RESUMEN
We have found a previously unreported precerebellar nucleus located among the emerging fibers of the motor root of the trigeminal nerve in the mouse, which we have called the interfascicular trigeminal nucleus (IF5). This nucleus had previously been named the tensor tympani part of the motor trigeminal nucleus (5TT) in rodent brain atlases, because it was thought to be a subset of small motor neurons of the motor trigeminal nucleus innervating the tensor tympani muscle. However, following injection of retrograde tracer in the cerebellum, the labeled neurons in IF5 were found to be choline acetyltransferase (ChAT) negative, indicating that they are not motor neurons. The cells of IF5 are strongly labeled in mice from Wnt1Cre and Atoh1 CreER lineage fate mapping, in common with the major precerebellar nuclei that arise from the rhombic lip and that issue mossy fibers. Analysis of sections from mouse Hoxa3, Hoxb1, and Egr2 Cre labeled lineages shows that the neurons of IF5 arise from rhombomeres caudal to rhombomere 4, most likely from rhombomeres 6-8. We conclude that IF5 is a significant precerebellar nucleus in the mouse that shares developmental gene expression characteristics with mossy fiber precerebellar nuclei that arise from the caudal rhombic lip.
Asunto(s)
Vías Eferentes/citología , Vías Eferentes/embriología , Puente/citología , Puente/embriología , Núcleos del Trigémino/citología , Núcleos del Trigémino/embriología , Animales , Factores de Transcripción con Motivo Hélice-Asa-Hélice Básico/genética , Factores de Transcripción con Motivo Hélice-Asa-Hélice Básico/metabolismo , Linaje de la Célula/genética , Cerebelo/citología , Cerebelo/embriología , Cerebelo/fisiología , Colina O-Acetiltransferasa/metabolismo , Proteína 2 de la Respuesta de Crecimiento Precoz/genética , Proteína 2 de la Respuesta de Crecimiento Precoz/metabolismo , Vías Eferentes/fisiología , Femenino , Regulación del Desarrollo de la Expresión Génica/fisiología , Proteínas Fluorescentes Verdes/genética , Proteínas de Homeodominio/genética , Proteínas de Homeodominio/metabolismo , Masculino , Ratones , Ratones Endogámicos C57BL , Ratones Transgénicos , Fibras Nerviosas/fisiología , Trazadores del Tracto Neuronal , Puente/fisiología , Núcleos del Trigémino/fisiología , Proteína Wnt1/genética , Proteína Wnt1/metabolismoRESUMEN
The principal sensory (PrV) nucleus-based trigeminal lemniscus conveys whisker-specific neural patterns to the ventroposteromedial (VPM) nucleus of the thalamus and subsequently to the primary somatosensory cortex. Here we examined the perinatal development of this pathway with carbocyanine dye labeling in embryonic and early postnatal mouse brains. We developed a novel preparation in which the embryonic hindbrain and the diencephalon are flattened out, allowing a birds-eye view of the PrV lemniscus in its entirety. For postnatal brains we used another novel approach by sectioning the brain along an empirically determined oblique horizontal angle, again preserving the trigeminothalamic pathway. PrV neurons are born along the hindbrain ventricular zone and migrate radially for a short distance to coalesce into a nucleus adjacent to the ascending trigeminal tract. During migration of the spindle-shaped cell bodies, slender axonal processes grow along the opposite direction towards the floor plate. As early as embryonic day (E) 11, pioneering axons tipped with large growth cones cross the ventral midline and immediately make a right angle turn. By E13 many PrV axons form fascicles crossing the midline and follow a rostral course. PrV axons reach the midbrain by E15 and the thalamus by E17. While the target recognition and invasion occurs prenatally, organization of PrV axon terminals into whisker-specific rows and patches takes place during the first 4 postnatal (P) days. Initially diffuse and exuberant projections in the VPM at P1 coalesce into row and whisker specific terminal zones by P4.
Asunto(s)
Núcleos del Trigémino/embriología , Núcleos del Trigémino/crecimiento & desarrollo , Animales , Carbocianinas , Diferenciación Celular , Movimiento Celular , Femenino , Procesamiento de Imagen Asistido por Computador , Inmunohistoquímica , Ratones , Ratones Endogámicos C57BL , Vías Nerviosas/citología , Vías Nerviosas/embriología , Embarazo , Terminales Presinápticos/fisiología , Tálamo/anatomía & histología , Tálamo/crecimiento & desarrollo , Proteína 2 de Transporte Vesicular de Glutamato/metabolismoRESUMEN
Both lineages of the modern monotremes have been reported to be capable of electroreception using the trigeminal pathways and it has been argued that electroreception arose in an aquatic platypus-like ancestor of both modern monotreme groups. On the other hand, the trigeminal sensory nuclear complex of the platypus is highly modified for processing tactile and electrosensory information from the bill, whereas the trigeminal sensory nuclear complex of the short-beaked echidna (Tachyglossus aculeatus) is not particularly specialized. If the common ancestor for both platypus and echidna were an electroreceptively and trigeminally specialized aquatic feeder, one would expect the early stages of development of the trigeminal sensory nuclei in both species to show evidence of structural specialization from the outset. To determine whether this is the case, we examined the development of the trigeminal sensory nuclei in the platypus and short-beaked echidna using the Hill and Hubrecht embryological collections. We found that the highly specialized features of the platypus trigeminal sensory nuclei (i.e. the large size of the principal nucleus and oral part of the spinal trigeminal nuclear complex, and the presence of a dorsolateral parvicellular segment in the principal nucleus) appear around the time of hatching in the platypus, but are never seen at any stage in the echidna. Our findings support the proposition that the modern echidna and platypus are derived from a common ancestor with only minimal trigeminal specialization and that the peculiar anatomy of the trigeminal sensory nuclei in the modern platypus emerged in the ornithorhynchids after divergence from the tachyglossids.
Asunto(s)
Evolución Biológica , Ornitorrinco/embriología , Células Receptoras Sensoriales/clasificación , Tachyglossidae/embriología , Núcleos del Trigémino/embriología , Animales , Fenómenos Electrofisiológicos , Vías Nerviosas/embriología , Células Receptoras Sensoriales/fisiologíaRESUMEN
Achieving an appropriate balance between inhibitory and excitatory neuronal fate is critical for development of effective synaptic transmission. However, the molecular mechanisms dictating such phenotypic outcomes are not well understood, especially in the whisker-to-barrel cortex neuraxis, an oft-used model system for revealing developmental mechanisms. In trigeminal nucleus principalis (PrV), the brainstem link in the whisker-barrel pathway, the transcription factor Lmx1b marks glutamatergic cells. In PrV of Lmx1b knockout mice (-/-), initial specification of glutamatergic vs. GABAergic cell fate is normal until embryonic day 14.5. Subsequently, until the day of birth, glutamatergic markers (e.g., VGLUT2) stain significantly fewer PrV neurons, whereas, GABAergic markers (Pax2 and Gad1) stain significantly more PrV cells, notably in Lmx1b null PrV cells. These changes also occurred in Lmx1b/Bax double-/- mice, where PrV cells are rescued from Lmx1b-/- induced apoptosis; thus, effects upon excitatory/inhibitory cell ratios do not reflect a cell death confound. Electroporation-induced ectopic expression of Lmx1b in an array of sites decreases numbers of neurons that express GABAergic markers, but increases VGLUT2+ cell numbers or stain intensity. Thus, Lmx1b is not involved in the initial specification of glutamatergic cell fate, but is essential for maintaining a glutamatergic phenotype. Other experiments suggest that Lmx1b acts to suppress Pax2, a promoter of GABAergic cell fate, in a cell-autonomous manner, which may be a mechanism for maintaining a functional balance of glutamatergic and GABAergic cell types in development.
Asunto(s)
Regulación del Desarrollo de la Expresión Génica/genética , Ácido Glutámico/metabolismo , Proteínas con Homeodominio LIM/fisiología , Neuronas/metabolismo , Factores de Transcripción/fisiología , Núcleos del Trigémino/citología , Ácido gamma-Aminobutírico/metabolismo , Animales , Animales Recién Nacidos , Recuento de Células , Electroporación , Embrión de Mamíferos , Glutamato Descarboxilasa/metabolismo , Proteínas Fluorescentes Verdes/genética , Proteínas Fluorescentes Verdes/metabolismo , Proteínas con Homeodominio LIM/deficiencia , Ratones , Ratones Endogámicos C57BL , Ratones Transgénicos , Neuronas/clasificación , Factor de Transcripción PAX2/metabolismo , Factores de Transcripción/deficiencia , Núcleos del Trigémino/embriología , Proteína 2 de Transporte Vesicular de Glutamato/metabolismo , Proteínas del Transporte Vesicular de Aminoácidos Inhibidores/metabolismo , Proteína X Asociada a bcl-2/deficiencia , Proteína X Asociada a bcl-2/genéticaRESUMEN
Little is known of transcriptional mechanisms underlying the development of the trigeminal (V) principal sensory nucleus (PrV), the brainstem nucleus responsible for the development of the whisker-to-barrel cortex pathway. Lmx1b, a LIM homeodomain transcription factor, is expressed in embryonic PrV. In Lmx1b knockout ((-)(/)(-)) mice, V primary afferent projections to PrV are normal, albeit reduced in number, whereas the PrV-thalamic lemniscal pathway is sparse and develops late. Excess cell death occurs in the embryonic Lmx1b(-)(/)(-) PrV, but not in Lmx1b/Bax double null mutants. Expression of Drg11, a downstream transcription factor essential for PrV development and pattern formation, is abolished in PrV, but not in the V ganglion. Consequently, whisker patterns fail to develop in PrV by birth. Rescued PrV cells in Lmx1b/Bax double (-)(/)(-)s failed to rescue whisker-related PrV pattern formation. Thus, Lmx1b and Drg11 may act in the same genetic signaling pathway that is essential for PrV pattern formation.
Asunto(s)
Tipificación del Cuerpo/genética , Proteínas de Homeodominio/fisiología , Factores de Transcripción/fisiología , Núcleos del Trigémino/embriología , Vibrisas/inervación , Vías Aferentes/fisiología , Animales , Animales Recién Nacidos , Muerte Celular/genética , Proteínas de Homeodominio/genética , Proteínas con Homeodominio LIM , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Proteínas del Tejido Nervioso/deficiencia , Proteínas del Tejido Nervioso/genética , Tálamo/citología , Tálamo/embriología , Factores de Transcripción/deficiencia , Factores de Transcripción/genética , Ganglio del Trigémino/citología , Ganglio del Trigémino/embriología , Núcleos del Trigémino/citología , Núcleos del Trigémino/metabolismo , Proteína X Asociada a bcl-2/deficienciaRESUMEN
The purpose of this study was to demonstrate a micro-computed tomography (CT) method for observations of the mouse embryo. At 13.0 days post-coitum, mouse embryos were fixed in 4% paraformaldehyde for 24 h and stained en bloc by osmium tetroxide overnight. The embryos were then embedded in paraffin using standard methods for 24 h. Specimens were analyzed by micro-CT and image processing was performed. Organs containing nervous and blood systems could be viewed as a result of different osmium-staining densities. The trigeminal ganglion was imaged using three-dimensional techniques. Observation of the embryo was possible by micro-CT with osmium tetroxide staining.
Asunto(s)
Embrión de Mamíferos/anatomía & histología , Desarrollo Embrionario , Imagenología Tridimensional/veterinaria , Núcleos del Trigémino/embriología , Microtomografía por Rayos X/veterinaria , Anatomía Transversal/métodos , Animales , Vasos Sanguíneos/embriología , Desarrollo Fetal , Ratones , Organogénesis , Núcleos del Trigémino/anatomía & histologíaRESUMEN
Morphometric and histological studies of the pons were performed by light microscopy in 28 cases of externally normal human fetuses ranging from 90 to 246 mm in crown-rump length (CRL) and from 13 to 28 weeks of gestation. The brainstems of fetuses were embedded in celloidin or paraffin, and transverse sections were prepared. The pons was divided into two regions at the most ventral margin of the medial lemniscus at the level of the motor trigeminal nucleus. The relationships between the total dorsoventral length, ventral length, and dorsal length of the pons versus CRL and gestational ages were calculated, and empiric formulas were fitted. It was found that the ventral portion increased in size more rapidly than the dorsal portion. The proportion of the ventral portion in the total dorsoventral length was constitutively higher than that of the dorsal portion in the present range of CRL. In the pontine nuclei, from 235 mm in the CRL, some large cells with rich cytoplasm, pale nuclei, and a distinct nucleolus appeared on the dorsal side of the pyramidal tract. According to Weigert stained preparations, the first myelinated fibers in each motor root of the trigeminal, abducent, and facial nerves were recognized at 130-140 mm in CRL and the medial lemniscus at 230-235 mm.
Asunto(s)
Biología Evolutiva/métodos , Feto/anatomía & histología , Puente/embriología , Tronco Encefálico/anatomía & histología , Tronco Encefálico/embriología , Diferenciación Celular , Largo Cráneo-Cadera , Femenino , Edad Gestacional , Humanos , Masculino , Vaina de Mielina/metabolismo , Neuronas/metabolismo , Puente/anatomía & histología , Embarazo , Factores de Tiempo , Núcleos del Trigémino/anatomía & histología , Núcleos del Trigémino/embriologíaRESUMEN
The mesencephalic trigeminal nucleus (Me5) innervates muscle spindles and is responsible for receiving and transmitting proprioception from the oro-facial region. Molecular mechanisms underlying the development of the Me5 are poorly understood. Evidence is provided here that transcription factor Drg11 is required for Me5 development. Drg11 was expressed in the Me5 cells of the embryonic and early postnatal mouse brains, and the Me5 cells were absent in Drg11-/- mice at birth. The absence of the Me5 cells in Drg11-/- mice appeared to be caused by increased cell death in the Me5 during embryonic development. In postnatal Drg11-/- mice, Me5 cell innervation of masseter muscle spindles was undetectable, while robust trigeminal motoneuron innervation of masseter muscle fibers was detected. The postnatal body weight of Drg11-/- mice was notably less than that of wild-type mice, and this might result, in part, from disruption of the oro-facial proprioceptive afferent pathway. Taken together, our results demonstrate an essential role for Drg11 in the development of the Me5.
Asunto(s)
Regulación del Desarrollo de la Expresión Génica , Proteínas de Homeodominio/metabolismo , Proteínas del Tejido Nervioso/metabolismo , Factores de Transcripción/metabolismo , Núcleos del Trigémino , Factores de Edad , Animales , Animales Recién Nacidos , Peso Corporal/genética , Embrión de Mamíferos , Regulación del Desarrollo de la Expresión Génica/genética , Proteínas de Homeodominio/genética , Hibridación in Situ/métodos , Etiquetado Corte-Fin in Situ/métodos , Ratones , Ratones Noqueados , Proteínas del Tejido Nervioso/genética , Parvalbúminas/metabolismo , Factores de Transcripción/genética , Núcleos del Trigémino/embriología , Núcleos del Trigémino/crecimiento & desarrollo , Núcleos del Trigémino/metabolismoAsunto(s)
Vías Aferentes/embriología , Cara/inervación , Proteínas de Homeodominio/fisiología , Rombencéfalo/embriología , Sensación/fisiología , Corteza Somatosensorial/embriología , Nervio Trigémino/embriología , Vibrisas/embriología , Vías Aferentes/fisiología , Animales , Mapeo Encefálico , Complejo IV de Transporte de Electrones/análisis , Desarrollo Embrionario/genética , Cara/embriología , Humanos , Nervio Mandibular/embriología , Nervio Mandibular/fisiología , Ratones , Ratones Noqueados , Proteínas del Tejido Nervioso/análisis , Propiocepción/fisiología , Corteza Somatosensorial/fisiología , Núcleos Talámicos/embriología , Núcleos Talámicos/fisiología , Nervio Trigémino/fisiología , Núcleos del Trigémino/embriología , Núcleos del Trigémino/fisiología , Núcleo Espinal del Trigémino/embriología , Núcleo Espinal del Trigémino/fisiología , Vibrisas/fisiologíaRESUMEN
The occurrence of Ret and GFRalpha-1 receptors is shown by immunohistochemistry in the human trigeminal sensory system at pre-, postnatal and adult age. Receptor-labeled neurons occur in both trigeminal ganglion and mesencephalic nucleus. In adult trigeminal ganglion, about 75% of Ret- and 65% of GFRalpha-1-labeled neurons are small- and medium-sized. The proportion of Ret+ and GFRalpha-1+ trigeminal ganglion neurons in the adult is about 25 and 60%, respectively. The majority of Ret+ are double labeled for GFRalpha-1 and glial cell line-derived neurotrophic factor (GDNF). Most of the GFRalpha-1+ cells contain GDNF and about 50% of them contain Ret. Triple labeling shows many Ret+/GDNF+/GFRalpha-1+ neurons, but also a number of Ret-/GDNF+/GFRalpha-1+ and Ret+/GDNF-/GFRalpha-1+ cells. Both Ret+ and GFRalpha-1+ neuronal subpopulations overlap with that containing calcitonin gene-related peptide. Ret+ pericellular basket-like nerve fibers occur in the adult trigeminal ganglion. Centrally, immunoreactivity is restricted to the spinal nucleus pars caudalis and pars interpolaris and to the mesencephalic nucleus. In adult specimens, Ret+ nerve fibers and puncta gather in the inner substantia gelatinosa. Ret+ neurons occur in the spinal nucleus and are more frequent in newborn than in adult subjects. Central GFRalpha-1+-labeled neurons and punctate elements are sparse. These findings support the involvement of GDNF and possibly other cognate ligands in the trophism of human trigeminal primary sensory neurons from prenatal life to adulthood, indicating a selective commitment to cells devoted to protopathic and proprioceptive sensory transmission. They also support the possibility that receptor molecules other than Ret could be active in transducing the ligand signal.
Asunto(s)
Receptores del Factor Neurotrófico Derivado de la Línea Celular Glial/metabolismo , Proteínas Proto-Oncogénicas c-ret/metabolismo , Ganglio del Trigémino/metabolismo , Núcleos del Trigémino/metabolismo , Adulto , Anciano , Anciano de 80 o más Años , Péptido Relacionado con Gen de Calcitonina/metabolismo , Feto/metabolismo , Factor Neurotrófico Derivado de la Línea Celular Glial/metabolismo , Humanos , Inmunohistoquímica , Lactante , Recién Nacido , Persona de Mediana Edad , Ganglio del Trigémino/embriología , Ganglio del Trigémino/crecimiento & desarrollo , Núcleos del Trigémino/embriología , Núcleos del Trigémino/crecimiento & desarrolloRESUMEN
The distribution of motor and proprioceptive neurons was investigated in the trigeminal nervous system of wild-type and Brn-3a knockout mice at embryonic day 18.5 and postnatal day 0. We found that the trigeminal motor nucleus (Mo5) contained abundant motoneurons in wild-type (mean number +/- SD per section = 128 +/- 22, range = 93-167) and knockout (mean number +/- SD per section = 121 +/- 23, range = 75-158) mice and that the cell size of Mo5 neurons was similar between these mice (wild-type, mean +/- SD = 165 +/- 59 microm2, range = 65-326 microm2; knockout, mean +/- SD = 167 +/- 59 microm2, range = 71-327 microm2). Mo5 neurons were immunoreactive for calcitonin gene-related peptide and such immunoreactive neurons were abundant in both wild-type and mutant mice. In the mesencephalic tract nucleus (Mes5) of wild-type mice, many proprioceptors (mean number +/- SD per section = 56 +/- 19, range = 27-85) that contained parvalbumin immunoreactivity were also observed. In knockout mice, however, Mes5 neurons could not be detected. The area of brainstems which normally contained the Mes5 was devoid of parvalbumin-immunoreactive proprioceptors. The present study suggests that Brn-3a is required for the development of proprioceptors but not motoneurons in the trigeminal nervous system.
Asunto(s)
Proteínas de Unión al ADN/fisiología , Regulación del Desarrollo de la Expresión Génica/fisiología , Neuronas Aferentes/metabolismo , Factores de Transcripción/fisiología , Núcleos del Trigémino/citología , Animales , Péptido Relacionado con Gen de Calcitonina/genética , Péptido Relacionado con Gen de Calcitonina/metabolismo , Recuento de Células/métodos , Tamaño de la Célula , Proteínas de Unión al ADN/deficiencia , Embrión de Mamíferos , Inmunohistoquímica/métodos , Mesencéfalo/citología , Mesencéfalo/embriología , Mesencéfalo/metabolismo , Ratones , Ratones Noqueados , Neuronas Motoras/metabolismo , Parvalbúminas/genética , Parvalbúminas/metabolismo , Factor de Transcripción Brn-3 , Factor de Transcripción Brn-3A , Factores de Transcripción/deficiencia , Núcleos del Trigémino/embriología , Núcleos del Trigémino/metabolismoRESUMEN
The normal development of the mesencephalic trigeminal nucleus (MesV) of the white Peking duck (Anas platyrhynchos) was studied from the 9th day of incubation until hatching and during adulthood. In the early days of embryonic development, neurons are present in the posterior commissure and in the mesenchymal tissue outside the leptomeninges in addition to those in the tectal commissure (TC) and in the optic tectum. Following the internucleosomal cleavage of DNA, a massive loss of neurons in the MesV starts in the 11-day embryo and continues until the 15th day of incubation. On the 16th day, the nucleus consists of a numerically larger medial division located in the TC and a smaller lateral division within the stratum griseum periventriculare as is found in the adult animal. The programmed cell death occurring in the MesV is discussed herein and correlated with the analogous apoptotic phenomena observed in the trigeminal motor nucleus.
Asunto(s)
Apoptosis , Mesencéfalo/embriología , Núcleos del Trigémino/embriología , Envejecimiento , Animales , Patos , Mesencéfalo/anatomía & histología , Mesencéfalo/citología , Núcleos del Trigémino/citologíaRESUMEN
Little is known about the molecular mechanisms underlying the formation of the principal sensory nucleus (PrV) of the trigeminal nerve, a major relay station for somatotopic pattern formation in the trigeminal system. Here, we show that mice lacking Drg11, a homeodomain transcription factor, exhibit defects within the PrV, which include an aberrant distribution of Drg11-/- cells, altered expression of a molecular marker, unusual projections of primary afferents from trigeminal ganglion cells, and, subsequently, increased cell death. In addition, surviving PrV cells exhibit delayed and more spatially restricted ascending projections to the ventral posterior medial nucleus of the thalamus (VPm). These early embryonic abnormalities in the PrV lead to the failure to develop whisker-related patterns in the PrV, VPm, and somatosensory cortex. By contrast, somatotopic patterns exist in the spinal trigeminal subnuclei interpolaris (SpVi) and subnuclei caudalis (SpVc) and the dorsal column nucleus-based lemniscal and cortical pathway. Thus, the deficits in the trigeminal system of Drg11-/- mice are specific to the PrV. Our results demonstrate that Drg11 is essential for proper cellular differentiation and, subsequently, for the formation of the whisker-related lemniscal and cortical structures.
Asunto(s)
Proteínas de Homeodominio/fisiología , Proteínas del Tejido Nervioso/fisiología , Factores de Transcripción/fisiología , Núcleos del Trigémino/embriología , Vibrisas/inervación , Vías Aferentes , Animales , Muerte Celular , Proteínas de Unión al ADN/metabolismo , Complejo IV de Transporte de Electrones/análisis , Proteínas de Homeodominio/genética , Ratones , Ratones Noqueados , Proteínas del Tejido Nervioso/genética , Tálamo/citología , Tálamo/embriología , Transactivadores/metabolismo , Factores de Transcripción/genética , Ganglio del Trigémino/citología , Ganglio del Trigémino/embriología , Núcleos del Trigémino/citología , Núcleos del Trigémino/metabolismoRESUMEN
The developing mesencephalic trigeminal nucleus (nucleus of the fifth cranial nerve; Mes5) is composed of four neuron populations: 1) the medial group, located at the tectal commissure; 2) the lateral group distributed along the optic tectum hemispheres; 3) a group outside the neural tube; and 4) a population located at the posterior commissure. The present work aims to elucidate the site of appearance, temporal evolution, and spatial distribution of the four Mes5 populations during development. According to detailed qualitative observations Mes5 neurons appear as a primitive unique population along a thin dorsal medial band of the mesencephalon. According to quantitative analyses (changes in cell density along defined reference axes performed as a function of time and space), the definitive spatial pattern of Mes5 neurons results from a process of differential cell movements along the tangential plane of the tectal hemispheres. Radial migration does not have a relevant developmental role. Segregation of medial and lateral group populations depends on the intensity of the lateral displacements. The mesenchymal population appears as an outsider subset of neurons that migrate from the cephalic third of the neural tube dorsal midregion to the mesenchymal compartment. This process, together with the intensive lateral displacements that the insider subset undergoes, contributes to the disappearance of this transient population. We cannot find evidence indicating that neural crest-derived precursors enter the neural tube and differentiate into Mes5 neurons. Our results can be better interpreted in terms of the notion that a dorsal neural tube progenitor cell population behaves as precursor of both migrating peripheral descendants (neural crest) and intrinsic neurons (Mes5).
Asunto(s)
Embrión de Pollo/fisiología , Neuronas/citología , Colículos Superiores/embriología , Núcleos del Trigémino/embriología , Animales , Mesencéfalo/embriología , Colículos Superiores/citología , Factores de Tiempo , Núcleos del Trigémino/citologíaRESUMEN
Axons that carry information from the sensory periphery first elongate unbranched and form precisely ordered tracts within the CNS. Later, they begin collateralizing into their proper targets and form terminal arbors. Target-derived factors that govern sensory axon elongation and branching-arborization are not well understood. Here we report that Slit2 is a major player in branching-arborization of central trigeminal axons in the brainstem. Embryonic trigeminal axons initially develop unbranched as they form the trigeminal tract within the lateral brainstem; later, they emit collateral branches into the brainstem trigeminal nuclei and form terminal arbors therein. In whole-mount explant cultures of this pathway, embryonic day 15 (E15) rat central trigeminal axons retain their unbranched growth within the tract, whereas E17 trigeminal axons show branching and arborization in the brainstem trigeminal nuclei, much like that seen in vivo. Similar observations were made in E13 and E15 mouse embryos. We cocultured Slit2-expressing tissues or cells with the whole-mount explant cultures of the central trigeminal pathway derived from embryonic rats or mice. When central trigeminal axons are exposed to ectopic Slit2 during their elongation phase, they show robust and premature branching and arborization. Blocking available Slit2 reverses this effect on axon growth. Spatiotemporal expression of Slit2 and Robo receptor mRNAs within the brainstem trigeminal nuclei and the trigeminal ganglion during elongation and branching-arborization further corroborates our experimental results.
Asunto(s)
Axones/metabolismo , Tronco Encefálico/metabolismo , Proteínas del Tejido Nervioso/metabolismo , Neuronas Aferentes/metabolismo , Animales , Axones/efectos de los fármacos , Tronco Encefálico/citología , Tronco Encefálico/embriología , Células Cultivadas , Plexo Coroideo/citología , Plexo Coroideo/metabolismo , Técnicas de Cocultivo , Regulación del Desarrollo de la Expresión Génica , Humanos , Péptidos y Proteínas de Señalización Intercelular , Riñón/citología , Riñón/metabolismo , Ratones , Proteínas del Tejido Nervioso/genética , Proteínas del Tejido Nervioso/farmacología , Neuronas Aferentes/citología , ARN Mensajero/biosíntesis , Ratas , Receptores Inmunológicos/genética , Receptores Inmunológicos/metabolismo , Transfección , Núcleos del Trigémino/citología , Núcleos del Trigémino/embriología , Núcleos del Trigémino/metabolismo , Proteínas RoundaboutRESUMEN
The cells of the mesencephalic trigeminal nucleus (MTN) are the proprioceptive sensory neurons that innervate the jaw muscles. Interestingly, their evolution is generally thought to have been concomitant with that of the jaws. They are also the first born neurons of the mesencephalon, and their axons pioneer some of the major tracts within the brain. The cells of the MTN are also paradoxical in being the only group of intramedullary primary sensory neurons in amniotes. However, we know little about the early development of these important neurons, and we have analysed this here. To study the earliest stages of MTN development, we have used a battery of neural crest markers to try and pinpoint the progenitors of the MTN. We find that, contrary to current perceptions, the progenitors of the MTN are not highlighted by these markers, suggesting that they are not neural crest derived. However, the cells of the MTN are marked by means of their expression of Brn-3a. This gene labels cells that arise either side of the dorsal midline, extending rostrally from the isthmus across the roof of the mesencephalon. We have further demonstrated that the MTN develops under the influence of the Fgf-8 secreted by the isthmus. Ectopic Fgf-8 application promotes MTN development, whereas inhibiting Fgf-8 function in vivo drastically affects MTN development.
Asunto(s)
Mesencéfalo/embriología , Núcleos del Trigémino/embriología , Animales , Biomarcadores/análisis , División Celular/efectos de los fármacos , División Celular/fisiología , Embrión de Pollo/citología , Embrión de Pollo/fisiología , Factor 8 de Crecimiento de Fibroblastos , Factores de Crecimiento de Fibroblastos/farmacología , Factores de Crecimiento de Fibroblastos/fisiología , Cresta Neural/citología , Cresta Neural/metabolismo , Neuronas/fisiología , Células Madre/metabolismo , Núcleos del Trigémino/citologíaRESUMEN
We examined whether the postsynaptic responses of cells in the principal sensory nucleus of the trigeminal nerve (PrV) are subject to long-term changes in synaptic strength, and if such changes were correlated the whisker-specific patterning during and just after the critical period for pattern formation. We used an in vitro brainstem preparation in which the trigeminal ganglion (TG) and PrV remained attached. By electrically activating TG afferents, we evoked large-amplitude extracellular field potentials. These responses were postsynaptic in origin and blocked by the glutamate antagonist, DNQX. At P1, a time when barrelettes are consolidating, high frequency stimulation of their afferents led to an immediate (<1 min) and long-lasting (> or =90 min) reduction (35%) in the amplitude of the evoked response. At P3-7, when the pattern of barrelettes have stabilized, the same form of tetanus led to an immediate and long-lasting increase (40%) in the amplitude of the response. Both forms of synaptic plasticity were mediated by the activation of L-type Ca(2+) channels. Application of the L-type channel blocker, nitrendipine, led to a complete blockade of any the tetanus induced changes. These associative processes may regulate the patterning and maintenance of whisker-specific patterns in the brainstem trigeminal nuclei.
Asunto(s)
Plasticidad Neuronal/fisiología , Núcleos del Trigémino/embriología , Núcleos del Trigémino/fisiología , 2-Amino-5-fosfonovalerato/farmacología , Potenciales de Acción/efectos de los fármacos , Potenciales de Acción/fisiología , Animales , Bloqueadores de los Canales de Calcio/farmacología , Canales de Calcio Tipo L/fisiología , Estimulación Eléctrica , Potenciales Evocados/efectos de los fármacos , Potenciales Evocados/fisiología , Antagonistas de Aminoácidos Excitadores/farmacología , Potenciación a Largo Plazo/fisiología , Inhibición Neural/fisiología , Nitrendipino/farmacología , Quinoxalinas/farmacología , Ratas , Sinapsis/fisiologíaRESUMEN
Nerve growth factor (NGF) and related neurotrophins induce differential axon growth patterns from embryonic sensory neurons (Lentz et al. [1999] J. Neurosci. 19:1038-1048; Ulupinar et al. [2000a] J. Comp. Neurol 425:622-630). In wholemount explant cultures of embryonic rat trigeminal ganglion and brainstem or in dissociated cell cultures of the trigeminal ganglion, exogenous supply of NGF leads to axonal elongation, whereas neurotrophin-3 (NT-3) treatment leads to short branching and arborization (Ulupinar et al. [2000a] J. Comp. Neurol. 425:622-630). Axonal responses to neurotrophins might be mediated via the Rho GTPases. To investigate this possibility, we prepared wholemount trigeminal pathway cultures from E15 rats. We infected the ganglia with recombinant vaccinia viruses that express GFP-tagged dominant negative Rac, Rho, or constitutively active Rac or treated the cultures with lysophosphatitic acid (LPA) to activate Rho. We then examined axonal responses to NGF by use of the lipophilic tracer DiI. Rac activity induced longer axonal growth from the central trigeminal tract, whereas the dominant negative construct of Rac eliminated NGF-induced axon outgrowth. Rho activity also significantly reduced, and the Rho dominant negative construct increased, axon growth from the trigeminal tract. Similar alterations in axonal responses to NT-3 and brain-derived neurotrophic factor were also noted. Our results demonstrate that Rho GTPases play a major role in neurotrophin-induced axonal differentiation of embryonic trigeminal axons.
Asunto(s)
Vectores Genéticos/fisiología , Conos de Crecimiento/ultraestructura , Factores de Crecimiento Nervioso/farmacología , Neuronas Aferentes/citología , Ganglio del Trigémino/embriología , Proteínas de Unión al GTP rho/metabolismo , Vías Aferentes/efectos de los fármacos , Vías Aferentes/embriología , Vías Aferentes/enzimología , Animales , Factor Neurotrófico Derivado del Encéfalo/metabolismo , Factor Neurotrófico Derivado del Encéfalo/farmacología , Carbocianinas/farmacocinética , Diferenciación Celular/efectos de los fármacos , Diferenciación Celular/fisiología , Tamaño de la Célula/efectos de los fármacos , Tamaño de la Célula/fisiología , Feto , Colorantes Fluorescentes/farmacología , Regulación del Desarrollo de la Expresión Génica/efectos de los fármacos , Regulación del Desarrollo de la Expresión Génica/fisiología , Conos de Crecimiento/efectos de los fármacos , Conos de Crecimiento/enzimología , Inmunohistoquímica , Lisofosfolípidos/farmacología , Factor de Crecimiento Nervioso/metabolismo , Factor de Crecimiento Nervioso/farmacología , Factores de Crecimiento Nervioso/metabolismo , Neuronas Aferentes/efectos de los fármacos , Neuronas Aferentes/enzimología , Neurotrofina 3/metabolismo , Neurotrofina 3/farmacología , Ratas , Ratas Sprague-Dawley , Transfección , Ganglio del Trigémino/efectos de los fármacos , Ganglio del Trigémino/enzimología , Núcleos del Trigémino/efectos de los fármacos , Núcleos del Trigémino/embriología , Núcleos del Trigémino/enzimología , Virus Vaccinia/genética , Proteínas de Unión al GTP rac/efectos de los fármacos , Proteínas de Unión al GTP rac/genética , Proteínas de Unión al GTP rac/metabolismo , Proteínas de Unión al GTP rho/efectos de los fármacos , Proteínas de Unión al GTP rho/genéticaRESUMEN
The Krox-20 null mutation results in a loss of rhombomeres 3 and 5, which give rise to neurons that are essential to oral motor behaviors. Thus, the Krox-20 null mutant is an excellent model to investigate the development of oral motor circuitry. Our morphological examination of embryonic and neonatal Krox-20 null mutants revealed that a significant reduction of anterior digastric and mylohyoid muscles, the primary jaw openers, occurs between embryonic days 15 and 19. There are no gross morphological alterations in other masticatory muscles. These findings demonstrate that Krox-20 expression is critical for the normal development of the primary jaw opener musculature and they help explain previous studies documenting a reduction in jaw opening in Krox-20 null mutants. Since jaw opening is the power stroke of suckling behavior, our data help explain the reduction of colostrum/milk ingestion in Krox-20 null mutant neonates.
Asunto(s)
Proteínas de Unión al ADN/genética , Músculos Masticadores/embriología , Factores de Transcripción/genética , Animales , Animales Lactantes , Atrofia , Proteína 2 de la Respuesta de Crecimiento Precoz , Femenino , Masculino , Músculos Masticadores/inervación , Músculos Masticadores/patología , Ratones , Ratones Endogámicos C57BL , Ratones Mutantes , Neuronas Motoras/citología , Mutación , Embarazo , Conducta en la Lactancia , Nervio Trigémino/citología , Nervio Trigémino/embriología , Núcleos del Trigémino/citología , Núcleos del Trigémino/embriologíaRESUMEN
A novel in vitro preparation, consisting of the rat brainstem with the trigeminal ganglion attached, has been used to study the anatomical and functional development of the trigeminal nucleus from embryonic day (E)13 to postnatal day (P)6. Neurobiotin injections into the trigeminal ganglion showed that primary afferents had reached the trigeminal tract by E13 and had grown simple, mainly unbranched, collaterals into all levels of the nucleus by E15. By E17, these collaterals were extensively branched, with occasional boutons present. Patches of intense neurobiotin-labelled terminals, corresponding to whisker-related patterns, were first seen at E20 and became clearer over the next few days. Terminal arbours at this stage were relatively localized and densely branched, with many boutons. Responses from the trigeminal nucleus were recorded with suction electrodes, following stimulation of the trigeminal ganglion. Recordings from the main sensory nucleus showed a postsynaptic response was first present at E15. At E16, bath application of AP5 and DNQX showed that the response contained both NMDA and AMPA components, with NMDA predominating (75%). The NMDA : AMPA ratio remained high until P1, then gradually declined to 50% by P6. The postsynaptic response was also reduced by bath application of bicuculline, indicating the presence of a GABAA-mediated excitatory component. GABAergic excitation was present at all ages but was maximal from E20 to P1, the age at which whisker-related patterns are developing. It is hypothesized that both GABAergic excitation and NMDA receptor activation play a role in the consolidation of trigeminal connections, and are thus important in the development of whisker-related patterns.