Ultrastructural studies of rodent vestibular periphery in normal and hypergravity conditions

Ultrastructural studies (Lysakowski and Goldberg, 1997) emphasized the regional variation in the synaptic organization of mammalian cristae ampullares. Previous studies showed similarities between the utricular macula and the crista ampullaris, in terms of synaptic architecture and zonal variations between extrastriolar/peripheral region and striolar/central region, respectively. Calyceal invaginations and synaptic ribbons are more prominent in the central zone, where the synaptic activity is believed to be highest, compared to the periphery in chinchilla crista. Synaptic ribbons provide innervation to the utricular macula by conveying head motion signals between hair cells and afferent terminals. Calyceal invaginations are hypothesized to play a role in synaptic transmission by facilitating vesicle recycling, and are only present between calyces and type I hair cells. Other studies have suggested a role for calyceal invaginations in ephaptic transmission between type I hair cells and calyx endings (Goldberg, 1996).; The utricular macula is an excellent model to study the effect of hypergravity due to its morphology and response to linear forces. We are using a variable linear force paradigm to prevent adaptation in the irregular afferents. The rat utricular macula was studied in ten samples. Consecutive serial sections are taken that include each region of the utricular in each corresponding region. The results showed a significant difference in the number of synaptic ribbons between type I hair and type II cells. Calyceal invaginations were in each corresponding region. The results showed a significant difference in the number of synaptic ribbons between type I hair and type II cells. Calyceal invaginations were significantly decreased in type I hair cells especially on the excited side of the striola. The majority of ribbon shapes were spherules in both types of hair cells.; The utricular macula and crista ampullaris synaptic ultrastructure of three rodent species were studied: the rat, mouse and chinchilla. The synaptic ultrastructure was a variant of the vestibular epithelium location and species studied. A variety of shapes, ranging from spheroids to elongate and intermediate forms, were present also. The most widely expressed form in all species of ribbon was spheres.