Background Autism involves early brain overgrowth and dysfunction, which is most strongly evident in the prefrontal cortex. As assessed on pathological analysis, an excess of neurons in the prefrontal cortex among children with autism signals a disturbance in prenatal development and may be concomitant with abnormal cell type and laminar development. Methods To systematically examine neocortical architecture during the early years after the onset of autism, we used RNA in situ hybridization with a panel of layer- and cell-type– specific molecular markers to phenotype cortical microstructure. We assayed markers for neurons and glia, along with genes that have been implicated in the risk of autism, in prefrontal, temporal, and occipital neocortical tissue from postmortem samples obtained from children with autism and unaffected children between the ages of 2 and 15 years. Results We observed focal patches of abnormal laminar cytoarchitecture and cortical disorganization of neurons, but not glia, in prefrontal and temporal cortical tissue from 10 of 11 children with autism and from 1 of 11 unaffected children. We observed heterogeneity between cases with respect to cell types that were most abnormal in the patches and the layers that were most affected by the pathological features. No cortical layer was uniformly spared, with the clearest signs of abnormal expression in layers 4 and 5. Three-dimensional reconstruction of layer markers confirmed the focal geometry and size of patches. Conclusions In this small, explorative study, we found focal disruption of cortical laminar architecture in the cortexes of a majority of young children with autism. Our data support a probable dysregulation of layer formation and layer-specific neuronal differentiation at prenatal developmental stages. (Funded by the Simons Foundation and others.)

Several neurodegenerative diseases are typified by intraneuronal ␣-synuclein deposits, synaptic dysfunction, and dementia. While even modest ␣-synuclein elevations can be pathologic, the precise cascade of events induced by excessive ␣-synuclein and eventually culminating in synaptotoxicity is unclear. To elucidate this, we developed a quantitative model system to evaluate evolving ␣-synucleininduced pathologic events with high spatial and temporal resolution, using cultured neurons from brains of transgenic mice overexpressing fluorescent-human-␣-synuclein. Transgenic ␣-synuclein was pathologically altered over time and overexpressing neurons showed striking neurotransmitter release deficits and enlarged synaptic vesicles; a phenotype reminiscent of previous animal models lacking critical presynaptic proteins. Indeed, several endogenous presynaptic proteins involved in exocytosis and endocytosis were undetectable in a subset of transgenic boutons ("vacant synapses") with diminished levels in the remainder, suggesting that such diminutions were triggering the overall synaptic pathology. Similar synaptic protein alterations were also retrospectively seen in human pathologic brains, highlighting potential relevance to human disease. Collectively the data suggest a previously unknown cascade of events where pathologic ␣-synuclein leads to a loss of a number of critical presynaptic proteins, thereby inducing functional synaptic deficits.

Low-light live imaging of F-actin–selective probes, quantitative tools, and super-resolution microscopy reveals a dynamic, formin-dependent deep F-actin cytoskeletal network in axons.

Slow axonal transport conveys cytoskeletal proteins from cell body to axon tip. This transport provides the axon with the architectural elements that are required to generate and maintain its elongate shape and also generates forces within the axon that are necessary for axon growth and navigation. The mechanisms of cytoskeletal transport in axons are unknown. One hypothesis states that cytoskeletal proteins are transported within the axon as polymers. We tested this hypothesis by visualizing individual cytoskeletal polymers in living axons and determining whether they undergo vectorial movement. We focused on neurofilaments in axons of cultured sympathetic neurons because individual neurofilaments in these axons can be visualized by optical microscopy. Cultured sympathetic neurons were infected with recombinant adenovirus containing a construct encoding a fusion protein combining green fluorescent protein (GFP) with the heavy neurofilament protein subunit (NFH). The chimeric GFP-NFH coassembled with endogenous neurofilaments. Time lapse imaging revealed that individual GFP-NFH-labeled neurofilaments undergo vigorous vectorial transport in the axon in both anterograde and retrograde directions but with a strong anterograde bias. NF transport in both directions exhibited a broad spectrum of rates with averages of approximately 0.6-0.7 microm/sec. However, movement was intermittent, with individual neurofilaments pausing during their transit within the axon. Some NFs either moved or paused for the most of the time they were observed, whereas others were intermediate in behavior. On average, neurofilaments spend at most 20% of the time moving and rest of the time paused. These results establish that the slow axonal transport machinery conveys neurofilaments.

SUMMARY The normal functions and pathologic facets of the small presynaptic protein α-synuclein (α-syn) are of exceptional interest. In previous studies, we found that α-syn attenuates synaptic exo/endocytosis [1, 2]; however underlying mechanisms remain unknown. More recent evidence suggests that α-syn exists as metastable multimers and not solely as a natively-unfolded monomer [11-16]. However conformations of α-syn at synapses – its physiologic locale – are unclear; and potential implications of such higher-order conformations to synaptic function is unknown. Exploring α-syn conformations and synaptic function in neurons, we found that α-syn promptly organizes into physiological multimers at synapses. Furthermore, our experiments indicate that α-syn multimers cluster synaptic-vesicles and restrict their motility – suggesting a novel role for these higher-order structures. Supporting this, α-syn mutations that disrupt multimerization also fail to restrict synaptic-vesicle motility or attenuate exo/endocytosis. We propose a model where α-syn multimers cluster synaptic-vesicles, restricting their trafficking and recycling – consequently attenuating neurotransmitter release.