The number of primary auditory afferents in the rat.
Published estimates of the number of primary auditory afferents in the rat differ by as much as 30%. We undertook to determine if the widely varying estimates were related to methodological differences, especially the difference between counting cells in Rosenthal's canal and fibers in the cochlear nerve. Type I ganglion cells and myelinated cochlear nerve fibers in the same ears were counted in Long-Evans and Sprague-Dawley strains. Type II spiral ganglion cells were also counted. In each strain the numbers of myelinated fibers and type I ganglion cells were essentially the same. Means for the Long-Evans were 18,036 fibers and 17,749 cells. Means for Sprague-Dawleys were higher: 19,444 fibers and 19,229 cells. The mean number of type II ganglion cells was also greater in Sprague-Dawley than in Long-Evans rats: 1,388 and 1,170, respectively. Cell and fiber counts from the two ears of the same animal differed on average by only 1%. The number of auditory afferents did not change with age over the range (2-10 months) studied here. Several methodological differences have probably contributed to the varying estimates of type I primary auditory afferents, but the discrepancies are not inherent in counts of fibers and spiral ganglion cells.
Hall
R D
RD
Department of Otolaryngology, Massachusetts Eye and Ear Infirmary, Boston 02114, USA.
Massengill
J L
JL
D000344:Afferent Pathways / Q000166:cytology; D000367:Age Factors; D000818:Animals; D001306:Auditory Pathways / Q000166:cytology*; D002452:Cell Count; D003056:Cochlear Nerve / Q000166:cytology; D009413:Nerve Fibers, Myelinated / Q000648:ultrastructure; D051381:Rats; D017207:Rats, Sprague-Dawley; D013045:Species Specificity; D013136:Spiral Ganglion / Q000166:cytology