Furthermore, synapsin puncta are closely apposed with PSD95 puncta as would be anticipated from imaging pre- and postsynaptic proteins at single synapses

Furthermore, synapsin puncta are closely apposed with PSD95 puncta as would be anticipated from imaging pre- and postsynaptic proteins at single synapses. high-throughput acquisition of proteomic data from individual cortical synapsesin situ. == Introduction == Rapidly accumulating physiological and genetic evidence establishes that the molecular diversity of synapses extends far beyond that envisioned by traditional classification schemes based solely on neurotransmitter identity. For instance, it is now clear that within each neurotransmitter category (e.g., glutamatergic, GABAergic, cholinergic) there is substantial diversity in the expression of many intrinsic synaptic proteins, including neurotransmitter transporters and receptors (Gupta et al., 2000;Hausser et al., 2000;Staple et al., 2000;Cherubini and Conti, 2001;Craig and Boudin, 2001;Cull-Candy et al., 2001;Grabowski and Black, 2001;Huang and Bergles, 2004;Mody and Pearce, 2004;Grant, 2006). Until synapse molecular diversity is properly fathomed, it is likely to be a troublesome source of variability in physiological and neurodevelopmental experimentation. Conversely, a systematic understanding of synapse diversity (i.e. the synaptome) is likely to provide valuable new perspectives on the organization of synaptic circuitry (i.e. the connectome), its development, plasticity and disorders. It is easy to envision, for instance, that a potential catalog of molecular synapse types (Grant, 2007) would help explorations of the synaptic basis of specific memory or disease processes to focus more fruitfully on specific synapse subpopulations. To place a possible molecular catalog of synapse types on a firm footing, two broad experimental challenges remain. First, it is essential that synapse populations be explored at the single-synapse level. Until recently, the only way to reliably resolve and characterize individual synapses was by way of electron microscopy (EM). While traditionally Rabbit polyclonal to ZNF544 a time-consuming and very volume-limited method, recent advances in EM (Denk and Horstmann, 2004;Harris et al., 2006;Knott et al., 2008;Anderson et al., 2009;Kasthuri and Lichtman, 2010) have greatly improved its throughput, even offering the possibility of detailed neuronal circuit reconstruction. Nonetheless, EM still provides only very limited proteomic discrimination (althoughAnderson et al., 2009, describe a very Furilazole powerful new approach to integrating small-molecule discrimination with EM). Secondly, synapse diversity must be exploredin situ, in ways that retain full fidelity to the intact tissue setting and allow for the acquisition of as much information as possible about circuit context and cellular morphology. Array tomography (AT) is a high-resolution proteomic imaging method (Micheva and Smith, 2007;Micheva et al., 2010) that exploits a combination of light and EM approaches to resolve fine details at the level of synapses across Furilazole large fields of view spanning entire circuits. Of prime significance to the present application, AT allows the immunofluorescence resolution of single synapses within cortical neuropil, where such resolution is highly problematic for other optical methods. Additionally, AT can acquire many more dimensions of immunofluorescence information about single synapses than previous methods (up to 17 in the present work, as compared to the standard immunofluorescence limit of three or four). AT also benefits from greatly improved quantitative reliability, since both staining and imaging are completely independent of depth within a tissue sample. Finally, AT delivers very high experimental throughput: our present automated methods acquire image data at a rate of approximately one million synaptic protein puncta per hour. Such throughput will help advance the analysis of synaptic diversity from the anecdote to the realm of solid bioinformatics. AT thus seems uniquely suited to meet the challenges of exploring the molecular diversity of cortical synapses. Here, we describe array tomographic immunofluorescence methods for the single-synapse analysis of mouse cortex, focusing on the discrimination and analysis of glutamatergic and GABAergic synapses. Toward a goal of identifying every single cortical synapse as unambiguously as possible, we evaluated antibody markers to presynaptic proteins likely to be common to all synapses, such as synaptophysin, bassoon, and synapsin. We find that antibodies to the presynaptic phosphoprotein synapsin I (De Furilazole Camilli et al., 1983;Hilfiker et al., 1999) are particularly robust and useful, labeling the vast majority of cortical synapses with a minimum of labeling at non-synaptic loci. For increased confidence in synapse identification, we also develop here a basis for conjoint use of multiple synaptic markers. We argue that antibodies to the glutamatergic synaptic proteins VGluT1, VGluT2, PSD-95, GluR2, NMDAR1 and the GABAergic synaptic proteins GAD, VGAT and gephyrin can be used both Furilazole to distinguish reliably between glutamatergic and GABAergic synapses and begin the work of searching for finer synapse molecular subtypes within these broad categories. == Results == == A note about color use == We have adopted a colorblind-friendly scheme in as many figures as possible. In figures with only two immunofluorescence channels (Figures 3,6,7,8C,D) we use magenta and.