Projections from auditory cortex to midbrain cholinergic neurons that project to the inferior colliculus.
Acetylcholine/*metabolism; Amidines; Animals; Auditory Cortex/*cytology/metabolism; Auditory Perception/physiology; Brain Mapping; Choline O-Acetyltransferase/metabolism; Cholinergic Fibers/metabolism/ultrastructure; Dextrans; Female; Functional Laterality/physiology; Guinea Pigs; Immunohistochemistry; Inferior Colliculi/*cytology/metabolism; Male; Mesencephalon/*cytology/metabolism; Neural Pathways/cytology/metabolism; Neuroanatomical Tract-Tracing Techniques; Neuronal Tract-Tracers; Neurons/*cytology/metabolism; Pedunculopontine Tegmental Nucleus/*cytology/metabolism; Rhodamines; Synaptic Transmission/physiology
We have shown that auditory cortex projects to cholinergic cells in the pedunculopontine tegmental nucleus (PPT) and laterodorsal tegmental nucleus (LDT). PPT and LDT are the sources of cholinergic projections to the inferior colliculus, but it is not known if the cortical inputs contact the cholinergic cells that project to the inferior colliculus. We injected FluoroRuby into auditory cortex in pigmented guinea pigs to label cortical projections to PPT and LDT. In the same animals, we injected Fast Blue into the left or right inferior colliculus to label PPT and LDT cells that project to the inferior colliculus. We processed the brain to identify cholinergic cells with an antibody to choline acetyltransferase, which was visualized with a green fluorescent marker distinguishable from both FluoroRuby and Fast Blue. We then examined the PPT and LDT to determine whether boutons of FluoroRuby-labeled cortical axons were in close contact with cells that were double-labeled with the retrograde tracer and the immunolabel. Apparent contacts were observed ipsilateral and, less often, contralateral to the injected cortex. On both sides, the contacts were more numerous in PPT than in LDT. The results indicate that auditory cortex projects directly to brainstem cholinergic cells that innervate the ipsilateral or contralateral inferior colliculus. This suggests that cortical projections could elicit cholinergic effects on both sides of the auditory midbrain.
Schofield B R
Neuroscience
2010
2010-03
Article information provided for research and reference use only. All rights are retained by the journal listed under publisher and/or the creator(s).
<a href="http://doi.org/10.1016/j.neuroscience.2009.12.008" target="_blank" rel="noreferrer noopener">10.1016/j.neuroscience.2009.12.008</a>
Cholinergic cells in the tegmentum send branching projections to the inferior colliculus and the medial geniculate body.
Acetylcholine/metabolism; Animals; Auditory Pathways/*cytology; Female; Geniculate Bodies/*cytology; Guinea Pigs; Immunohistochemistry; Inferior Colliculi/*cytology; Male; Neurons/*cytology/metabolism; Tegmentum Mesencephali/*cytology
The pontomesencephalic tegmentum (PMT) provides cholinergic input to the inferior colliculus (IC) and the medial geniculate body (MG). PMT cells are often characterized as projecting to more than one target. The purpose of this study was to determine whether individual PMT cholinergic cells, (1) innervate the auditory pathways bilaterally via collateral projections to left and right auditory thalamus; or, (2) innervate multiple levels of the auditory pathways via collateral projections to the auditory thalamus and inferior colliculus. We used multiple retrograde tracers to identify individual PMT cells that project to more than one target. We combined the retrograde tracer studies with immunohistochemistry for choline acetyltransferase to determine whether the projecting cells were cholinergic. We found that individual PMT cells send branching axonal projections to two or more auditory targets in the midbrain and thalamus. The collateral projection pattern that we observed most frequently was to the ipsilateral IC and ipsilateral MG. Cells projecting to both MGs were somewhat less common, followed by cells projecting to the contralateral IC and ipsilateral MG. Both cholinergic and non-cholinergic cells contribute to each of these projection patterns. Less often, we found cells that project to one IC and both MGs; there was no evidence for non-cholinergic cells in this projection pattern. It is likely that collateral projections from PMT cells could have coordinated effects bilaterally and at multiple levels of the ascending auditory pathways.
Motts S D; Schofield B R
Neuroscience
2011
2011-04
Article information provided for research and reference use only. All rights are retained by the journal listed under publisher and/or the creator(s).
<a href="http://doi.org/10.1016/j.neuroscience.2011.01.044" target="_blank" rel="noreferrer noopener">10.1016/j.neuroscience.2011.01.044</a>