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[Development of cutaneous innervation in the chick: ultrastructural and quantitative analysis (author's transl)]
Insights
The development of chick skin innervation shows a critical stage around 14-15 days of incubation, establishing the adult pattern of cutaneous nerves and initiating myelogenesis, which primarily occurs post-hatching.
Area of Science:
- Neuroscience
- Developmental Biology
- Histology
Context:
- The peripheral nervous system's development is crucial for sensory and motor functions.
- Understanding nerve development in avian models provides insights into vertebrate neurogenesis.
Purpose:
- To detail the chronological development of cutaneous innervation in the chick embryo.
- To characterize the process and timing of myelogenesis in chick peripheral nerves.
Summary:
- Dorsal spinal nerves form early in chick development, reaching the skin by 6 days of incubation.
- By 14 days of incubation, the adult pattern of cutaneous innervation is established, with myelogenesis beginning but largely occurring after hatching.
- Two distinct modes of myelogenesis were observed: early and delayed, dependent on axon diameter.
Impact:
- Identifies a critical developmental window (14-15 days of incubation) for chick skin nerve stabilization.
- Provides a detailed timeline for peripheral nerve maturation in a vertebrate model.
- Highlights the significant post-hatching contribution to myelination in the avian peripheral nervous system.
Abstract:
In the chick, at the thoracic level, the dorsal branches of spinal nerves form at 4 days of incubation (stage 25) and reach the skin between 5 1/2 and 6 days (stages 28-29). At 6 days, the growing nervous peripheral processes ("axons") form large bundles (200-1,000 fibers). At 10 days, young Schwann cells divide the bundles into groups of axons. The perineurium and endoneurium differentiate between 10 and 14 days (but epineurium is formed after hatching). At 14 days of incubation, the adult pattern of cutaneous innervation is established. At this same stage, myelogenesis begins but develops mainly after hatching : 1% of the axons is myelinated at 16 days of incubation, 4% at hatching, 40% in 6-week old chickens and 60% in adults. Thus, less than 10% of myelinated axons of the adult are already myelinated at hatching. Two modes of myelogenesis were observed: 1) early myelination, starting in the embryo around axons measuring about 1 micrometer in diameter: 2) delayed myelination, occurring in the older chickens after an increase in axon diameter. These observations suggest that there is, in the development of chick skin innervation, a critical stage (14-15 days of incubation) apparently corresponding to the stabilization of cutaneous nerve supply.