Monoamines in the early chick embryo: Demonstration of serotonin synthesis and the regional distribution of serotonin‐concentrating cells during morphogenesis
Tóm tắt
Monoamine compounds, such as serotonin (5‐HT), have been previously suggested to regulate the early development of the chick embryo. Possible roles for 5‐HT in chick morphogenesis were investigated further by examining the distribution of sites that concentrate 5‐HT as well as the ability of embryos to synthesize 5‐HT during this period. Following the in vitro incubation of chick embryos with 5‐HT, cells accumulating 5‐HT were localized by the formaldehyde‐induced fluorescence (FIF) technique; these sites of 5‐HT concentration were mapped and studied with respect to changes in their developmental patterns during morphogenesis. Locations of 5‐HT FIF included two regions of the brain within the floor plate of the mesencephalon and caudal myelencephalon, and within scleratome cells of somites advanced in differentiation. Additionally, two separate zones of 5‐HT FIF appeared in the neural tube caudal to the somites in conjunction with a small band of intense FIF in the caudal end of the notochord. Once established, the capabilities for 5‐HT concentration in the brain and somites persisted at the same locations during development, whereas these capabilities in caudal portions of the embryo were transient and appeared to move down the embryo as the embryo lengthened. These changes in the patterns of 5‐HT FIF in caudal segments of the neural tube and notochord correlated spatio‐temporally with the progression of caudal neuropore closure. Additional experiments, involving the use of anti‐5‐HT immunocytochemistry, were undertaken to examine the characteristics of 5‐HT concentration. The mechanism(s) of 5‐HT concentration at all locations appeared to have a high affinity and specificity for 5‐HT; however, in contrast to the transient mechanism situated more caudally in the embryos, the uptake mechanism at rostral locations required energy and was blocked by a 5‐HT uptake inhibitor (fluoxetine). The ability of embryos to synthesize 5‐HT was demonstrated by the generation of 5‐HT (localized by FIF and immunocytochemistry) in embryos treated with the 5‐HT precursors, 5‐hydroxytryptophan or L‐tryptophan. Confirming evidence of 5‐HT synthesis was provided by a marked reduction in immunostaining obtained with either precursor in the presence of 5‐HT synthesis inhibitors (R04–4602 or para‐chlorophenylalanine). Although the sites of synthesis remain uncertain, endogenous 5‐HT was detected (after monoamine oxidase inhibition) at all sites of 5‐HT concentration. These results provide further support for the suggestion that 5‐HT may be involved in various aspects of morphogenesis at specific sites within the chick embryo.
Từ khóa
Tài liệu tham khảo
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