Protargol silver impregnation and neuronal selectivity. Light and electron microscopic observations

Area of Science:

• Neuroscience
• Cell Biology
• Histology

Background:

• Protargol silver staining is a histological technique used to visualize nervous tissue.
• Understanding the precise cellular targets of protargol silver is crucial for accurate interpretation of neuronal morphology.

Purpose of the Study:

• To determine the neuronal selectivity of protargol silver staining.
• To identify the specific cellular components within neurons that are impregnated by protargol silver.

Main Methods:

• Light microscopy (LM) and transmission electron microscopy (TEM) were used to examine embedded and cultured nervous tissue.
• Ultrastructural analysis was performed to pinpoint the location and characteristics of silver deposits.

Main Results:

• Silver deposits were exclusively found in neuronal perikarya and cell processes, not in glial cells.
• Silver grains formed elongated arrays associated with neurofibrils, suggesting these are the primary sites of impregnation.
• Microtubules and neurofilaments were identified as potential components of the impregnated neurofibrils.
• Nuclei and nucleoli of both neuronal and non-neuronal cells were also densely stained.

Conclusions:

• Protargol silver demonstrates high neuronal selectivity, distinguishing neurons from glial cells.
• The staining targets neurofibrillar structures, likely composed of microtubules and neurofilaments, aiding in their visualization.
• While generally selective for neurons, improper fixation can lead to non-specific silver affinity in some neuronal cytoplasm.