Cadherin‐7 mediates proper neural crest cell–placodal neuron interactions during trigeminal ganglion assembly

The cranial trigeminal ganglia play a vital role in the peripheral nervous system through their relay of sensory information from the vertebrate head to the brain. These ganglia are generated from the intermixing and coalescence of two distinct cell populations: cranial neural crest cells and placodal neurons. Trigeminal ganglion assembly requires the formation of cadherin‐based adherens junctions within the neural crest cell and placodal neuron populations; however, the molecular composition of these adherens junctions is still unknown. Herein, we aimed to define the spatio‐temporal expression pattern and function of Cadherin‐7 during early chick trigeminal ganglion formation. Our data reveal that Cadherin‐7 is expressed exclusively in migratory cranial neural crest cells and is absent from trigeminal neurons. Using molecular perturbation experiments, we demonstrate that modulation of Cadherin‐7 in neural crest cells influences trigeminal ganglion assembly, including the organization of neural crest cells and placodal neurons within the ganglionic anlage. Moreover, alterations in Cadherin‐7 levels lead to changes in the morphology of trigeminal neurons. Taken together, these findings provide additional insight into the role of cadherin‐based adhesion in trigeminal ganglion formation, and, more broadly, the molecular mechanisms that orchestrate the cellular interactions essential for cranial gangliogenesis.     

P2X_3受体在感觉神经节的表达

用免疫组织化学与原位杂交研究 P2 X3受体在背根神经节、三叉神经节和结状神经节的分布。结果显示 :1.原位杂交 :在三种感觉神经节中 ,95 %左右的神经节细胞为 P2 X3m RNA阳性 ,中、小型神经节细胞的杂交信号一般要比大型的神经节细胞强一些。 2 .免疫组织化学 :免疫组织化学结果与原位杂交结果基本一致。此外 ,在各神经节内 ,均显示出许多P2 X3免疫阳性神经纤维 ,在足掌表皮也显示许多 P2 X3免疫反应阳性纤维。结果提示 :P2 X3不仅参与机体的痛觉的形成 ,还可能参与其它感觉 ,如本体感觉等的形成     

Expression of Trk receptors in the developing mouse trigeminal ganglion: in vivo evidence for NT-3 activation of TrkA and TrkB in addition to TrkC

Animals lacking neurotrophin-3 (NT-3) are born with deficits in almost all sensory ganglia. Among these, the trigeminal ganglion is missing 70% of the normal number of neurons, a deficit which develops during the major period of neurogenesis between embryonic stages (E) 10.5 and E13.5. In order to identify the mechanisms for this deficit, we used antisera specific for TrkA, TrkB, and TrkC to characterize and compare the expression patterns of each Trk receptor in trigeminal ganglia of wild type and NT-3 mutants between E10.5 and E15.5. Strikingly, TrkA, TrkB, and TrkC proteins appear to be exclusively associated with neurons, not precursors. While some neurons show limited co-expression of Trk receptors at E11.5, by E13. 5 each neuron expresses only one Trk receptor. Neuronal birth dating and cell counts show that in wild-type animals all TrkB- and TrkC-expressing neurons are generated before E11.5, while the majority of TrkA-expressing neurons are generated between E11.5 and E13.5. In mice lacking NT-3, the initial formation of the ganglion, as assessed at E10.5, is similar to that in wild-type animals. At E11.5, however, the number of TrkC-expressing neurons is dramatically reduced and the number of TrkC-immunopositive apoptotic profiles is markedly elevated. By E13.5, TrkC-expressing neurons are virtually eliminated. At E11.5, compared to wild type, the number of TrkB-expressing neurons is also reduced and the number of TrkB immunoreactive apoptotic profiles is increased. TrkA neurons are also reduced in the NT-3 mutants, but the major deficit develops between E12.5 and E13.5 when elevated numbers of TrkA-immunoreactive apoptotic profiles are detected. Normal numbers of TrkA- and TrkB-expressing neurons are seen in a TrkC-deficient mutant. Therefore, our data provide evidence that NT-3 supports the survival of TrkA-, TrkB- and TrkC-expressing neurons in the trigeminal ganglion by activating directly each of these receptors in vivo.     

Carbonic anhydrase enzyme histochemistry of cranial nerve primary sensory afferent neurons in the rat

Hanssons' enzyme histochemical method for the demonstration of carbonic anhydrase has been used to examine primary sensory neurons of cranial nerves in the rat (cochlear ganglion cells excluded). Numerous carbonic anhydrase positive neurons were present in the trigeminal and geniculate ganglia as well as in the mesencephalic trigeminal nucleus. A few carbonic anhydrase positive ganglion cells were found in the nodose ganglion, but none in the petrosal and vestibular ganglia. However, in the latter ganglia, satellite cells surrounding the neurons frequently showed staining for carbonic anhydrase.     

Carbonic anhydrase enzyme histochemistry of cranial nerve primary sensory afferent neurons in the rat

Summary Hansson's enzyme histochemical method for the demonstration of carbonic anhydrase has been used to examine primary sensory neurons of cranial nerves in the rat (cochlear ganglion cells excluded). Numerous carbonic anhydrase positive neurons were present in the trigeminal and geniculate ganglia as well as in the mecencephalic trigeminal nucleus. A few carbonic anhydrase positive ganglion cells were found in the nodose ganglion, but none in the petrosal and vestibular ganglia. However, in the latter ganglia, satellite cells surrounding the neurons frequently showed staining for carbonic anhydrase.     

Pax3-expressing trigeminal placode cells can localize to trunk neural crest sites but are committed to a cutaneous sensory neuron fate

The cutaneous sensory neurons of the ophthalmic lobe of the trigeminal ganglion are derived from two embryonic cell populations, the neural crest and the paired ophthalmic trigeminal (opV) placodes. Pax3 is the earliest known marker of opV placode ectoderm in the chick. Pax3 is also expressed transiently by neural crest cells as they emigrate from the neural tube, and it is reexpressed in neural crest cells as they condense to form dorsal root ganglia and certain cranial ganglia, including the trigeminal ganglion. Here, we examined whether Pax3+ opV placode-derived cells behave like Pax3+ neural crest cells when they are grafted into the trunk. Pax3+ quail opV ectoderm cells associate with host neural crest migratory streams and form Pax3+ neurons that populate the dorsal root and sympathetic ganglia and several ectopic sites, including the ventral root. Pax3 expression is subsequently downregulated, and at E8, all opV ectoderm-derived neurons in all locations are large in diameter, and virtually all express TrkB. At least some of these neurons project to the lateral region of the dorsal horn, and peripheral quail neurites are seen in the dermis, suggesting that they are cutaneous sensory neurons. Hence, although they are able to incorporate into neural crest-derived ganglia in the trunk, Pax3+ opV ectoderm cells are committed to forming cutaneous sensory neurons, their normal fate in the trigeminal ganglion. In contrast, Pax3 is not expressed in neural crest-derived neurons in the dorsal root and trigeminal ganglia at any stage, suggesting either that Pax3 is expressed in glial cells or that it is completely downregulated before neuronal differentiation. Since Pax3 is maintained in opV placode-derived neurons for some considerable time after neuronal differentiation, these data suggest that Pax3 may play different roles in opV placode cells and neural crest cells.     

Contributions of placodal and neural crest cells to avian cranial peripheral ganglia

The method of embryonic tissue transplantation was used to confirm the dual origin of avian cranial sensory ganglia, to map precise locations of the anlagen of these sensory neurons, and to identify placodal and neural crest-derived neurons within ganglia. Segments of neural crest or strips of presumptive placodal ectoderm were excised from chick embryos and replaced with homologous tissues from quail embryos, whose cells contain a heterochromatin marker. Placode-derived neurons associated with cranial nerves V, VII, IX, and X are located distal to crest-derived neurons. The generally larger, embryonic placodal neurons are found in the distal portions of both lobes of the trigeminal ganglion, and in the geniculate, petrosal and nodose ganglia. Crest-derived neurons are found in the proximal trigeminal ganglion and in the combined proximal ganglion of cranial nerves IX and X. Neurons in the vestibular and acoustic ganglia of cranial nerve VIII derive from placodal ectoderm with the exception of a few neural crest-derived neurons localized to regions within the vestibular ganglion. Schwann sheath cells and satellite cells associated with all these ganglia originate from neural crest. The ganglionic anlagen are arranged in cranial to caudal sequence from the level of the mesencephalon through the third somite. Presumptive placodal ectoderm for the VIIIth, the Vth, and the VIIth, IXth, and Xth ganglia are located in a medial to lateral fashion during early stages of development reflecting, respectively, the dorsolateral, intermediate, and epibranchial positions of these neurogenic placodes.     

Evidence for Glutamate as a Neuroglial Transmitter within Sensory Ganglia

This study examines key elements of glutamatergic transmission within sensory ganglia of the rat. We show that the soma of primary sensory neurons release glutamate when depolarized. Using acute dissociated mixed neuronal/glia cultures of dorsal root ganglia (DRG) or trigeminal ganglia and a colorimetric assay, we show that when glutamate uptake by satellite glial cells (SGCs) is inhibited, KCl stimulation leads to simultaneous increase of glutamate in the culture medium. With calcium imaging we see that the soma of primary sensory neurons and SGCs respond to AMPA, NMDA, kainate and mGluR agonists, and selective antagonists block this response. Using whole cell patch-clamp technique, inward currents were recorded from small diameter (<30 µm) DRG neurons from intact DRGs (ex-vivo whole ganglion preparation) in response to local application of the above glutamate receptor agonists. Following a chronic constriction injury (CCI) of either the inferior orbital nerve or the sciatic nerve, glutamate expression increases in the trigeminal ganglia and DRG respectively. This increase occurs in neurons of all diameters and is present in the somata of neurons with injured axons as well as in somata of neighboring uninjured neurons. These data provides additional evidence that glutamate can be released within the sensory ganglion, and that the somata of primary sensory neurons as well as SGCs express functional glutamate receptors at their surface. These findings, together with our previous gene knockdown data, suggest that glutamatergic transmission within the ganglion could impact nociceptive threshold.     

Trigeminal ganglion cells cocultured with gut express vasoactive intestinal peptide

The plasticity of neural crest cells for the expression of adrenergic and cholinergic transmitter phenotypes has been well studied. The object of this study was to determine if cells of a sensory ganglion are capable of neuropeptide transmitter plasticity. We studied whether cells of the trigeminal ganglion, which do not express the neuropeptide vasoactive intestinal peptide (VIP) in vivo, would express this peptide when grown with a tissue the gut, that contains large numbers of VIP neurons. Embryonic aneural chick rectum was explanted with the embryonic quail trigeminal ganglion on the chorioallantoic membrane of chick hosts for 7-8 days. The explants were fixed, sectioned, and stained for VIP immunoreactivity (IR), for neurofilament protein immunoreactivity, and for the quail nucleolar marker. In sections of the explants we observed two populations of quail neurons: small (10-13 microns) VIP-IR cells and large (25-32 microns) cells lacking VIP-IR and resembling native trigeminal neurons. Trigeminal ganglia explanted with embryonic heart or trigeminal ganglia explanted alone lacked small VIP-IR cells but contained large VIP-negative neurons. These results show that cells of the trigeminal ganglion grown with the gut can express a neuropeptide they do not express in the absence of the gut or in vivo. Thus the embryonic trigeminal ganglion contains cells that are plastic with respect to neuropeptide expression.     

Transient expression of a Ca2+-activated Cl- current during development of quail sensory neurons

The expression of a calcium-activated chloride current (ICl(Ca)) was studied during the development of the sensory neurons of quail trigeminal ganglia. This current is expressed in 20% of the neurons by the 5th day of embryonic development; it can be found in nearly all neurons by the 7th day and subsequently disappears in half of them. Similar results were obtained with dorsal root ganglion neurons. The disappearance of ICl(Ca) in part of the sensory neurons during development is not due to a selective death of the neurons possessing this current and our results suggest that it is mediated by an interaction of the sensory neurons with their target tissue.     

Embryonic origin of substance P containing neurons in cranial and spinal sensory ganglia of the avian embryo

The ontogeny of the neurons exhibiting substance P-like immunoreactivity (SPLI) was examined in the spinal and cranial sensory ganglia of chick and quail embryos. It was shown that in dorsal root ganglia (DRG) virtually all neuronal somas occupying the mediodorsal (MD) region of the ganglia are SPLI-positive while the larger neurons of the lateroventral (LV) area are SPLI-negative. In the cranial nerve ganglia, both types of neurons coexist in the trigeminal ganglion but with a different distribution: small neurons with SPLI are proximal while large neurons without SPLI occupy the maxillomandibular and ophthalmic lobes. The distal ganglia of nerves VII and IX (i.e., geniculate, petrosal) do not show cell bodies with SPLI in the two species considered. A few of them only (about 12%) are found in the nodose (distal ganglion of nerve X). The proximal ganglia of nerves IX and X (i.e., superior-jugular complex) are composed of small neurons which virtually all exhibit SPLI. Chimaeric cranial sensory ganglia were constructed by grafting the quail hind-brain primordium into chick embryos. Revelation of SPLI was combined with acridine orange staining on the same sections in order to ascertain the placodal (chick host) or neural crest (quail donor) origin of the SP-positive neurons in each type of ganglion. We found that all the neurons showing SPLI are derived from the neural crest in the trigeminal and in the superior and jugular ganglia. In the geniculate, petrosal, and nodose all the neurons are derived from the placodal ectoderm. The small number of SPLI-positive cells of the nodose ganglia are not an exception to this rule. Therefore, generally speaking, the sensory neurons of the cranial ganglia that express the SP phenotype are derived from the crest, with the exception of some neurons present in the nodose of both quail and chick embryos and which are of placodal origin. The vast majority of placode-derived neurons do not have amounts of SP that can be detected under the conditions of the present study.     

Chondrogenic and gliogenic subpopulations of neural crest play distinct roles during the assembly of epibranchial ganglia

In vertebrates, the sensory neurons of the epibranchial (EB) ganglia transmit somatosensory signals from the periphery to the CNS. These ganglia are formed during embryogenesis by the convergence and condensation of two distinct populations of precursors: placode-derived neuroblasts and neural crest- (NC) derived glial precursors. In addition to the gliogenic crest, chondrogenic NC migrates into the pharyngeal arches, which lie in close proximity to the EB placodes and ganglia. Here, we examine the respective roles of these two distinct NC-derived populations during development of the EB ganglia using zebrafish morphant and mutants that lack one or both of these NC populations. Our analyses of mutant and morphant zebrafish that exhibit deficiencies in chondrogenic NC at early stages reveal a distinct requirement for this NC subpopulation during early EB ganglion assembly and segmentation. Furthermore, restoration of wildtype chondrogenic NC in one of these mutants, prdm1a, is sufficient to restore ganglion formation, indicating a specific requirement of the chondrogenic NC for EB ganglia assembly. By contrast, analysis of the sox10 mutant, which lacks gliogenic NC, reveals that the initial assembly of ganglia is not affected. However, during later stages of development, EB ganglia are dispersed in the sox10 mutant, suggesting that glia are required to maintain normal EB ganglion morphology. These results highlight novel roles for two subpopulations of NC cells in the formation and maintenance of EB ganglia: chondrogenic NC promotes the early-stage formation of the developing EB ganglia while glial NC is required for the late-stage maintenance of ganglion morphology.     

E-cadherin expression in a particular subset of sensory neurons.

We found that the dorsal root ganglia (DRG) and trigeminal ganglia of mouse embryos express the E-cadherin cell-cell adhesion molecule and analyzed its expression profile. E-cadherin expression began around Embryonic Day 12 (E12) in these ganglia, thereafter increased, and persisted to the adult stage. This cadherin was expressed by 10 and 30% of DRG neurons in E17 and postnatal animals, respectively, as well as by satellite cells and some Schwann cells. E-cadherin-positive primary sensory fibers terminated only in a narrow region of the dorsal horn of the spinal cord, which was identified as part of lamina II by double-staining for E-cadherin and substance P or somatostatin. This E-cadherin expressing area of the spinal cord extended to part of the trigeminal nucleus in the medulla. These results showed that E-cadherin is expressed in a particular subset of primary sensory neurons which may have specific functional properties. We suggest that this adhesion molecule may play a role in the selective adhesion of sensory neuronal fibers.     

Effects of antibodies to nerve growth factor on intrauterine development of derivatives of cranial neural crest and placode in the guinea pig

Fetal guinea pigs transplacentally exposed to maternal nerve growth factor antibodies in the latter part of gestation show marked depletion of sensory neurons in the trigeminal ganglion. Sensory neurons of the nodose ganglion and spiral ganglion which are derived from placodes, and parasympathetic motor neurons of the ciliary, otic, and sphenopalatine ganglia which are derived, like the bulk of the trigeminal ganglion, from cranial neural crest, are unaffected by the antibodies. Previous studies showed that sensory and some sympathetic derivatives of spinal neural crest are effected but that more peripherally located structures of similar origin are not. The local microenvironment in the fetus appears to alter the NGF requirements of structures derived from the same primordia. The model described provides a useful means of studying the effect of trophic factor inhibition in the natural fetal setting and is free of many potential artifacts of tissue culture. Comparison of the animal results with the pathology of familial dysautonomia indicates that nerve growth factor dysfunction alone does not, in our current state of knowledge, adequately account for the etiology of the disease.     

Wise promotes coalescence of cells of neural crest and placode origins in the trigeminal region during head development

While most cranial ganglia contain neurons of either neural crest or placodal origin, neurons of the trigeminal ganglion derive from both populations. The Wnt signaling pathway is known to be required for the development of neural crest cells and for trigeminal ganglion formation, however, migrating neural crest cells do not express any known Wnt ligands. Here we demonstrate that Wise, a Wnt modulator expressed in the surface ectoderm overlying the trigeminal ganglion, play a role in promoting the assembly of placodal and neural crest cells. When overexpressed in chick, Wise causes delamination of ectodermal cells and attracts migrating neural crest cells. Overexpression of Wise is thus sufficient to ectopically induce ganglion-like structures consisting of both origins. The function of Wise is likely synergized with Wnt6, expressed in an overlapping manner with Wise in the surface ectoderm. Electroporation of morpholino antisense oligonucleotides against Wise and Wnt6 causes decrease in the contact of neural crest cells with the delaminated placode-derived cells. In addition, targeted deletion of Wise in mouse causes phenotypes that can be explained by a decrease in the contribution of neural crest cells to the ophthalmic lobe of the trigeminal ganglion. These data suggest that Wise is able to function cell non-autonomously on neural crest cells and promote trigeminal ganglion formation.