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PubMed1989

Individual correlation of morphology, muscle mechanics, and locomotion in a salamander.

Measurements were made on locomotor performance (burst run and swim speed, run and swim endurance), morphology (body, tail, and hindlimb length, body mass), and skeletal muscle mechanics (isometric: twitch and tetanic tension, rates of force development and relaxation; isotonic: maximal velocity of shortening and power output) in a size range of individual salamanders (Ambystoma tigrinum nebulosum) at 10 and 20 degrees C. The size dependence of each factor was determined, and the interindividual correlations among factors were measured after removal of size effects. Locomotor performance is positively related to body size: larger animals are faster and have higher endurance. Isometric tensions (standardized for muscle cross-sectional area) and isotonic properties are mass independent; rates of isometric force development and relaxation are negatively related to body mass. Locomotor performance capacities are not intercorrelated among individuals. Isometric force and rates of force development are highly intercorrelated as are maximal shortening velocity and power output. Several statistical techniques failed to uncover correlations among sets of variables (performance, morphology, muscle mechanics): neither fast individuals nor individuals with high endurance necessarily have relatively fast muscles or long limbs or tails after the effects of body size have been removed.

Ambystoma↗
PubMed1981

Isolated perfused salamander proximal tubule. II. Monovalent ion replacement and rheogenic transport.

Early proximal tubules of the salamander kidney (Ambystoma tigrinum) were isolated and perfused in vitro. Transepithelial and basolateral electrical potential differences, transepithelial resistances, and intracellular ionic activities were measured during removal of Na+, K+, or Cl- from the lumen, the bath, or both lumen and bath. The effects of these external ionic replacements are interpreted in terms of an equivalent circuit that represents the renal epithelium as a network of passive ionic resistances, ionic diffusion potentials, and active transport current sources. Results indicate that rheogenic transport across the basolateral membrane is substantially diminished by removal of Na+ from either lumen or bath or by removal of K+ from the bath. On the other hand, bilateral chloride removal produces an increase in transepithelial resistance but almost no change in the calculated rate of basolateral rheogenic transport. This suggests that the source of the basolateral rheogenic ion flux ia a Na-K-ATPae that actively transports an excess of outward Na+ over inward K+.

Animals↗
PubMed1987

Electrophysiological analysis of beta-receptor stimulation in salamander proximal tubules.

Electrophysiological response to isoproterenol stimulation was studied in isolated perfused salamander proximal tubules. The addition of 10(-5) M isoproterenol to the bath superfusate depolarized both the cell membrane, and transepithelial potentials by 2.2 +/- 0.2 and 0.31 +/- 0.04 mV, respectively (P less than 0.01, n = 35) and significantly reduced the apical-to-basolateral membrane resistance ratio by 30% (P less than 0.01, n = 7) from a control value of 3.7 +/- 0.6. These responses were blocked by 10(-6) M propranolol but not mimicked by 10(-4) M adenosine 3',5'-cyclic monophosphate. Qualitatively similar effects were observed with 10(-3) and 10(-7) M isoproterenol. Further characterization of the 10(-5) M isoproterenol response revealed 1) a 50% reduction in the response following the removal of organic substrates from the luminal perfusate, 2) an absolute requirement for sodium, and 3) an absolute requirement for a functioning basolateral Na+-K+-ATPase. The data suggest that beta-receptor stimulation may increase sodium reabsorption by activating sodium cotransport systems.

Animals↗
PubMed1991

Sodium transport in salamander proximal tubule at 5.5 degrees C.

Na+ transport and electrophysiology of isolated perfused proximal tubules of the salamander Ambystoma tigrinum were compared at 22 and 5.5 degrees C, a range over which these animals normally live. Both intracellular Na+ activity and basolateral membrane potential were unaffected by temperature, whereas transepithelial potential depolarized from -6.5 +/- 0.8 mV at 22 degrees C to -3.5 +/- 0.6 mV at 5.5 degrees C (P less than 0.05). Compared with 22 degrees C, reduction of temperature to 5.5 degrees C included major increases in apical membrane resistance (2,052 +/- 473 omega.cm2 to 18,464 +/- 2,667 omega.cm2) and basolateral membrane resistance (491 +/- 113 omega.cm2 to 1,780 +/- 256 omega.cm2) (P less than 0.01). Sequential increases of luminal glucose concentration allowed characterization of the Na(+) -glucose cotransporter at both temperatures. The Km was stable (2 mM), but the maximal activity (Vmax) at 5.5 degrees C of 167 peq/5 cm2 increased to 1,000 peq/5 cm2 at 22 degrees C (P less than 0.05). In parallel with this temperature sensitivity of apical Na+ entry, basolateral Na+ pump activity was reduced at low temperature. Rubidium uptake at 22 degrees C was reduced by 40% at 5.5 degrees C. The rate of decrease of intracellular Na+ activity when tubules were perfused with substrate-free solution was -2.6 +/- 0.7 mM/min at 5.5 degrees C, compared with -4.9 +/- 1.2 mM/min at 22 degrees C. We conclude that low temperature reduces both Na+ uptake and efflux, allowing stability of intracellular milieu despite reduction in net transepithelial transport.

Ambystoma↗
PubMed1994

Adaptive responses to Na(+)-coupled solute transport and osmotic cell swelling in salamander proximal tubule.

Measurements of basolateral membrane potential and relative K+ conductance were performed in isolated perfused proximal tubules from Ambystoma. To investigate adaptive increases in basolateral membrane K+ conductance (gK) associated with Na(+)-solute cotransport, measurements were made comparing transport of glucose and alanine, with changes caused by hypotonicity- and solute-induced cell swelling. Luminal perfusion with alanine produced results consistent with an adaptive increase in gK; perfusion with glucose failed to show this response. Hypotonic peritubular solutions also produced results consistent with an adaptive increase in gK, but isosmotic increases of peritubular glucose sufficient to swell the cells failed to produce this. No changes in the responses to luminal perfusion with alanine or glucose were induced by hypotonic peritubular solutions. With a high concentration of glucose in isosmotic peritubular solutions, perfusion of the lumen with glucose now produced results consistent with an adaptive increase in gK. Isosmotic peritubular solutions containing urea produced adaptive changes similar to those observed using hypotonic peritubular solutions, but when glucose was subsequently added to the lumen, no further adaptive response occurred. We conclude that cell swelling alone is insufficient to explain the mechanisms involved in the adaptive responses of gK occurring during Na(+)-solute cotransport in the salamander proximal tubule.

Adaptation, Physiological↗
PubMed2005

Imaging of Ca2+ dynamics within the presynaptic terminals of salamander rod photoreceptors.

Although the overall importance of Ca(2+) as a mediator of cell signaling and neurotransmitter release has long been appreciated, the details of Ca(2+) dynamics within the inner segments of vertebrate rod photoreceptors are just beginning to be elucidated. Even less is known regarding Ca(2+) dynamics within the rod presynaptic terminal compartment. Using fura-2 to report changes in intracellular Ca(2+), we imaged the responses of enzymatically dissociated salamander rod photoreceptors retaining intact axons and presynaptic terminals stimulated with a brief depolarizing puff of KCl (30 mM pipette concentration). In the vast majority of cells, the response was a large increase in Ca(2+) levels in the terminal compartment, but not in the soma. In contrast, rods exhibited a substantial elevation in somatic Ca(2+) levels when depolarized with a brief puff of 100 mM KCl (pipette concentration). These data are consistent with previously reported differences in Ca(2+) buffering mechanisms within the somatic and terminal compartments. Additionally, they may reflect the presence of Ca(2+) channels having distinct properties within the membranes of the two compartments. Consistent with this hypothesis, fluorescent immunocytochemistry using an antibody against the L-type Ca(2+) channel Ca(v)1.2 (alpha1C) subunit and semiquantitative confocal microscopy revealed a high concentration of immunoreactivity in the membranes of terminals of intact rods compared with the somata. Further investigations using enzymatically dissociated preparations of intact rod photoreceptors retaining their presynaptic terminals will allow further testing of these and other hypotheses regarding the compartmentalized regulation of Ca(2+) dynamics within rod photoreceptors.

Animals↗
PubMed1981

Physiological activity of newly differentiated olfactory receptor neurons correlated with morphological recovery from olfactory nerve section in the salamander.

1. Extracellular unitary recordings were made from the olfactory epithelium of the salamander, Ambystoma tigrinum, at numerous time points following olfactory nerve section. Unitary response properties were correlated with histological examination of the same tissues. 2. At 10 days following nerve section, unitary activity was rarely recorded in all regions of the epithelium. Histological examination indicated that virtually the entire mature olfactory receptor cell population had undergone retrograde degeneration. Transneuronal degeneration was not observed in the olfactory bulb, although the olfactory nerve and glomerular layers were substantially reduced in size. 3. At subsequent times, unitary impulse activity gradually returned, consisting of both spontaneous activity and odor-evoked discharges. Anatomical recovery of the olfactory epithelium preceded that of the olfactory bulb. A positive correlation was found between neuronal differentiation in the olfactory epithelium and the recovery of receptor cell function. 4. Patterns of spontaneous activity, odor specificities, intensity-response functions, and adaptive properties studied in newly differentiated olfactory receptor neurons were indistinguishable from those observed in control units. This indicated that these properties were intrinsic to the receptor neurons. 5. Spontaneously active and responsive units were encountered prior to olfactory nerve connection with the bulb. It is concluded that receptor neurons pass through two phases of functional maturity: the first independent of bulbar contact and the second dependent on presumed synaptic contact with bulbar neurons.

Ambystoma↗
PubMed1982

Topographic coding of olfactory quality: odorant-specific patterns of epithelial responsivity in the salamander.

1. Electrophysiological recordings were made on the ventral olfactory epithelium of the salamander Ambystoma tigrinum in order to investigate whether individual odorants can elicit unique patterns of receptor neuron responses. 2. Slow transepithelial voltage transients, Veog(-), were recorded from 30 sites on each epithelium. For each odorant a topographic pattern was derived from the Veog(-) amplitudes across the 30 recording sites. 3. Nine odorants were tested, each in seven animals, and topographic patterns of Veog(-) amplitudes were drawn for each animal. Due to the morphological variability among animals, the electrode sites for each animal were assigned to six epithelial regions for which responses were then compared by analysis of variance. 4. Odorant-specific regional differences in responsivity were observed. The odorants can be grouped according to the similarity of the topographic distributions of responses elicited by them. We observed that no two odorants elicited exactly the same response patterns. This suggests that olfactory receptor neurons with similar responses are grouped together in the same region of the epithelium. 5. Dramatic differences in responsivity among the various epithelial regions, irrespective of the test odorant, were also noted. This observation may be due to regional differences in receptor neuron density or overall sensitivity. 6. It is concluded that differences between the topographic distributions of receptor cell responses, elicited by the nine test odorants, permits these responses to be discriminated as unique patterns of information at the olfactory bulb.

Ambystoma↗
PubMed1987

Structure of the receptive fields of bipolar cells in the salamander retina.

1. The receptive-field structure of bipolar cells in the salamander retina has been examined using isolated retinae from dark-adapted eyes. 2. Receptive-field mapping was carried out with a 25-microns diam spot of light whose wavelength and intensity was intended to stimulate rods rather than cones. 3. Both hyperpolarizing and depolarizing bipolar cells showed receptive fields having a single central point of maximum sensitivity from which sensitivity declined radially. Antagonistic surrounds could not be demonstrated using a small spot of light. 4. The diameter of receptive fields was found to vary between 374 and 662 micron, consistent with a single bipolar cell being effectively connected to 323-1,275 rods. 5. Lucifer yellow injections of bipolar cells revealed dendritic arbors whose greatest dimensions varied between 43 and 70 microns, consistent with a direct synaptic connection of between 10 and 24 rods to each bipolar cell. 6. We rule out signal spread within the rod network, extensive lateral ramification of rod process, nonlinearity of synaptic transmission, and light scatter, as possible explanations of large bipolar cell receptive fields. It seems likely, instead, that signals are extensively shared between bipolar cells.

Ambystoma↗
PubMed1988

Responses of mitral/tufted cells to orthodromic and antidromic electrical stimulation in the olfactory bulb of the tiger salamander.

1. Responses evoked by electrical stimulation of the olfactory nerve and olfactory tracts were analyzed in 46 output cells of the salamander olfactory bulb, in vivo. Labeling of several cells with horseradish peroxidase indicated that they were mitral and/or tufted neurons. The responses contained reproducible sequences of depolarizing and hyperpolarizing potentials, which changed with increases in stimulus intensity. 2. Stimulation of the nerve with intensities subthreshold for evoking spikes in the recorded cell resulted in a small depolarization followed by a period of hyperpolarization, during which spontaneous spikes were suppressed. With suprathreshold stimulus intensities, a single spike or often a burst of spikes was evoked, followed by a complex prolonged hyperpolarization. When full spikes were blocked by injecting hyperpolarizing current through the recording electrode, an excitatory postsynaptic potential (EPSP) with two major components and sometimes a fast prepotential were observed at the beginning of the response. Amplitudes of the EPSP and hyperpolarization increased with graded increases in stimulus intensity. In tests with paired stimulus volleys, spike generation was inhibited for at least 1 s and often for several seconds during the hyperpolarization. 3. Stimulation of the tracts with intensities subthreshold for evoking spikes in the recorded cell resulted in a complex prolonged hyperpolarization. With suprathreshold stimulus intensities, a single spike was evoked, followed by a similar period of hyperpolarization. When full spikes were blocked by injecting hyperpolarizing current through the recording electrode, a small antidromic spike, presumably generated in the axon or initial segment, was often observed. Amplitude of the hyperpolarization increased with graded increases in stimulus intensity. In tests with paired volleys, generation of a full antidromic spike was inhibited for a period that usually began 20-30 ms, following the spike evoked by the conditioning stimulus and lasted 100-500 ms. Full antidromic spikes were evoked prior to the period of inhibition and small antidromic spikes were evoked during the period. 4. The mean latencies of single evoked spikes or the first spikes of bursts decreased from 22 to 17 ms with increases in the intensity of nerve stimulation and from 7 to 6 ms with increases in the intensity of tract stimulation. Only decreases in orthodromic latency were significant at P less than or equal to 0.05, as determined by one-sided t tests between the means of responses subdivided according to response pattern and relative stimulus intensity.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1989

Effects of prolonged light exposure, GABA, and glycine on horizontal cell responses in tiger salamander retina.

1. The effects of prolonged light exposure, gamma-aminobutyric acid (GABA), and glycine on the horizontal cell (HC) light responses were studied in the superfused flat-mounted isolated retinas of the larval tiger salamander. 2. Under prolonged dark-adapted conditions, the time-to-peak of the HC light response was approximately 2-4 s, and after the termination of prolonged (6-8 min) light exposure, the time-to-peak became approximately 0.5-1 s. 3. This prolonged light-induced change in response rise time was not observed in either photoreceptors or bipolar cells, and thus the change in HC response rise time may occur postsynaptically in the HC membrane. 4. Application of 100 microM of GABA mimicked prolonged darkness and reversibly slowed down the HC response rise time, and application of 100 microM bicuculline mimicked prolonged light exposure and reversibly sped up the HC response rise time. 5. Glycine also slowed down the HC response rise course, but its effect was not observable until the concentration was raised to 1-3 mM. Strychnine did not exert any effect on HC responses when applied alone, but it could reverse the glycine actions. 6. The actions of glycine disappeared in the presence of bicuculline, indicating that the GABA and glycine pathways were probably not independent. Application of 5-10 mM glycine produced an increase of flow of preloaded 3H-GABA from the retina. 7. These results indicate that GABA may be the primary modulator that slows down the kinetics of the postsynaptic membrane proteins in the HCs. The extracellular concentration of GABA is probably high in prolonged darkness, and it is low after prolonged light exposure. Glycine, when applied at high dose, results in an increase of GABA release that slows down the HC response time course. 8. Prolonged darkness and light exposure appear to modulate the HC response in the time domain through GABA, and this change in HC response time course is probably responsible for shaping the bipolar cell responses and making the retinal signals more transient under light-adapted conditions.

Acclimatization↗
PubMed1989

Patterns of intracellular potentials in salamander mitral/tufted cells in response to odor stimulation.

1. Changes in membrane potential and temporal patterns of spikes were analyzed in 30 output cells in the salamander olfactory bulb in response to stimulation with 1-s pulses of the odorants isoamyl acetate, cineole, and camphor. The odor responses were more complex than responses to electrical stimulation of the olfactory nerve or olfactory tracts, with which they were compared. Most began with hyperpolarization and contained prolonged hyperpolarizing and depolarizing potentials that appeared to be compound postsynaptic potentials. These potentials were related to periods of spike inhibition and excitation. The temporal patterns of the responses resembled S-type (for suppression) and E-type (for excitation) patterns described previously in extracellular-unit studies. 2. In single cells, graded but nonmonotonic changes in the responses were observed with increases in the odor concentration from 10(-3) to 10(-1) vapor-phase saturation. Abrupt changes from one category of temporal response pattern to another were generally not observed in response to different concentrations of a single odorant but were frequently observed when the stimulus was changed from one odorant to another. 3. In S-type patterns, the first event was always membrane hyperpolarization and spike inhibition, regardless of the odor concentration. At all concentrations, simple S-type responses were observed in which a single period of hyperpolarization and inhibition lasted several seconds. At moderate to high concentrations, complex S-type responses were observed in which a period of excitation followed an initial period of hyperpolarization and inhibition. In these responses, spikes were often elicited near the termination of the odor pulse, occasionally as early as 300-400 ms after pulse onset. A prolonged period of inhibition followed the period of excitation. 4. In E-type patterns, the first event depended on the odor concentration. At all concentrations, complex responses were observed in which a period of excitation occurred with short latency, followed by a period of inhibition. At low to moderate concentrations, a brief initial period of hyperpolarization preceded the excitation. This initial period of hyperpolarization was always shorter than those in complex S-type responses to equivalent concentrations. However, the range of spike latencies overlapped that of S-type responses to high concentrations. With increasing odor concentration, spike latencies in the E-type responses decreased relative to the onset and peak of the initial hyperpolarization. At high concentrations. spikes were frequently elicited preceding a single period of hyperpolarization and inhibition.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1991

Dual effect of glycine on horizontal cells of the tiger salamander retina.

1. The effects of glycine on horizontal cells have been examined by microelectrode recording from superfused retinas isolated from the salamander. 2. Low concentrations of glycine (less than 50 microM) hyperpolarized horizontal cells and increased the magnitude of their light responses. Millimolar concentrations produced the opposite effect of depolarizing these cells and reducing their light response amplitudes. 3. In the presence of Co2+ and Mg2+ at concentrations sufficient to suppress the light response, millimolar glycine still exerted a depolarizing effect on horizontal cells, implying that this effect was largely a direct one on horizontal cell membranes. 4. Although both the rod and the cone contributions to horizontal cell light responses were reduced by millimolar glycine, rod input was reduced more, suggesting that millimolar glycine may also exert a presynaptic effect. 5. Strychnine (10 microns) antagonized the effects of millimolar glycine and, in the absence of exogenously applied glycine, caused horizontal cells to hyperpolarize and their light responses to increase in amplitude. This result implies that, in darkness, glycine is tonically released onto horizontal cells and maintains them in a state of partial depolarization. 6. The low-concentration effect of glycine was accompanied by an increased membrane resistance and receptive field size but no change in the balance of rod and cone input. 7. Low concentrations of glycine were often seen to cause a speeding of light responses, whereas high concentrations sometimes caused a slowing of response kinetics. Response kinetics were found to correlate with horizontal cell dark membrane potential so that, positive to -30 mV, depolarization slowed responses whereas kinetics at more negative values were largely independent of voltage.

Ambystoma↗
PubMed1991

The effects of glycine and GABA on isolated horizontal cells from the salamander retina.

1. Horizontal cells, identified by their morphology, were isolated from the salamander retina and examined in whole cell patch clamp. 2. All cells showed large outward currents activating positive to about -50 mV, and a minority of cells showed fast, tetrodotoxin-suppressible Na+ currents. Slow inward currents that might shape the light responses were never observed. 3. All cells showed conductance increases to both gamma-aminobutyric acid (GABA) and glycine that were completely blocked by bicuculline and strychnine, respectively. No cross-blocking by these antagonists was observed. Partial replacements of Cl- with large, impermeant anions indicated that both GABA- and glycine-evoked currents were carried by Cl- ions. 4. Responses to both GABA and glycine desensitized strongly with time constants of approximately 2 s. 5. Responses to glutamate were not enhanced by glycine. Similarly, responses to GABA were not enhanced by glutamate. 6. GABA-mediated synaptic interactions between horizontal cells may account for the changes in the kinetics of horizontal cell light responses seen when glycine is applied to the intact retina.

Action Potentials↗
PubMed1992

Dendritic origin of late events in optical recordings from salamander olfactory bulb.

1. Optical recordings of membrane-potential changes were used to characterize the origin and properties of the electrical signals from the dendritic level in slices of the salamander olfactory bulb. 2. The optical events were correlated with field-potential waves recorded simultaneously. Both responses exhibited patterns similar to those found in other species. 3. Orthodromic stimulation evoked a compound action potential in the olfactory nerve fibers, followed by two additional principal waves (N1 and N2). These field-potential waves reflected excitatory postsynaptic potentials at the primary mitral/tufted and granule cell dendrites, respectively. 4. Extrinsic optical signals from horizontal slices stained with the pyrazo-oxonal dye RH-155 showed a characteristic sequence of depolarizing and hyperpolarizing events. All of the signals exhibited a wavelength dependence expected for this dye and were abolished in the presence of high K+ in the bath. 5. According to their time courses, depolarizing responses under normal recording conditions were divided into two components, fast and slow. Orthodromic stimuli evoked a fast presynaptic response that represents synchronous compound action potentials from olfactory nerve fibers. At subglomerular levels, additional fast responses could often be recorded at the peri/subglomerular level and in the mitral/tufted somata region. These postsynaptic responses partially coincided with the rising phase of a different depolarizing signal, a slow component characterized by its prolonged time course. 6. With orthodromic stimulation, this slow signal attained its largest amplitude in the zone between the glomeruli and the superficial part of the external plexiform layer (EPL). Antidromic stimuli evoked a signal with some similarities to the one evoked orthodromically, but originating in deeper EPL regions. 7. Slow components were characterized by their Ca dependence. Low Ca2+ medium, or calcium channel blockers, suppressed this optical component, whether evoked orthodromically, antidromically, or by direct stimulation. In addition, Ba2+ (2.5-3.6 mM) in the bath did not abolish these responses, suggesting that they do not reflect a glial depolarization in response to elevated extracellular K+ concentration ([K+]o). 8. Locally applied stimuli next to the glomerular layer elicited these signals in 5-10 microM tetrodotoxin (TTX) or in low extracellular Na+ concentration ([Na+]o) medium, but antidromic or orthodromic stimuli failed to evoke the response under these conditions. The sizes of the responses to local stimuli remained constant, but an increase in their duration was observed in either TTX or low [Na+]o. 9. gamma-Aminobutyric acid (GABA) and baclofen reduced the size of the slow components in a dose-dependent manner.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1995

Salamander olfactory bulb neuronal activity observed by video rate, voltage-sensitive dye imaging. II. Spatial and temporal properties of responses evoked by electric stimulation.

1. Video imaging of changes in voltage-sensitive dye (VSD) fluorescence was used to analyze spatial and temporal properties of activity patterns in the in vivo salamander olfactory bulb and primordium piriform cortex after electric stimulation. Distribution of activity among and within the neuronal layers was analyzed after orthodromic stimulation of the whole olfactory nerve (ON), isolated fascicles, or local epithelial sites, and after antidromic stimulation of the medial olfactory tract (OT). 2. Optical signals propagated through the bulbar layers with a sequence that correlates with electrophysiological responses. After orthodromic stimulation, VSD responses started in the glomerular layer, spread to the deeper laminae, and, after reaching the region of mitral/tufted somata, were observed as a brief burst of activity in the OT. Compound action potentials in the ON were associated with short-duration, rapidly depolarizing optical responses in the ON layer. Responses in glomerular layer and external plexiform layer (EPL) first showed in some recordings a brief, small-amplitude hyperpolarization, followed by a period of depolarization, followed by a second, longer-lasting hyperpolarization. The periods of optical hyperpolarization could be related to events observed in intracellular mitral/tufted cell recordings. 3. With shocks delivered to the entire ON, depolarizing responses were nonhomogeneously distributed, appearing as multiple foci or bands of activity. Spatial patterns within each bulbar layer had poorly defined borders. Sites showing short-latency responses were often those with the largest and longest-lasting activity. 4. Increasing the intensity of stimulation to the ON enhanced the size and duration of the depolarizing and hyperpolarizing responses. The short-latency, early hyperpolarization was best seen with low-intensity, peripherally placed stimuli. 5. ON stimulation also elicited activity in the contralateral bulb. Activity started at the innermost layers and spread in patches to regions of the EPL just beneath the glomeruli. These had durations similar to ipsilateral responses, but longer latencies. A period of early hyperpolarization, longer than that on the ipsilateral side, was followed by prolonged depolarization and then by a second, later hyperpolarization. 6. Antidromic stimuli applied to the OT evoked optical responses consisting of a period of depolarization followed by hyperpolarization, similar to the components elicited by orthodromic stimuli. These responses had short time courses, began in the deeper layers, and spread to the superficial region of the bulb usually without reaching the glomerular region. 7. Punctate stimulation of the mucosa or nerve elicited depolarizing and hyperpolarizing events that depended on the stimulation site.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1995

Salamander olfactory bulb neuronal activity observed by video rate, voltage-sensitive dye imaging. III. Spatial and temporal properties of responses evoked by odorant stimulation.

1. Activity patterns across and within the laminae of the olfactory bulb were analyzed by imaging voltage-sensitive dye responses during odorant stimulation of all or part of the ventral olfactory mucosa. 2. The time course of the signals was generally characterized by a brief, small hyperpolarization, followed by a period of depolarization, and then a longer-lasting hyperpolarization similar to that seen with electric stimulation but with longer durations. 3. The activity was distributed nonhomogeneously across the bulbar laminae in the form of spatially segregated clusters having bandlike appearances. Clusters were observed with three monomolecular odorants, amyl acetate, ethyl-n-butyrate, and limonene, and with the complex odor of meal worms. Although response patterns to different odorants overlapped, they also showed differences in overall distribution. 4. Delivery of high odorant concentrations increased the size of the activated areas and accentuated the degree of response pattern overlap among different odorants. The general properties of the response patterns generated by each odorant were, however, similar at different odorant concentrations and in each of the animals tested. 5. The spatial and temporal distributions of the bulbar responses were somewhat similar regardless of whether the odorants were applied to local epithelial regions via punctate stimulation or to the entire mucosa. Certain regions did, however, have lower thresholds than others for eliciting bulbar activity in response to particular odorants. 6. Odorants applied to regions of the epithelium outside the areas of maximum sensitivity elicited odorant-related activity patterns with depolarizing and hyperpolarizing components similar to those seen with overall stimulation, but only if higher concentrations were used. Activation of distributed odorant sensitivities presumably gave rise to these patterns. 7. These data suggest that subsets of odorant receptor types are found in different areas of the olfactory epithelium, and demonstrate that there is widespread distribution across the epithelium of receptors sensitive to particular odorants. On the basis of the structure of these epithelial fields and the bulb response patterns that they relate to, these findings also provide evidence for complex spatial relationships between the olfactory epithelium and bulb. 8. The findings from this study suggest that representation of odor information in the salamander olfactory bulb does not occur by activation of a few selective bulbar regions, each related to a different odorant species. Instead, large regions of bulbar circuitry are involved in which molecular epitopes may be the unit of representation. Incorporation of new data presented here into a hypothesis of odor coding is discussed.

Animals↗
PubMed1995

Glutamate-gated chloride channel with glutamate-transporter-like properties in cone photoreceptors of the tiger salamander.

1. Using the patch-clamp technique, we investigated whether the glutamate-elicited current in mechanically isolated cone photoreceptors from the salamander retina is generated by a Cl- channel or a glutamate transporter. 2. The current reversed near the equilibrium potential for Cl-, was decreased by three Cl- channel blockers, 5-nitro-2-(3-phenyl-propylamino) benzoic acid, 4,4'-diisothiocyanostilbene-2,2'-disulfonate, and diphenylamine 2,2'-dicarboxylic acid, and was eliminated when gluconate was substituted for both internal and external Cl-, features consistent with the current being mediated by a Cl- channel. 3. The single-channel conductance of the Cl- channel was estimated by noise analysis of the glutamate-elicited current fluctuations to be 0.7 pS with an open time of 2 ms. 4. The magnitude of the current was dependent on both internal and external Na+ and K+, features consistent with the current being related to the activation of a glutamate transporter. Yet changes in their concentrations did not affect the reversal potential of the current. 5. Taken together with earlier reports on this current showing that it has a glutamate-transporter-like pharmacology, our results suggest that the glutamate-elicited current is carried by a Cl- channel but gated by a glutamate receptor whose pharmacology and ionic requirement resemble those previously described for glutamate transporters.

ATP-Binding Cassette Transporters↗