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PubMed1981

Acid-base balance and temperature in a predominantly skin-breathing salamander, Cryptobranchus alleganiensis.

Blood gases and pH and plasma [Na+], [K+], [Cl-] and [lactate] were measured on arterial blood of the large predominantly skin-breathing salamander, the hellbender (Cryptobranchus alleganiensis), at 5, 15 and 25 degrees C, both with and without access to air. Access to air had no effect of any of the acid-base variables, but temperature had significant effects on both pH and PCO2. Blood pH decreased with temperature by about 0.016 unit/degrees C both in vivo and in vitro (over the range studied) which is similar to the change previously observed on other ectotherms. Blood PCO2 rose significantly with temperature while plasma [HCO-3] rose slightly but insignificantly. Other ions were unaffected by temperature. This is the first demonstration that the characteristics ectothermic acid-base response to temperature occurs in a vertebrate respiring exclusively through its skin. We suggest that the response in this animal is essentially passive and uncontrolled and is due to: (1) the proportional effects of temperature upon metabolic CO2 production and blood PCO2, and (2) the temperature-independent CO2 conductance of the skin.

Acid-Base Equilibrium↗
PubMed1982

Acid-base regulation in response to environmental hypercapnia in two aquatic salamanders, Siren lacertina and Amphiuma means.

The partial pressure of CO2 (PCO2) in certain areas of the aquatic habitat of the salamanders Siren lacertina and Amphiuma means frequently rises to values of up to 60 mm Hg. This ambient hypercapnia occurs due to hindrance of gas exchange between water and air caused by dense water-surface vegetation. In order to investigate the acid-base regulation in response to the respiratory acidosis, which wound be expected to result from the high CO2 conductance of the amphibian skin, specimens of both species were subjected to water PCO2 of 47 mm Hg while having free access to normocapnic air in a closed water recirculation system. Arterial PCO2 rose considerably from 12 to 35 mm Hg in Siren and from 17 to 36 mm Hg in Amphiuma. The resultant fall in plasma pH remained uncompensated, whereas intracellular pH of white muscle and heart muscle of Siren were little affected owing to elevated intracellular bicarbonate concentrations. The bicarbonate accumulated in the intracellular compartments was in part produced by intracellular and extracellular nonbicarbonate buffering, and in part gained from the environment in exchange for Cl- ions. Elevated water bicarbonate concentration or bicarbonate infusion into Siren had no effect on the acid-base regulation. These data suggest that the availability of bicarbonate is not a limiting factor for extracellular compensation of increased PCO2, but that the threshold of the bicarbonate-regulating structures is simply not readjusted in hypercapnia. This type of regulation may have evolved as a result of the specific environmental conditions of these animals and may be considered as an energetically efficient way of maintaining a constant milieu for the pH-sensitive intracellular structures.

Acid-Base Equilibrium↗
PubMed1983

Receptive field properties of horizontal cells in the tiger salamander retina: contributions of rods and cones.

The spatial properties of horizontal cells in the tiger salamander retina were studied with intracellular electrodes. It was found that when the rod input to horizontal cells is dominant the receptive fields are smaller than those measured under conditions of strong cone activation. A possible explanation for this finding is that rod signals undergo greater lateral attenuation within the horizontal cell network.

Action Potentials↗
PubMed1984

Electrical coupling between horizontal cell bodies in the tiger salamander retina.

We studied lateral interactions between horizontal cells in the tiger salamander retina in order to determine the underlying mode of synaptic transmission. Pairs of cells, visually identified by inspection of the in vitro retinal slices, were impaled with two separate electrodes and the transmission between them was examined by injecting current into one cell while recording the resulting voltage response from the other soma. It was found that coupling between horizontal cells remained intact and even increased somewhat during the light response and in the presence of cobalt or acetylcholine. It was also observed that a fluorescent dye injected into one cell would often migrate and stain neighbouring horizontal cells. These results suggest that synaptic transmission between horizontal cell bodies is mediated mainly by electrotonic conduction. The increase in apparent coupling observed under certain experimental conditions can be explained by the increase in input resistance of each horizontal cell.

Acetylcholine↗
PubMed1984

Absorptance and spectral sensitivity measurements of rod photoreceptors of the tiger salamander, Ambystoma tigrinum.

The spectral sensitivity of the extracellularly-recorded photoresponse of isolated rods of the tiger salamander, Ambystoma tigrinum, was compared to the absorptance spectrum. Both measurements were made with the same optical system on the same portion of each cell to avoid errors that could occur when the two kinds of measurement were made under different conditions. The relative spectral sensitivity and absorptance spectrum were found to be in excellent agreement between 450 and 700 nm.

Ambystoma↗
PubMed1987

Light-dependent synaptic delay between photoreceptors and horizontal cells in the tiger salamander retina.

A long delay between the time to peak of the photoreceptor and horizontal cell light responses was observed in dark-adapted tiger salamander retinas. The rise of the HC light responses follows a biphasic time-course which is probably mediated by the removal of the rod and cone transmitters, but not by voltage-dependent mechanisms in the HC membrane. A bleaching white light shortens the signal delay and results in a faster and monophasic rise of the HC light responses mediated predominantly by the cones.

Action Potentials↗
PubMedDate not supplied

Reproducible proliferative responses of salamander (Ambystoma mexicanum) lymphocytes cultured with mitogens in serum-free medium.

There are several reports that proliferative responses (tritiated thymidine incorporation (3HTdR)) of salamander splenocytes cultured with phytohemagglutinin-P (PHA) or concanavalin A (Con A) in 1% fetal bovine serum (FBS)-supplemented medium are either statistically insignificant or never approach the magnitude typically observed in similarly treated cultures of frog lymphocytes. The present study confirms these findings, but also reports highly significant and reproducible PHA-induced proliferation of axolotl splenocytes and thymocytes when the medium is supplemented with 0.25% bovine serum albumin (BSA) rather than 1% FBS. In one study, splenocytes from six of six axolotls cultured in BSA-supplemented medium displayed a dose-dependent response to PHA with stimulation indices (SLs) ranging from 4.2 to 14.1. In contrast, SLs of PHA-treated cells from the same animals, cultured in parallel in FBS-supplemented medium, ranged from 0.8 to 3.0. In a kinetic study (cells harvested from days 3-7), maximal proliferation in BSA-supplemented medium was noted after 5 days; cells cultured in parallel in FBS-containing medium were not responsive to the mitogen at any time point. Although axolotl splenocytes do not exhibit PHA-stimulated growth in FBS-supplemented medium, they are reproducibly stimulated in this serum-containing medium by phorbol 12-myristate, 13-acetate (PMA). This suggests that FBS may interfere with (or does not support) some early step(s) in lectin-induced signalling, rather than with proliferation itself.

Ambystoma↗
PubMed1985

Acclimation to constant and variable temperatures in plethodontid salamanders--I. Rates of oxygen consumption.

In preliminary experiments, salamanders of three species (Desmognathus ochrophaeus, Plethodon cinereus and Plethodon jordani) required 5-11 days to complete metabolic acclimation to a constant warm temperature; the rate of oxygen consumption (VO2) decreased 16-28% during acclimation. Unfed animals of each species underwent cyclic exposure to 5 and 21 degrees C at three different cycle periods (12 hr, 4-5 days, 51 days), or constant exposure to 14 degrees C for 102 days. The experimental treatments significantly affected the VO2 measured at 5, 14, 17.5 and 21 degrees C. The direction and magnitude of the acclimatory effects upon VO2 were inconsistent among species and among experimental temperatures, and resulted in little energy saving. The VO2 during exposure to cyclic temperatures averaged only 83% of that during preliminary experiments, perhaps as a response to starvation.

Acclimatization↗
PubMed1987

Effects of metamorphosis on water permeability of skin in the salamander, Ambystoma tigrinum.

Developmentally associated changes in the pressure driven water permeability of the skin of the salamander Ambystoma tigrinum were measured at 20 degrees C in neotenic (gilled), transitional, and fully transformed adults. Mean values for the hydraulic conductivity of the skin (Lp, X 10(-5) cm.sec-1.ATM-1) were, respectively, 1.54, 0.54 and 0.13. This nearly 12-fold decrease in the H2O permeability coincides with the transition from aquatic to terrestrial life and may be related to the changing role of the skin in water conservation. The increase in hydraulic conductivity is opposite to the decrease in H2O diffusion rates reported by others. We suggest a theoretical basis for the apparently conflicting results.

Ambystoma↗
PubMed1982

Afferent visual projections in three species of lungless salamanders (family Plethodontidae).

Afferent visual projections were demonstrated in three species of plethodontid salamanders by means of anterograde transport of horseradish peroxidase. On the contralateral side three optic tracts and seven neuropil areas can easily be distinguished, which are similar among the three species examined as well as in European salamandrids. On the ipsilateral side the marginal optic tract shows great diversity. The retinal projections of the latter range from weakly labeled terminal fields restricted to the thalamus to heavily labeled fields covering the entire tectum opticum.

Animals↗
PubMed1983

Intracellular recordings from two cell types in an in vitro preparation of the salamander olfactory epithelium.

Two electrophysiologically distinct cell types were found with intracellular recordings for the first time in an in vitro preparation of the olfactory epithelium of the salamander, Ambystoma tigrinum. Intracellular recordings showed that Type I cells did not discharge action potentials but had high resting membrane potentials (-50 to -104 mV) and relatively low input resistances. Type II cells had resting membrane potentials of -24 to -52 mV, high input resistances, and discharged upon penetration and to depolarizing current steps. The discharge pattern of Type II cells showed the following characteristics: (1) decreased spike latency and increased discharge frequency with increasing current step intensity; (2) relatively slowly adapting spike trains; and (3) varying spike amplitude during repetitive discharges. The superficial location in the epithelium of the Type I cells implies that they may be sustentacular cells with glial-like electrophysiological properties. The Type II cells are presumably olfactory receptor cells, based on the characteristics of their spike discharge to depolarizing current and their intermediate location within the olfactory epithelium.

Action Potentials↗
PubMed1984

Distribution of accessory and hypoglossal nerves in the hindbrain and spinal cord of lungless salamanders, family Plethodontidae.

Study of the innervation of the musculature related to feeding behavior in plethodontid salamanders by means of the horseradish peroxidase (HRP) technique has demonstrated the existence of a true spinal accessory nerve which innervates neck musculature, enters the brain via the ganglion of IX/X cranial nerves and has its motor neurons within the nucleus of the second spinal nerve. Further, it has been shown that the first spinal nerve, being strictly motor, alone constitutes the ramus hypoglossus and is, therefore, homologous to the hypoglossus of amniotes.

Animals↗
PubMed1988

Colocalization of GABA and glycine immunoreactivities in a subset of retinal neurons in tiger salamander.

Alternate serial 1 micron Durcupan resin sections of tiger salamander retina were stained with antisera against GABA and glycine using postembed immunocytochemical techniques. Although the vast majority of neurons were labeled by either GABA or glycine antiserum, a small percentage of presumed amacrine cells in the inner nuclear layer and cells in the ganglion cell layer were clearly labeled by both antisera, indicative of colocalization of endogenous GABA and glycine. Although there is a greater than 90% chance that a labeled cell will be clearly labeled for either GABA or glycine immunoreactivity, the possibility for cotransmission of two inhibitory transmitters must be considered for a small percentage of these retinal neurons.

Animals↗
PubMed1992

Intracellular injection of vital dyes into single cells in the salamander olfactory epithelium.

Intracellular vital dye injection was used to examine the morphology of single sustentacular and receptor cells and the developmental fate of individual basal cells in the olfactory epithelium of the tiger salamander. In acute experiments, Lucifer yellow injections were used to identify single basal, receptor or sustentacular cells on the basis of their overall morphology. Dye-coupling between a number of the different epithelial cells was observed. Progeny of basal cells were examined by following labeled cells for up to 2 weeks using intracellular injection of rhodamine-labeled dextran. These experiments indicate that some olfactory epithelial cells are dye-coupled and that dye-filled basal cells can undergo division and migration.

Ambystoma↗
PubMed1993

Gonadotropin-releasing hormone agonist binding in tiger salamander nasal cavity.

Binding of the iodinated gonadotropin-releasing hormone (GnRH) agonist, buserelin, was examined in the nasal cavities of tiger salamanders using in vitro autoradiography. Binding of [125I]buserelin was seen within the chemosensory epithelium of the main nasal cavity and Jacobson's (vomeronasal) organ. Highest levels of binding were observed over the chemosensory neuron dendrites. Given the apparent lack of GnRH-immunoreactive fibers within the chemosensory epithelium as we have observed in a previous study, these observations suggest that GnRH may diffuse from fibers in the lamina propria of the chemosensory mucosa into the sensory epithelium to modulate chemosensory reception.

Ambystoma↗
PubMed1983

Hepatic arginase activity in intra- and extrauterine larvae of the ovoviviparous salamander. Salamandra salamandra (L.) (Amphibia, Urodela).

The hepatic arginase activity of Salamandra salamandra was determined at three different stages of intra- and extrauterine larval development and at fully metamorphosed juveniles. The highest enzymatic activity was found in intrauterine larvae in November, the lowest in intrauterine larvae in June of the following year. These data can be correlated with the ureotelism of intrauterine larvae previously described and are discussed with respect to the metabolism of larval and juvenile fire salamanders.

Animals↗
PubMed1987

Intracellular recordings from isolated salamander olfactory receptor neurons.

Isolated receptor cells were obtained by enzymatic dissociation of nasal sacs from the land-phase tiger salamander. The isolated cells have an ovoid soma, a dendrite of variable length which terminates in a cilia-bearing knob and an axon, also of variable length. Intracellular recordings were obtained using patch pipettes. Good recordings were characterized by resting potentials of -40 mV, high input impedance and the presence of fast overshooting action potentials upon depolarization or rebound excitation. With one cell, chemical stimulation evoked large depolarizations which produced action potentials. The reversal potential of this response was +2.7 mV. The results show that these cells can be dissociated for patch recordings, and they support previous studies indicating that transduction of olfactory stimuli leads to a depolarization of vertebrate olfactory receptor neurons.

1-Butanol↗
PubMed1990

Synaptic organization of serotonin-like immunoreactive amacrine cells in the larval tiger salamander retina.

Immunoelectron microscopy was used to investigate the ultrastructural features and synaptic relationships of serotonin-like immunoreactive amacrine cells in the larval tiger salamander retina. Serotonin-positive somas exhibited an evenly distributed peroxidase reaction product throughout their cytoplasm. Their nuclei were unstained and possessed indented nuclear membranes. Serotonin-immunoreactive processes were generally stained throughout with the exception of their mitochondria, whose morphology was often disrupted by the staining reaction. They were further characterized by an occasional dense-cored vesicle/s in addition to a generally homogeneous population of small, round, clear synaptic vesicles. Serotonin-immunoreactive amacrine cell processes formed conventional synapses that were characterized by symmetrical synaptic membrane densities. A total of 222 synaptic arrangements were observed that involved the immunostained processes of serotonin-amacrine cells. As presynaptic elements, they primarily contacted amacrine cells processes (37.8%). They also provided substantial synaptic input to processes that lacked synaptic vesicles (16.2%) and whose origin was unidentified. Serotonin-processes provided a far fewer number of synaptic contacts onto the processes of bipolar cells (1.4%) and the somas of cells in the amacrine cell layer (0.5%). As postsynaptic elements, they received synaptic inputs from amacrine cells (27.9%) and bipolar cells (16.2%). With the exception of their synapses onto bipolar cells and the somas of cells in the amacrine cell layer, each of the synaptic relationships of serotonin-amacrine cells was observed in each of sublayers 1-5 of the inner plexiform layer.

Ambystoma↗