Abstract
In rodents, the superior paraolivary nucleus (SPON) is one of the major nuclei of the superior olivary complex that innervate the inferior colliculus. To analyze the intrinsic organization of the SPON and to gain further insight into its relationship with the inferior colliculus, the neuroanatomical tracers biotinylated dextran and horseradish peroxidase were unilaterally injected into different regions of the central nucleus of the inferior colliculus of adult albino rats. Both tracers resulted in retrograde labeling of SPON cell bodies. In addition, biotinylated dextran rendered excellent filling of dendri-tic and axonal processes within the nucleus. Our results confirm that the projection from the SPON to the central nucleus of the inferior colliculus is nearly exclusively ipsilateral and strictly topographic. Furthermore, our data show that virtually all SPON neurons participate in this projection. The labeling with biotinylated dextran reveals that typical SPON neurons are medium to large multipolar cells with four to seven thick, long, scarcely branched and smooth dendrites that extend over long distances within a nearly parasagittal plane and intermingle with similarly oriented axonal plexuses. Some of the neurons located ventrally within the nucleus possess dendrites that extend ventrally beyond the limits of the SPON to penetrate into the underlying ventral nucleus of the trapezoid body. The parallel arrangement of flattened dendritic and axonal fields within the SPON is reminiscent of the fibrodendritic laminae found in other mammalian auditory nuclei. This fact and the available data about the connectivity of the nucleus stress the similarities between the SPON and the principal nuclei of the superior olivary complex.
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Accepted: 7 April 2000
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Saldaña, E., Berrebi, A. Anisotropic organization of the rat superior paraolivary nucleus. Anat Embryol 202, 265–279 (2000). https://doi.org/10.1007/s004290000109
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DOI: https://doi.org/10.1007/s004290000109
- Key words Auditory brainstem
- Biotinylated dextran
- Horseradish peroxidase
- Inferior colliculus
- Superior olivary complex
- Abbreviations BD Biotinylated dextran
- CNIC central nucleus of the inferior colliculus
- DAB diaminobenzidine
- DAB-Ni nickel-enhanced diaminobenzidine
- DCIC dorsal cortex of the inferior colliculus
- DMPO dorsomedial periolivary nucleus
- ECIC external cortex of the inferior colliculus
- GABA gamma amino butyric acid
- GAD glutamic acid decarboxylase
- HRP horseradish peroxidase
- IC: inferior colliculus
- LNTB lateral nucleus of the trapezoid body
- LSO lateral superior olive
- MNTB medial nucleus of the trapezoid body
- MSO medial superior olive
- PB phosphate buffer
- SOC superior olivary complex
- SPON superior paraolivary nucleus
- VLL ventral nucleus of the lateral lemniscus
- VNTB ventral nucleus of the trapezoid body