Dense core vesicles can be highly purified and obtained in large quantity from rabbit platelets, which are a rich source of dense core vesicles and contain 10X more 5-HT than human platelets. Figure 2 (below) is an electron micrograph of 5-HT dense core vesicles that have been purified from rabbit platelets.
Dense osmiophilic organelles were first identified in the adrenal medulla of the gut. The cytoplasm of enterochromaffin cells stains readily with potassium bichromate, showing fine brown granules as chromium salts. The investigation of these "chromaffin vesicles" in the gut led to the discovery of amine-containing vesicles in the brain (Wolfe,D.E. 1962). The electron micrograph below shows monoaminergic dense core vesicles forming a synapse in the cortex of 6-day-old rat. Vesicles nearest to the cell membrane can fuse with it, emptying neurotransmitters that may cross to the adjacent cell.
Dense core vesicles are found in the axon terminals of noradrenaline-, dopamine-, and 5-HT-containing neurons, but the majority of dense core vesicles are located in dendrites.
The dendrites of raphe neurons are characterized by many 5-HT-containing dense core vesicles. Dopamine in the dendrites of rat substantia nigra and norepinephrine in dendrites of rhesus monkey locus coeruleus suggest that the storage, release, and uptake of catecholamines may not be exclusive properties of the terminal axons.
