Donut-like topology of synaptic vesicles with a central cluster of mitochondria wrapped into membrane protrusions: a novel structure-function module of the adult calyx of Held.
Structural and functional properties of synapses are intricately and reciprocally coupled. To cope with the functional requirements in auditory processing, the calyx of Held developed distinct structural specializations such as a large number of active zones, large size, elaborate morphology, and defined distribution of ion channels. These specializations typically appear during postnatal maturation within the first 3 weeks of life and are accompanied by marked changes in the properties of synaptic transmission. We examined the arrangement of synaptic vesicles at different postnatal stages of maturation by genetically labeling vesicles with the fluorescent fusion protein synaptophysin-enhanced green fluorescent protein. Fluorescence and electron microscopy-based analyses revealed a new anatomical specialization in the mature calyx of Held. Within small, membrane-delimited compartments (swellings), synaptic vesicles formed donut-like assemblies around a central cluster of interconnected mitochondria. Adult calyces contained approximately 100 such structural units, each of them consisting of approximately 800 synaptic vesicles, six to nine mitochondria, and five to nine active zones. A donut of synaptic vesicles measured approximately 1 microm in diameter and was placed in a swelling with a volume of approximately 5 fl. Conspicuously, this structural specialization appears with the onset of hearing and may contribute to maturational changes in presynaptic function.
Wimmer
Verena C
VC
Abteilung Zellphysiologie, Max-Planck-Institut für medizinische Forschung, 69120 Heidelberg, Germany.
Horstmann
Heinz
H
Groh
Alexander
A
Kuner
Thomas
T
D000367:Age Factors; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D000831:Animals, Newborn; D001933:Brain Stem / Q000737:chemistry / Q000502:physiology; D002462:Cell Membrane / Q000737:chemistry / Q000502:physiology; D003056:Cochlear Nerve / Q000737:chemistry / Q000254:growth & development*; D017626:Cochlear Nucleus / Q000737:chemistry / Q000254:growth & development*; D008928:Mitochondria / Q000737:chemistry / Q000502:physiology*; D008969:Molecular Sequence Data; D011554:Pseudopodia / Q000737:chemistry / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013329:Structure-Activity Relationship; D013572:Synaptic Vesicles / Q000737:chemistry / Q000502:physiology*