Optimization of protocols for pre-embedding immunogold electron microscopy of neurons in cell cultures and brains

Immunogold labeling allows localization of proteins at the electron microscopy (EM) level of resolution, and quantification of signals. The present paper summarizes methodological issues and experiences gained from studies on the distribution of synaptic and other neuron-specific proteins in cell cultures and brain tissues via a pre-embedding method. An optimal protocol includes careful determination of a fixation condition for any particular antibody, a well-planned tissue processing procedure, and a strict evaluation of the credibility of the labeling. Here, tips and caveats on different steps of the sample preparation protocol are illustrated with examples. A good starting condition for EM-compatible fixation and permeabilization is 4% paraformaldehyde in PBS for 30 min at room temperature, followed by 30 min incubation with 0.1% saponin. An optimal condition can then be readjusted for each particular antibody. Each lot of the secondary antibody (conjugated with a 1.4 nm small gold particle) needs to be evaluated against known standards for labeling efficiency. Silver enhancement is required to make the small gold visible, and quality of the silver-enhanced signals can be affected by subsequent steps of osmium tetroxide treatment, uranyl acetate en bloc staining, and by detergent or ethanol used to clean the diamond knife for cutting thin sections. Most importantly, verification of signals requires understanding of the protein of interest in order to validate for correct localization of antibodies at expected epitopes on particular organelles, and quantification of signals needs to take into consideration the penetration gradient of reagents and clumping of secondary antibodies.

Optimization of Protocols for Pre-Embedding Immunogold Electron Microscopy of Neurons in Cell Cultures and Brains

Immunogold labeling allows localization of proteins at the electron microscopy (EM) level of resolution, and quantification of signals. The present paper summarizes methodological issues and experiences gained from studies on the distribution of synaptic and other neuron-specific proteins in cell cultures and brain tissues via a pre-embedding method. An optimal protocol includes careful determination of a fixation condition for any particular antibody, a well-planned tissue processing procedure, and a strict evaluation of the credibility of the labeling. Here, tips and caveats on different steps of the sample preparation protocol are illustrated with examples. A good starting condition for EM-compatible fixation and permeabilization is 4% paraformaldehyde in PBS for 30 min at room temperature, followed by 30 min incubation with 0.1% saponin. An optimal condition can then be readjusted for each particular antibody. Each lot of the secondary antibody (conjugated with a 1.4 nm small gold particle) needs to be evaluated against known standards for labeling efficiency. Silver enhancement is required to make the small gold visible, and quality of the silver-enhanced signals can be affected by subsequent steps of osmium tetroxide treatment, uranyl acetate en bloc staining, and by detergent or ethanol used to clean the diamond knife for cutting thin sections. Most importantly, verification of signals requires understanding of the protein of interest in order to validate for correct localization of antibodies at expected epitopes on particular organelles, and quantification of signals needs to take into consideration the penetration gradient of reagents and clumping of secondary antibodies.

Oxygen vacancies dependent Au nanoparticle deposition and CO oxidation

Au deposition on CeO2 support is oxygen vacancies dependent. Optimized VOs result in small gold particle size and positively charged Auδ+ to promote CO oxidation; excess VOs lead to agglomerated Au NPs and the reduction of Au3+ reactive species, with catalysis deactivation.

Freeze-drying technique in electron microscopic immunohistochemistry.

Postembedding immunocytochemical labeling was performed on sections of rat neurohypophysis prepared by either freeze-drying, vapor fixation and Spurr resin embedding, or conventional aqueous fixation and Spurr resin embedding. Arginine vasopressin (AVP) and oxytocin (OXT) were immunolabeled with protein A-gold-anti-AVP and protein A-gold-anti-OXT complexes, respectively. The freeze-drying procedure (FD) resulted in excellent preservation of ultrastructure and greater antigenicity than the conventional procedure (Con). More gold particles were seen over secretory granules in FD sections than in Con sections. In addition, in FD sections, the gold label was restricted to secretory granules while in Con sections, both the granules and the extragranular axoplasm exhibited label. The two antigens in FD sections could be labeled simultaneously with protein A-small gold particle-anti-OXT complex and protein A-large gold particles-anti-AVP complex. In this way the two antigens were seen to be present in secretory granules within different axon terminals. Thus FD preparations should be useful for demonstrating the presence of multiple antigens in the same granules of nerve terminals.