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Silver-enhanced diaminobenzidine-sulfide (SEDS): a technique for high-resolution immunoelectron microscopy
J F Smiley1, P S Goldman-Rakic
1Section of Neurobiology, Yale School of Medicine, New Haven, CT 06510.
Abstract:
A common frustration of immunoelectron microscopy (IEM) is the density of the 3,3'-diaminobenzidine (DAB) label, which obscures intracellular details of labeled structures. To overcome this problem, a silver enhancement protocol was developed which leaves silver deposits on very low levels of DAB. The resulting label is composed of easily visualized punctate silver deposits, localized in processes with little or no detectable DAB. This technique incorporates several modifications into previously described methods for silver enhancement of DAB. The principal innovation is to pretreat the DAB label with sodium sulfide before silver enhancement, which substantially increases the sensitivity of the silver enhancement. In addition, cysteine was used in place of thioglycolic acid to suppress tissue argyrophilia, allowing use of both glutaraldehyde- and paraformaldehyde-fixed tissue without degradation of ultrastructure. We demonstrate this technique with dopamine, norepinephrine (NE), and serotonin (5HT) immunoreactivity in monkey prefrontal cerebral cortex and with dopamine immunoreactivity in the anterior caudate. The punctate label allows essentially unobscured visualization of the intracellular details and cell membranes of these monoamine axons. Whereas 5HT axons formed small asymmetric synapses, dopamine and NE axons typically formed small symmetric synapses with notably subtle membrane specializations. It is likely that these are often obscured by conventional DAB labeling. The use of several preparations indicates that this technique will be useful with a variety of antibodies. It might also provide an attractive alternative to colloidal gold, especially with glutaraldehyde-fixed tissue which is not easily penetrated by gold particles.
Insights
A new silver enhancement protocol for immunoelectron microscopy (IEM) improves visualization of fine cellular structures by reducing 3,3'-diaminobenzidine (DAB) density. This method enhances contrast for detailed ultrastructural analysis of neural pathways.
Area of Science:
- Neuroscience
- Cell Biology
- Microscopy Techniques
Background:
- Conventional 3,3'-diaminobenzidine (DAB) staining in immunoelectron microscopy (IEM) often results in excessive label density, obscuring fine intracellular details and ultrastructure.
- This limitation hinders the detailed analysis of cellular morphology and synaptic connections, particularly for monoaminergic systems.
Purpose of the Study:
- To develop and validate a novel silver enhancement protocol for IEM that overcomes the limitations of dense DAB labeling.
- To improve the visualization of intracellular details and ultrastructure in immunolabeled specimens, specifically for monoamine neurotransmitters.
Main Methods:
- A modified silver enhancement protocol was developed, featuring a sodium sulfide pretreatment of the DAB label to increase sensitivity.
- Cysteine was used to suppress tissue argyrophilia, enabling the use of both glutaraldehyde- and paraformaldehyde-fixed tissues without ultrastructural degradation.
- The technique was applied to visualize dopamine, norepinephrine (NE), and serotonin (5HT) immunoreactivity in primate brain tissue.
Main Results:
- The protocol yields a punctate silver deposit label with significantly reduced DAB density, allowing clear visualization of intracellular details and cell membranes.
- Detailed synaptic morphology was observed for 5HT, dopamine, and NE axons, including subtle membrane specializations often obscured by conventional DAB.
- The punctate labeling strategy proved effective across multiple antibody preparations and tissue fixation types.
Conclusions:
- This silver enhancement technique offers a powerful alternative for IEM, providing enhanced contrast and resolution for ultrastructural studies.
- It enables unobscured visualization of fine neural structures and synaptic connections, particularly beneficial for studying monoaminergic systems.
- The method presents a viable alternative to colloidal gold, especially for glutaraldehyde-fixed tissues.