RESUMEN
Sensory circuits in the dorsal spinal cord integrate and transmit multiple cutaneous sensory modalities including the sense of light touch. Here, we identify a population of excitatory interneurons (INs) in the dorsal horn that are important for transmitting innocuous light touch sensation. These neurons express the ROR alpha (RORα) nuclear orphan receptor and are selectively innervated by cutaneous low threshold mechanoreceptors (LTMs). Targeted removal of RORα INs in the dorsal spinal cord leads to a marked reduction in behavioral responsiveness to light touch without affecting responses to noxious and itch stimuli. RORα IN-deficient mice also display a selective deficit in corrective foot movements. This phenotype, together with our demonstration that the RORα INs are innervated by corticospinal and vestibulospinal projection neurons, argues that the RORα INs direct corrective reflex movements by integrating touch information with descending motor commands from the cortex and cerebellum.
Asunto(s)
Mecanotransducción Celular , Vías Nerviosas , Asta Dorsal de la Médula Espinal/metabolismo , Tacto , Animales , Interneuronas/metabolismo , Ratones , Actividad Motora , Neuronas Motoras/metabolismo , Miembro 1 del Grupo F de la Subfamilia 1 de Receptores Nucleares/metabolismo , Asta Dorsal de la Médula Espinal/citología , SinapsisRESUMEN
Pain information processing in the spinal cord has been postulated to rely on nociceptive transmission (T) neurons receiving inputs from nociceptors and Aß mechanoreceptors, with Aß inputs gated through feed-forward activation of spinal inhibitory neurons (INs). Here, we used intersectional genetic manipulations to identify these critical components of pain transduction. Marking and ablating six populations of spinal excitatory and inhibitory neurons, coupled with behavioral and electrophysiological analysis, showed that excitatory neurons expressing somatostatin (SOM) include T-type cells, whose ablation causes loss of mechanical pain. Inhibitory neurons marked by the expression of dynorphin (Dyn) represent INs, which are necessary to gate Aß fibers from activating SOM(+) neurons to evoke pain. Therefore, peripheral mechanical nociceptors and Aß mechanoreceptors, together with spinal SOM(+) excitatory and Dyn(+) inhibitory neurons, form a microcircuit that transmits and gates mechanical pain. PAPERCLIP:
Asunto(s)
Neuronas/fisiología , Dolor/metabolismo , Médula Espinal/fisiología , Animales , Dinorfinas/metabolismo , Mecanorreceptores/metabolismo , Ratones , Percepción del Dolor , Somatostatina/metabolismoRESUMEN
Neural progenitors undergo temporal identity transitions to sequentially generate the neuronal and glial cells that make up the mature brain. Proneural genes have well-characterised roles in promoting neural cell differentiation and subtype specification, but they also regulate the timing of identity transitions through poorly understood mechanisms. Here, we investigated how the highly related proneural genes Neurog1 and Neurog2 interact to control the timing of neocortical neurogenesis. We found that Neurog1 acts in an atypical fashion as it is required to suppress rather than promote neuronal differentiation in early corticogenesis. In Neurog1-/- neocortices, early born neurons differentiate in excess, whereas, in vitro, Neurog1-/- progenitors have a decreased propensity to proliferate and form neurospheres. Instead, Neurog1-/- progenitors preferentially generate neurons, a phenotype restricted to the Neurog2+ progenitor pool. Mechanistically, Neurog1 and Neurog2 heterodimerise, and while Neurog1 and Neurog2 individually promote neurogenesis, misexpression together blocks this effect. Finally, Neurog1 is also required to induce the expression of neurogenic factors (Dll1 and Hes5) and to repress the expression of neuronal differentiation genes (Fezf2 and Neurod6). Neurog1 thus employs different mechanisms to temper the pace of early neocortical neurogenesis.
Asunto(s)
Factores de Transcripción con Motivo Hélice-Asa-Hélice Básico/metabolismo , Neocórtex/embriología , Neocórtex/metabolismo , Proteínas del Tejido Nervioso/metabolismo , Neurogénesis , Neuronas/metabolismo , Animales , Factores de Transcripción con Motivo Hélice-Asa-Hélice Básico/genética , Diferenciación Celular/genética , Proliferación Celular/genética , Autorrenovación de las Células/genética , Embrión de Mamíferos/citología , Regulación del Desarrollo de la Expresión Génica , Ratones Transgénicos , Proteínas del Tejido Nervioso/genética , Células-Madre Neurales/citología , Células-Madre Neurales/metabolismo , Neurogénesis/genética , Neuroglía/citología , Neuroglía/metabolismo , Neuronas/citología , Unión Proteica , Factores de Tiempo , Transcripción GenéticaRESUMEN
Mechanical hypersensitivity is a debilitating symptom for millions of chronic pain patients. It exists in distinct forms, including brush-evoked dynamic and filament-evoked punctate hypersensitivities. We reduced dynamic mechanical hypersensitivity induced by nerve injury or inflammation in mice by ablating a group of adult spinal neurons defined by developmental co-expression of VGLUT3 and Lbx1 (VT3Lbx1 neurons): the mice lost brush-evoked nocifensive responses and conditional place aversion. Electrophysiological recordings show that VT3Lbx1 neurons form morphine-resistant polysynaptic pathways relaying inputs from low-threshold Aß mechanoreceptors to lamina I output neurons. The subset of somatostatin-lineage neurons preserved in VT3Lbx1-neuron-ablated mice is largely sufficient to mediate morphine-sensitive and morphine-resistant forms of von Frey filament-evoked punctate mechanical hypersensitivity. Furthermore, acute silencing of VT3Lbx1 neurons attenuated pre-established dynamic mechanical hypersensitivity induced by nerve injury, suggesting that these neurons may be a cellular target for treating this form of neuropathic pain.
Asunto(s)
Sistemas de Transporte de Aminoácidos Acídicos/fisiología , Neuronas/fisiología , Médula Espinal/fisiología , Tacto/fisiología , Potenciales de Acción/efectos de los fármacos , Potenciales de Acción/fisiología , Sistemas de Transporte de Aminoácidos Acídicos/biosíntesis , Sistemas de Transporte de Aminoácidos Acídicos/genética , Animales , Reacción de Prevención/fisiología , Clozapina/farmacología , Toxina Diftérica/farmacología , Femenino , Técnicas de Sustitución del Gen , Factor de Crecimiento Similar a EGF de Unión a Heparina/genética , Hiperalgesia/fisiopatología , Masculino , Ratones , Ratones Transgénicos , Morfina/farmacología , Proteínas Musculares/biosíntesis , Fibras Nerviosas Amielínicas/fisiología , Vías Nerviosas/efectos de los fármacos , Vías Nerviosas/fisiología , Neuronas/efectos de los fármacos , Neuronas/metabolismo , Dimensión del Dolor/efectos de los fármacos , Somatostatina/fisiología , Médula Espinal/efectos de los fármacosRESUMEN
V1 and V2b interneurons (INs) are essential for the production of an alternating flexor-extensor motor output. Using a tripartite genetic system to selectively ablate either V1 or V2b INs in the caudal spinal cord and assess their specific functions in awake behaving animals, we find that V1 and V2b INs function in an opposing manner to control flexor-extensor-driven movements. Ablation of V1 INs results in limb hyperflexion, suggesting that V1 IN-derived inhibition is needed for proper extension movements of the limb. The loss of V2b INs results in hindlimb hyperextension and a delay in the transition from stance phase to swing phase, demonstrating V2b INs are required for the timely initiation and execution of limb flexion movements. Our findings also reveal a bias in the innervation of flexor- and extensor-related motor neurons by V1 and V2b INs that likely contributes to their differential actions on flexion-extension movements.
Asunto(s)
Interneuronas/fisiología , Actividad Motora , Médula Espinal/citología , Animales , Animales Modificados Genéticamente , RatonesRESUMEN
Light mechanical stimulation of hairy skin can induce a form of itch known as mechanical itch. This itch sensation is normally suppressed by inputs from mechanoreceptors; however, in many forms of chronic itch, including alloknesis, this gating mechanism is lost. Here we demonstrate that a population of spinal inhibitory interneurons that are defined by the expression of neuropeptide Y::Cre (NPY::Cre) act to gate mechanical itch. Mice in which dorsal NPY::Cre-derived neurons are selectively ablated or silenced develop mechanical itch without an increase in sensitivity to chemical itch or pain. This chronic itch state is histamine-independent and is transmitted independently of neurons that express the gastrin-releasing peptide receptor. Thus, our studies reveal a dedicated spinal cord inhibitory pathway that gates the transmission of mechanical itch.
Asunto(s)
Interneuronas/fisiología , Mecanotransducción Celular/fisiología , Inhibición Neural , Prurito/fisiopatología , Médula Espinal/fisiología , Transmisión Sináptica , Potenciales de Acción , Animales , Cabello/fisiología , Mecanorreceptores/fisiología , Mecanotransducción Celular/genética , Ratones , Ratones Transgénicos , Neuropéptido Y/genética , Neuropéptido Y/fisiología , Piel/inervaciónRESUMEN
Reciprocal activation of flexor and extensor muscles constitutes the fundamental mechanism that tetrapod vertebrates use for locomotion and limb-driven reflex behaviors. This aspect of motor coordination is controlled by inhibitory neurons in the spinal cord; however, the identity of the spinal interneurons that serve this function is not known. Here, we show that the production of an alternating flexor-extensor motor rhythm depends on the composite activities of two classes of ventrally located inhibitory neurons, V1 and V2b interneurons (INs). Abrogating V1 and V2b IN-derived neurotransmission in the isolated spinal cord results in a synchronous pattern of L2 flexor-related and L5 extensor-related locomotor activity. Mice lacking V1 and V2b inhibition are unable to articulate their limb joints and display marked deficits in limb-driven reflex movements. Taken together, these findings identify V1- and V2b-derived neurons as the core interneuronal components of the limb central pattern generator (CPG) that coordinate flexor-extensor motor activity.
Asunto(s)
Extremidades/fisiología , Interneuronas/fisiología , Locomoción/fisiología , Actividad Motora/fisiología , Inhibición Neural/fisiología , Reflejo/fisiología , Potenciales de Acción/efectos de los fármacos , Potenciales de Acción/genética , Potenciales de Acción/fisiología , Animales , Animales Recién Nacidos , Toxina del Cólera/metabolismo , Embrión de Mamíferos , Lateralidad Funcional/efectos de los fármacos , Lateralidad Funcional/genética , Locomoción/efectos de los fármacos , Locomoción/genética , Ratones , Ratones Transgénicos , Actividad Motora/efectos de los fármacos , Actividad Motora/genética , Músculo Esquelético/citología , Músculo Esquelético/efectos de los fármacos , Músculo Esquelético/fisiología , Mutación/genética , Inhibición Neural/efectos de los fármacos , Inhibición Neural/genética , Neurotransmisores/farmacología , Reflejo/efectos de los fármacos , Médula Espinal/citología , Cola (estructura animal)/inervaciónRESUMEN
Simple motor behaviors such as locomotion and respiration involve rhythmic and coordinated muscle movements that are generated by central pattern generator (CPG) networks in the spinal cord and hindbrain. These CPG networks produce measurable behavioral outputs and thus represent ideal model systems for studying the operational principles that the nervous system uses to produce specific behaviors. Recent advances in our understanding of the transcriptional code that controls neuronal development have provided an entry point into identifying and targeting distinct neuronal populations that make up locomotor CPG networks in the spinal cord. This has spurred the development of new genetic approaches to dissect and manipulate neuronal networks both in the spinal cord and hindbrain. Here we discuss how the advent of molecular genetics together with anatomical and physiological methods has begun to revolutionize studies of the neuronal networks controlling rhythmic motor behaviors in mice.
Asunto(s)
Locomoción/genética , Locomoción/fisiología , Red Nerviosa/anatomía & histología , Red Nerviosa/fisiología , Periodicidad , Animales , Encéfalo/anatomía & histología , Encéfalo/fisiología , Diferenciación Celular/fisiología , Interneuronas/fisiología , Ratones , Médula Espinal/anatomía & histología , Médula Espinal/fisiología , Células Madre/fisiología , Factores de Transcripción/metabolismoRESUMEN
We showed previously that the proneural genes Neurogenin1 (Ngn1) and Ngn2 are required to specify the phenotypes of early- and not late-born neurons in the neocortex, acting in part through repression of Mash1, a third cortically expressed proneural gene. The precise timing of Ngn1/2 specification activity was unexpected given these genes are expressed throughout cortical development, prompting us to search for a later function. Here we reveal that Ngn2 and Mash1 are expressed in a dynamic fashion, acquiring a cell cycle-biased, nonoverlapping distribution, with preferential expression in prospective basal progenitors, during mid corticogenesis. We also identified a new function for Ngn2 during this latter period, demonstrating that it is required to regulate the transit of cortical progenitors from the ventricular zone (VZ) to the subventricular zone. Notably, Ngn2 regulates progenitor maturation at least in part through repression of Mash1 as misexpression of Mash1 strongly enhanced progenitor cell exit from the VZ. Significantly, the ability of Mash1 to promote progenitor cell maturation occurred independently of its ability to respecify cortical cells and is thus a novel function for Mash1. Taken together, these data support a model whereby Ngn2 and Mash1 function together to regulate the zonal distribution of progenitors in the developing neocortex.
Asunto(s)
Factores de Transcripción con Motivo Hélice-Asa-Hélice Básico/metabolismo , Corteza Cerebral/citología , Corteza Cerebral/embriología , Proteínas del Tejido Nervioso/metabolismo , Neuronas/citología , Células Madre/citología , Envejecimiento/patología , Envejecimiento/fisiología , Animales , Agregación Celular , Diferenciación Celular , Movimiento Celular , Células Cultivadas , Técnicas In Vitro , Masculino , Ratones , Neuronas/fisiología , Organogénesis/fisiología , Células Madre/fisiologíaRESUMEN
Progenitors in the telencephalic subventricular zone (SVZ) remain mitotically active throughout life, and produce different cell types at embryonic, postnatal and adult stages. Here we show that Mash1, an important proneural gene in the embryonic telencephalon, is broadly expressed in the postnatal SVZ, in progenitors for both neuronal and oligodendrocyte lineages. Moreover, Mash1 is required at birth for the generation of a large fraction of neuronal and oligodendrocyte precursors from the olfactory bulb. Clonal analysis in culture and transplantation experiments in postnatal brain demonstrate that this phenotype reflects a cell-autonomous function of Mash1 in specification of these two lineages. The conservation of Mash1 function in the postnatal SVZ suggests that the same transcription mechanisms operate throughout life to specify cell fates in this structure, and that the profound changes in the cell types produced reflect changes in the signalling environment of the SVZ.
Asunto(s)
Encéfalo/citología , Proteínas de Unión al ADN/metabolismo , Neuroglía/citología , Neuronas/citología , Factores de Transcripción/metabolismo , Animales , Animales Recién Nacidos , Factores de Transcripción con Motivo Hélice-Asa-Hélice Básico , Trasplante de Tejido Encefálico , Bromodesoxiuridina/metabolismo , Diferenciación Celular , Linaje de la Célula , Células Cultivadas , Técnicas de Cocultivo , Cruzamientos Genéticos , Proteínas de Unión al ADN/genética , Heterocigoto , Inmunohistoquímica , Hibridación in Situ , Operón Lac , Ratones , Ratones Mutantes , Mutación , Bulbo Olfatorio/citología , Células Madre/fisiología , Telencéfalo/citología , Telencéfalo/embriología , Telencéfalo/trasplante , Factores de Transcripción/genética , Factores de Transcripción/fisiología , Trasplante HeterotópicoRESUMEN
Neurogenin (Ngn) 1 and Ngn2 encode basic-helix-loop-helix transcription factors expressed in the developing neocortex. Like other proneural genes, Ngns participate in the specification of neural fates and neuronal identities, but downstream effectors remain poorly defined. We set out to identify Ngn2 effectors in the cortex using a subtractive hybridization screen and identified several regionally expressed genes that were misregulated in Ngn2 and Ngn1;Ngn2 mutants. Included were genes down-regulated in germinal zone progenitors (e.g., Nlgn1, Unc5H4, and Dcc) and in postmitotic neurons in the cortical plate (e.g., Bhlhb5 and NFIB) and subplate (e.g., Mef2c, srGAP3, and protocadherin 9). Further analysis revealed that Ngn2 mutant subplate neurons were misspecified and that thalamocortical afferents (TCAs) that normally target this layer instead inappropriately projected towards the germinal zone. Strikingly, EphA5 and Sema3c, which encode repulsive guidance cues, were down-regulated in the Ngn2 and Ngn1;Ngn2 mutant germinal zones, providing a possible molecular basis for axonal targeting defects. Thus, we identified several new components of the differentiation cascade(s) activated downstream of Ngn1 and Ngn2 and provided novel insights into a new developmental process controlled by these proneural genes. Further analysis of the genes isolated in our screen should provide a fertile basis for understanding the molecular mechanisms underlying corticogenesis.
Asunto(s)
Neocórtex/embriología , Neocórtex/metabolismo , Proteínas del Tejido Nervioso/genética , Proteínas del Tejido Nervioso/metabolismo , Animales , Axones/ultraestructura , Factores de Transcripción con Motivo Hélice-Asa-Hélice Básico , Tipificación del Cuerpo , Diferenciación Celular , Regulación del Desarrollo de la Expresión Génica , Biblioteca de Genes , Marcadores Genéticos , Hibridación in Situ , Ratones , Ratones Noqueados , Ratones Mutantes , Ratones Transgénicos , Modelos Neurológicos , Proteínas del Tejido Nervioso/deficiencia , Neuronas/citología , Neuronas/metabolismo , Factores de Transcripción/deficiencia , Factores de Transcripción/genética , Factores de Transcripción/metabolismoRESUMEN
Neocortical projection neurons, which segregate into six cortical layers according to their birthdate, have diverse morphologies, axonal projections and molecular profiles, yet they share a common cortical regional identity and glutamatergic neurotransmission phenotype. Here we demonstrate that distinct genetic programs operate at different stages of corticogenesis to specify the properties shared by all neocortical neurons. Ngn1 and Ngn2 are required to specify the cortical (regional), glutamatergic (neurotransmitter) and laminar (temporal) characters of early-born (lower-layer) neurons, while simultaneously repressing an alternative subcortical, GABAergic neuronal phenotype. Subsequently, later-born (upper-layer) cortical neurons are specified in an Ngn-independent manner, requiring instead the synergistic activities of Pax6 and Tlx, which also control a binary choice between cortical/glutamatergic and subcortical/GABAergic fates. Our study thus reveals an unanticipated heterogeneity in the genetic mechanisms specifying the identity of neocortical projection neurons.