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The distribution of somatostatin immunoreactivity in the subcortical auditory system of three mammalian species

University of British Columbia

Using current immunohistochemical methods the distribution of somatostatin was examined in the subcortical auditory pathways of three mammalian species. The distributions of immunoreactivity were similar in some respects and quite varied in others. The differences and similarities could be considered in the context of three categories of previously described projections: ascending auditory pathways; ascending auditory and somatosensory pathways; and descending auditory pathways. The greatest heterogeneity was associated with immunostaining in the ascending auditory nuclei; this was only found in rodents. Immunolabelled cells were seen in the rat spherical cell region of the anterior ventral cochlear nucleus (SC-AVCN) and in the dorsal region of the ventral nucleus of the lateral lemniscus (VLL), while immunoreactive puncta were prominent in the MNTB (medial nucleus of the trapezoid body). In the guinea pig a density of SOM-IR cells, much lower than that of the rat, was seen in the SC-AVCN while immunoreactive neuropil was only seen apposing the principal cells of the medial superior olive. In all species somatostatin immunoreactivity was associated with the ascending projection from immunolabelled cells in the intercollicular area (ICA), and possibly the external cortex of the inferior colliculus (EC), which project to the midbrain reticular formation (MRF), a site of common imraunolabelled neuropil. These regions are associated with both ascending auditory and somatosensory information. In the descending auditory regions somatostatin immunoreactivity was prominent in all species examined. All species showed immunolabelled cells in the dorsal and external cortices of the inferior colliculus. Cells seen in the medial VLL region do not appear to form ascending pathways and the VLL is known to provide descending pathways. All species showed immunoreactive neuropil in the medial VLL, the dorsal periolivary regions of the superior olivary complex and in the ventral nucleus of the trapezoid body. Comparison of the immunoreactivities, both similarities and differences, to known projections, is used to describe the possible projections of somatostatin immunoreactive cells. The discussion includes some speculation on the possible coexistence of somatostatin with other peptides and its possible functional significance. The possibility of descending mechanisms of cortical and subcortical auditory control of the cochlear nucleus and cochlea is derived from a comparison of peptide and classical neurotransmitter distributions with physiology and pharmacology.

Text

2010-06-30

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http://hdl.handle.net/2429/26098

Neuroscience

University of British Columbia

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