Electron microscopy demonstrating noise exposure alters synaptic vesicle size in the inferior colliculus of cat

Abstract

Context: White noise is known to have detrimental effects on different brain regions, especially auditory regions, including inferior colliculus. Although the basis for such alterations has been hypothesized to result from abnormalities in neurotransmitter release, the mechanism is unclear. The final step in neurotransmission is the docking and transient fusion of synaptic vesicles at the base of cup-shaped lipoprotein structures called porosomes at the presynaptic membrane and the consequent release of neurotransmitters. Earlier studies in cat brain document altered morphology of the secretory portal the porosome at nerve terminals in the inferior colliculus following white noise exposure. The current study was performed to test the hypothesis of possible changes to synaptic vesicle size in the colliculus, following white noise exposure. Material and Methods: Electron microscopic morphometry of synaptic vesicles size in axo-dendritic synapses at the colliculus region of the cat brain was performed. Results: We report, for first time, decreased size of both docked and undocked vesicles in high-intensity white noise-exposed animals. In both control and experimental animals, docked vesicles are demonstrated to be smaller than undocked vesicles, suggesting fractional discharge of vesicular contents via porosome-mediated kiss-and-run mechanism. Conclusion: These studies advance our understanding of neurotransmitter release and the impact of white noise on brain function.

Keywords

• electron microscopy
• inferior colliculus
• synaptic vesicle size
• white noise