title: Synaptic ribbon plasticity, ribbon size and potential regulatory mechanisms in utricular and saccular maculae.
abstract: The mean number of synaptic ribbons in type II hair cells of the rat utricular macula increased significantly in weightlessness. In contrast, ribbon synapses of saccular type I hair cells displayed a significant decline early inflight and postflight, and a late numerical overshoot. Further study indicated that the saccular macula had less ultrastructural complexly than the utricular. Additionally, synaptic ribbons were statistically larger in type II hair cells of both maculae, apparently a locus-related scaling effect. A major new finding is that mitochondria in calyces and collateral terminals were linked to vesicles, tubules of smooth endoplasmic reticulum and cell membranes by filaments, forming mitochondrial complexes (MCs). MCs predominated basally in the calyx where calyceal/type I hair cell borders were bound by filaments; at calyceal invaginations of type I hair cells; in calyces and collaterals near synaptic ribbon sites; and in collaterals near reciprocal synapses. MCs may participate in feedback mechanisms at these locations to help regulate synaptic ribbon activity and plasticity in altered gravitational environments.
authors.affiliation: The University of New Mexico, Department of Neurosciences, Albuquerque, NM 87131-45223, USA. mross@salud.unm.edu
authors.forename: Muriel D
authors.initials: MD
authors.lastname: Ross
authors.forename: Joseph
authors.initials: J
authors.lastname: Varelas
mesh_terms: D000818:Animals; D018871:Endoplasmic Reticulum, Smooth / Q000378:metabolism / Q000648:ultrastructure; D006198:Hair Cells, Auditory / Q000502:physiology / Q000648:ultrastructure; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D009473:Neuronal Plasticity / Q000502:physiology*; D009475:Neurons, Afferent / Q000502:physiology; D051381:Rats; D011916:Rats, Inbred F344; D012444:Saccule and Utricle / Q000294:innervation / Q000502:physiology*; D013569:Synapses / Q000502:physiology* / Q000648:ultrastructure*; D013572:Synaptic Vesicles / Q000378:metabolism / Q000648:ultrastructure; D014893:Weightlessness