Serial section reconstruction of the guinea pig outer and inner hair cells as studied with a high-voltage electron microscope.

1989 Fiscal Year Final Research Report Summary

• Project/Area Number: 62570774
• Research Category: Grant-in-Aid for General Scientific Research (C)
• Allocation Type: Single-year Grants
• Research Field: Otorhinolaryngology
• Research Institution: Hirosaki University (1989); Tohoku University (1987-1988)
• Principal Investigator: SHINKAWA Hideichi Hirosaki Univ. Sch.of Medicine Associate Prof., 医学部・耳鼻咽喉科, 助教授 (90125584)
• Co-Investigator(Kenkyū-buntansha): TAKASAKA Tomonori Tohoku Univ. Sch.of Medicine Prof., 医学部・耳鼻咽喉科, 教授 (80004646) ; KIKUCHI Toshihiko Tohoku Univ. Sch.of Medicine Clinical Assist.
• Project Period (FY): 1987 – 1989
• Keywords: High-voltage electron microscope / Guinea pig / Cochlea / Outer hair cell / Inner hair cell / Afferent nerve terminal / Efferent nerve terminal

Research Abstract

The fine structural arrangement of neural terminals on outer and inner hair cells of guinea pig was investigated by thick consecutive sectioning techniques. Specimens collected on single hole grids were observed under a high-voltage electron microscope.
Complete serial sections from 89 outer hair cells(OHCs) were available for the present study. Both afferent and efferent neural terminals on each OHC varied in number from 5 to 35. Minimum and maximum values were obtained at the hook portion and at the second and third rows of the third turn,respectively. As regarding the afferent nerve, numerous endings were seen in the second and third rows of the second and third turns. In contrast with afferent terminals, efferent endings showed less remarkable changes in number from the basal end to the apex, ranging from 1 to 11. OHCs in the first row possessed maximum innervation density of efferents at the upper part of the second and third turns. On the other hand, those in the second and third rows had maximum number of endings in the basal turn. Longest diameters of the afferent nerve terminals were measured, varying from 500 to 3300 nm. Most of endings ranged in size from 600 to 1700nm.
Consecutive sections from 27 inner hair cells (IHCs) were observed in the present experiment. Both afferent and efferent nerve endings on each IHC varied in number from 8 to 24 and 4 to 7, respectively. IHCs in the basal turn was most densely innervated by afferent nerve terminals. Efferent endings showed no remarkable change in number from the hook portion to the apex. These endings rarely formed synapses with IHCs. Many of the radial afferent fibers examined contacted single IHCs with single terminal swellings. Among IHCs, 60% of the afferent synapses possessed presynaptic bodies.