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PubMed1992

Influence of temperature and photoperiod on plasma melatonin in the mudpuppy, Necturus maculosus.

A melatonin (MEL) radioimmunoassay employed previously only in mammals was used to estimate plasma MEL in a salamander, Necturus maculosus. Validation procedures included thin-layer chromatography of plasma extracts, parallel inhibition curves of authentic MEL and serially diluted plasma and plasma extracts and quantitative recovery of authentic MEL added to pooled Necturus plasma. A diel cycle of plasma MEL was demonstrated in mudpuppies acclimatized for a minimum of 3 weeks under a 12L:12D photoperiod and 15 +/- 1 degrees and sampled in late March. The MEL cycle persisted under a reversed photoperiod (lights on, 1800 hr), but the amplitude of the MEL peak was diminished, and the peak was more than 180 degrees out of phase with the corresponding peak under a normal photoperiod. In animals acclimated to 5 degrees in mid-June under a 12L:12D photoperiod, the diel cycle of plasma MEL continued, but both midphotophase and midscotophase concentrations were reduced compared with 15 degrees controls. The diel cycle was also present in animals acclimated to 25 degrees, but the decrease in MEL concentrations was less marked than that in 5 degrees animals. Photoperiod is apparently the primary cue for cycles in plasma MEL in Necturus, but the cycle can be influenced by temperature.

Animals↗
PubMed1985

New amphibian models for the study of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP).

We report the development of two animal models in amphibians (frogs and salamanders) in whom 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) produces the behavioral (neurological) and biochemical equivalents of the human disease and, in addition, a measurable modification in at least one form of pigment-bearing cell from the neural crest, the skin melanocyte. We propose that this new approach can become an inexpensive, easily quantifiable model for the study of the effect of MPTP on the central and peripheral nervous systems. We also demonstrate that the toxic effect of MPTP can be completely abolished in vivo by treatment with a monoamine oxidase inhibitor and potentiated by an inhibitor of catechol-O-methyltransferase. MPTP is catabolised by oxidation into toxic metabolites, but 1-methyl-4-phenylpyridinium ion (MPP+), the proposed end-metabolite, is even more toxic than MPTP in this model, possibly through a different mechanism.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed1994

Electrophysiological and behavioral studies of taste discrimination in the axolotl (Ambystoma mexicanum).

Electrophysiological and behavioral experiments were performed to determine whether the taste system of the aquatic salamander, axolotl, discriminates taste stimuli. Taste responses were recorded extracellularly from the glossopharyngeal nerve bundle. The behavioral responses of axolotls towards various concentrations of NaCl, KCl, citric acid, quinine-hydrochloride, and sucrose were quantified by measuring the ratio of rejection towards gel pellets, each containing either unitary stimuli or binary mixtures of these chemicals. Rejection ratios [rejection/(rejection+swallowing)] towards the unitary stimuli except sucrose increased with concentration, but were not a single function of the magnitude of neural response induced by the stimuli. Degree of rejection was different depending on the quality of taste stimuli, suggesting that information processing of taste quality occurs in axolotls. The potential of NaCl to induce positive feeding behavior (swallowing) was suggested by a reduction in the rejection ratio of quinine-tainted pellets when they were mixed with 100 mM NaCl. Differential behavioral responses to quinine and NaCl show that axolotls have the ability to discriminate the taste quality of these stimuli.

Ambystoma mexicanum↗
PubMed1975

Gas transport efficacy of gills, lungs and skin: theory and experimental data.

The general functional principles encountered in respiratory organs of vertebrates are investigated. Generally three steps are involved in external gas exchange in vertebrates: (1) convective transport by flow of external respiratory medium, air or water (=ventilation); (2) transfer of gas between external respiratory medium and blood by diffusion (=medium/blood transfer); (3) convective transport by blood flow (=perfusion). According to the arrangement of external medium flow relative to capillary blood flow four construction principles may be distinguished: (a) counter-current system (fish gills), (b) cross-current system (avian lungs), (c) ventilated pool system (mammalian lungs), and (d) infinite pool system (amphibian skin). The gas transfer performance of these systems is analyzed in terms of conductances, relative partial pressure differences and limitations attributable to ventilation. to medium/blood transfer and to perfusion. The theory is applied to analysis of gas exchange data obtained in an elasmobranch fish, domestic fowl, dog and a lungless salamander. The analysis shows that, despite distinct differences in maximum efficiencies of these systems, the differences in efficiency values actually attained are much less pronounced, and may be even less marked when taking functional inhomogeneities into account which are neglected in this study.

Animals↗
PubMed1976

Aquatic life at high altitude: respiratory adaptations in the Lake Titicaca frog, Telmatobius culeus.

Telmatobius culeus has a combination of behavioral, morphological and physiological adaptations which allows an aquatic life in cool (10 degrees C) O2-saturated (at 100 mm Hg) waters at high altitude (3812 m). The skin surgace area is increased by pronounced folds and the cutaneous capillaries penetrate to the outer layers of the skin. The erythrocyte volume (394 mu3) is the smallest reported for amphibians. The P50 (15.6 at ph 7.65 and 10 degrees C) is the lowest, and the erythrocyte count (729 - 103/mm3) the highest for an anuran. The O2 capacity (11.7 vol%), hemoglobin (8.1 g/100 ml), hemoglobin concentration (0.281 pg/mu3) and hematocrit (27.9%) measured at 18 degrees C and 3800 m are all elevated in comparison with most amphibians. The O2 dissociation curve is sigmoid (n = 2), the Bohr factor is small (deltalog P50/deltapH = -0.30) and the buffering capacity (-8.9 m M HCO3 - 1-1) is typical for an aquatic amphibian. The metabolic rate (14.1 mul -g-1-h-u) is the lowest reported for a frog and among amphibians only the giant salamanders (Amphiuma, Necturus and Siren) have lower values. If prevent from surfacing in hypoxic waters, the frogs ventilate the skin by "bobbing" behavior; if allowed to surface, they will ventilate the small lungs and the metabolic rate increases to 23 mul-g-1-h-1.

Adaptation, Physiological↗
PubMed1981

Respiratory, circulatory and acid-base adjustments to hypercapnia in a strictly aquatic and predominantly skin-breathing urodele, Cryptobranchus alleganiensis.

Upon initial exposure to increased ambient CO2, Cryptobranchus is titrated along an in vivo buffer line whose slope is considerably reduced from that observed when whole blood samples are equilibrated in vitro. During this time, there is no apparent reduction in the PCO2 difference between arterial blood and inspired media (PaCO2 -PICO2), despite an increase in auxiliary respiratory activities (lung and buccopharyngeal ventilation). The development of this non-compensated respiratory acidosis in the skin-breathing salamander is reminiscent of the situation seen in gill-breathing fish where the control of the acid-base balance is achieved by means other than ventilation. The increased ventilatory activities in Cryptobranchus can be interpreted as a response to the effect that the acidotic conditions have on arterial oxygenation (i.e.: CO2 Bohr effect); as a result, PaO2 increases and appears to counteract the arterial hypoxaemia which would otherwise result. More prolonged hypercapnia leads to compensatory phase of acid-base adjustment whereby plasma bicarbonate increases along a gently rising PaCO2 line to a new steady state equilibrium. This compensatory stage is slow acting and offers little by way of restoring the arterial blood pH, at least over the 36-h CO2 exposure period studied. The recovery period in air-saturated conditions is very gradual with PaCO2 levels exhibiting an exponential pattern of decline. This, together with the PaCO2 -PICO2 observations above, lends support to an accumulating body of evidence which suggests that respiratory CO2 losses across the amphibian skin are passive or at best only poorly controlled.

Acid-Base Equilibrium↗
PubMed1991

Diffusion and perfusion limitation in alveolar O2 exchange: shape of the blood O2 equilibrium curve.

The limitations imposed by diffusion (Ldiff) and perfusion (Lperf) on alveolar gas exchange can be estimated using a simple model of alveolar-capillary gas transfer (Piiper and Scheid (1981) Respir, Physiol. 46: 193-208). These limitations indicate the fractional increase of gas exchange that would occur by raising pulmonary conductances for diffusion or perfusion to functionally infinite values. The (simple) model assumes linear relations between concentration and partial pressure for the gases studied. We have investigated in this study the effects of this assumption for estimating Ldiff and Lperf for O2 whose blood equilibrium curve is particularly non-linear in normoxia. The calculations suggest that Lperf is only slightly overestimated by the assumption of linear blood O2 binding. For Ldiff, there is a significant overestimation in normoxia, but in hypoxia the linear equilibrium curve yields sufficiently accurate estimates. Calculations for data estimated for man on the summit of Mt. Everest suggest that alveolar O2 uptake in deep hypoxia at rest is mainly limited by perfusion and to a lesser degree by diffusion (Lperf greater than Ldiff). For the sustained exercise of climbing, on the other hand, diffusion limitation is more prominent than perfusion limitation (Ldiff greater than Lperf). Large values of Ldiff are estimated for normoxic O2 uptake across the skin of the gill-less and lung-less salamander, and here, the effects of the alinearity of the O2 equilibrium curve are pronounced. It is concluded that the simplified model of alveolar-capillary gas transfer, with linear O2 equilibrium curve, can be very useful to estimate diffusion and perfusion limitations from experimental data.

Altitude↗
PubMed1976

Quantitative and comparative ultrastructure of the vertebrate cornea. I. Urodele Amphibia.

The cornea of the urodele amphibian Triturus c. cristatus was studied ultrastructurally in order to provide the basis for a comparison among corneas throughout the vertebrate phylum. The cornea of this salamander consists of relatively thick epithelium and basement membrane and thin Descemet's membrane, unlike the mammalian corneas. The outermost epithelial cells contain Ruthenium Red stainable extracellular filaments and intracellular vesicles which are thought to play a role in the process of lubricating the corneal surface. Occluding junctions have been observed in the apical region of the superficial epithelial cells and are considered as barriers to the intercellular passage of material. A thin substantia propria (stroma) consists of about 40 collagenous highly organized lamellae. The thicknesses of the basement membrane, Descemet's membrane and the epithelium are believed to represent the primitive situation in the process of corneal evolution.

Animals↗
PubMed1987

Changes in response waveform of retinal horizontal cells during dark and light adaptation.

Changes in response waveform of retinal horizontal cells during dark and light adaptation were examined in the tiger salamander retina. In addition to sensitivity changes, the response waveform of HC was altered during visual adaptation: following bleaching or in the presence of background illumination, a transient depolarizing overshoot was observed at the cessation of the test flash. In contrast to the hyperpolarizing light responses, the depolarizing off-overshoots do not follow the standard threshold recovery time course during dark adaptation, neither do they obey Weber's law for increment thresholds during light adaptation. Simultaneous intracellular recordings from photoreceptors and HC revealed that the off-overshoot responses in light-adapted HC are probably originated from a population of cells in the photoreceptor layer which are strongly coupled with the cones.

Adaptation, Ocular↗
PubMed1991

Regenerative sodium and calcium currents in goldfish retinal ganglion cell somata.

Whole-cell patch-clamp recordings were made from isolated goldfish retinal ganglion cell somata. Sodium- and calcium-dependent action potentials--blocked with tetrodotoxin (TTX) and Co2+ ions, respectively--were evoked under current-clamp. Depolarization of these somata under voltage clamp activated distinguishable Na+ and Ca2+ conductances: the former was permeable to Na+, blocked by TTX, impermeable to N-methyl-D-glucamine and tris(hydroxymethyl)aminomethane, and began to activate around -45 mV; the latter were permeable to Ca2+, but not Co2+, and began to activate around -55 mV. These results are consistent with recordings from carp, frog, salamander and rat retinal ganglion cells.

Animals↗
PubMed1993

Motion sickness in amphibians.

We explored the question of whether amphibians get motion sickness by exposing anurans (frogs) and urodeles (salamanders) to the provocative stimulus of parabolic aircraft flight. Animals were fed before flight, and the presence of vomitus in their containers after flight was used to indicate motion-induced emesis. None of the species that we studied vomited during the 8 to 10 parabolas of each flight. However, at least one specimen from each of the anuran species Rana rugosa, Rana nigromaculata, Hyla japonica, and Rhacophorus schlegelii vomited in a period of 0.5 to 42 h after flight. Some specimens of R. nigromaculata, H. japonica, and R. schlegelii were also observed retching without emesis either during or shortly after exposure to parabolic flight. We were unable to induce either emesis or retching behavior in the aquatic from Xenopus laevis. Among the urodeles studied we saw no signs of motion sickness in either adult or larval Cynops pyrrhogaster, but at least one larval Hynobius nebulosus vomited shortly after parabolic flight. The amphibian species that exhibited the most motion sickness were the same ones that showed the greatest amount of tumbling during the microgravity phases of their parabolic flights. The most distinctive difference between motion sickness in amphibians and mammals that vomit, including man, is the long delay between a provocative stimulus and emesis proper in the amphibians. The retching behavior we induced in the frogs was identical to that described previously for frogs treated with emetic drugs. H. japonica, exposed to extended periods of microgravity on the MIR Space Station, flattened their bellies against the substrate and dorsiflexed their heads in a manner reminiscent of drug-induced nausea. In light of our current observations of retching behavior in motion sick H. japonica, we suggest that the previously observed behavior of three frogs on the MIR Space Station was a manifestation of motion sickness.

Animals↗
PubMed1993

Monoclonal antibody substrates facilitate long-term regenerative growth of adult primate retinal neurons.

A culture system for adult monkey and human retinal cells was developed utilizing monoclonal antibodies as substrates. Monoclonal antibodies were made using monkey retinal membranes as immunogen, and screening for the ability to bind and facilitate growth of dissociated retinal neurons when used as a culture substrate. Two antibodies, MR1 and 9B5, which recognize immunohistochemically distinct cell surface antigens, were found to work effectively as a culture substrate for dissociated monkey retinal cells. A variety of dissociated monkey retinal neurons and glial cells grew extensive processes on MR1 and 9B5, and continued to express cell-specific antigens. In addition, many multipolar neurons remained electrically excitable after several days in culture. Dissociated human retinal cells did not cross-react with MR1 but grew well on 9B5. These results extend previous work showing that antibody substrates can support the growth of neurons derived from other vertebrate species (e.g., neonatal rat, adult salamander). The long-term survival and growth of primate cells in culture supports the current view that neurons in the adult mammalian central nervous system (CNS) may regenerate under permissive circumstances. Further, these data provide evidence that direct support by non-neuronal cells is not required and that regeneration in vitro may be mediated by suitably adhesive non-cellular substrates.

Animals↗
PubMed1994

Biocytin: a neuronal tracer compatible with rapid decalcification procedures.

The compatibility of neuronal tract-tracing and decalcification procedures was examined in salamander nasal chemosensory systems. Biocytin, but not horseradish peroxidase, retained its labeling capacity following rapid decalcification of the cranial bone. The combination of biocytin tract-tracing and decalcification procedures allows the visualization of labeled neurons and/or their projections within bony regions of intact specimens.

Ambystoma↗
PubMed1995

Hyperosmotic activation of transmitter release from presynaptic terminals onto retinal ganglion cells.

A method for evoking neurotransmitter release without light stimulation has been developed and applied to a retinal slice preparation of the tiger salamander (Ambystoma Tigrum). This method utilizes a micropipette containing hyperosmotic levels of sucrose in Ringer, positioned within the inner plexiform layer (IPL) under visual control. Intermittent pressure (between 0.1 and 2 bars) applied to the pipette evoked release of neurotransmitters which were evaluated with whole-cell recording (WCR) technique applied to cells in the ganglion cell layer. Pharmacological studies were used to characterize the properties of the hyperosmotic sucrose-evoked response (HSER) and in some cases, we compared the HSER with synaptic currents evoked by light stimulation. The HSER typically consisted of both inhibitory and excitatory components with a reversal potential in between that for chloride (approximately -60 mV) and non-specific cation channels (approximately 0 mV). Relatively pure inhibition or excitation could be revealed through pharmacological techniques by blocking the inhibition with picrotoxin/strychnine or by blocking the glutamatergic neurotransmission with D-AP7 (D-2-amino-7-phosphonoheptanoate) and NBQX (2,3-dihydroxy-6-nitro-sulfamoyl -benzo (F) quinoxaline). A comparison of light-evoked responses (LER) and the HSER suggested that they activate the same pool of releasable neurotransmitter.

2-Amino-5-phosphonovalerate↗
PubMed1984

Radioimmunoassay of pancreatic polypeptide in mammalian and submammalian vertebrates using a carboxyl-terminal hexapeptide antiserum.

Pancreatic polypeptide (PP) immunoreactivity in acid-ethanol extracts of the pancreas of representative species of mammals, birds, reptiles, amphibians, and fish was studied by a radioimmunoassay (RIA) that utilizes an antiserum which cross-reacts exclusively with the COOH-terminal hexapeptide of PP (CTPP). PP immunoreactivity in acid-ethanol extracts of rat nonpancreas tissues (stomach, duodenum, skeletal muscle, brain) was also examined. Significant concentrations of PP immunoreactivity were detected in the pancreatic extracts of all species, except fish. Appreciable quantities of PP immunoreactivity were also found in the stomach and duodenum of rats. In all cases, tissue extracts showed parallelism with reference PP (bovine) in the RIA. Gel chromatography (Sephadex G-50sf) of tissue extracts (rat, turtle) demonstrated a major peak of PP immunoreactivity, which eluted in the region of the reference PP. Salamander PP immunoreactivity eluted after bovine PP. In addition, the CTPP RIA can be applied to measure plasma levels of PP in rats, dogs, and humans. By using this PP RIA, we observed that plasma PP levels increase significantly in dogs (P less than 0.05) after intravenous administration of neurotensin. In rats, administration of intravenous bombesin resulted in a significant elevation of plasma PP.

Animals↗
PubMed1985

Swimming movements initiate bubble formation in fish decompressed from elevated gas pressures.

Young specimens of trout, catfish, sculpin and salamanders were equilibrated with elevated gas pressures, then rapidly decompressed to ambient pressure. The newly hatched forms tolerated extremely high gas supersaturations; equilibration pressures of 80-120 atm argon or 150-250 atm helium were required for in vivo bubble formation. During subsequent larval development, the equilibration pressures required decreased to just 5-10 atm and bubbles originated in the fins. Anesthetising older fish before decompression prevented bubble formation in the fins; this suggests that swimming movements mechanically initiate bubbles, possibly by a tribonucleation mechanism.

Ambystoma↗
PubMed1986

Freeze tolerance and intolerance as strategies of winter survival in terrestrially-hibernating amphibians.

The ability to tolerate extracellular freezing as an adaptation for winter survival was tested in seven species of terrestrially-hibernating amphibians found in eastern Canada. All species had only moderate supercooling abilities, with whole animal supercooling points of -1.5 to -3 degrees C. Two salamander species, Plethodon cinereus and Ambystoma laterale, and the toad, Bufo americanus, were freezing intolerant and were killed when frozen for 24 hr at temperatures just below their supercooling points. The major winter strategy of these animals appears to behavioural avoidance of subzero temperatures. Four species of frogs Rana sylvatica, Hyla versicolor, Hyla crucifer and Pseudacris triseriata, survived extracellular freezing at moderate subzero temperatures (-2 to -4 degrees C) for periods of time ranging up to 2 weeks. All four frog species accumulated low molecular weight carbohydrates as cryoprotectants, glycerol being the major cryoprotectant in adult H. versicolor, while immature adults of this species as well as the other three species all produced high levels of glucose as the cryoprotectant.

Acclimatization↗
PubMedDate not supplied

DIfferential ability of Ambystoma tigrinum hepatic microsomes to produce mutagenic metabolites from polycyclic aromatic hydrocarbons and aromatic amines.

A number of carcinogenic aromatic amines when activated by liver microsomes from a salamander, Ambystoma tigrinum, are mutagenic for Salmonella tester strains sensitive to frameshift mutagens. However, 2 polycyclic aromatic hydrocarbons (PAH) (benzo[alpha]pyrene (BaP) and perylene) that are rendered mutagenic by mammalian microsomes are not activated by Ambystoma mixed-function oxidases. BaP was chosen for study because it is a well-known environmental carcinogen; perylene, an isomer of BaP, has been implicated as a etiological agent in cutaneous neoplasia in Ambystoma. These results support the observation that amphibians are quite resistant to PAH carcinogenesis and suggest that aromatic amines may be more appropriate model carcinogens.

Animals↗