Differential branchial and renal handling of urea, acetamide and thiourea in the gulf toadfish Opsanus beta: evidence for two transporters.
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The possible presence of a urea transporter in the kidney of the gulf toadfish (Opsanus beta) and further characterization of the pulsatile facilitated transporter previously identified in its gills were investigated by comparing the extra-renal and renal handling of two urea analogues with the handling of urea. Toadfish were fitted with caudal artery and indwelling urinary ureteral catheters and injected with an iso-osmotic dose of (14)C-labelled urea analogue (acetamide or thiourea) calculated to bring plasma analogue concentrations close to plasma urea concentrations. Branchial permeabilities to urea, acetamide and thiourea were similar during non-pulsing periods and all increased during pulse events, although urea permeability was greater than analogue permeability during pulses. The incidence and magnitude of acetamide and urea pulses at the gills were significantly correlated, acetamide pulses being 35-50 % of the size of urea pulses. However, the thiourea and urea pulses at the gills were only weakly correlated, thiourea pulses being less than 16 % of the size of urea pulses. Thiourea inhibited branchial urea excretion by reducing the pulse frequency. The renal handling of thiourea and urea were similar in that both substances were more concentrated in the urine than in the plasma, whereas acetamide was found in equal concentrations in the urine and plasma. Urea and thiourea were secreted 2-3 times more effectively than Cl(-) and water, whereas acetamide was secreted at a similar relative rate. The differential handling of the urea analogues by the gills and kidney indicates the presence of a different, possibly unique, transporter in the kidney. The movement of thiourea and urea into the renal tubule against an apparent concentration gradient suggests the presence of an active transport mechanism. (+info)
In ovo time-lapse analysis of chick hindbrain neural crest cell migration shows cell interactions during migration to the branchial arches.
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Hindbrain neural crest cells were labeled with DiI and followed in ovo using a new approach for long-term time-lapse confocal microscopy. In ovo imaging allowed us to visualize neural crest cell migration 2-3 times longer than in whole embryo explant cultures, providing a more complete picture of the dynamics of cell migration from emergence at the dorsal midline to entry into the branchial arches. There were aspects of the in ovo neural crest cell migration patterning which were new and different. Surprisingly, there was contact between neural crest cell migration streams bound for different branchial arches. This cell-cell contact occurred in the region lateral to the otic vesicle, where neural crest cells within the distinct streams diverted from their migration pathways into the branchial arches and instead migrated around the otic vesicle to establish a contact between streams. Some individual neural crest cells did appear to cross between the streams, but there was no widespread mixing. Analysis of individual cell trajectories showed that neural crest cells emerge from all rhombomeres (r) and sort into distinct exiting streams adjacent to the even-numbered rhombomeres. Neural crest cell migration behaviors resembled the wide diversity seen in whole embryo chick explants, including chain-like cell arrangements; however, average in ovo cell speeds are as much as 70% faster. To test to what extent neural crest cells from adjoining rhombomeres mix along migration routes and within the branchial arches, separate groups of premigratory neural crest cells were labeled with DiI or DiD. Results showed that r6 and r7 neural crest cells migrated to the same spatial location within the fourth branchial arch. The diversity of migration behaviors suggests that no single mechanism guides in ovo hindbrain neural crest cell migration into the branchial arches. The cell-cell contact between migration streams and the co-localization of neural crest cells from adjoining rhombomeres within a single branchial arch support the notion that the pattern of hindbrain neural crest cell migration emerges dynamically with cell-cell communication playing an important guidance role. (+info)
Second branchial cleft cysts: variability of sonographic appearances in adult cases.
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BACKGROUND AND PURPOSE: Previous reports have suggested that second branchial cleft cysts (BCCs) appear on sonograms as well-defined, cystic masses with thin walls and posterior enhancement. Previous CT and MR imaging findings, however, have indicated heterogeneity of these masses, and, in our experience, sonography also shows a similar variable appearance. In this communication, we report the cases of 17 patients with second BCCs and document the variability of sonographic patterns. METHODS: The sonograms of 17 adults with second BCCs were reviewed. Only patients with surgical or cytologic evidence of BCCs were included in this study. The features evaluated were the location, internal echogenicity, posterior enhancement, and presence of septa and fistulous tract. RESULTS: Four patterns of second BCCs were identified: anechoic (41%), homogeneously hypoechoic with internal debris (23.5%), pseudosolid (12%), and heterogeneous (23.5%). The majority (70%) showed posterior enhancement. All were situated in their classical location, posterior to the submandibular gland, superficial to the carotid artery and internal jugular vein, and closely related to the medial and anterior margin of the sternomastoid muscle. Fourteen (82%) of the 17 BCCs had imperceptible walls, and all were well defined. For none of the patients was a fistulous tract revealed by sonography; the presence of internal septations was revealed for three patients. CONCLUSION: As previously suggested by CT and MR imaging findings, sonography reinforces that second BCCs in adults are not simple cysts but have a complex sonographic pattern ranging from a typical anechoic to a pseudosolid appearance. (+info)
Retinoid signaling is essential for patterning the endoderm of the third and fourth pharyngeal arches.
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The requirement of retinoic acid (RA) in the initial formation of the pharyngeal arches was investigated by treating headfold-stage mouse embryos with a pan-RAR antagonist in vitro and in vivo. This results in a complete absence of mesenchyme, arteries, nerves and epibranchial placodes of the 3rd and 4th pharyngeal arches, complete agenesis of the 3rd and 4th pouches and consistent lack of the 6th arch artery. Mesodermally derived endothelial cells are absent from the 3rd and 4th pharyngeal arch region and the distribution domain of EphA2 transcripts in mesodermal cells is shifted caudally. In situ hybridization with CRABPI, kreisler and EphA4 probes and the pattern of expression of a Wnt1-lacZ transgene show that neural crest cells (NCC) normally destined to the 3rd and 4th arches migrate ectopically. Most interestingly, the appearance of the 3rd and 4th arches is prevented by the antagonist only during a very narrow window of time, which does not correspond to the period of post-otic NCC migration. Both the timing of appearance and the nature of the defects in RAR antagonist-treated embryos indicate that migrating NCC and mesodermal cells destined to the caudal pharyngeal arches do not represent primary targets of RA action. Alterations in the endodermal expression pattern of Hoxa1, Hoxb1, Pax1, Pax9, Fgf3 and Fgf8 in response to the antagonist-induced block in RA signal transduction demonstrate for the first time that RA signaling is indispensable for the specification of the pharyngeal endoderm and suggest that this signaling is necessary to provide a permissive environment locally for the migration of NCC and mesodermal cells. Our study also indicates that the formation of the 2nd pharyngeal arch and that of the 3rd and 4th pharyngeal arches probably involve distinct RA-dependent developmental processes. (+info)
The branchial arches and HGF are growth-promoting and chemoattractant for cranial motor axons.
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During development, cranial motor neurons extend their axons along distinct pathways into the periphery. For example, branchiomotor axons extend dorsally to leave the hindbrain via large dorsal exit points. They then grow in association with sensory ganglia, to their targets, the muscles of the branchial arches. We have investigated the possibility that pathway tissues might secrete diffusible chemorepellents or chemoattractants that guide cranial motor axons, using co-cultures in collagen gels. We found that explants of dorsal neural tube or hindbrain roof plate chemorepelled cranial motor axons, while explants of cranial sensory ganglia were weakly chemoattractive. Explants of branchial arch mesenchyme were strongly growth-promoting and chemoattractive for cranial motor axons. Enhanced and oriented axon outgrowth was also elicited by beads loaded with Hepatocyte Growth Factor (HGF); antibodies to this protein largely blocked the outgrowth and orientation effects of the branchial arch on motor axons. HGF was expressed in the branchial arches, whilst Met, which encodes an HGF receptor, was expressed by subpopulations of cranial motor neurons. Mice with targetted disruptions of HGF or Met showed defects in the navigation of hypoglossal motor axons into the branchial region. Branchial arch tissue may thus act as a target-derived factor that guides motor axons during development. This influence is likely to be mediated partly by Hepatocyte Growth Factor, although a component of branchial arch-mediated growth promotion and chemoattraction was not blocked by anti-HGF antibodies. (+info)
Neck infection associated with pyriform sinus fistula: imaging findings.
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BACKGROUND AND PURPOSE: Acute suppurative neck infections associated with branchial fistulas are frequently recurrent. In this study, we describe the imaging findings of acute suppurative infection of the neck caused by a third or fourth branchial fistula (pyriform sinus fistula). METHODS: Imaging findings were reviewed in 17 patients (11 female and six male patients, 2 to 49 years old) with neck infection associated with pyriform sinus fistula. Surgery or laryngoscopic examination confirmed the diagnoses. Fourteen patients had a history of recurrent neck infection and seven had cutaneous openings on the anterior portion of the neck (all lesions were on the left side). Imaging studies included barium esophagography (n = 16), CT (n = 14), MR imaging (n = 2), and sonography (n = 3). RESULTS: A sinus or fistulous tract was identified in eight of 16 patients on barium esophagograms. In 14 patients, CT studies showed the inflammatory infiltration and/or abscess formation along the course of the sinus or fistulous tract from the pyriform fossa to the thyroid gland. In nine patients, CT scans showed the entire course or a part of the sinus or fistulous tract as a tiny spot containing air. MR images showed a sinus or fistulous tract in two patients, whereas sonograms could not depict a sinus or fistulous tract in three patients. All 17 patients were treated with antibiotics. In one patient, the sinus tract was surgically excised, while 15 patients underwent chemocauterization of the sinus or fistulous tract with good outcome. Follow-up was possible for 16 of the 17 patients. CONCLUSION: When an inflammatory infiltration or abscess is present between the pyriform fossa and the thyroid bed in the lower left part of the neck, an infected third or fourth branchial fistula should be strongly suspected. (+info)
MMP-2 expression during early avian cardiac and neural crest morphogenesis.
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Matrix metalloproteinase-type 2 (MMP-2) degrades extracellular matrix, mediates cell migration and tissue remodeling, and is implicated in mediating neural crest (NC) and cardiac development. However, there is little information regarding the expression and distribution of MMP-2 during cardiogenesis and NC morphogenesis. To elucidate the role of MMP-2, we performed a comprehensive study on the temporal and spatial distribution of MMP-2 mRNA and protein during critical stages of early avian NC and cardiac development. We found that ectodermally derived NC cells did not express MMP-2 mRNA during their initial formation and early emigration but encountered MMP-2 protein in basement membranes deposited by mesodermal cells. While NC cells did not synthesize MMP-2 mRNA early in migration, MMP-2 expression was seen in NC cells within the cranial paraxial and pharyngeal arch mesenchyme at later stages but was never detected in NC-derived neural structures. This suggested NC MMP-2 expression was temporally and spatially dependent on tissue interactions or differed within the various NC subpopulations. MMP-2 was first expressed within cardiogenic splanchnic mesoderm before and during the formation of the early heart tube, at sites of active pharyngeal arch and cardiac remodeling, and during cardiac cushion cell migration. Collectively, these results support the postulate that MMP-2 has an important functional role in early cardiogenesis, NC cell and cardiac cushion migration, and remodeling of the pharyngeal arches and cardiac heart tube. (+info)
Combinatorial expression of zebrafish Brn-1- and Brn-2-related POU genes in the embryonic brain, pronephric primordium, and pharyngeal arches.
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Vertebrate class III POU genes are widely expressed in the embryonic and adult central nervous system, where they act as transcriptional regulators of cell- and/or region-specific gene expression. We isolated four zebrafish class III POU genes, named zp-12, zp-23, zp-47 and zp-50. In this study, we examined the developmental expression patterns of the Brn-1- and Brn-2-related zp-12, zp-23 and zp-47 genes by means of whole-mount in situ hybridization. Similarly to their mammalian orthologues, the major expression site of all zebrafish zp genes is the CNS. Neurectodermal expression was first detected at the beginning of somitogenesis in spatially restricted segment-like domains in different parts of the neural plate. During somitogenesis transcript distributions changed from highly restricted to widespread but nevertheless distinct patterns found in all major subdivisions of the CNS. While zp-47 expression was detected exclusively in the CNS, localized expression of zp-12 and zp-23 was also found in the pronephric primordium and in cell clusters within the mandibular and hyoid arches. Furthermore, zp-23 transcripts were transiently detected in a restricted region of the paraxial mesendoderm and, at late embryogenesis stages, in the auditory vesicles. The early regionalized expression of all three zp genes is compatible with roles in regional specification of the neural plate. Comparison of the distinct yet overlapping expression of zp-12, zp-23, zp-47 and the previously characterized zp-50 gene implies both unique, as well as redundant functions for each family member. We propose that coordinate expression of particular combinations of class III POU genes contribute to pattern formation or cell fate determination in the developing CNS and other structures. (+info)