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PubMed1986

Neurotoxic action of kainic acid in the isolated toad and goldfish retina: I. Description of effects.

The neurotoxic action of kainic acid (KA) was investigated by histological methods in the isolated retina of toads and goldfish. Particular attention was paid to the earliest and most sensitive response to KA in the outer plexiform layer (OPL). KA caused vacuolization of proximal and distal segments of horizontal cell dendrites in the OPL as well as perikaryal vacuolization and/or chromatin clumping in selected classes of neurons in the inner nuclear layer. Further, KA caused vacuolization and swelling in the inner plexiform layer. These effects were very similar in the retinae of goldfish and toad. The extent of vacuolization in the OPL was graded with KA concentration and with length of incubation. For 15-minute incubations, half-maximal vacuolization was found at 10-20 microM KA. At 25 microM KA, OPL vacuolization was evident within 1-2 minutes of application of KA. In goldfish, but not in toad, rod-connecting dendrites were less sensitive to KA than cone-connecting dendrites.

Animals↗
PubMedDate not supplied

Lack of teratogenicity of microcystin-LR in the mouse and toad.

Microcystin-LR (MC-LR) is a cyanobacterial toxin generated by the organism Microcystis aeruginosa. Although the hepatotoxicity of this chemical has been characterized, the potential developmental toxicity in vertebrates has not been well studied. The purpose of this study was to elucidate the effects of this toxin on the in vivo and in vitro development of mammals and the development of an Anuran (toad). Initial acute toxicity experiments with female CD-1 mice were accomplished with MC-LR administered i.p. in saline. Lethality occurred at 128 and 160 microg kg (-1) and histopathology revealed massive hepatic necrosis with diffuse hemorrhage. Developmental toxicity studies were done with MC-LR administered i.p. for 2-day periods: gestation days 7-8, 9-10 or 11-12. Doses used ranged from 2 to 128 microg kg(-1). On gestation day 17, fetuses were weighed and analyzed for gross morphological and skeletal defects. No treatment-related differences were seen in litter size, viability, weight or the incidence of anomalies. Groups of dams dosed with 32-128 microg kg(-1) on gestation days 7-8, 9-10 or 11-12 were allowed to give birth and the growth and development of their pups were followed postnatally. There were no significant effects noted in the offspring of the treated dams. Neurulation-staged CD-1 mouse conceptuses were exposed to 50-1000 nM MC-LR in whole embryo culture for 24 h. No significant increase in abnormalities or developmental delays was observed. Finally, exposure of the developing toad. Bufo arenarum was done from stage 17 (tail bud) for 10 days at concentrations of 1-20 mg l(-1). No effect on morphological development or survival was noted in any exposed groups. These data indicate that microcystin does not appear to affect development adversely in the mouse (in vivo or in vitro) or the toad at the doses and exposure parameters used.

Animals↗
PubMed1991

Behavioral thermoregulation of the toad, Bufo marinus: effects of air humidity.

Two experiments were performed. The first tested the hypothesis that the toad, Bufo marinus, will select a lower ambient temperature under dry environmental conditions. This behavioral response would reduce evaporative water loss and facilitate survival on land. The second experiment measured the effects of temperature on evaporative water loss. In the first experiment, toads were placed in a thermal gradient (11-40 degrees C) for 3 days. On days 1 and 3, water-filled dishes were placed along the temperature gradient and humid air was circulated through the chamber. On day 2, water dishes were removed, and dry air was circulated through the chamber. Body temperature (Tb) was recorded with a cloacal thermistor. Selected Tb was approximately 8.6 degrees C lower during the dry conditions than during the humid conditions. The behavioral hypothermia took about 6 h to develop. In the second experiment, a reduction in Tb from 17.7 to 12 degrees C reduced evaporative water loss by 42%. Consequently, behavioral hypothermia of the toad is an important adaptation to dry environmental conditions.

Animals↗
PubMed1992

The role of hypoglossal sensory feedback during feeding in the marine toad, Bufo marinus.

Behavioral observations demonstrate that bilateral deafferentation of the hypoglossal nerves in the marine toad (Bufo marinus) prevents mouth opening during feeding. In the present study, we used high-speed videography, electromyography (EMG), deafferentation, muscle stimulation, and extracellular recordings from the trigeminal nerve to investigate the mechanism by which sensory feedback from the tongue controls the jaw muscles of toads. Our results show that sensory feedback from the tongue enters the brain through the hypoglossal nerve during normal feeding. This feedback appears to inhibit both tonic and phasic activity of the jaw levators. Hypoglossal feedback apparently functions to coordinate tongue protraction and mouth opening during feeding. Among anurans, the primitive condition is the absence of a highly protrusible tongue and the absence of a hypoglossal sensory feedback system. The hypoglossal feedback system evolved in parallel with the acquisition of a highly protrusible tongue in toads and their relatives.

Animals↗
PubMed2006

The tactile-stimulated startle response of tadpoles: acceleration performance and its relationship to the anatomy of wood frog (Rana sylvatica), bullfrog (Rana catesbeiana), and American toad (Bufo americanus) tadpoles.

I described the tactile-stimulated startle response (TSR) of wood frog (Rana sylvatica), bullfrog (Rana catesbeiana), and American toad (Bufo americanus) tadpoles. One purpose was to rank species in terms of maximum acceleration performance. Also, I tested whether anatomical indicators of performance potential were predictive of realized performance. TSRs were elicited in a laboratory setting, filmed at 250 Hz, and digitally analyzed. TSRs began with two, initial body curls during which tadpoles showed a broad spectrum of movement patterns. TSR performance was quantified by maximum linear acceleration and maximum rotational acceleration of the head/body, both of which tended to occur immediately upon initiation of motion (< 0.012 sec into the response). Bullfrog tadpoles had higher maximum acceleration than the other species, but other interspecific differences were not significant. The species' rank order for the anatomical indicator of linear acceleration potential was bullfrog > wood frog > American toad. The species' rank order for the anatomical indicator of rotational acceleration potential was bullfrog > wood frog = American toad. Thus, the anatomical indicators roughly predicted the rank order of interspecific average performance. However, the anatomical indicators did not correlate with individual tadpole performance. Variability in behavioral patterns may obscure the connection between anatomy and performance. This is seen in the current lack of intraspecific correlation between a morphological indicator of acceleration capacity and acceleration performance.

Animals↗
PubMed1998

Behavioural responses of Mallorcan midwife toad tadpoles to natural and unnatural snake predators

The activity levels of Mallorcan midwife toad tadpoles, Alytes muletensis, were compared in two natural torrent pools which differed in their use by predatory viperine snakes, Natrix maura. Activity levels were lower in a pool regularly used by snakes than they were in a snake-free pool, but were reduced in both pools when snakes were experimentally introduced in nylon bags. In the presence of snakes, however, activity was more suppressed in the pool that was usually snake-free. Corresponding reductions in activity were also observed when tadpoles were treated with chemical cues from Mallorcan N. maura in a gravitational flow-through system. However, tadpoles failed to respond to chemical cues from other species of amphibian-eating snakes, or even to those from N. maura collected from a different population in mainland Spain. As none of the snakes used had previously eaten midwife toads, the responses cannot be related to previous diet, and seem to be specific to those N. maura from the island of Mallorca. As viperine snakes were probably introduced to Mallorca about 2000 years ago, the evolution of anti-predator behaviour in midwife toad tadpoles must have occurred relatively recently. Copyright 1998 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed2000

Juvenile western toads, Bufo boreas, avoid chemical cues of snakes fed juvenile, but not larval, conspecifics.

Previous investigations have demonstrated the importance of predator diet in chemically mediated antipredator behaviour. However, there are few data on responses to life-stage-specific predator diets, which could be important for animals like amphibians that undergo metamorphosis and must respond to different suites of predators at different life-history stages. In laboratory choice tests, we investigated the chemically mediated avoidance response of juvenile western toads, Bufo boreas, to four different chemical stimuli: (1) live conspecific juveniles; (2) live earthworms; (3) snakes fed juvenile conspecifics; and (4) snakes fed larval conspecifics (tadpoles). Juvenile toads avoided chemical cues from snakes that had eaten juvenile conspecifics, but did not respond to the other three stimuli, including chemical cues from snakes fed larval conspecifics. In addition, the response to cues from snakes fed juveniles differed significantly from that of snakes fed larvae. To our knowledge, this is the first study to demonstrate the importance of diet in predator avoidance of juvenile anurans and the ability of juvenile toads to distinguish between chemical cues from predators that have consumed larval versus juvenile conspecifics. Copyright 2000 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed1995

Diurnal variation in alpha-melanocyte-stimulating hormone content of various brain regions and plasma of the Texas toad, Bufo speciosus.

We measured the concentrations of alpha-melanocyte-stimulating hormone (alpha-MSH) in various brain regions as well as in the pituitary gland and plasma of the toad Bufo speciosus during a 24-hr light:dark cycle. There was significant diurnal variation of alpha-MSH concentrations in the hypothalamus and brainstem. In both areas alpha-MSH concentrations were highest during the scotophase. Peak alpha-MSH concentrations in the hypothalamus were observed at 21.00 and 05.00 hr, while a single peak in alpha-MSH concentrations was observed in the brainstem at 21.00 hr. In contrast, peak alpha-MSH concentrations in the plasma were observed during the photophase at 17.00 hr, when brain concentrations of alpha-MSH were low. There was no significant diurnal variation observed in the pituitary content of alpha-MSH throughout the 24-hr light:dark cycle. These data suggest that different mechanisms control hypothalamic and pituitary alpha-MSH cells in the toad during the 24-hr light:dark cycle. The fact that peak alpha-MSH concentrations were observed in the hypothalamus during the activity period of the toad is consistent with the proposed role of alpha-MSH peptides in learning and memory processes.

Animals↗
PubMed1997

Reproductive endocrinology of the explosively breeding desert spadefoot toad, Scaphiopus couchii.

The spadefoot toad, Scaphiopus couchii, is an explosively breeding, desert dwelling amphibian that shows two characteristics hypothesized to select for a dissociated breeding pattern: it lives in a harsh environment and it has a very short, but predictable breeding period. We tested the hypothesis that these factors select for a dissociated breeding cycle by measuring plasma steroid hormones and the gametogenic cycles in a free-living population of S. couchii. Blood and tissue samples were obtained from prebreeding, calling (males only), amplexed, and postbreeding toads. In males, plasma testosterone (T), dihydrotestosterone (DHT), and corticosterone (B) differed significantly among reproductive groups, with calling and amplexing toads having the highest levels of each of these steroids. In females, plasma T, DHT, B, progesterone (P), and estradiol (E2) were measured; all steroids except B changed significantly among mating groups. Plasma T and E2 were greatest in prebreeding and amplexed females, while P and DHT were highest only in amplexed females. Primary spermatogonia (SPG I), secondary spermatogonia (SPG II), spermatocytes, spermatids (SPT), and spermatozoa embedded in Sertoli cells (SPS) all changed significantly among male breeding groups. Although all stages were present in all breeding groups, early stages of spermatozoa (SPG I and SPG II) were greatest in postbreeding males, while late stages (SPT and SPS) were highest in prebreeding, calling, and amplexing males. In females, oocyte stages I, II, III, V, and VI and atretic follicles also differed significantly among mating groups. Prebreeding female ovaries were dominated by late-stage (V and VI) oocytes which were subsequently ovulated during amplexus. In postbreeding females, oogenesis was well under way as indicated by the rising numbers of stage II and III oocytes. These results indicate that aspects of gametogenesis occur during and after breeding in both sexes. Although the results demonstrate that gonadal activity was high during the period of sexual activity, suggesting that S. couchii most closely fits an associated pattern of reproduction as defined by Crews (1984, Horm. Behav. 18, 22-28), we also found that gonadal activity continued past the breeding season. For this reason, S. couchii does not completely conform to an associated pattern.

Animals↗
PubMed1999

Hormone coexpression in the adult toad endocrine pancreas: double-label immunofluorescence under basal conditions and after glucose injection.

We have investigated the type and frequency of hormone coexpression in the endocrine pancreas of amphibians both under basal conditions and after sustained glucose loading. Adult male specimens of the wild toad Bufo arenarum were injected with a 50% (w/v) glucose solution (2 g/100 g) for 2 days, while control animals received an equal volume of the vehicle. Serum glucose levels were measured at the time of sacrifice and the pancreatic free lobe was processed for light microscopy. A double-labeling immunofluorescence study was performed for the detection of insulin (I), glucagon (G), somatostatin (S), and pancreatic polypeptide (PP). Heterospecific antisera against the following hormone combinations were used for their detection and immunocytochemical localization: I+G, I+PP, G+PP, S+G, and S+PP; visualization of the reacted IgG's was effected by fluorescein- and rhodamine-conjugated species-specific antibodies as fluorophores. Intracellular hormone coexpression was found to occur in the combinations G+PP, S+G, and S+PP. Moreover, glucose administration caused, together with a marked hyperglycemia (123 +/- 17 vs 23 +/- 1 mg/dl; P < 0.05), a decrease in the fraction of cells containing both G and PP together (from 106.3 +/- 8.1 to 26 +/- 4 cell/mm2) along with a reciprocal rise in the number of cells possessing G alone (from 128.7-152.3 to 235.9-274 cell/mm2). The fewer number of cells coexpressing either of the other two hormone combinations, however, were unaffected by glucose injection. With respect to the simultaneous measurement of I+G and I+PP, no cells were detected with both hormones of either pair, and the I-containing cells were more frequent in each instance in the control toads (264.8 +/- 22.3 to 269.2 +/- 27 cell/mm2). For both combinations, however, this value diminished significantly in the glucose-treated animals (108 +/- 2 cell/mm2 for I+G and 112.1 +/- 7. 8 cell/mm2 for I+PP). While the G-containing cells became more numerous (rising to 235.9 +/- 12.4, 274 +/- 26, and 250.4 +/- 23.7 cell/mm2 for I-G, G-PP, and G-S combinations, respectively), the PP- and S-containing cells remained unaffected. We conclude that the copresence of different hormones within the same cell is a relatively common finding in the non-I-secreting elements of the adult toad pancreas and that the proportions of specific cell types are affected by glucose administration. We thus propose that intracellular hormonal coexpression in this fashion may well represent a rapid and efficient regulatory mechanism for compensating for the metabolic stress imposed by glucose loading.

Animals↗
PubMed2000

Possible relationship between the B-cell threshold for glucose-induced insulin secretion and blood glucose concentrations in the normal toad.

The aim of this work was to gain information on the possible relationship between basal glycemia in the toad and the B-cell threshold for glucose-induced insulin release. Hence, pieces of pancreas from Bufo arenarum were incubated with 2 to 20 mM glucose or preincubated with 2 mM glucose plus the hexokinase and glucokinase inhibitors (50 mM of 2-deoxyglucose and mannoheptulose, respectively) followed by an incubation with different glucose concentrations. The maximal rate of insulin release occurred at 8 mM glucose, while 50% of the release (K(s50)) was observed at 7 mM glucose. Regardless of the glucose concentration employed, pancreas pieces preincubated with 2-deoxyglucose released less insulin than the corresponding controls. On the other hand, mannoheptulose significantly inhibited the release of insulin at high glucose concentrations, having no effect at low glucose concentrations. The blocking effect of these two inhibitors is the first indirect evidence of the existence of the hexokinase/glucokinase enzymic system in the toad pancreas. Since the activity ratio of this system determines the glucose sensitivity of the insulin secretory mechanism, it is concluded that the possible existence of a higher ratio of these enzymes in toad B cells could explain the particular characteristics of glucose sensitivity in this animal, which in turn may explain its low blood glucose concentration.

Animals↗
PubMed2001

Effect of an acute glucose overload on Islet cell morphology and secretory function in the toad.

The aim of this work was to study the effect of induced hyperglycemia on islet cell mass and insulin secretion in normal toads. Immunolabeled beta cell area, replication (bromodeoxyuridine) and apoptosis (propidium iodide) rate, islet neogenesis (cytokeratin), and insulin secretion in vitro were measured in adult male specimens of Bufo arenarum during and after interruption of the injection of either a 50% glucose solution (2 g/100 g) or its vehicle for 4 days. Glucose administration caused hyperglycemia (122.6 +/- 16.7 and 508.3 +/- 115.9 mg/dl vs 23.5 +/- 1.26 and 22.8 +/- 1.8 mg/dl, at days 3 and 5, respectively, P < 0.05) and a significant decrease in the number of islets/mm(2) (day 3: 9.7 +/- 0.9 vs 3.3 +/- 0.4, P < 0.05; day 5: 9.4 +/- 0.8 vs 7.4 +/- 0.6; day 9: 9.6 +/- 0.9 vs 6.2 +/- 0.4, P < 0.05) and in the percentage of immunolabeled beta cell area (day 3: 2.07 +/- 0.2 vs 0.5 +/- 0.1%, P < 0.05; day 5: 1.8 +/- 0.1 vs 0.6 +/- 0.1%; day 9: 1.7 +/- 0.1 vs 0.7 +/- 0.1%, P < 0.05). Glucose-injected animals had a simultaneous significantly higher percentage of BrdU-labeled beta cells (day 3: 0.46 +/- 0.02 vs 0.23 +/- 0.03%; day 5: 0.54 +/- 0.13 vs 0.22 +/- 0.02%; day 9: 0.61 +/- 0.0 vs 0.27 +/- 0.05%, P < 0.05) and cytokeratin-labeled endocrine cells (day 3: 0.21 +/- 0.06 vs 0.01 +/- 0.00%; day 5: 0.17 +/- 0.06 vs 0.01 +/- 0.01%; day 9: 1.25 +/- 0.2 vs 0.01 +/- 0.008%, P < 0.05) and a higher rate of apoptotic beta cells (day 3: 0.14 +/- 0.04 vs 0.05 +/- 0.02%; day 5: 0.4 +/- 0.06 vs 0.05 +/- 0.2, P < 0.05; day 9: 0.47 +/- 0.04 vs 0.06 +/- 0.03, P < 0.05). Comparable amounts of insulin were secreted in vitro by both groups in response to 2 mM glucose, whereas there was a significantly reduced response to 8 mM glucose in treated animals (day 3: 73 +/- 12 vs 165 +/- 20%; day 5: 74 +/- 11 vs 204 +/- 18%, P < 0.05). This decreased response to high glucose reverted to normal after removal of the glucose injection. These results show for the first time that short-term hyperglycemia triggers marked morphological and transient secretory changes in the toad pancreas similar in part to those elicited in the pancreas of several mammals. As with other results previously reported, these results support the usefulness of the toad as an alternative easily handled model to study the growth and secretory function of the endocrine pancreas.

Animals↗
PubMed2001

Molecular phylogeny and biogeography of West Indian toads (Anura: Bufonidae).

Toads of the Bufo peltocephalus Group (Anura: Bufonidae) occur throughout the Greater Antilles (Cuba to the Virgin Islands), a geographic region of relatively high endemicity. Previous morphological and immunological studies suggested that the West Indian toads are a monophyletic lineage derived from Neotropical Bufo but were unable to clarify relationships within the group. We examined the evolutionary relationships and biogeography of this group of frogs by collecting approximately 2 kb of mitochondrial DNA sequence data from eight West Indian species and selected non-West Indian species from the New World and the Old World. Our analyses support the monophyly of native West Indian toads and a New World origin for the group. Relationships among the West Indian species are less certain, but a Cuban lineage is defined in most analyses.

Animals↗
PubMed1994

Enhancement of angiogenesis in regenerating gastrocnemius muscle of the toad (Bufo viridis) by low-energy laser irradiation.

The effect of low-energy laser (He-Ne) irradiation on the process of neoformation of blood capillaries during regeneration in the toad (Bufo viridis) gastrocnemius muscle was studied using histomorphometric methods. The injured zones of the experimental toads were subjected to four direct He-Ne laser irradiations (632.8 nm wavelength; 6.0 mW for 2.3 min) every alternate day, commencing on the second day after injury. Muscles that were injured as above and subjected to red light irradiation served as control. The volume density (cm3/cm3) of the capillaries in the injured zone at 9 days after injury was significantly (P < 0.01) higher (0.09 +/- 0.006) than in the control muscles (0.048 +/- 0.007). At 14 days after injury, the volume density in the injured zone of the control muscles further increased, while the value in the laser-irradiated muscles remained unchanged. The surface density (m2/cm3) of the capillaries in the injured zone was 2.3-fold higher in the laser-irradiated muscles than in the control muscles at 9 days after injury. The surface density further increased in the control muscles between 9 and 14 days after injury, while in the laser-irradiated muscles there was a decrease in this value during the above period. The surface-to-volume ratios of the capillaries in the injured zone of control and laser-irradiated muscles indicate a straighter, rather than a convoluted appearance between 9 and 14 days after injury. It is concluded that He-Ne laser irradiation during skeletal muscle regeneration in the toad markedly promotes the process of neoformation of blood vessels in the injured zone.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Local motion processing in the optic tectum of the Japanese toad, Bufo japonicus.

The results of previous behavioral studies can be so interpreted that the prey-catching behavior in the toad is elicited if there is a 'local' motion restricted within a small part of the visual field, while it is suppressed if there is a 'global' motion over a large part of the visual field. This has led us to design experiments to answer a specific question (yet a very essential one for understanding neural processes underlying this behavior): Are there 'local motion detectors' in the toad's visual system that are not activated by 'global' motion over a large part of the visual field but are activated by 'local' motion confined within a smaller part of it? The present study showed that (1) the majority of the toad's tectal neurons exhibit properties of the 'local motion detectors' as defined above, and (2) these properties can be explained from the receptive field structure revealed in the present experiments. Based on these results, we suggest that the tectal 'local motion detectors' are essential for the detection and localization of small moving prey-objects in the natural environment while ignoring the large moving objects or the self-induced motion of the visual field.

Animals↗
PubMed1991

How does the toad's visual system discriminate different worm-like stimuli?

Behavioral experiments show that toads exhibit stimulus- and locus-specific habituation. Different worm-like stimuli that toads can discriminate at a certain visual location form a dishabituation hierarchy. What is the neural mechanism which underlies these behaviors? This paper proposes that the toad discriminates visual objects based on temporal responses, and that discrimination is reflected in different average neuronal firing rates at some higher visual center, hypothetically anterior thalamus. This theory is developed through a large-scale neural simulation which includes retina, tectum and anterior thalamus. The neural model based on this theory predicts that retinal R2 cells play a primary role in the discrimination via tectal small pear cells (SP) and R3 cells refine the feature analysis by inhibition. The simulation demonstrates that the retinal response to the trailing edge of a stimulus is as crucial for pattern discrimination as the response to the leading edge. The new dishabituation hierarchies predicted by this model by reversing contrast and shrinking stimulus size need to be tested experimentally.

Animals↗
PubMed1983

Peptide-containing nerves in the urinary bladder of the toad, Bufo marinus.

The distributions of peptide-containing nerves in the urinary bladder of the toad, Bufo marinus, were studied by means of fluorescence immunohistochemistry of whole-mount preparations. The bundles of smooth muscle in the bladder are well supplied by varicose nerve fibres displaying somatostatin-like immunoreactivity; these fibres probably arise from intrinsic perikarya. The urinary bladder also has a well-developed plexus of nerves containing substance P-like immunoreactive material; these elements probably represent sensory nerves of extrinsic origin. Nerve fibres showing immunoreactivity to vasoactive intestinal polypeptide (VIP) or enkephalin are rare within the urinary bladder of the toad. It is considered unlikely that any of these peptides directly mediates the hyoscine-resistant excitatory response of the smooth muscle to nerve stimulation in the toad bladder.

Animals↗
PubMed1982

Splenic white pulp as a thymus-independent area in the African clawed toad, Xenopus laevis.

An indirect immunofluorescence study of the frozen sections of the spleen of an anuran amphibian, Xenopus laevis, showed that lymphocytes bearing a small amount of immunoglobulin (Ig) were localized mostly in the white pulp of non-immunized toads. There were fewer fluorescent cells in the red pulp. In the toads hyperimmunized with human gamma globulin (HGG), cells with strong cytoplasmic fluorescence increased significantly in the outer part of the white pulp. Electron microscopy of spleens from these toads showed that plasma cells at different stages of maturation were abundant in the white pulp, whereas in the red pulp, a smaller number of maturer plasma cells were observed. These results indicate that, in contrast with its mammalian counterpart, the splenic white pulp of this anuran is the site where thymus-independent lymphocytes commence blast formation and transformation into plasma cells.

Animals↗