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Projections from auditory cortex to midbrain cholinergic neurons that project to the inferior colliculus
1Department of Anatomy and Neurobiology, Northeastern Ohio Universities College of Medicine, 4209 State Route 44, PO Box 95, Rootstown, OH 44272, USA. bschofie@neoucom.edu
Neuroscience
|December 17, 2009
Summary
Auditory cortex directly impacts brainstem cholinergic cells, influencing both sides of the auditory midbrain. This pathway, involving the pedunculopontine tegmental nucleus and laterodorsal tegmental nucleus, suggests a novel mechanism for auditory processing.
Area of Science:
- Neuroscience
- Auditory System
- Cholinergic Pathways
Background:
- The auditory cortex sends projections to cholinergic cells in the pedunculopontine tegmental nucleus (PPT) and laterodorsal tegmental nucleus (LDT).
- PPT and LDT are known sources of cholinergic projections to the inferior colliculus.
- It was previously unknown if direct cortical inputs contacted the specific cholinergic cells projecting to the inferior colliculus.
Purpose of the Study:
- To investigate whether auditory cortical projections directly contact cholinergic cells in the PPT and LDT that project to the inferior colliculus.
- To determine the laterality and relative abundance of these cortico-cholinergic connections.
Main Methods:
- In pigmented guinea pigs, retrograde tracers (FluoroRuby into auditory cortex, Fast Blue into inferior colliculus) were used to label projecting neurons.
- Cholinergic cells were identified using an antibody against choline acetyltransferase, visualized with a distinct fluorescent marker.
- Brains were processed to examine close appositions between FluoroRuby-labeled cortical axons and double-labeled (retrograde tracer + choline acetyltransferase) PPT/LDT cells.
Main Results:
- Direct contacts were observed between auditory cortical axons and cholinergic cells projecting to the inferior colliculus in both the PPT and LDT.
- These contacts occurred ipsilaterally and, less frequently, contralaterally to the injected auditory cortex.
- Contacts were more numerous in the PPT compared to the LDT on both sides.
Conclusions:
- The auditory cortex directly innervates brainstem cholinergic cells that project to the ipsilateral and contralateral inferior colliculus.
- These findings reveal a direct pathway for cortical modulation of cholinergic signaling in the auditory midbrain.
- This suggests that auditory cortex can exert cholinergic influences on both sides of the auditory midbrain.
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