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Macaque monkey trigeminal blink reflex circuits targeting orbicularis oculi motoneurons
1Department of Neurobiology and Anatomical Sciences, University of Mississippi Medical Center, Jackson, Mississippi, USA.
The Journal of Comparative Neurology
|February 18, 2021
Summary
The trigeminal blink reflex circuitry was mapped in macaques. Findings suggest multiple trigeminal nuclei and the reticular formation contribute to lid closure, challenging previous R1/R2 component assignments.
Area of Science:
- Neuroscience
- Ophthalmology
- Sensory systems
Background:
- The trigeminal blink reflex protects the eye.
- It involves orbicularis oculi (ObOc) muscle activation.
- The reflex has distinct R1 (ipsilateral) and R2 (bilateral) components.
Purpose of the Study:
- To investigate the neural circuitry of the trigeminal blink reflex in macaque monkeys.
- To determine the contribution of different trigeminal nuclei to ObOc motoneuron activation.
- To clarify the anatomical basis for the R1 and R2 blink reflex components.
Main Methods:
- Single and dual tracer injections in macaque brains (Macaca fascicularis and Macaca mulatta).
- Retrograde tracing from the facial nucleus to identify sensory input.
- Anterograde tracing from trigeminal nuclei to map projections to ObOc motoneurons.
Main Results:
- Trigeminal nuclei (principal, spinalis oralis/interpolar/caudalis) project to ObOc motoneurons.
- Projections show ipsilateral predominance from principal and spinalis caudalis.
- Reticular formation provides bilateral input to ObOc motoneurons.
Conclusions:
- Multiple trigeminal sensory complex subdivisions and adjacent reticular formation contribute to blink reflex circuitry.
- Direct (monosynaptic) and indirect (disynaptic) pathways exist for lid closure.
- The R1 and R2 components cannot be solely attributed to specific trigeminal subdivisions based on these connectional patterns.
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