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Published on: November 17, 2010
Diverse synaptic terminals on rat stapedius motoneurons
Daniel J Lee1, Thane E Benson, M Christian Brown
1Department of Otolaryngology, Eaton-Peabody Laboratory, Massachusetts Eye and Ear Infirmary, Boston, MA 02114, USA. daniel_lee@meei.harvard.edu
Summary
Stapedius motoneurons (SMNs) involved in hearing protection receive diverse synaptic inputs. Most terminals contain round vesicles, suggesting predominantly excitatory connections to these crucial auditory neurons.
Area of Science:
- Neuroscience
- Auditory Neuroscience
- Cell Biology
Background:
- Stapedius motoneurons (SMNs) control the stapedius muscle, vital for protecting the inner ear and mitigating noise masking.
- The synaptic inputs and their ultrastructural characteristics on SMNs remain largely uncharacterized.
Purpose of the Study:
- To investigate and classify the ultrastructure of synaptic terminals innervating stapedius motoneurons.
Main Methods:
- Retrograde labeling of stapedius motoneurons (SMNs).
- Serial section electron microscopy to reconstruct synaptic terminals.
- Ultrastructural analysis of synaptic vesicle morphology, synapse type, and terminal characteristics.
Main Results:
- Approximately 80% of synaptic terminals on SMNs contained round synaptic vesicles, indicating primarily excitatory input.
- Identified five terminal types: Sm Rnd (small, round vesicles, asymmetric synapse), Lg Rnd (large, round vesicles, asymmetric synapse), Pleo (pleomorphic vesicles, symmetric synapse), Het Rnd (heterogeneous round vesicles, asymmetric synapse), and Cist (large round vesicles, subsurface cistern).
- Observed variations in terminal size and synaptic contact number, with some Lg Rnd terminals being extensive and forming numerous synapses.
Conclusions:
- Stapedius motoneurons receive a diverse array of synaptic inputs, with a significant majority exhibiting characteristics of excitatory transmission.
- The ultrastructural findings provide novel insights into the connectivity and potential function of SMNs within the auditory pathway.
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