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The development of peptidergic neurons in the foregut of the chick
Insights
Neuropeptides like somatostatin and VIP develop early in chick foregut neurons, appearing as early as 4-9 days of incubation. Their early emergence challenges the idea that other neuron types develop first.
Area of Science:
- Neuroscience
- Developmental Biology
- Gastroenterology
Background:
- The development of the enteric nervous system (ENS) involves complex neuronal differentiation.
- Peptidergic neurons, which use neuropeptides as neurotransmitters, play crucial roles in gut function.
- The precise timing and sequence of peptidergic neuron development within the embryonic gut remain incompletely understood.
Purpose of the Study:
- To investigate the ontogeny of neurons containing Met-enkephalin (met-ENK), somatostatin (SOM), substance P (SP), and vasoactive intestinal peptide (VIP) in the developing chick foregut.
- To determine the temporal and spatial patterns of appearance for these four key neuropeptides during embryonic development.
- To compare the developmental timeline of peptidergic neurons with that of cholinergic and serotonergic neurons.
Main Methods:
- Utilized specific antisera against met-ENK, SOM, SP, and VIP for immunocytochemical analysis.
- Examined tissue from chick embryos at various developmental stages (4 to 21 days of incubation).
- Focused on the myenteric and submucosal plexuses, as well as smooth muscle and mucosal layers of the proventriculus, gizzard, and duodenum.
Main Results:
- All four neuropeptides were detected early in development (4-9 days of incubation) in the primitive myenteric plexus.
- Distinct temporal patterns were observed for the appearance of each peptide, with VIP and SOM appearing earliest in the duodenum.
- met-ENK neurons were not found in the submucosal plexus, while VIP and SP neurons were observed in both myenteric and submucosal plexuses, as well as smooth muscle and mucosal layers at later stages.
Conclusions:
- Neuropeptides emerge very early in the ontogeny of enteric neurons, co-occurring with or preceding the expression of cholinergic and serotonergic phenotypes.
- The findings suggest that peptidergic neurons are not necessarily the last to differentiate in the developing ENS.
- This early development of peptidergic neurons indicates a complex and potentially parallel developmental process within the embryonic gut.
Abstract:
We have used antisera specifically directed against Met-enkephalin (met-ENK), somatostatin (SOM), substance P (SP), and vasoactive intestinal peptide (VIP), to study the development of neurons containing these peptides in the foregut of the chick. All four peptides were detected early in ontogeny, at 4 to 9 days of incubation (d.i.), and were localized primarily to cell bodies in the primitive myenteric plexus. There were differences in the times at which they were first detected and in the sequence of their appearance in the proventriculus, gizzard, and duodenum. The differentiation of these peptidergic neurons in the duodenum was examined in some detail. Cell bodies containing these peptides were first detected in the primitive myenteric plexus at 5 to 7 d.i. and increased in number from 7 to 11 d.i. Processes containing varicosities became prominent between 11 and 13 d.i. VIP was the first of the peptides to appear in the submucosal plexus and was found in more proximal regions of the duodenum at 5 d.i. Shortly thereafter, SOM- and SP-containing cell bodies were seen; met-ENK-containing cell bodies were never detected in the submucosal plexus. At 13 d.i., the circular smooth muscle contained a number of VIP-immunoreactive and a smaller number of SOM-immunoreactive processes. met-ENK- and SP-immunoreactive processes appeared in the circular smooth muscle between 17 and 21 d.i.; VIP- and SP-immunoreactive processes appeared in the mucosal plexus at 17 to 21 d.i. Our results suggest that neuropeptides appear very early in the ontogeny of enteric neurons, at the same time or even before cholinergic and serotonergic neurons express their phenotypes. These findings argue against a sequential developmental order in which peptidergic neurons appear after those containing acetylcholine and serotonin.