Introduction

Synaptic vesicles are specialized organelles that store neurotransmitters in neurons. Under transmission electron microscopy (TEM), these vesicles exhibit distinct morphological features related to their neurotransmitter contents. Catecholamines, such as dopamine, norepinephrine, and epinephrine, are stored in specific vesicle types distinguishable by their size, shape, and electron density. Understanding these vesicular differences is crucial in neurobiology and neurotransmission studies.

Types of Synaptic Vesicles

Synaptic vesicles are generally classified into three main types based on their appearance under TEM:

1. Small, clear, round vesicles
   Size: 30-60 nm
   Contents: Classical neurotransmitters like acetylcholine, glutamate, GABA—usually not catecholamines.testbook+1

2. Small, dense core vesicles (SDCV)
   Size: 50-90 nm
   Appearance: Round shape with an electron-dense core visible under TEM due to the dense packing of neurotransmitters with associated proteins.
   Contents: Catecholamines such as dopamine, norepinephrine, epinephrine; also histamine, serotonin (5-HT).pubs.acs+2

3. Large dense core vesicles (LDCV)
   Size: 90-130 nm
   Contents: Peptide neurotransmitters and neurohormones, including neuropeptide Y (NPY), cholecystokinin (CCK), galanin.sciencedirect+1

Catecholamines and Synaptic Vesicles

• Catecholamines are monoamine neurotransmitters synthesized in neural and adrenal chromaffin cells.

• Small, round-shaped dense core vesicles (SDCVs) are prominently involved in storing and releasing catecholamines.

• The dense core corresponds to high concentration of catecholamines complexed with acidic proteins, making these vesicles electron-dense under TEM.pubmed.ncbi.nlm.nih+1

Correct Answer

Among the given options:

The synaptic vesicles containing catecholamines are:

(2) Small, round shaped and dense core