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Development of cutaneous and proprioceptive afferent projections in the chick spinal cord
B Mendelson1, H R Koerber, E Frank
1Department of Neurobiology, Anatomy and Cell Science, University of Pittsburgh School of Medicine, PA 15261.
Insights
Sensory afferent nerve development in chick embryos shows distinct spinal cord projection patterns. Muscle afferents target motoneurons, while cutaneous afferents arborize in the dorsal horn by embryonic day 8.5.
Area of Science:
- Neuroscience
- Developmental Biology
- Neuroanatomy
Background:
- Understanding sensory neuron development is crucial for comprehending nervous system organization.
- Distinct peripheral nerve types (muscle and cutaneous) innervate the central nervous system.
- Early developmental stages provide insights into neuronal pathway formation.
Purpose of the Study:
- To investigate the developmental trajectory of muscle and cutaneous sensory afferent arborizations in the embryonic chick spinal cord.
- To identify the timing and spatial differences in the projections of these two sensory neuron populations.
Main Methods:
- Individual labeling of muscle and cutaneous nerves using DiI in chick embryos.
- Microscopic analysis of spinal cord tissue to visualize and map afferent projections.
- Staging of embryos based on developmental milestones (e.g., embryonic days).
Main Results:
- Both muscle and cutaneous afferents initially entered the spinal gray matter at embryonic day 6 (stage 28-29).
- By embryonic day 8.5 (late stage 34), distinct projection patterns emerged: muscle afferents projected unbranched towards motoneuronal dendrites, while cutaneous afferents branched within the dorsal horn.
- Projections of small caliber axons into superficial laminae (1 and 2) were observed later, around embryonic day 13-14.
Conclusions:
- Muscle and cutaneous sensory afferents follow divergent developmental paths within the embryonic spinal cord.
- The timing of projection differences suggests distinct developmental programs for different sensory modalities.
- This study provides a detailed map of early sensory afferent development in the chick model.
Abstract:
Muscle and cutaneous nerves were individually labeled with DiI in chick embryos to examine the development of sensory afferent arborizations in the spinal cord. Initially, cutaneous and muscle arbors were similar; both types first entered the spinal gray matter at stage 28-29 (embryonic day (E) 6). Differences in projections were first observed by late stage 34 (E8.5): muscle afferent collaterals extended almost unbranched to the level of motoneuronal dendrites while cutaneous afferents branched frequently and remained within the dorsal horn. Projections of putative small caliber axons into laminae 1 and 2, located laterally in the chick, did not develop until E13-14.