TY - JOUR
T1 - Olivocochlear neurons in the chinchilla
T2 - A retrograde fluorescent labelling study
AU - Azeredo, William J.
AU - Kliment, Molly L.
AU - Morley, Barbara J.
AU - Relkin, Evan
AU - Slepecky, Norma B.
AU - Sterns, Anita
AU - Warr, W. Bruce
AU - Weekly, J. Mathew
AU - Woods, Charles I.
N1 - Funding Information:
Supported by NIH Grants 5 P60 DC00982 (MJK, BJM, WBW and JMW) and 2 PO1 DC00215 (WBW) and to BTNRH and by NIH Grant 2PO1 DC00380-09A2 (NBS and ER). We thank JoEllen Boche for her expert histological work and Skip Kennedy and Diane Schmidt of the BTNRH Media/Graphics Department for their work on the drawings and digital images in Figs. 1, 2 and 5 .
PY - 1999/8
Y1 - 1999/8
N2 - Although the chinchilla is widely used as a model for auditory research, little is known about the distribution and morphology of its olivocochlear neurons. Here, we report on the olivocochlear neurons projecting to one cochlea, as determined by single and double retrograde fluorescent tracer techniques. 10 adult chinchillas were anesthetized and given either unilateral or bilateral injections of a fluorescent tracer (either Fluoro- Gold or Fast Blue) into scala tympani or as a control, a unilateral injection into the middle ear cavity. The results indicate that there are similarities as well as significant differences between the chinchilla and other species of rodents in the distributions of their olivocochlear neurons. Based on three well-labelled cases, there was a mean total of 1168 olivocochlear neurons in the chinchilla. Of these, the majority (mean 787) were small, lateral olivocochlear neurons found almost exclusively within the ipsilateral lateral superior olivary nucleus. The next largest group consisted of a mean of 280 medial olivocochlear neurons virtually all of which were located in the dorsomedial peri-olivary nucleus. Chinchilla medial olivocochlear neurons were more predominantly crossed in their projections (4:1) than in any known species. The smallest group of olivocochlear neurons (mean 101) consisted of larger lateral olivocochlear neurons (shell neurons) which were located on the margins of the superior olivary nucleus and which projected mainly (2.2:1) ipsilaterally. Double retrograde labelling was observed only in medial olivocochlear neurons and occurred in only 1-2% of these cells. The results confirm previous findings which indicated a relative paucity of fibers belonging to the uncrossed as compared to the crossed olivocochlear bundle. This, together with the strong apical bias of the uncrossed projection reported previously, offers possible explanations for the apparent absence of efferent-mediated suppressive effects of contralateral acoustic stimulation in this species. Regarding the lateral olivocochlear system, the chinchilla is shown to possess both intrinsic and shell neurons, as in the rat.
AB - Although the chinchilla is widely used as a model for auditory research, little is known about the distribution and morphology of its olivocochlear neurons. Here, we report on the olivocochlear neurons projecting to one cochlea, as determined by single and double retrograde fluorescent tracer techniques. 10 adult chinchillas were anesthetized and given either unilateral or bilateral injections of a fluorescent tracer (either Fluoro- Gold or Fast Blue) into scala tympani or as a control, a unilateral injection into the middle ear cavity. The results indicate that there are similarities as well as significant differences between the chinchilla and other species of rodents in the distributions of their olivocochlear neurons. Based on three well-labelled cases, there was a mean total of 1168 olivocochlear neurons in the chinchilla. Of these, the majority (mean 787) were small, lateral olivocochlear neurons found almost exclusively within the ipsilateral lateral superior olivary nucleus. The next largest group consisted of a mean of 280 medial olivocochlear neurons virtually all of which were located in the dorsomedial peri-olivary nucleus. Chinchilla medial olivocochlear neurons were more predominantly crossed in their projections (4:1) than in any known species. The smallest group of olivocochlear neurons (mean 101) consisted of larger lateral olivocochlear neurons (shell neurons) which were located on the margins of the superior olivary nucleus and which projected mainly (2.2:1) ipsilaterally. Double retrograde labelling was observed only in medial olivocochlear neurons and occurred in only 1-2% of these cells. The results confirm previous findings which indicated a relative paucity of fibers belonging to the uncrossed as compared to the crossed olivocochlear bundle. This, together with the strong apical bias of the uncrossed projection reported previously, offers possible explanations for the apparent absence of efferent-mediated suppressive effects of contralateral acoustic stimulation in this species. Regarding the lateral olivocochlear system, the chinchilla is shown to possess both intrinsic and shell neurons, as in the rat.
KW - Chinchilla
KW - Efferent innervation of the cochlea
KW - Olivocochlear bundle
KW - Olivocochlear neuron
KW - Superior olivary complex
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UR - http://www.scopus.com/inward/citedby.url?scp=0032817424&partnerID=8YFLogxK
U2 - 10.1016/S0378-5955(99)00069-6
DO - 10.1016/S0378-5955(99)00069-6
M3 - Article
C2 - 10452376
AN - SCOPUS:0032817424
SN - 0378-5955
VL - 134
SP - 57
EP - 70
JO - Hearing Research
JF - Hearing Research
IS - 1-2
ER -