When the vesicular hypothesis is no longer the vesicular hypothesis

Morphological changes in neuromuscular junctions during exercise

Long lasting exercise produces several morphological changes in teleostean neuromuscular junctions (NJs), consisting of progressive synaptic vesicles (SVs) depletion and lamellar branching of the nerve endings. Exercised fishes kept swimming during 1 hr against a 3.5 1/min flow of oxygenated water in spite of the fact that the number of SVs was reduced in about 70% after 10 min of exercise. This observation indicates that the SVs formation fails to restore their original number and consequently, under such circumstances, the transmitter release may occur by a different mechanism.

The subsynaptosomal distribution and release of [3H]acetylcholine synthesized by rat cerebral cortical synaptosomes

Synaptosomes were prepared from rat cerebral cortex and incubated in [3H]choline for periods ranging from 1 to 90 min. The [3H]ACh synthesized during this period was found only in the cytoplasm and in a membrane-associated fraction. A negligible amount of the newly formed [3H]ACh was recovered in the vesicular fraction despite concerted efforts to protect a hypothetical population of labile vesicles. The specific activity of the membrane-associated component, accounting for 21% of the total [3H]ACh, was by far the highest. This membrane-associated fraction was not released by hypotonic shock or homogenization and apparently was not in association with the monodisperse synaptic vesicles. The [3H]ACh was released in a calcium dependent manner. This investigation has determined that the ACh synthesized by synaptosomes is localized in only two fractions, cytoplasmic and membrane-associated; that this newly synthesized ACh can be released from synaptosomes by a process consistent with physiological release; and that at least part of the ACh released was originally present in the cytoplasm.

Subcellular origin of cholinergic transmitter release from mouse brain

Samples of minced mouse forebrain were treated in a way that resulted in a high ratio of false cholinergic transmitter (acetylhomocholine) to true transmitter (acetylcholine) in a synaptic vesicle fraction, and a low ratio of false to true transmitter in the nerve terminal cytoplasm. The spontaneous release of cholinergic transmitters from this minced tissue occurred independently of calcium and had a ratio of false to true transmitter similar to that of the cytoplasm, whereas the evoked transmitter release required calcium and had a ratio of false to true transmitter similar to that of the vesicular fraction.