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Development of enkephalinergic neurons in the gut of the chick
Insights
Met-enkephalin, a key peptide, appears early in the developing chick gut. Its presence in the enteric nervous system suggests a primary role in regulating gut motility from early development.
Area of Science:
- Neuroscience
- Developmental Biology
- Gastroenterology
Background:
- The enteric nervous system (ENS) controls gut function.
- Peptides like Met-enkephalin are neurotransmitters within the ENS.
- Understanding peptide development in the ENS is crucial for comprehending gut motility regulation.
Purpose of the Study:
- To investigate the presence and distribution of Met-enkephalin in the developing chick gut.
- To determine the developmental timeline of Met-enkephalin expression in the chick ENS.
- To explore the potential role of Met-enkephalin in the early organization of gut motility.
Main Methods:
- Radioimmunoassay (RIA) was used to quantify Met-enkephalin concentrations.
- Immunocytochemistry visualized the distribution of Met-enkephalin immunoreactivity.
- Studies were conducted on chick embryos at various developmental stages (from 5 days incubation) and newly hatched chickens.
Main Results:
- Met-enkephalin was detected in the embryonic chick duodenum by day 5.
- Concentrations increased significantly by day 13 of incubation in the duodenum and midgut.
- Immunoreactivity localized to the myenteric and submucosal plexuses, and later to smooth muscle layers, with increasing developmental complexity.
Conclusions:
- Met-enkephalin is present early in the developing chick ENS.
- Its distribution pattern suggests a role in the formation and function of the ENS.
- The peptide likely acts as a primary neurotransmitter regulating gut motility during development.
Abstract:
The content and distribution of Met-enkephalin immunoreactivity in the developing chick gut was studied by radioimmunoassay and immunocytochemistry. Met-enkephalin was detected by radioimmunoassay in the duodenum of the 5-day chick embryo. The concentration in this region increased 4-fold by 13 days of incubation and declined thereafter to the levels found in the 4-week chicken. The concentration of enkephalin in the midgut increased about 2-fold between 9 and 13 days of incubation and remained constant until hatching. In the 7-day duodenum, metenkephalin immunoreactivity was found in a network of darkly stained nodes (accumulations of ganglion cells) faintly stained internodal nerve bundles; this network of immunoreactivity was localized to the myenteric plexus. By 9 days of incubation, the network was more extensive and the intensity of staining was increased. At 13 days of incubation, varicosities were found in the region of the ganglion cells and in internodal nerve bundles. At this time, immunoreactivity was clearly visualized in the submucosal plexus. In the newly hatched chicken, met-enkephalin was found in nerves within the circular smooth muscle, as well as the myenteric and submucosal plexuses. The early appearance of met-enkephalin in the developing chick enteric nervous system suggests this peptide may act as a primary neurotransmitter in the organization and control of gut motility.