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Mesencephalic projections from superficial and deep laminae of the medullary dorsal horn
1Department of Oral Physiology, Osaka University Faculty of Dentistry, Japan.
Abstract:
The mesencephalic projection pattern of axons arising from the medullary dorsal horn (MDH) was studied on the basis of axonal transport of Phaseolus vulgaris Leucoagglutinin (PHA-L). After large injections of PHA-L into both the superficial and deep laminae of the MDH, labeled fibers were observed in the anterior pretectal area (ATP), internal gray matter of the superior colliculus (InG), and rostral linear raphe nucleus (RLi) in the contralateral mesencephalon, and also in the ipsilateral parabrachial nucleus (PBA). Restriction of PHA-L to only the superficial laminae resulted in heavy axon labeling and varicosity in the APT and little labeling in the lateral part of the InG of the contralateral mesencephalic nuclei and the dorsal part of the ipsilateral PBA. On the other hand, after injections into the deep laminae, labeled axons were distributed mainly in the contralateral InG and RLi. Therefore, it is concluded that there are two different major pain pathways from the superficial and deep laminae of the MDH to the mesencephalic nuclei, processing nociceptive information in the trigeminal system.
Insights
This study reveals two distinct pain pathways originating from the medullary dorsal horn (MDH). These pathways project to different mesencephalic areas, suggesting specialized processing of nociceptive information in the trigeminal system.
Area of Science:
- Neuroscience
- Pain Research
- Trigeminal System Anatomy
Background:
- The medullary dorsal horn (MDH) plays a crucial role in processing sensory information, including pain.
- Understanding the projection patterns of MDH neurons is essential for elucidating pain pathways.
Purpose of the Study:
- To investigate the mesencephalic projection patterns of axons originating from the superficial and deep laminae of the MDH.
- To differentiate the pathways involved in processing nociceptive information within the trigeminal system.
Main Methods:
- Utilized Phaseolus vulgaris Leucoagglutinin (PHA-L) for anterograde axonal tracing.
- Administered PHA-L injections into superficial and deep laminae of the MDH in rodents.
- Analyzed labeled fiber distribution in mesencephalic nuclei, including the anterior pretectal area (ATP), superior colliculus (InG), and parabrachial nucleus (PBA).
Main Results:
- Large MDH injections revealed contralateral projections to ATP, InG, RLi, and ipsilateral projections to PBA.
- Superficial lamina injections primarily targeted ATP and lateral InG (contralaterally) and dorsal PBA (ipsilaterally).
- Deep lamina injections predominantly projected to contralateral InG and RLi.
Conclusions:
- Identified two distinct major pain pathways from the superficial and deep laminae of the MDH to mesencephalic nuclei.
- These findings suggest differential processing of nociceptive information by these pathways within the trigeminal system.