae. Immunoreactive free nerve endings gathered at the summits of the connective tissue papillae, some of them entering deeply into the epithelium. Electron microscopy demonstrated that nerves in the postrugal filiform papillae reached the stratum corneum. The atrial region, possibly the most sensitive in the hard palate, showed unique innervation: its anterior part, adjacent to incisors, developed intraepithelial networks of fine and beaded nerves, whereas its posterior part revealed cone-shaped nerve terminals formed on the connective tissue papillae of the atrial folds which comprised two lines of longitudinal flaps. Taste bud-like corpuscles gathered in the medial walls of the incisal canals and in the "Geschmacksstreifen" (taste stripes) present at the most anterior part of the soft palate. The hard palate of the rat is thus richly innervated, and is characterized by region-specific nerve endings which may be involved in mechano- and chemoreception in the oral cavity.

Vanilloid receptor 1-like receptor-immunoreactive primary sensory neurons in the rat trigeminal nervous system

Immunohistochemistry for vanilloid receptor 1-like receptor (VRL-1), a candidate transducer for high-threshold noxious heat, was performed on rat trigeminal primary sensory neurons. The immunoreactivity was detected in 14% of the trigeminal ganglion cell bodies, while the neurons in the mesencephalic trigeminal tract nucleus were almost devoid of it (0.5%). The immunoreactive neurons in the trigeminal ganglion were mostly of medium to large size (mean+/-S.D. of 956+/-376microm(2)). Nerve bundles in the tooth pulp, periodontal ligament, facial skin and oral mucosa contained VRL-1-positive smooth nerve fibers. The immunoreactivity could not be traced to the isolated nerve fibers, except in the tooth pulp. In the brainstem trigeminal nuclear complex, a notable concentration of the immunoreactivity was seen in laminae I and II of the medullary dorsal horn. Thirty-seven per cent of the trigeminal ganglion neurons retrogradely labeled from the tooth pulp exhibited VRL-1 immunoreactivity, while the immunoreactivity was detected in only 9% of those labeled from the skin. Co-expression of calcitonin gene-related peptide was common among the VRL-1-immunoreactive tooth pulp neurons (45%) and cutaneous neurons (25%). Moreover, as many as 41% of the VRL-1-immunoreactive tooth pulp neurons co-expressed parvalbumin immunoreactivity. Parvalbumin immunoreactivity was never detected in the VRL-1-immunoreactive cutaneous neurons. From the findings of the present study, we propose that large primary neurons responding to high-threshold noxious heat are abundant in the tooth pulp, but not in the facial skin.

Osteopontin-immunoreactive primary sensory neurons in the rat spinal and trigeminal nervous systems

1200 micrometer(2) and 9% of those in the range 600-1200 micrometer(2) showed the immunoreactivity (ir). DRG neurons <600 micrometer(2)800 micrometer(2) showed the ir and 21% of those in the range 400-800 micrometer(2) were immunoreactive for this protein. TG neurons <400 micrometer(2) were mostly devoid of OPN-ir (2%). Virtually all (99%) Mes5 primary sensory neurons exhibited the ir. Muscle spindles in the soleus and masseter muscles contained OPN-ir spiral axon terminals. In the hard palate and incisor periodontal ligament, unencapsulated corpuscular endings exhibited the ir. The co-expression of OPN with parvalbumin and calcitonin gene-related peptide (CGRP) was also examined in the DRG and TG. In the DRG, virtually all (97%) OPN-ir neurons exhibited parvalbumin-ir. Conversely, 66% of parvalbumin-ir DRG neurons co-expressed OPN-ir. In the TG, 81% of OPN-ir neurons exhibited parvalbumin-ir and 69% of parvalbumin-ir ones showed OPN-ir. Virtually all OPN-ir DRG and TG neurons were devoid of CGRP-ir. The present study indicates that OPN-ir primary sensory neurons in the DRG and Mes5 are spinal and trigeminal proprioceptors. OPN-ir TG neurons appear to include low-threshold mechanoreceptors.

Peptide 19-immunoreactive primary sensory neurons in the rat trigeminal ganglion

Peptide 19-immunoreactivity (PEP 19-IR) was examined in the trigeminal ganglion (TG) of the adult rat. A half of TG neurons were immunoreactive(IR) for PEP 19. PEP 19-IR neurons were mostly medium-sized to large. 66% of TG neurons > 600 microm(2) and 38% of those in the range 300-600 microm(2) showed the IR. TG neurons <300 microm(2) were mostly devoid of PEP 19-IR (86%). A double immunofluorescence method revealed the coexpression of PEP 19 and calcium-binding proteins. 31% and 16% of PEP 19-IR neurons exhibited parvalbumin- and calbindin D-28k-IRs, respectively. Conversely, a half of parvalbumin- (53%) and calbindin D-28k-IR (55%) neurons coexpressed PEP 19-IR. PEP 19-IR neurons were mostly IR for S100 (91%) and 80% of S100-IR neurons showed PEP 19-IR. Virtually all (99%) PEP 19-IR neurons were devoid of calcitonin gene-related peptide (CGRP)-IR. The molar tooth pulp contained PEP 19-IR nerve fibers. In the root pulp, PEP 19-IR nerve fibers projected straight until they reached the coronal pulp. Accompanied by blood vessels, these nerve fibers ascended toward the pulp horn. They formed nerve plexuses in the subodontoblastic layer, and reached the base of the odontoblastic layer. However, PEP 19-IR nerve fibers could not be observed within the odontoblastic layer, predentine or dentine. The distribution of these nerve fibers was similar to that of parvalbumin-IR ones. In the TG, PEP 19-IR was found in 34% of primary sensory neurons retrogradely labeled from the molar tooth pulp. 80% of PEP 19-IR tooth pulp TG neurons coexpressed parvalbumin-IR. An immunoelectron microscopic method revealed that a half of radicular axons showed PEP 19-IR. 80% of myelinated axons exhibited PEP 19-IR, whereas 20% of unmyelinated ones showed the IR. In the subodontoblastic layer, PEP 19-IR nerve fibers mostly lost myelin sheath or Schwann cell ensheathment. At the base of the odontoblastic layer, PEP 19-IR neurites made close contact with odontoblasts. PEP 19-IR nerve endings could not be observed in other oro-facial tissues. The coexpression of PEP 19 and CaBPs suggests that low-threshold mechanoreceptors contain PEP 19-IR in the TG. It is also likely that PEP 19-IR TG neurons include myelinated nociceptors.

Osteocalcin-immunoreactive primary sensory neurons in the rat spinal and trigeminal nervous systems

Osteocalcin-immunoreactivity (OC-ir) was examined in spinal and trigeminal primary sensory neurons of the adult rat. Sixteen percent of dorsal root ganglion (DRG) neurons were immunoreactive (ir) for this protein. These neurons were mostly large and measured 594-4583 microm(2) (mean+/-S.D.=2243+/-748 microm(2)). Thirty-four percent of DRG neurons >1200 microm(2) and 4% of those in the range 600-1200 microm(2) showed the ir. Virtually all DRG neurons <600 microm(2) were devoid of OC-ir. In the trigeminal ganglion (TG), 25% of neurons exhibited the ir. Such neurons were of various sizes (range=156-2825 microm(2), mean+/-S.D.=1234+/-543 microm(2)). Forty-five percent of TG neurons >800 microm(2) and 6% of those <400 microm(2) were immunoreactive for this protein. Twelve percent of TG neurons in the range 400-800 microm(2) showed the ir. In the mesencephalic trigeminal tract nucleus (Mes5), 63% of primary sensory neurons contained OC-ir. Virtually all OC-ir DRG and Mes5 neurons co-expressed parvalbumin-ir but not CGRP-ir. On the other hand, only 31% of OC-ir neurons co-expressed parvalbumin-ir and 10% co-expressed CGRP-ir in the TG. The present study indicates that DRG and Mes5 primary sensory neurons co-expressing OC- and parvalbumin-irs are spinal and trigeminal proprioceptors. OC-ir TG neurons which co-express parvalbumin- and CGRP-irs appear to include low-threshold mechanoreceptors and nociceptors, respectively.