RESUMO
Many behaviors require the coordinated actions of somatic and autonomic functions. However, the underlying mechanisms remain elusive. By opto-stimulating different populations of descending spinal projecting neurons (SPNs) in anesthetized mice, we show that stimulation of excitatory SPNs in the rostral ventromedial medulla (rVMM) resulted in a simultaneous increase in somatomotor and sympathetic activities. Conversely, opto-stimulation of rVMM inhibitory SPNs decreased both activities. Anatomically, these SPNs innervate both sympathetic preganglionic neurons and motor-related regions in the spinal cord. Fiber-photometry recording indicated that the activities of rVMM SPNs correlate with different levels of muscle and sympathetic tone during distinct arousal states. Inhibiting rVMM excitatory SPNs reduced basal muscle and sympathetic tone, impairing locomotion initiation and high-speed performance. In contrast, silencing the inhibitory population abolished muscle atonia and sympathetic hypoactivity during rapid eye movement (REM) sleep. Together, these results identify rVMM SPNs as descending spinal projecting pathways controlling the tone of both the somatomotor and sympathetic systems.
Assuntos
Bulbo , Medula Espinal , Sistema Nervoso Simpático , Animais , Masculino , Camundongos , Locomoção/fisiologia , Bulbo/fisiologia , Camundongos Endogâmicos C57BL , Neurônios Motores/fisiologia , Neurônios/fisiologia , Sono REM/fisiologia , Medula Espinal/fisiologia , Sistema Nervoso Simpático/fisiologia , Comportamento Animal , Contagem de Células , Músculo EsqueléticoRESUMO
Numerous well-defined classes of retinal ganglion cells innervate the thalamus to guide image-forming vision, yet the rules governing their convergence and divergence remain unknown. Using two-photon calcium imaging in awake mouse thalamus, we observed a functional arrangement of retinal ganglion cell axonal boutons in which coarse-scale retinotopic ordering gives way to fine-scale organization based on shared preferences for other visual features. Specifically, at the â¼6 µm scale, clusters of boutons from different axons often showed similar preferences for either one or multiple features, including axis and direction of motion, spatial frequency, and changes in luminance. Conversely, individual axons could "de-multiplex" information channels by participating in multiple, functionally distinct bouton clusters. Finally, ultrastructural analyses demonstrated that retinal axonal boutons in a local cluster often target the same dendritic domain. These data suggest that functionally specific convergence and divergence of retinal axons may impart diverse, robust, and often novel feature selectivity to visual thalamus.
Assuntos
Axônios/fisiologia , Retina/fisiologia , Células Ganglionares da Retina/fisiologia , Tálamo/fisiologia , Animais , Análise por Conglomerados , Dendritos/fisiologia , Lógica Fuzzy , Corpos Geniculados/fisiologia , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Movimento (Física) , Neurônios/fisiologia , Terminações Pré-Sinápticas/fisiologia , Visão Ocular , Vias VisuaisRESUMO
How is the picture of the visual scene that the eye encodes represented by neural circuits in the brain? In this issue of Cell, Morgan et al. address this question by forming an ultrastructural "connectome" of the mouse's visual thalamus that depicts individual retinal afferents and every contact these form with target relay cells.
Assuntos
Conectoma , Tálamo , Animais , Encéfalo , Retina , Vias VisuaisRESUMO
Although a number of repair strategies have been shown to promote axon outgrowth following neuronal injury in the mammalian CNS, it remains unclear whether regenerated axons establish functional synapses and support behavior. Here, in both juvenile and adult mice, we show that either PTEN and SOCS3 co-deletion, or co-overexpression of osteopontin (OPN)/insulin-like growth factor 1 (IGF1)/ciliary neurotrophic factor (CNTF), induces regrowth of retinal axons and formation of functional synapses in the superior colliculus (SC) but not significant recovery of visual function. Further analyses suggest that regenerated axons fail to conduct action potentials from the eye to the SC due to lack of myelination. Consistent with this idea, administration of voltage-gated potassium channel blockers restores conduction and results in increased visual acuity. Thus, enhancing both regeneration and conduction effectively improves function after retinal axon injury.
Assuntos
Axônios/fisiologia , Colículos Superiores/fisiologia , 4-Aminopiridina/farmacologia , Animais , Axônios/efeitos dos fármacos , Fator Neurotrófico Ciliar/metabolismo , Fenômenos Eletrofisiológicos , Olho/metabolismo , Fator de Crescimento Insulin-Like I/metabolismo , Camundongos , Bainha de Mielina/metabolismo , Nervo Óptico , Osteopontina/metabolismo , PTEN Fosfo-Hidrolase/metabolismo , Bloqueadores dos Canais de Potássio/farmacologia , Regeneração/efeitos dos fármacos , Proteína 3 Supressora da Sinalização de Citocinas , Proteínas Supressoras da Sinalização de Citocina/metabolismo , SinapsesRESUMO
Mutations in MECP2 give rise to Rett syndrome (RTT), an X-linked neurodevelopmental disorder that results in broad cognitive impairments in females. While the exact etiology of RTT symptoms remains unknown, one possible explanation for its clinical presentation is that loss of MECP2 causes miswiring of neural circuits due to defects in the brain's capacity to respond to changes in neuronal activity and sensory experience. Here, we show that MeCP2 is phosphorylated at four residues in the mouse brain (S86, S274, T308, and S421) in response to neuronal activity, and we generate a quadruple knock-in (QKI) mouse line in which all four activity-dependent sites are mutated to alanines to prevent phosphorylation. QKI mice do not display overt RTT phenotypes or detectable gene expression changes in two brain regions. However, electrophysiological recordings from the retinogeniculate synapse of QKI mice reveal that while synapse elimination is initially normal at P14, it is significantly compromised at P20. Notably, this phenotype is distinct from the synapse refinement defect previously reported for Mecp2 null mice, where synapses initially refine but then regress after the third postnatal week. We thus propose a model in which activity-induced phosphorylation of MeCP2 is critical for the proper timing of retinogeniculate synapse maturation specifically during the early postnatal period.
Assuntos
Proteína 2 de Ligação a Metil-CpG , Síndrome de Rett , Feminino , Camundongos , Animais , Fosforilação , Proteína 2 de Ligação a Metil-CpG/genética , Proteína 2 de Ligação a Metil-CpG/metabolismo , Síndrome de Rett/genética , Síndrome de Rett/metabolismo , Encéfalo/metabolismo , Sinapses/metabolismo , Neurônios/metabolismo , Camundongos Knockout , Modelos Animais de DoençasRESUMO
Current models of somatosensory perception emphasize transmission from primary sensory neurons to the spinal cord and on to the brain1-4. Mental influence on perception is largely assumed to occur locally within the brain. Here we investigate whether sensory inflow through the spinal cord undergoes direct top-down control by the cortex. Although the corticospinal tract (CST) is traditionally viewed as a primary motor pathway5, a subset of corticospinal neurons (CSNs) originating in the primary and secondary somatosensory cortex directly innervate the spinal dorsal horn via CST axons. Either reduction in somatosensory CSN activity or transection of the CST in mice selectively impairs behavioural responses to light touch without altering responses to noxious stimuli. Moreover, such CSN manipulation greatly attenuates tactile allodynia in a model of peripheral neuropathic pain. Tactile stimulation activates somatosensory CSNs, and their corticospinal projections facilitate light-touch-evoked activity of cholecystokinin interneurons in the deep dorsal horn. This touch-driven feed-forward spinal-cortical-spinal sensitization loop is important for the recruitment of spinal nociceptive neurons under tactile allodynia. These results reveal direct cortical modulation of normal and pathological tactile sensory processing in the spinal cord and open up opportunities for new treatments for neuropathic pain.
Assuntos
Vias Neurais/fisiopatologia , Neuralgia/fisiopatologia , Tratos Piramidais/fisiopatologia , Tato/fisiologia , Animais , Axônios , Colecistocinina/metabolismo , Feminino , Membro Posterior/fisiopatologia , Hiperalgesia/patologia , Hiperalgesia/fisiopatologia , Interneurônios/metabolismo , Masculino , Camundongos , Neuralgia/patologia , Nociceptividade/fisiologia , Tratos Piramidais/patologia , Córtex Somatossensorial/patologia , Córtex Somatossensorial/fisiopatologia , Corno Dorsal da Medula Espinal/patologia , Corno Dorsal da Medula Espinal/fisiopatologiaRESUMO
The retinogeniculate synapse transmits information from retinal ganglion cells (RGC) in the eye to thalamocortical relay neurons in the visual thalamus, the dorsal lateral geniculate nucleus (dLGN). Studies in mice have identified genetic markers for distinct classes of RGCs encoding different features of the visual space, facilitating the dissection of RGC subtype-specific physiology and anatomy. In this study, we examine the morphological properties of axon arbors of the BD-RGC class of ON-OFF direction selective cells that, by definition, exhibit a stereotypic dendritic arbor and termination pattern in the retina. We find that axon arbors from the same class of RGCs exhibit variations in their structure based on their target region of the dLGN. Our findings suggest that target regions may influence the morphologic and synaptic properties of their afferent inputs.
Assuntos
Axônios/classificação , Corpos Geniculados/citologia , Plasticidade Neuronal , Células Ganglionares da Retina/citologia , Animais , Axônios/fisiologia , Corpos Geniculados/fisiologia , Camundongos , Células Ganglionares da Retina/fisiologiaRESUMO
To achieve its precise neural connectivity, the developing mammalian nervous system undergoes extensive activity-dependent synapse remodelling. Recently, microglial cells have been shown to be responsible for a portion of synaptic pruning, but the remaining mechanisms remain unknown. Here we report a new role for astrocytes in actively engulfing central nervous system synapses. This process helps to mediate synapse elimination, requires the MEGF10 and MERTK phagocytic pathways, and is strongly dependent on neuronal activity. Developing mice deficient in both astrocyte pathways fail to refine their retinogeniculate connections normally and retain excess functional synapses. Finally, we show that in the adult mouse brain, astrocytes continuously engulf both excitatory and inhibitory synapses. These studies reveal a novel role for astrocytes in mediating synapse elimination in the developing and adult brain, identify MEGF10 and MERTK as critical proteins in the synapse remodelling underlying neural circuit refinement, and have important implications for understanding learning and memory as well as neurological disease processes.
Assuntos
Astrócitos/metabolismo , Proteínas de Membrana/metabolismo , Vias Neurais/metabolismo , Fagocitose , Proteínas Proto-Oncogênicas/metabolismo , Receptores Proteína Tirosina Quinases/metabolismo , Sinapses/metabolismo , Animais , Astrócitos/citologia , Encéfalo/citologia , Técnicas In Vitro , Núcleos Laterais do Tálamo/citologia , Núcleos Laterais do Tálamo/metabolismo , Aprendizagem/fisiologia , Proteínas de Membrana/deficiência , Proteínas de Membrana/genética , Camundongos , Camundongos Transgênicos , Vias Neurais/citologia , Proteínas Proto-Oncogênicas/deficiência , Proteínas Proto-Oncogênicas/genética , Receptores Proteína Tirosina Quinases/deficiência , Receptores Proteína Tirosina Quinases/genética , Retina/fisiologia , c-Mer Tirosina QuinaseRESUMO
The thalamocortical (TC) relay neuron of the dorsoLateral Geniculate Nucleus (dLGN) has borne its imprecise label for many decades in spite of strong evidence that its role in visual processing transcends the implied simplicity of the term "relay". The retinogeniculate synapse is the site of communication between a retinal ganglion cell and a TC neuron of the dLGN. Activation of retinal fibers in the optic tract causes reliable, rapid, and robust postsynaptic potentials that drive postsynaptics spikes in a TC neuron. Cortical and subcortical modulatory systems have been known for decades to regulate retinogeniculate transmission. The dynamic properties that the retinogeniculate synapse itself exhibits during and after developmental refinement further enrich the role of the dLGN in the transmission of the retinal signal. Here we consider the structural and functional substrates for retinogeniculate synaptic transmission and plasticity, and reflect on how the complexity of the retinogeniculate synapse imparts a novel dynamic and influential capacity to subcortical processing of visual information.
Assuntos
Corpos Geniculados/fisiologia , Células Ganglionares da Retina/fisiologia , Sinapses/fisiologia , Vias Visuais/fisiologia , Animais , Potenciais Pós-Sinápticos Excitadores , Técnicas de Patch-Clamp , Transmissão SinápticaRESUMO
Visual circuits mature and are refined by sensory experience. However, significant gaps remain in our understanding how deprivation influences the development of visual acuity in mice. Here, we perform a longitudinal study assessing the effects of chronic deprivation on the development of the mouse subcortical and cortical visual circuits using a combination of behavioral optomotor testing, in vivo visual evoked responses (VEP) and single-unit cortical recordings. As previously reported, orientation tuning was degraded and onset of ocular dominance plasticity was delayed and remained open in chronically deprived mice. Surprisingly, we found that the development of optomotor threshold and VEP acuity can occur in an experience-independent manner, although at a significantly slower rate. Moreover, monocular deprivation elicited amblyopia only during a discrete period of development in the dark. The rate of recovery of optomotor threshold upon exposure of deprived mice to light confirmed a maturational transition regardless of visual input. Together our results revealed a dissociable developmental trajectory for visual receptive-field properties in dark-reared mice suggesting a differential role for spontaneous activity within thalamocortical and intracortical circuits.
Assuntos
Plasticidade Neuronal/fisiologia , Neurônios/fisiologia , Privação Sensorial/fisiologia , Visão Monocular/fisiologia , Acuidade Visual/fisiologia , Córtex Visual/fisiologia , Animais , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Córtex Visual/crescimento & desenvolvimentoRESUMO
Recent studies have demonstrated that vision influences the functional remodeling of the mouse retinogeniculate synapse, the connection between retinal ganglion cells and thalamic relay neurons in the dorsal lateral geniculate nucleus (LGN). Initially, each relay neuron receives a large number of weak retinal inputs. Over a 2- to 3-wk developmental window, the majority of these inputs are eliminated, and the remaining inputs are strengthened. This period of refinement is followed by a critical period when visual experience changes the strength and connectivity of the retinogeniculate synapse. Visual deprivation of mice by dark rearing from postnatal day (P)20 results in a dramatic weakening of synaptic strength and recruitment of additional inputs. In the present study we asked whether experience-dependent plasticity at the retinogeniculate synapse represents a homeostatic response to changing visual environment. We found that visual experience starting at P20 following visual deprivation from birth results in weakening of existing retinal inputs onto relay neurons without significant changes in input number, consistent with homeostatic synaptic scaling of retinal inputs. On the other hand, the recruitment of new inputs to the retinogeniculate synapse requires previous visual experience prior to the critical period. Taken together, these findings suggest that diverse forms of homeostatic plasticity drive experience-dependent remodeling at the retinogeniculate synapse.
Assuntos
Corpos Geniculados/fisiologia , Potenciação de Longa Duração , Sinapses/fisiologia , Vias Visuais/crescimento & desenvolvimento , Animais , Potenciais Pós-Sinápticos Excitadores , Corpos Geniculados/citologia , Corpos Geniculados/crescimento & desenvolvimento , Homeostase , Interneurônios/fisiologia , Camundongos , Camundongos Endogâmicos C57BL , Células Ganglionares da Retina/fisiologia , Vias Visuais/fisiologiaRESUMO
The retinogeniculate synapse, the connection between retinal ganglion cells (RGC) and thalamic relay neurons, undergoes robust changes in connectivity over development. This process of synapse elimination and strengthening of remaining inputs is thought to require synapse specificity. Here we show that glutamate spillover and asynchronous release are prominent features of retinogeniculate synaptic transmission during this period. The immature excitatory postsynaptic currents exhibit a slow decay time course that is sensitive to low-affinity glutamate receptor antagonists and extracellular calcium concentrations, consistent with glutamate spillover. Furthermore, we uncover and characterize a novel, purely spillover-mediated AMPA receptor current from immature relay neurons. The isolation of this current strongly supports the presence of spillover between boutons of different RGCs. In addition, fluorescence measurements of presynaptic calcium transients suggest that prolonged residual calcium contributes to both glutamate spillover and asynchronous release. These data indicate that, during development, far more RGCs contribute to relay neuron firing than would be expected based on predictions from anatomy alone.
Assuntos
Corpos Geniculados/crescimento & desenvolvimento , Neurônios/fisiologia , Células Ganglionares da Retina/fisiologia , Sinapses/fisiologia , Animais , Cálcio/fisiologia , Potenciais Pós-Sinápticos Excitadores , Glutamatos/fisiologia , Camundongos Endogâmicos C57BL , Vias Neurais/fisiologia , Receptores de AMPA/fisiologia , Receptores de N-Metil-D-Aspartato/fisiologiaRESUMO
The cerebral cortex is vital for the processing and perception of sensory stimuli. In the somatosensory axis, information is received primarily by two distinct regions, the primary (S1) and secondary (S2) somatosensory cortices. Top-down circuits stemming from S1 can modulate mechanical and cooling but not heat stimuli such that circuit inhibition causes blunted perception. This suggests that responsiveness to particular somatosensory stimuli occurs in a modality specific fashion and we sought to determine additional cortical substrates. In this work, we identify in a mouse model that inhibition of S2 output increases mechanical and heat, but not cooling sensitivity, in contrast to S1. Combining 2-photon anatomical reconstruction with chemogenetic inhibition of specific S2 circuits, we discover that S2 projections to the secondary motor cortex (M2) govern mechanical and heat sensitivity without affecting motor performance or anxiety. Taken together, we show that S2 is an essential cortical structure that governs mechanical and heat sensitivity.
Assuntos
Temperatura Alta , Córtex Somatossensorial , Camundongos , Animais , Córtex Somatossensorial/fisiologia , Córtex CerebralRESUMO
Over the first few postnatal weeks, extensive remodeling occurs at the developing murine retinogeniculate synapse, the connection between retinal ganglion cells (RGCs) and the visual thalamus. Although numerous studies have described the role of activity in the refinement of this connection, little is known about the mechanisms that regulate glutamate concentration at and around the synapse over development. Here we show that interactions between glutamate transporters and metabotropic glutamate receptors (mGluRs) dynamically control the peak and time course of the excitatory postsynaptic current (EPSC) at the immature synapse. Inhibiting glutamate transporters by bath application of TBOA (DL-threo-ß-benzyloxyaspartic acid) prolonged the decay kinetics of both α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) and N-methyl-D-aspartate receptor (NMDAR) currents at all ages. Moreover, at the immature synapse, TBOA-induced increases in glutamate concentration led to the activation of group II/III mGluRs and a subsequent reduction in neurotransmitter release at RGC terminals. Inhibition of this negative-feedback mechanism resulted in a small but significant increase in peak NMDAR EPSCs during basal stimulation and a substantial increase in the peak with coapplication of TBOA. Activation of mGluRs also shaped the synaptic response during high-frequency trains of stimulation that mimic spontaneous RGC activity. At the mature synapse, however, the group II mGluRs and the group III mGluR7-mediated response are downregulated. Our results suggest that transporters reduce spillover of glutamate, shielding NMDARs and mGluRs from the neurotransmitter. Furthermore, mechanisms of glutamate clearance and release interact dynamically to control the glutamate transient at the developing retinogeniculate synapse.
Assuntos
Sistema X-AG de Transporte de Aminoácidos/metabolismo , Receptores de Glutamato Metabotrópico/metabolismo , Transmissão Sináptica/fisiologia , Tálamo/fisiologia , Vias Visuais/fisiologia , Sistema X-AG de Transporte de Aminoácidos/antagonistas & inibidores , Animais , Antagonistas de Aminoácidos Excitatórios/farmacologia , Potenciais Pós-Sinápticos Excitadores/efeitos dos fármacos , Potenciais Pós-Sinápticos Excitadores/fisiologia , Camundongos , Camundongos Endogâmicos C57BL , Receptores de Glutamato Metabotrópico/antagonistas & inibidores , Transmissão Sináptica/efeitos dos fármacos , Tálamo/efeitos dos fármacos , Vias Visuais/efeitos dos fármacosRESUMO
Retinal ganglion cell (RGC) types relay parallel streams of visual feature information. We hypothesized that neuromodulators might efficiently control which visual information streams reach the cortex by selectively gating transmission from specific RGC axons in the thalamus. Using fiber photometry recordings, we found that optogenetic stimulation of serotonergic axons in primary visual thalamus of awake mice suppressed ongoing and visually evoked calcium activity and glutamate release from RGC boutons. Two-photon calcium imaging revealed that serotonin axon stimulation suppressed RGC boutons that responded strongly to global changes in luminance more than those responding only to local visual stimuli, while the converse was true for suppression induced by increases in arousal. Converging evidence suggests that differential expression of the 5-HT1B receptor on RGC presynaptic terminals, but not differential density of nearby serotonin axons, may contribute to the selective serotonergic gating of specific visual information streams before they can activate thalamocortical neurons.
Assuntos
Corpos Geniculados , Receptor 5-HT1B de Serotonina , Serotonina , Tálamo , Animais , Camundongos , Axônios/fisiologia , Cálcio , Corpos Geniculados/fisiologia , Receptor 5-HT1B de Serotonina/metabolismo , Células Ganglionares da Retina/fisiologia , Serotonina/metabolismo , Tálamo/fisiologiaRESUMO
Mutations in MECP2 give rise to Rett syndrome (RTT), an X-linked neurodevelopmental disorder that results in broad cognitive impairments in females. While the exact etiology of RTT symptoms remains unknown, one possible explanation for its clinical presentation is that loss of MeCP2 causes miswiring of neural circuits due to defects in the brain's capacity to respond to changes in neuronal activity and sensory experience. Here we show that MeCP2 is phosphorylated at four residues in the brain (S86, S274, T308, and S421) in response to neuronal activity, and we generate a quadruple knock-in (QKI) mouse line in which all four activity-dependent sites are mutated to alanines to prevent phosphorylation. QKI mice do not display overt RTT phenotypes or detectable gene expression changes in two brain regions. However, electrophysiological recordings from the retinogeniculate synapse of QKI mice reveal that while synapse elimination is initially normal at P14, it is significantly compromised at P20. Notably, this phenotype is distinct from that previously reported for Mecp2 null mice, where synapses initially refine but then regress after the third postnatal week. We thus propose a model in which activity-induced phosphorylation of MeCP2 is critical for the proper timing of retinogeniculate synapse maturation specifically during the early postnatal period. SIGNIFICANCE STATEMENT: Rett syndrome (RTT) is an X-linked neurodevelopmental disorder that predominantly affects girls. RTT is caused by loss of function mutations in a single gene MeCP2. Girls with RTT develop normally during their first year of life, but then experience neurological abnormalities including breathing and movement difficulties, loss of speech, and seizures. This study investigates the function of the MeCP2 protein in the brain, and how MeCP2 activity is modulated by sensory experience in early life. Evidence is presented that sensory experience affects MeCP2 function, and that this is required for synaptic pruning in the brain. These findings provide insight into MeCP2 function, and clues as to what goes awry in the brain when the function of MeCP2 is disrupted.
RESUMO
The cerebral cortex is vital for the perception and processing of sensory stimuli. In the somatosensory axis, information is received by two distinct regions, the primary (S1) and secondary (S2) somatosensory cortices. Top-down circuits stemming from S1 can modulate mechanical and cooling but not heat stimuli such that circuit inhibition causes blunted mechanical and cooling perception. Using optogenetics and chemogenetics, we find that in contrast to S1, an inhibition of S2 output increases mechanical and heat, but not cooling sensitivity. Combining 2-photon anatomical reconstruction with chemogenetic inhibition of specific S2 circuits, we discover that S2 projections to the secondary motor cortex (M2) govern mechanical and thermal sensitivity without affecting motor or cognitive function. This suggests that while S2, like S1, encodes specific sensory information, that S2 operates through quite distinct neural substrates to modulate responsiveness to particular somatosensory stimuli and that somatosensory cortical encoding occurs in a largely parallel fashion.
RESUMO
The cerebral cortex is vital for the perception and processing of sensory stimuli. In the somatosensory axis, information is received by two distinct regions, the primary (S1) and secondary (S2) somatosensory cortices. Top-down circuits stemming from S1 can modulate mechanical and cooling but not heat stimuli such that circuit inhibition causes blunted mechanical and cooling perception. Using optogenetics and chemogenetics, we find that in contrast to S1, an inhibition of S2 output increases mechanical and heat, but not cooling sensitivity. Combining 2-photon anatomical reconstruction with chemogenetic inhibition of specific S2 circuits, we discover that S2 projections to the secondary motor cortex (M2) govern mechanical and thermal sensitivity without affecting motor or cognitive function. This suggests that while S2, like S1, encodes specific sensory information, that S2 operates through quite distinct neural substrates to modulate responsiveness to particular somatosensory stimuli and that somatosensory cortical encoding occurs in a largely parallel fashion.
RESUMO
In the mouse visual system, multiple types of retinal ganglion cells (RGCs) each encode distinct features of the visual space. A clear understanding of how this information is parsed in their downstream target, the dorsal lateral geniculate nucleus (dLGN), remains elusive. Here, we characterized retinogeniculate connectivity in Cart-IRES2-Cre-D and BD-CreER2 mice, which labels subsets of on-off direction-selective ganglion cells (ooDSGCs) tuned to the vertical directions and to only ventral motion, respectively. Our immunohistochemical, electrophysiological, and optogenetic experiments reveal that only a small fraction (<15%) of thalamocortical (TC) neurons in the dLGN receives primary retinal drive from these subtypes of ooDSGCs. The majority of the functionally identifiable ooDSGC inputs in the dLGN are weak and converge together with inputs from other RGC types. Yet our modeling indicates that this mixing is not random: BD-CreER+ ooDSGC inputs converge less frequently with ooDSGCs tuned to the opposite direction than with non-CART-Cre+ RGC types. Taken together, these results indicate that convergence of distinct information lines in dLGN follows specific rules of organization.
Assuntos
Corpos Geniculados , Vias Visuais , Animais , Corpos Geniculados/fisiologia , Camundongos , Retina , Células Ganglionares da Retina/fisiologia , Tálamo , Vias Visuais/fisiologiaRESUMO
Visual system circuitry, a canonical model system for the study of experience-dependent development, matures before and following the onset of vision. Sensory experience or deprivation during an early critical period results in substantial plasticity and is a crucial factor in establishing the mature circuitry. In adulthood, plasticity has been thought to be reduced or absent. However, recent studies point to the potential for change in neuronal circuits within the mature brain, raising the possibility that aberrant circuit function can be corrected. In this review, we will discuss recent exciting findings in the field of experience-dependent plasticity that advance our understanding of mechanisms underlying the activation, expression, and closure of critical periods in the visual system.