title: Dopaminergic Input to the Inferior Colliculus in Mice.
abstract: The response of sensory neurons to stimuli can be modulated by a variety of factors including attention, emotion, behavioral context, and disorders involving neuromodulatory systems. For example, patients with Parkinson's disease (PD) have disordered speech processing, suggesting that dopamine alters normal representation of these salient sounds. Understanding the mechanisms by which dopamine modulates auditory processing is thus an important goal. The principal auditory midbrain nucleus, the inferior colliculus (IC), is a likely location for dopaminergic modulation of auditory processing because it contains dopamine receptors and nerve terminals immunoreactive for tyrosine hydroxylase (TH), the rate-limiting enzyme in dopamine synthesis. However, the sources of dopaminergic input to the IC are unknown. In this study, we iontophoretically injected a retrograde tracer into the IC of mice and then stained the tissue for TH. We also immunostained for dopamine beta-hydroxylase (DBH), an enzyme critical for the conversion of dopamine to norepinephrine, to differentiate between dopaminergic and noradrenergic inputs. Retrogradely labeled neurons that were positive for TH were seen bilaterally, with strong ipsilateral dominance, in the subparafascicular thalamic nucleus (SPF). All retrogradely labeled neurons that we observed in other brain regions were TH-negative. Projections from the SPF were confirmed using an anterograde tracer, revealing TH-positive and DBH-negative anterogradely labeled fibers and terminals in the IC. While the functional role of this dopaminergic input to the IC is not yet known, it provides a potential mechanism for context dependent modulation of auditory processing.
authors.affiliation: School of Biological Sciences, Washington State University Vancouver Vancouver, WA, USA.
authors.forename: Alexander A
authors.initials: AA
authors.lastname: Nevue
authors.affiliation: School of Biological Sciences, Washington State University Vancouver Vancouver, WA, USA.
authors.forename: Cameron J
authors.initials: CJ
authors.lastname: Elde
authors.affiliation: Department of Biology, University of WashingtonSeattle, WA, USA; Department of Otolaryngology-Head and Neck Surgery, University of WashingtonSeattle, WA, USA; The Virginia Merrill Bloedel Hearing Research Center, University of WashingtonSeattle, WA, USA.
authors.forename: David J
authors.initials: DJ
authors.lastname: Perkel
authors.affiliation: School of Biological Sciences, Washington State University Vancouver Vancouver, WA, USA.
authors.forename: Christine V
authors.initials: CV
authors.lastname: Portfors
keywords: auditory midbrain; catecholamines; subparafascicular thalamic nucleus; tract tracing; tyrosine hydroxylase
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