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Integrated single-cell analysis reveals coupled molecular gradient and functional subnetworks in the thalamic reticular nucleus

ABSTRACT: The thalamic reticular nucleus (TRN), the major source of thalamic inhibition, is known to regulate thalamocortical interactions critical for sensory processing, attention and cognition. TRN dysfunction has been linked to sensory abnormality, attention deficit and sleep disturbance across multiple neurodevelopmental disorders. Currently, little is known about the organizational principles underlying its divergent functions. We performed an integrative study linking single-cell molecular and electrophysiological features of the mouse TRN to connectivity and systems-level function. We found that TRN cellular heterogeneity is characterized by a transcriptomic gradient of two negatively correlated gene expression profiles, each containing hundreds of genes. Neurons in the extremes of this transcriptomic gradient express mutually exclusive markers, exhibit core/shell-like anatomical structure and have distinct electrophysiological properties. The two TRN subpopulations make differential connections to the functionally distinct first-order and higher order thalamic nuclei to form molecularly defined TRN-thalamus subnetworks. Selective perturbation of the two subnetworks in vivo revealed their differential role in regulating sleep. Taken together, our study provides a comprehensive atlas for TRN neurons at the single-cell resolution, and links molecularly defined subnetworks to the functional organization of the thalamo-cortical circuits.

ORGANISM(S): Mus musculus

PROVIDER: GSE145273 | GEO | 2020/07/22

REPOSITORIES: GEO

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Project description:“Dysbiosis" of the maternal gut microbiome, in response to environmental challenges such as infection, altered diet and stress during pregnancy, has been increasingly associated with abnormalities in offspring brain function and behavior. However, whether the maternal gut microbiome regulates neurodevelopment in the absence of environmental challenge remains unclear. In addition, whether the maternal microbiome exerts such influences during critical periods of embryonic brain development is poorly understood. Here we investigate how depletion, and selective reconstitution, of the maternal gut microbiome influences fetal neurodevelopment in mice. Embryos from antibiotic-treated and germ-free dams exhibit widespread transcriptomic alterations in the fetal brain relative to conventionally-colonized controls, with reduced expression of several genes involved in axonogenesis. In addition, embryos from microbiome-depleted mothers exhibit deficient thalamocortical axons and impaired thalamic axon outgrowth in response to cell-extrinsic guidance cues and growth factors. Consistent with the importance of fetal thalamocortical axonogenesis for shaping neural circuits for sensory processing, restricted depletion of the maternal microbiome from pre-conception through mid-gestation yields offspring that exhibit tactile hyposensitivity in select sensorimotor behavioral tasks. Gnotobiotic colonization of antibiotic-treated dams with a limited consortium of spore-forming bacteria indigenous to the gut microbiome prevents abnormalities in fetal brain gene expression, fetal thalamocortical axonogenesis and adult tactile sensory behavior associated with maternal microbiome depletion. Metabolomic profiling reveals that the maternal microbiota regulates levels of numerous small molecules in the maternal serum as well as the brains of fetal offspring. Select microbiota-dependent metabolites – trimethylamine N-oxide, 5-aminovalerate, imidazole propionate, and hippurate – sufficiently promote axon outgrowth from fetal thalamic explants. Moreover, maternal supplementation with the metabolites during early gestation abrogates deficiencies in fetal thalamocortical axons and prevents abnormalities in tactile sensory behavior in offspring from microbiome-depleted dams. Altogether, these findings reveal that the maternal gut microbiome promotes fetal thalamocortical axonogenesis and select tactile sensory behaviors in mice, likely by signaling of microbially modulated metabolites to neurons in the developing brain.

Project description:Unified visual perception relies on the integration of bottom-up and top-down inputs in the primary visual cortex (V1), with top-down inputs known to provide behavior-related modulation on visual processing. However, the organization of top-down inputs in V1 remains unclear. Here, using optogenetics-assisted circuit mapping, we characterized how multiple top-down inputs from higher-order cortical and thalamic areas engage excitatory and inhibitory neurons in V1. Systematic layer- and cell-type-specific profiling of the innervation properties of top-down inputs ultimately revealed that each top-down input employs a unique laminar profile when innervating V1. These profiles partially overlap in superficial layers, bypass layer 4 (L4), and clearly segregate upon reaching deep layers. Specifically, inputs from the medial secondary visual cortex (V2M) and anterior cingulate cortex (ACA) preferentially activate L6 neurons, while inputs from the ventrolateral orbitofrontal cortex (ORBvl) and lateral posterior thalamic nucleus (LP) activate L5 neurons. Having defined the inputs, we conducted independent optogenetic activation studies and discovered that ORBvl and LP inputs selectively activate two types of pyramidal neurons (Pyrs) in L5: Pyr <-- ORBvl and Pyr <-- LP neurons, each with specific electrophysiological properties and gene expression profiles. Retrograde mapping subsequently revealed that Pyr <-- ORBvl neurons preferentially innervate subcortical areas and Pyr <-- LP neurons innervate cortical areas, indicating parallel processing of ORBvl and LP inputs in Pyr-type-specific subnetworks. Further, we found mutual inhibition between these two subnetworks, as LP inputs indirectly inhibit Pyr <-- ORBvl neurons and ORBvl inputs inhibit Pyr <-- LP neurons through local inhibitory neurons. Our study thus deepens understanding of the neuronal mechanisms involved in top-down modulation of visual processing by providing a valuable resource characterizing the layer- and cell-type-specific organization of top-down inputs in V1 and by revealing that L5 Pyr-type-specific subnetworks engage in parallel processing of corticocortical and thalamocortical top-down inputs.

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Integrated single-cell analysis reveals coupled molecular gradient and functional subnetworks in the thalamic reticular nucleus

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