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M J Tyler

Publications and source records attributed to M J Tyler.

At least 37 records · Page 2Linked to original sources
PubMed1995

Superficial mandibular musculature and vocal sac structure in hemiphractine hylid frogs.

Three patterns of superficial mandibular musculature are described in hemiphractine hylid frogs. One of these is unique to the morphologically bizarre Hemiphractus. A second pattern is found in Flectonotus and also occurs in some species of Gastrotheca and Stefania. A third pattern involves a differentiated apical element of the m. intermandibularis and is found in Cryptobatrachus, many species of Gastrotheca, and one species of Stefania. Evidence supports the plesiomorphic state of an undifferentiated m. intermandibularis and two derived states of differentiation of that muscle. One of these is the development of supplementary posterolateral elements characteristic of the Phyllomedusinae, whereas the differentiation of an apical element has occurred in at least six independent lineages--the entire Pelodryadinae, three unrelated genera of Hylinae, and two genera of Hemiphractinae. Gastrotheca and Stefania are the only anuran genera known to include species possessing, and others lacking, differentiation of the m. intermandibularis. Vocal sacs and apertures are absent in Cryptobatrachus, Hemiphractus, Stefania, and six species of Gastrotheca.

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PubMed1994

Physical mapping of the uterine leiomyoma t(12;14)(q13-15;q24.1) breakpoint on chromosome 14 between SPTB and D14S77.

Uterine leiomyoma is the most common tumor of smooth muscle cell origin and is often associated with the recurrent balanced translocation t(12;14)(q13-15;q24). As an initial step toward finding the gene or genes that are interrupted by the translocation breakpoint, a somatic cell hybrid carrying the derivative 14 as the single t(12;14) translocated chromosome was constructed from a leiomyoma cell line with this translocation. Sequence tagged sites (STS) whose locations on the genetic map of chromosome 14 were known were used to map the breakpoint in the translocated chromosomes. The results of this analysis place the translocation breakpoint on the long arm of chromosome 14 between the proximal marker SPTB and the distal marker D14S77, narrowing the chromosomal translocation breakpoint to a region of approximately 7 cM. The identification of flanking markers on chromosome 14 lays the foundation for efforts to clone the breakpoint and to identify the genes involved in the formation of leiomyoma.

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PubMed1986

Pepsin in the toad Bufo marinus.

The macroscopic localization of pepsinogen in the upper gastrointestinal tract of the anuran Bufo marinus was studied by means of biochemical assay. The pH optimum of the anuran pepsin was determined to be 1.6. The effect of lowered ambient temperature on stored pepsinogen and proteolytic activity was studied. Both parameters were reduced. The results are extrapolated to speculate on the mechanisms of gastric brooding in gastric brooding frogs of the genus Rheobatrachus.

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PubMed1985

Gastric acid secretion in the toad Bufo marinus with the description of a new technique for in vivo monitoring.

A technique for the implantation of a pH electrode into the stomach of the toad, Bufo marinus, is described. The technique permits continuous monitoring of gastric pH for extended periods. Results from continuous monitoring and from acute measurements of gastric pH are compared in fasting and fed toads. Prostaglandin E, given orally with food, caused a dose-related delay in the fall of gastric pH which followed feeding.

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PubMed1985

Gastric emptying and intestinal transit in Bufo marinus and the actions of E prostaglandins.

Gastric emptying and intestinal transit have been studied in the anuran Bufo marinus using Tc99-labelled chicken liver as the test meal. Gastric emptying was measured as the proportion of the test meal remaining in the stomach after 3 or 6 h. Intestinal transit was calculated by the geometric centre method at the same time intervals. There was a high degree of variability in these parameters between individual animals, in both control and treated groups. Both SC29333 (Searle), a synthetic E prostaglandin, and prostaglandin E2 given orally delayed gastric emptying. These results complement the finding that prostaglandin E2 causes relaxation of anuran longitudinal muscle in vitro, and lend further support to the suggestion that prostaglandin E2 may be responsible for the gut stasis associated with gastric brooding in the gastric brooding frog Rheobatrachus silus.

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PubMed1984

On the possible role of prostaglandin E2 in intestinal stasis in the gastric brooding frog Rheobatrachus silus.

Responses of isolated intestinal preparations from the anurans Bufo marinus and Limnodynastes tasmaniensis to various agents have been studied, as models for the intestinal stasis reported in the rare gastric brooding frog, Rheobatrachus silus. It is inferred from the responses that the preparations possessed excitatory muscarinic and histamine receptors and inhibitory adrenergic receptors, conforming to the typical vertebrate pattern. The circular muscle was unresponsive to prostaglandin E2, whereas longitudinal muscle relaxed to prostaglandin E2. Some of the longitudinal preparations exhibited a biphasic response to arachidonic acid, i.e. contraction followed by relaxation. Indomethacin prevented the relaxation phase, indicating that the intestine synthesised a prostaglandin E-like substance from arachidonic acid. These results draw attention to the possibility that PGE2 may be responsible for the intestinal stasis associated with gastric brooding in the gastric brooding frog.

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PubMed1983

Inhibition of gastric acid secretion in the gastric brooding frog, Rheobatrachus silus.

The female gastric brooding frog Rheobatrachus silus broods its young in its stomach. A substance that inhibits gastric acid secretion in a toad stomach preparation in vitro appears to be secreted by the developing young. This substance has been identified as prostaglandin E2. Rheobatrachus silus may thus have developed a mechanism whereby prostaglandin secreted by the larvae inhibits acid secretion in the stomach of the female until the larvae have completed development and emerged as juvenile frogs by way of the female's mouth.

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PubMed1983

Changes in the organization and ultrastructure of smooth muscle cells in the stomach of the gastric brooding frog, Rheobatrachus silus, during brooding.

The young of the aquatic Australian frog, Rheobatrachus silus (Leptodactylidae) develop from eggs to juvenile frogs in the mother's stomach. During brooding the stomach expands greatly and becomes very thin walled. Transmission electron microscopy showed that the distension of the stomach was accompanied by a severe disruption of the smooth muscle layers. Many of the smooth muscle cells seemed to be highly contracted and resembled smooth muscle cells contracted in the absence of an intact connective tissue matrix. Eight days after the birth of the juveniles through the mouth of the female, the stomach muscle cells had returned to a normal appearance. It is suggested that during gastric incubation of the young, smooth muscle cells become at least partially dissociated from their surrounding connective tissue matrix, allowing maximal distension of the stomach wall.

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PubMed1982

Converting a stomach to a uterus: the microscopic structure of the stomach of the gastric brooding frog Rheobatrachus silus.

Rheobatrachus silus is a rare aquatic frog of eastern Australia. The female ingests the eggs after fertilization and broods them in the stomach until fully formed. "Gastric brooding" takes place in the fundus and proximal part of the body of the stomach, which dilates to accommodate the growing young. The surface epithelium becomes attenuated and the cells contain fewer mucus droplets. The acini of the glands are less numerous because of stretching, and they contain oxyntic cells that show evidence of profound suppression or regression. Morphometric studies on the limited number of samples show that the oxyntic cells are attenuated with few surface projections, sparse tubulovesicular reticulum, and a few pepsinogen granules and mitochondria. Eight days after ejection of the young, and 4 days after feeding commences, the lining shows a return of gastric pits and glands. The oxyntic cells show many surface projections and a proliferation of the tubulovesicular reticulum and mitochondria. These findings suggest that the eggs, tadpoles, and juvenile frogs release a substance, or substances, that inhibit acid secretion immediately after the eggs are ingested and that persist throughout brooding.

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