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Ultrastructural analysis of the cristae ampullares in the squirrel monkey ( Saimiri sciureus )
Author(s) -
Lysakowski Anna,
Goldberg Jay M.
Publication year - 2008
Publication title -
journal of comparative neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.855
H-Index - 209
eISSN - 1096-9861
pISSN - 0021-9967
DOI - 10.1002/cne.21827
Subject(s) - efferent , squirrel monkey , biology , saimiri sciureus , calyx , anatomy , brainstem , afferent , neuroscience
Type I hair cells outnumber type II hair cells (HCs) in squirrel monkey ( Saimiri sciureus ) cristae by a nearly 3:1 ratio. Associated with this type I HC preponderance, calyx fibers make up a much larger fraction of the afferent innervation than in rodents (Fernández et al. [1995] J. Neurophysiol. 73:1253–1269). To study how this affects synaptic architecture, we used disector methods to estimate various features associated with type I and type II HCs in central (CZ) and peripheral (PZ) zones of monkey cristae. Each type I HC makes, on average, 5‐10 ribbon synapses with the inner face of a calyx ending. Inner‐face synapses outnumber those on calyx outer faces by a 40:1 ratio. Expressed per afferent, there are, on average, 15 inner‐face ribbon synapses, 0.38 outer‐face ribbons, and 2.6 efferent boutons on calyx‐bearing endings. Calyceal invaginations per type I HC range from 19 in CZ to 3 in PZ. For type II HCs, there are many more ribbons and afferent boutons in PZ than in CZ, whereas efferent innervation is relatively uniform throughout the neuroepithelium. Despite outer‐face ribbons being more numerous in chinchilla than in squirrel monkey, afferent discharge properties are similar (Lysakowski et al. [1995] J. Neurophysiol. 73:1270–1281), reinforcing the importance of inner‐face ribbons in synaptic transmission. Comparisons across mammalian species suggest that the prevalence of type I HCs is a primate characteristic, rather than an arboreal life‐style adaptation. Unlike cristae, type II HCs predominate in monkey maculae. Differences in hair‐cell counts may reflect the stimulus magnitudes handled by semicircular canals and otolith organs. J. Comp. Neurol. 511:47–64, 2008. © 2008 Wiley‐Liss, Inc.