**Core Concept**
Bipolar staining is a histological technique used to visualize the structure of neurons, particularly the axons and dendrites. This staining method helps in identifying the morphology of neurons and their connections in the brain.

**Why the Correct Answer is Right**
Bipolar staining involves the use of a silver nitrate solution, which stains the axons and dendrites of neurons, making them visible under a microscope. This technique is useful in neuropathological examinations to identify changes in the brain associated with various neurological disorders. The silver nitrate solution reacts with the proteins present in the axons and dendrites, causing them to precipitate and form a visible stain.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because bipolar staining is not characteristic of glial cells, which are a type of non-neuronal cell in the brain.
**Option B:** This option is incorrect because Gram staining is a technique used to identify bacteria, not neurons.
**Option C:** This option is incorrect because H&E staining is a general histological technique used to stain tissues, but it is not specific for neurons.

**Clinical Pearl / High-Yield Fact**
Bipolar staining can help in identifying the presence of neurofibrillary tangles, which are a hallmark of Alzheimer's disease.

**Correct Answer:** D.