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At least 19 recordsLinked to original sources
PubMed1976

Cyclicity and memory in the humoral immune response of the marine toad Bufo marinus.

Bufo marinus toads immunized with a single dose of 100 mug of polymerized flagellin (POL) produce a longlasting cyclic humoral response at 22 degrees C in which the serum antibody titers rise and fall within periods of 2-3 weeks. This seems to be regulated by the catabolism of immunoglobulins, since passive 125I-labeled IgM in the serum has a half-life of 17 days, corresponding to the cyclicity of the titers of active antibodies. In toads injected with between 10 ng and 10 mug antigen the serum antibody titer peaks between 4 and 7 weeks, depending on the antigen dose, and declines by the 9th week. At this time a second stimulation with an equal dose of POL induces a secondary response during which higher titers of antibodies rise faster than in the primary response. A dose of 10 mug POL stimulates an optimal primary response and a second equal dose, given when the serum antibodies are disappearing, induces a secondary response enhanced in time but not in antibody titers.

Animals↗
PubMed1982

Functional morphology of lingual protrusion in marine toads (Bufo marinus).

Bufo marinus catches its prey by stiffening the intrinsic muscles of the tongue, rapidly flipping the tongue out of the mouth. High-speed cinematography synchronized with computer-analyzed electromyograms (EMGs)shows that during the flip the tongue is supported by the M. genioglossus medialis and that this muscle stiffens into a rod when stimulated. Coincident stiffening of the transversely arranged M. genioglossus basalis provides a wedge under the anterior tip of this rod. Stiffening of the M. submentalis depresses the mandibular symphysis and brings the dentary tips together. The M. submentalis also acts on the wedge of the basalis to raise and rotate the rigid rod of the medialis over the symphysial attachment. The tip of this lingual rod carries along the pad and soft tissues of the tongue. The lingual pad, positioned the posterodorsal portion of the resting tongue, rotates during eversion so that its dorsal surface impacts onto the prey object. Retraction starts by contraction of the elongate, parallel fibers of the M. hyoglossus; this retracts the medical sulcus of the pad and holds the prey by a suction cup-like effect. The extensibility of the buccal membranes allows the pad to be retracted first; it reaches the posterior portion of the buccal cavity before the still-rigid, backward rotating M. genioglossus has reached the level of the symphysis. Protraction of the hyoid facilitates the extension of the M. hyoglossus. The M. sternohyoideus only retracts the hyoid and stabilizes it when the tongue starts to pull posteriorly; it does not assist tongue protrusion. The Mm. petrohyoideus and omohyoideus show only incidental activity, and the M. depressor mandibulae participate in mouth opening but is not otherwise involved in the flip. Previous hypotheses of the flipping mechanism are reviewed and evaluated.

Animals↗
PubMed1982

The effects of hypercapnia on intracellular and extracellular acid-base status in the toad Bufo marinus.

Toads (Bufo marinus) were exposed to environmental hypercapnia of 5% CO2 in air, and extracellular and intracellular acid-base parameters were determined 1 and 24 h after the onset of hypercapnia. The initial drop in pH was compensated by the elevation of extracellular and intracellular bicarbonate. Relating the pH compensation to the pH drop that is expected to occur by increased PCO2 at constant bicarbonate concentration, the pH compensation in the extracellular space was 30% and reached the following values for intracellular body compartments: 65% in skeletal muscle, 77% in heart muscle and 44% in skin. The additional bicarbonate was partly produced by blood and intracellular non-bicarbonate buffers; the major portion of the remainder was related to the excretion of ammonia into the environmental water. The hypercapnia-induced changes of pH were considerably smaller in all tissue cells than in the extracellular space. Thus Bufo marinus exhibits the relative preference of intracellular over extracellular acid-base regulation that has been observed in other vertebrates.

Acid-Base Equilibrium↗
PubMed2001

Lymph osmolality and rehydration from NaCl solutions by toads, Bufo marinus.

Toads, Bufo marinus, allowed to maintain an ad libitum state of hydration were dehydrated by 10 15% of their standard weight and allowed to rehydrate from either deionized water or from 10 or 50 mmol l(-1) NaCl solutions. Toads rehydrating from the dilute salt solutions recovered a larger fraction of their standard weight than did toads rehydrating from deionized water despite there being a reduced osmotic gradient. Amiloride did not reduce water gain from these solutions. Water uptake from 100 mmol l(-1) sucrose and 50 mmol l(-1) Na gluconate was reduced relative to deionized water by a fraction predicted from the osmotic gradient. Thus, the presence of both Na+ and Cl- are required for the augmentation of water gain from dilute salt solutions. Toads allowed to rehydrate from 120 mmol l(-1) NaCl for 180 min recovered nearly as much water as toads rehydrating from deionized water for 120 min and the lymph osmolality was not reduced relative to the dehydrated condition. The recovery of water from the salt solution was greater than that predicted from the reduced osmotic gradient and amiloride partially inhibited the rehydration from 120 mmol l(-1) NaCl. Solute coupled water transport can therefore be demonstrated in living animals but only from a NaCl solution that is nearly isoosmotic with the lymph. The mechanism for enhanced water gain from dilute salt solutions remains unresolved.

Amiloride↗
PubMed1999

Salt sensitivity and hydration behavior of the toad, Bufo marinus.

Toads, Bufo marinus, were placed on laboratory tissue saturated with water or with hyperosmotic (250 or 500 mM NaCl or KCl) solutions, and their behavior was observed for 5 min. Toads placed on water initially allowed their ventral skin to touch the surface without abducting the hind limbs. During this "seat patch down" (SPD) behavior toads appeared to be evaluating the suitability of a hydration source prior to initiating "water absorption response" (WR) behavior with the hind limbs fully abducted and the ventral skin pressed to the moist surface. Toads dehydrated by more than 10% showed significantly shorter periods of SPD behavior and initiated WR behavior more frequently than did hydrated toads. Dehydrated toads placed on 250 mM NaCl initiated WR behavior in only 18% of the trials, but spent significantly more time showing SPD behavior than they did on water, indicating that this concentration is marginally acceptable to them. Recordings from spinal nerve #6 showed an increase in activity when 250 mM NaCl or KCl solutions were perfused over the outer surface of the ventral skin. The response to KCl was significantly greater than NaCl. The addition of 10 microM amiloride to 250 mM NaCl resulted in a higher frequency of WR behavior and reversibly inhibited the neural response to 250 mM NaCl. These results suggest that epithelial Na+ channels in the skin serve a sensory function in this species. Neither the hydrated nor dehydrated toads initiated WR behavior on 250 or 500 mM KCl solutions, indicating that toads have a lower tolerance of K+ than of Na+ salts.

Amiloride↗
PubMed1977

The effect of progressive hypoxia on respiration in the toad Bufo marinus.

1. As Bufo marinus became progressively hypoxic over a period of 90 min, there was a rise in arterial pH, presumably brought about by hyperventilation. The alkalosis gradually disappeared when oxygen levels became very low. It is suggested that this is the result of a respiratory or a metabolic pH adjustment, or both. 2. Hypoxic animals developed a characteristic breathing pattern in which discrete periods of lung ventilations alternated with buccal oscillations or respiratory pauses. 3. A pronounced bradycardia was associated with the concomitant decline of inspired and arterial PO2. 4. Although respiratory rates were greater than normal resting values in the initial stages of post-hypoxia, the pre-exposure breathing pattern was quickly restored. Following recovery from bradycardia (60 min), the breathing rates, arterial blood gases and pHa returned to normal within 30 min.

Animals↗
PubMed1997

Detection of antibodies against iridoviruses in the serum of the amphibian Bufo marinus.

Sera from the amphibian Bufo marinus (cane or marine toad) were investigated using a newly-developed enzyme-linked immunosorbent assay for the detection of antibodies to ranaviruses (Family Iridoviridae). Epizootic haematopoietic necrosis virus (EHNV) or Bohle iridovirus (BIV) was affinity purified from cell culture supernatants and simultaneously bound to the solid phase using specific linker antibodies. After binding to antigen, antibodies in Bufo marinus serum were then detected with a specific anti-immunoglobulin reagent. Of 21 Bufo marinus sera, 3 contained antibodies against EHNV, BIV or related viruses in the ranavirus group, at titres greater than 3200. Reactivity of cane toad antibodies against BIV, an amphibian virus, was greater than that against similar concentrations of EHNV, a piscine virus.

Animals↗
PubMed1994

A new function for lactate in the toad Bufo marinus.

In the amphibian Bufo marinus, progressive hypoxia below a critical PO2 elicits a transient 50% increase in O2 consumption that coincides with the onset of lactate formation. The present study was designed to test the hypothesis that lactate causes the observed rise in metabolic rate. Arterial bolus infusions of pH-neutral sodium lactate solutions (4 mmol/kg body wt) in toads maintained under hypoxia actually elicit a similar increase in metabolic rate. The application of adrenergic antagonists (bretylium tosylate, phentolamine, propranolol, and reserpine) inhibits this response, suggesting that catecholamines are involved. Moreover, animals injected with lactate move to a cooler environment (behavioral hypothermia), a behavioral response that is beneficial during hypoxia. We hypothesize that, in accordance with Cannon's concept of an emergency response, lactate may function as an alarm signal during hypoxia. However, the signal function of lactate is observed in animals both under hypoxia and under normoxia and should thus be considered in future studies whenever elevated lactate levels are present, e.g., during and after exercise.

Alkalosis, Respiratory↗
PubMed1994

Effect of frequency and impulse pattern on the non-cholinergic cardiac response to vagal stimulation in the toad, Bufo marinus.

In the toad, Bufo marinus, stimulation of the vagosympathetic trunk to the heart in the presence of cholinergic and adrenergic blockade results in cardiac slowing. This study investigates the importance of impulse pattern and frequency of neural stimulation in determining this cardiac response. When 360 stimuli were delivered to the heart either continuously at 3 Hz for 2 min, 4 Hz for 1.5 min or 6 Hz for 1 min, or in pulses at 6 Hz for 1 s every 2 s, over a 2 min period, there were no significant differences in the size of the chronotropic responses observed. However, when 360 stimuli were delivered in pulses at 6 Hz for 0.5 s every 1 s over 2 min, the resulting cardiac slowing was significantly greater than in response to the other stimulus regimens. In addition, the cardiac slowing in response to 8 Hz for 0.5 s every 1 s over 2 min was significantly greater than the response to 4 Hz continuously for 2 min. The results provide evidence to support the suggestion that the non-cholinergic, non-adrenergic cardiac response to stimulation of the vagosympathetic trunk is peptidergic in origin, and that the frequency of impulses is important in the gain of the response.

Adrenergic Antagonists↗
PubMed2005

Testosterone secretion and pharmacological spermatozoal recovery in the cane toad (Bufo marinus).

The cane toad (Bufo marinus) was used as a model to study male anuran reproductive endocrinology and to develop a protocol for non-invasive sperm recovery. Circulating testosterone concentrations in 6-hourly samples did not vary significantly (P < 0.05) over a 24 h period although there was a tendency (P = 0.06) for testosterone to be elevated at 19:00 h relative to other times of the day, which may be related to the nocturnal activity pattern of this species. Testosterone secretion after intraperitoneal (IP) injection of either a GnRH agonist (5 microg IP) or hCG (1000 IU) was also examined. While the GnRH agonist did not produce a significant increase above basal plasma testosterone (0.29, 95% C.I. of 0.05-1.10 ng/ml), injection of hCG resulted in an increase (P < 0.01) of plasma testosterone with peak concentrations at approximately 120 min (4.17, 95% C.I. of 2.69-7.44 ng/ml) after injection. Non-invasive pharmaceutical sperm recovery was attempted following IP injection of graded doses of GnRH agonist, hCG or FSH. Urine was collected at 3, 6 and 12 h after treatment to assess sperm quality and quantity. The optimal protocol for sperm recovery in cane toads was injection of either 1000 or 2000 IU hCG; there was no significant difference in the quality of the spermic urine samples obtained using either dose of hCG or with respect to collection time. The findings indicated that hCG can be used to assess testicular steroidogenic status and also to induce sperm recovery in the cane toad. The hCG protocols developed in this study will have application in studies on the reproductive biology of rare and endangered male anurans.

Animals↗
PubMed1993

Digitalis-like and vasoconstrictor effects of endogenous digoxin-like factor(s) from the venom of Bufo marinus toad.

Digitalis glycoside-like properties of the Bufo marinus toad crude venom and one of its constituents, bufalin, were studied in various assay systems. In concentrations 0.3-30 micrograms/ml crude venom increased the contractility of isolated electrically driven rat atria, constricted rat aortic rings, inhibited ouabain-sensitive Na+,K(+)-ATPase in rat erythrocytes and the Na+,K(+)-pump in rat aorta, and cross-reacted with antidigoxin antibody from the dissociation enhanced lanthanide fluoroimmunoassay (DELFIA). These effects were unaffected by adrenoceptor blockers and the 5-HT antagonist, deseril, but were blocked by antidigoxin antibody. Bufalin (10-30 microM) increased myocardial contractility and inhibited Na+,K(+)-ATPase in rat erythrocytes similarly to crude Bufo marinus venom. In rat aorta bufalin showed weak and delayed vasoconstrictor activity which was antagonized by 2 microM phentolamine, and had a biphasic effect on the Na+,K(+)-pump; 0.5-1.0 microM bufalin stimulated the pump, while higher concentrations inhibited its activity. Although the effects of bufalin were blocked by antidigoxin antibody, bufalin showed very low digoxin-like immunoreactivity in the DELFIA. These observations suggest that, in addition to bufalin, Bufo marinus venom contains at least one more digitalis-like steroid with significant intrinsic vasoconstrictor activity which, unlike bufalin, constricts the blood vessels acting directly via inhibition of the sodium pump in the vascular smooth muscle membrane.

Amphibian Venoms↗
PubMed1983

Open-loop analysis of the pulmocutaneous baroreflex in the toad Bufo marinus.

In the conscious toad, Bufo marinus, heart rate responses to manipulations of arterial pressure by vascular occlusion confirm that receptors sensitive to changes in intravascular pressure are located in the pulmocutaneous arteries. The cardiovascular responses to electrical stimulation of the central end of the laryngeal branch of the vagosympathetic trunk indicate that their afferents lie within this nerve. Inflation of an isolated pulmocutaneous sac in conscious toads in which the contralateral laryngeal nerve was cut resulted in a reduction of mean aortic pressure, with an associated bradycardia in some animals. Maximum open-loop gain for the relationship between sac pressure and aortic pressure was 0.35 +/- 0.06 (n = 5), resulting in a predicted maximum closed-loop gain of 0.25 +/- 0.03. Maximum gain occurred at 4.0-6.0 kPa, which was higher than the normal range of mean pulmocutaneous pressures in conscious undisturbed B. marinus, suggesting that the baroreceptors may be more effective in compensating for a rise than for a fall in pressure. This functional characteristic of the receptors suggests that not only may they modulate mean pressure in both the systemic and pulmocutaneous circuits, but that they may be particularly important in protecting the lung vasculature from excessive hydrostatic pressures.

Animals↗
PubMed1997

Morphological features of the retinal pigment epithelium in the toad, Bufo marinus.

BACKGROUND: The toad's (Bufo marinus) retinal pigment epithelium (RPE) has been used in many studies as a model for understanding its role and interaction with the neural retina (NR). In this study, the fine structure of the RPE is described. METHODS: In vitro RPE-chorion preparations from the toad were studied after separation from the NR. Tissues were processed for light and electron microscopy. RESULTS: The RPE consists of a single layer of cells joined by a series of tight junctions forming part of the blood-retina barrier. These cells had minimal infolding of the basal membrane and numerous microvillous processes extending from the apical surface and surrounding photoreceptor outer segments. Internally, RPE cells display a large nucleus, numerous mitochondria located at the basal membrane, extensive smooth endoplasmic reticulum, myeloid bodies, phagosomes, scattered polysomes, large lipid droplets and melanin granules. Rough endoplasmic reticulum is relatively scarce within these cells. The choriocapillaris consists of large blood vessels facing Bruch's membrane. Bruch's membrane is typical of other vertebrates, being pentalaminate over the whole retina. The endothelium of the choriocapillaris facing Bruch's membrane is typically very thin but shows few fenestrations. CONCLUSIONS: Due to the ultrastructural similarities of toad RPE with that of mammals, it can serve as an excellent model for the study of retinal detachment/reattachment and their cellular and molecular mechanisms.

Adaptation, Ocular↗
PubMed1997

Direct measurement of flow from the posterior lymph hearts of hydrated and dehydrated toads (Bufo marinus).

Flow from the posterior lymph hearts of Bufo marinus was measured using Doppler flow probes. These probes were placed on the posterior vertebral vein and recorded flow as lymph was ejected from the heart. In resting, hydrated toads, mean lymph flow from one of the paired posterior lymph hearts was 25.9 +/- 4.9 ml kg-1 h-1, stroke volume was 8.9 +/- 1.4 microL kg-1 and lymph heart rate was 47.5 +/- 3.7 beats min-1. We estimate that, together, the paired posterior lymph hearts are capable of generating flows that are approximately one-sixtieth of the resting cardiac output. Mean peak systolic pressure developed by the posterior lymph hearts was 1.62 +/- 0.08 kPa. Simultaneous measurements of lymph heart pressure development and flow revealed that the outflow pore of the heart opened at a pressure of 0.71 +/- 0.04 kPa, approximately 113 +/- 5 ms into systole. When toads were moderately disturbed, stroke volume increased by as much as fourfold with little change in lymph heart rate (< 5 beats min-1). When toads were dehydrated, lymph flow decreased by 70% at 12h and by 80% and 24h. Since there was only a modest non-significant decrease in lymph heart rate (30%), this reduction in flow was attributed to decreases in stroke volume (approximately 80%). Lymph heart flow and stroke volume returned to control values 30 min after adding water back into the experimental chamber. Stroke volume was clearly more important in regulating lymph flow than lymph heart rate under these conditions in Bufo marinus.

Animals↗
PubMed1991

Physiological significance of behavioral hypothermia in hypoxic toads (Bufo marinus).

We tested the hypotheses that hypoxic toads (Bufo marinus) in a thermal gradient would select a lower than normal temperature and that this behavioral response would be beneficial. Under normoxic conditions, selected body temperature was 24.2 +/- 3.6 degrees C. When inspired O2 was 10% or less, mean selected temperature decreased to 15.3 +/- 2.4 degrees C. The theoretical advantages of hypoxia-induced hypothermia we tested include (1) a reduction of oxygen uptake (VO2) by a Q10 effect; (2) increased arterial saturation (SaO2), (3) a decreased ventilatory response, and (4) a decreased stress response. Gas exchange, hematocrit, hemoglobin, SaO2, PaO2 and pH were measured at 25 degrees C (normal preferred temperature) and 15 degrees C (hypoxia preferred temperature) in toads breathing normoxic or hypoxic gas mixtures. During graded hypoxia at 15 degrees C, SaO2 was significantly increased and VO2 was significantly reduced compared with 25 degrees C. Graded hypoxia did not significantly affect VO2 at 25 degrees C, despite evidence for increased ventilation at that temperature (increased pH and respiratory exchange ratio, RE). At 15 degrees C, graded hypoxia had a significant effect on VO2 only at an inspired O2 of 4%. Increased RE with hypoxia was significant at 25 degrees C but not at 15 degrees C. Hematocrit and [hemoglobin] rose significantly during graded hypoxia at 25 degrees C but did not change at 15 degrees C. Toads exposed to 10% O2 (the value that elicits behavioral hypothermia) showed a significant respiratory alkalosis at 25 degrees C but not at 15 degrees C. Likewise, hypoxia caused a significant drop in SaO2 and PO2 at 25 degrees C. Cooling to 15 degrees C during hypoxia caused a significant rise in SaO2 but no change in PaO2. In conclusion, behavioral hypothermia is a beneficial response to hypoxia in Bufo marinus.

Acid-Base Equilibrium↗
PubMed1985

The ventilatory and acid-base physiology of the toad, Bufo marinus, during exposure to environmental hyperoxia.

Bufo marinus which were exposed to a step increase of 330-350 torr O2 for a 20 h period ceased lung ventilations and buccal movements were markedly decreased. Toads which were sitting in water did not show elevations in PaCO2 or a depressed pHe but animals which were dehydrated for a 24 h period prior to high O2 exposure developed a mild acidosis, which, typical of most amphibian species, was uncompensated.

Acid-Base Equilibrium↗