Classic cadherin expressions balance postnatal neuronal positioning and dendrite dynamics to elaborate the specific cytoarchitecture of the mouse cortical area

The distribution of Cdh20 mRNA demarcates somatotopic subregions and subpopulations of spiny projection neurons in the rat dorsolateral striatum

The dorsolateral striatum (DLS) of rodents is functionally subdivided into somatotopic subregions that represent each body part along both the dorsoventral and anteroposterior (A-P) axes and play crucial roles in sensorimotor functions via corticostriatal pathways. However, little is known about the spatial gene expression patterns and heterogeneity of spiny projection neurons (SPNs) within somatotopic subregions. Here, we show that the cell adhesion molecule gene Cdh20, which encodes a Type II cadherin, is expressed in discrete subregions covering the inner orofacial area and part of the forelimb area in the ventral domain of the DLS (v-DLS) in rats. Cdh20-expressing cells were localized in the v-DLS at the intermediate level of the striatum along the A-P axis and could be classified as direct-pathway SPNs or indirect-pathway SPNs. Unexpectedly, comprehensive analysis revealed that Cdh20 is expressed in SPNs in the rat DLS but not in the mouse DLS or the ferret putamen (Pu). Our observations reveal that Cdh20 expression demarcates somatotopic subregions and subpopulations of SPNs specifically in the rat DLS and suggest divergent regulation of genes differentially expressed in the v-DLS and Pu among mammals.

Fundamental Elements in Autism: From Neurogenesis and Neurite Growth to Synaptic Plasticity

Autism spectrum disorder (ASD) is a set of neurodevelopmental disorders with a high prevalence and impact on society. ASDs are characterized by deficits in both social behavior and cognitive function. There is a strong genetic basis underlying ASDs that is highly heterogeneous; however, multiple studies have highlighted the involvement of key processes, including neurogenesis, neurite growth, synaptogenesis and synaptic plasticity in the pathophysiology of neurodevelopmental disorders. In this review article, we focus on the major genes and signaling pathways implicated in ASD and discuss the cellular, molecular and functional studies that have shed light on common dysregulated pathways using in vitro, in vivo and human evidence.

Highlights

Autism spectrum disorder (ASD) has a prevalence of 1 in 68 children in the United States.

ASDs are highly heterogeneous in their genetic basis.

ASDs share common features at the cellular and molecular levels in the brain.

Most ASD genes are implicated in neurogenesis, structural maturation, synaptogenesis and function.

mGluR5 Exerts Cell-Autonomous Influences on the Functional and Anatomical Development of Layer IV Cortical Neurons in the Mouse Primary Somatosensory Cortex

Glutamate neurotransmission refines synaptic connections to establish the precise neural circuits underlying sensory processing. Deleting metabotropic glutamate receptor 5 (mGluR5) in mice perturbs cortical somatosensory map formation in the primary somatosensory (S1) cortex at both functional and anatomical levels. To examine the cell-autonomous influences of mGluR5 signaling in the morphological and functional development of layer IV spiny stellate glutamatergic neurons receiving sensory input, mGluR5 genetic mosaic mice were generated through in utero electroporation. In the S1 cortex of these mosaic brains, we found that most wild-type neurons were located in barrel rings encircling thalamocortical axon (TCA) clusters while mGluR5 knock-out (KO) neurons were placed in the septal area, the cell-sparse region separating barrels. These KO neurons often displayed a symmetrical dendritic morphology with increased dendritic complexity, in contrast to the polarized pattern of wild-type neurons. The dendritic spine density of mGluR5 KO spiny stellate neurons was significantly higher than in wild-type neurons. Whole-cell electrophysiological recordings detected a significant increase in the frequencies of spontaneous and miniature excitatory postsynaptic events in mGluR5 KO neurons compared with neighboring wild-type neurons. Our mosaic analysis provides strong evidence supporting the cell-autonomous influence of mGluR5 signaling on the functional and anatomical development of cortical glutamatergic neurons. Specifically, mGluR5 is required in cortical glutamatergic neurons for the following processes: (1) the placement of cortical glutamatergic neurons close to TCA clusters; (2) the regulation of dendritic complexity and outgrowth toward TCA clusters; (3) spinogenesis; and (4) tuning of excitatory inputs.

SIGNIFICANCE STATEMENT

Glutamatergic transmission plays a critical role in cortical circuit formation. Its dysfunction has been proposed as a core factor in the etiology of many neurological diseases. Here we conducted mosaic analysis to reveal the cell-autonomous role of the metabotropic glutamate receptor 5 (mGluR5). We found that mGluR5 is required for several key steps in wiring up the thalamocortical connections to form the cortical somatosensory map. mGluR5-dependent processes during early postnatal brain development affect the following: (1) placement of activity-directed cortical neurons; (2) regulation of polarized dendritic outgrowth toward thalamocortical axons relaying sensory information, (3) synaptogenesis; and (4) development of functional connectivity in spiny stellate neurons. Perturbing mGluR5 expression could lead to abnormal neuronal circuits, which may contribute to neurological and psychiatric disease.

Impact of thalamocortical input on barrel cortex development

The development of cortical maps requires the balanced interaction between genetically determined programs and input/activity-dependent signals generated spontaneously or triggered from the environment. The somatosensory pathway of mice provides an excellent scenario to study cortical map development because of its highly organized cytoarchitecture, known as the barrel field. This precise organization makes evident even small alterations in the cortical map layout. In this review, we will specially focus on the thalamic factors that control barrel field development. We will summarize the role of thalamic input integration and identity, neurotransmission and spontaneous activity in cortical map formation and early cross-modal plasticity.