Autism spectrum disorders (ASDs) comprise a range of disorders that share a core of neurobehavioural deficits characterized by widespread abnormalities in social interactions, deficits in communication as well as restricted interests and repetitive behaviours. The neurological basis and circuitry mechanisms underlying these abnormal behaviours are poorly understood. Shank3 is a postsynaptic protein, whose disruption at the genetic level is thought to be responsible for development of 22q13 deletion syndrome (Phelan-McDermid Syndrome) and other non-syndromic ASDs. Here we show that mice with Shank3 gene deletions exhibit self-injurious repetitive grooming and deficits in social interaction. Cellular, electrophysiological and biochemical analyses uncovered defects at striatal synapses and cortico-striatal circuits in Shank3 mutant mice. Our findings demonstrate a critical role for Shank3 in the normal development of neuronal connectivity and establish causality between a disruption in the Shank3 gene and the genesis of autistic like-behaviours in mice.

Obsessive-compulsive disorder (OCD) is an anxiety-spectrum disorder characterized by persistent intrusive thoughts (obsessions) and repetitive actions (compulsions). Dysfunction of cortico-striatothalamo-cortical circuitry is implicated in OCD, though the underlying pathogenic mechanisms are unknown. SAP90/PSD95-associated protein 3 (SAPAP3) is a postsynaptic scaffolding protein at excitatory synapses that is highly expressed in the striatum. Here we show that mice with genetic deletion of SAPAP3 exhibit increased anxiety and compulsive grooming behavior leading to facial hair loss and skin lesions; both behaviors are alleviated by a selective serotonin reuptake inhibitor. Electrophysiological, structural, and biochemical studies of SAPAP3 mutant mice reveal defects in cortico-striatal synapses. Furthermore, lentiviral-mediated selective expression of SAPAP3 in the striatum rescues the synaptic and behavioral defects of SAPAP3 mutant mice. These findings demonstrate a critical role for SAPAP3 at cortico-striatal synapses and emphasize the importance of cortico-striatal circuitry in OCD-like behaviors.

Channelrhodopsin-2 (ChR2) is a light-gated, cation-selective ion channel isolated from the green algae Chlamydomonas reinhardtii. Here, we report the generation of transgenic mice that express a ChR2-YFP fusion protein in the CNS for in vivo activation and mapping of neural circuits. Using focal illumination of the cerebral cortex and olfactory bulb, we demonstrate a highly reproducible, light-dependent activation of neurons and precise control of firing frequency in vivo. To test the feasibility of mapping neural circuits, we exploited the circuitry formed between the olfactory bulb and the piriform cortex in anesthetized mice. In the olfactory bulb, individual mitral cells fired action potentials in response to light, and their firing rate was not influenced by costimulated glomeruli. However, in piriform cortex, the activity of target neurons increased as larger areas of the bulb were illuminated to recruit additional glomeruli. These results support a model of olfactory processing that is dependent upon mitral cell convergence and integration onto cortical cells. More broadly, these findings demonstrate a system for precise manipulation of neural activity in the intact mammalian brain with light and illustrate the use of ChR2 mice in exploring functional connectivity of complex neural circuits in vivo.

To permit rapid optical control of brain activity, we have engineered multiple lines of transgenic mice that express the lightactivated cation channel Channelrhodopsin-2 (ChR2) in subsets of neurons. Illumination of ChR2-positive neurons in brain slices produced photocurrents that generated action potentials within milliseconds and with precisely timed latencies. The number of light-evoked action potentials could be controlled by varying either the amplitude or duration of illumination. Furthermore, the frequency of light-evoked action potentials could be precisely controlled up to 30 Hz. Photostimulation also could evoke synaptic transmission between neurons, and, by scanning with a small laser light spot, we were able to map the spatial distribution of synaptic circuits connecting neurons within living cerebral cortex. We conclude that ChR2 is a genetically based photostimulation technology that permits analysis of neural circuits with high spatial and temporal resolution in transgenic mammals.brain networks ͉ cortical circuitry ͉ synaptic transmission

The thalamic reticular nucleus (TRN), the major source of thalamic inhibition, is known to regulate thalamocortical interactions critical for sensory processing, attention and cognition 1 - 5 . TRN dysfunction has been linked to sensory abnormality, attention deficit and sleep disturbance across multiple neurodevelopmental disorders 6 - 9 . 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.

Many candidate genes are now thought to confer susceptibility to autism spectrum disorder (ASD). Here we review four interrelated complexes, each composed of multiple families of genes that functionally coalesce on common cellular pathways. We illustrate a common thread in the organization of glutamatergic synapses and suggest a link between genes involved in Tuberous Sclerosis Complex, Fragile X syndrome, Angelman syndrome and several synaptic ASD candidate genes. When viewed in this context, progress in deciphering the molecular architecture of cellular protein-protein interactions together with the unraveling of synaptic dysfunction in neural networks may prove pivotal to advancing our understanding of ASDs.

Functional studies on postsynaptic scaffolding proteins at excitatory synapses have revealed a plethora of important roles for synaptic structure and function. In addition, a convergence of recent in vivo functional evidence together with human genetics data strongly suggest that mutations in a variety of these postsynaptic scaffolding proteins may contribute to the etiology of diverse human psychiatric disorders such as schizophrenia, autism spectrum disorders, and obsessive-compulsive spectrum disorders. Here we review the most recent evidence for several key postsynaptic scaffolding protein families and explore how mouse genetics and human genetics have intersected to advance our knowledge concerning the contributions of these important players to complex brain function and dysfunction.

Background: The development of materials with bioregenerative properties is critically important for vital pulp therapies and regenerative endodontic procedures. The aim of this study was to evaluate the cytocompatibility and cytotoxicity of a new endodontic biomaterial, PulpGuard, in comparison with two other biomaterials widely used in endodontic procedures, ProRoot Mineral Trioxide Aggregate (MTA) and Biodentine. Methods: Apical papilla cells (APCs) were isolated from third molars with incomplete rhizogenesis from patients with orthodontic indication for dental extraction. Cultured APCs were incubated for 24, 48, or 72 h with different dilutions of eluates prepared from the three materials. Cellular viability, mobility, and proliferation were assessed in vitro using the Alamar Blue assay and a wound-healing test. The cells were also cultured in direct contact with the surface of each material. These were then analyzed via Scanning Electron Microscopy (SEM), and the surface chemical composition was determined by Energy-Dispersive Spectroscopy (EDS). Results: Cells incubated in the presence of eluates extracted from ProRoot MTA and PulpGuard presented rates of viability comparable to those of control cells; in contrast, undiluted Biodentine eluates induced a significant reduction of cellular viability. The wound-healing assay revealed that eluates from ProRoot MTA and PulpGuard allowed for unhindered cellular migration and proliferation. Cellular adhesion was observed on the surface of all materials tested. Consistent with their disclosed composition, EDS analysis found high relative abundance of calcium in Biodentine and ProRoot MTA and high abundance of silicon in PulpGuard. Significant amounts of zinc and calcium were also present in PulpGuard discs. Concerning solubility, Biodentine and ProRoot MTA presented mild weight loss after eluate extraction, while PulpGuard discs showed significant water uptake. Conclusions: PulpGuard displayed a good in vitro cytocompatibility profile and did not significantly affect the proliferation and migration rates of APCs. Cells cultured in the presence of PulpGuard eluates displayed a similar profile to those cultured with eluates from the widely used endodontic cement ProRoot MTA.