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Musculotopic organization in the motor trigeminal nucleus of the reeler mutant mouse
T Terashima1, Y Kishimoto, T Ochiishi
1Department of Anatomy, Tokyo Metropolitan Institute for Neuroscience, Japan.
Abstract:
We examined the musculotopic organization in the motor trigeminal nucleus and the somatotopical arrangement in the trigeminal ganglion of the normal and reeler mice. To determine whether or not masticatory motoneurons are malpositioned in the reeler mouse, we injected horseradish peroxidase (HRP) into the masticatory muscles of normal and reeler mice. Injections of HRP into the jaw-closing muscles, i.e., the masseter and temporalis muscles, labeled large multipolar neurons in the dorsolateral division of the motor trigeminal nucleus of both normal and reeler mice. Similar injections into the jaw-opening muscles, i.e., the anterior belly of the digastric muscle and mylohyoid muscle, labeled large multipolar neurons in the ventromedial division of the motor trigeminal nucleus of both mouse strains. Thus, the normal myotopical arrangement of the masticatory muscles on the motor trigeminal nucleus is preserved in the reeler mouse. However, detailed analysis revealed that jaw-opening motoneurons were more widely scattered in the reeler mouse than in the normal control. To examine the somatotopical arrangement of the first-order sensory neurons in the trigeminal ganglion of the normal and reeler mice, we subcutaneously injected Fast blue (FB) into the mental region and Diamidino yellow (DY) into the vibrissal region of the same animals. No differences in distribution patterns of FB-labeled and DY-labeled neurons in the whole-mounted trigeminal ganglion could been seen between these two strains, suggesting that migration of trigeminal ganglion cells, which are derived from the neural crest and placode, is not deranged by the reeler genetic locus.
Insights
The reeler mouse preserves normal jaw muscle organization in the motor trigeminal nucleus, but jaw-opening motoneurons are more scattered. Trigeminal ganglion sensory neuron arrangement remains unaffected in reeler mice.
Area of Science:
- Neuroscience
- Developmental Biology
- Genetics
Background:
- The reeler mouse is a model organism with a mutation affecting neuronal migration.
- Understanding the organization of the motor trigeminal nucleus and trigeminal ganglion is crucial for masticatory function.
Purpose of the Study:
- To investigate the musculotopic organization of masticatory motoneurons in the motor trigeminal nucleus of reeler mice.
- To examine the somatotopical arrangement of sensory neurons in the trigeminal ganglion of reeler mice.
- To determine if the reeler mutation disrupts neuronal positioning in these cranial sensory and motor pathways.
Main Methods:
- Horseradish peroxidase (HRP) injections into masticatory muscles (masseter, temporalis, digastric, mylohyoid) to trace motoneuron organization.
- Fast blue (FB) and Diamidino yellow (DY) injections into facial regions to trace trigeminal ganglion sensory neuron distribution.
- Comparative analysis of neuronal labeling patterns between normal and reeler mice.
Main Results:
- Musculotopic organization in the motor trigeminal nucleus is largely preserved in reeler mice, with jaw-closing and jaw-opening muscles mapping to distinct nuclear divisions.
- Jaw-opening motoneurons exhibit increased scattering in the motor trigeminal nucleus of reeler mice compared to controls.
- Somatotopical arrangement of trigeminal ganglion sensory neurons, innervating vibrissal and mental regions, shows no difference between normal and reeler mice.
Conclusions:
- The reeler mutation does not fundamentally alter the established musculotopic map in the motor trigeminal nucleus for masticatory muscles.
- While the overall map is preserved, the reeler mutation leads to a wider dispersion of jaw-opening motoneurons.
- Trigeminal ganglion sensory neuron migration and organization are not affected by the reeler genetic locus, indicating pathway-specific effects of the mutation.