scholarly journals Heterogeneous Potassium Conductances Contribute to the Diverse Firing Properties of Postnatal Mouse Vestibular Ganglion Neurons

2006 ◽  
Vol 96 (5) ◽  
pp. 2364-2376 ◽  
Author(s):  
Jessica R. Risner ◽  
Jeffrey R. Holt
Keyword(s):  
Action Potential ◽  
Tuning Curve ◽  
Sine Wave ◽  
High Threshold ◽  
Whole Cell ◽  
Vestibular Ganglion ◽  
Potassium Conductances ◽  
Low Threshold ◽  
Firing Properties ◽  
Ganglion Neurons

How mechanical information is encoded in the vestibular periphery has not been clarified. To begin to address the issue we examined the intrinsic firing properties of postnatal mouse vestibular ganglion neurons using the whole cell, tight-seal technique in current-clamp mode. We categorized two populations of neurons based on the threshold required to evoke an action potential. Low-threshold neurons fired with an average minimum current injection of −43 pA, whereas high-threshold neurons required −176 pA. Using sine-wave stimuli, we found that the neurons were inherently tuned with best frequencies that ranged up to 40 Hz. To investigate the membrane properties that contributed to the variability in firing properties we examined the same neurons in voltage-clamp mode. High-threshold neurons had larger cell bodies and whole cell capacitances but a resting conductance density of 0.18 nS/pF, nearly identical to that of low-threshold neurons, suggesting that cell size was an important parameter determining threshold. We also found that vestibular ganglion neurons expressed a heterogeneous population of potassium conductances. TEA-sensitive conductances contributed to the position of the tuning curve in the frequency domain. A 4-AP–sensitive conductance was active at rest and hyperpolarized resting potential, limited spontaneous activity, raised threshold, and prevented repetitive firing. In response to sine-wave stimulation 4-AP–sensitive conductances prevented action potential generation at low frequencies and thus contributed to the high-pass corner of the tuning curve. The mean low-pass corner (about 29 Hz) was determined by the membrane time constant. Together these factors contributed to the sharply tuned, band-pass characteristics intrinsic to postnatal vestibular ganglion neurons.

Membrane Properties Related to the Firing Behavior of Zebrafish Motoneurons

2003 ◽  
Vol 89 (2) ◽  
pp. 657-664 ◽  
Author(s):  
Robert R. Buss ◽  
Charles W. Bourque ◽  
Pierre Drapeau
Keyword(s):  
Action Potential ◽  
Action Potentials ◽  
Membrane Conductance ◽  
Membrane Properties ◽  
High Threshold ◽  
Calcium Dependent ◽  
Larval Zebrafish ◽  
Plateau Potential ◽  
Potassium Conductances ◽  
Action Potential Burst

The physiological and pharmacological properties of the motoneuron membrane and action potential were investigated in larval zebrafish using whole cell patch current-clamp recording techniques. Action potentials were eliminated in tetrodotoxin, repolarized by tetraethylammonium (TEA) and 3,4-diaminopyridine (3,4-AP)-sensitive potassium conductances, and had a cobalt-sensitive, high-threshold calcium component. Depolarizing current injection evoked a brief (approximately 10–30 ms) burst of action potentials that was terminated by strong, outwardly rectifying voltage-activated potassium and calcium-dependent conductances. In the presence of intracellular cesium ions, a prolonged plateau potential often followed brief depolarizations. During larval development (hatching to free-swimming), the resting membrane conductance increased in a population of motoneurons, which tended to reduce the apparent outward rectification of the membrane. The conductances contributing to action potential burst termination are hypothesized to play a role in patterning the synaptically driven motoneuron output in these rapidly swimming fish.

Protein kinase activator 1-oleoyl-2-acetyl-sn-glycerol inhibits two types of calcium currents in GH3 cells

1988 ◽  
Vol 254 (1) ◽  
pp. C206-C210 ◽  
Author(s):  
C. Marchetti ◽  
A. M. Brown
Keyword(s):  
Protein Kinase ◽  
Chick Embryo ◽  
Calcium Currents ◽  
Gh3 Cells ◽  
High Threshold ◽  
Pituitary Cells ◽  
Excitable Cells ◽  
Whole Cell ◽  
Whole Cell Patch Clamp ◽  
Low Threshold

Two types of Ca2+ currents, high-threshold, long-lasting, or L currents and low-threshold, transient, or T currents, are present in many excitable cells. L-type Ca2+ current is modulated by, among others, beta- and alpha-adrenoreceptors and intracellular Ca2+, but modulation of T-type Ca2+ current is less well established. 1-Oleoyl-2-acetyl-sn-glycerol (OAG), a synthetic activator of protein kinase C (PKC), modulates whole cell Ca2+ currents in a variety of excitable cells. Whether activators of PKC affect preferentially L and T types of Ca2+ currents is unknown. We tested OAGs effects on whole cell Ca2+ currents in the clonal GH3 line of anterior pituitary cells. The currents were measured using the whole cell patch-clamp method. Four to 60 microM OAG reversibly reduced Ca2+ currents produced by test potentials to 10 mV, and the inhibition was half maximal at approximately 25 microM. Such concentrations depress Ca2+ currents in chick embryo dorsal root ganglion (DRG) cells and clonal AtT-20 pituitary cells. To test whether OAG acted preferentially on L or T current, we separated the two using depolarizing prepulses to inactivate T current. OAG (40 microM) attenuated T currents by 60% and L currents by 50%. The current waveforms were not changed and were simply scaled, and the effects on both occurred approximately 15 s after OAG was applied. In chick embryo DRGs OAG inhibited the T current by 30% and the L current by 50%. We conclude that PKC modulates Ca2+ currents by acting on both L and T Ca2+ channels.

Modulation of Voltage-Activated Calcium Currents by Mechanical Stimulation in Rat Sensory Neurons

1998 ◽  
Vol 80 (4) ◽  
pp. 1647-1652 ◽  
Author(s):  
Yona Bouskila ◽  
Hugh Bostock
Keyword(s):  
Action Potential ◽  
Sensory Neurons ◽  
Mechanical Stimulation ◽  
Action Potential Duration ◽  
Calcium Currents ◽  
Dorsal Root Ganglion Neurons ◽  
Patch Clamp Technique ◽  
Whole Cell Patch Clamp ◽  
Low Threshold ◽  
Ganglion Neurons

Bouskila, Yona and Hugh Bostock. Modulation of voltage-activated calcium currents by mechanical stimulation in rat sensory neurons. J. Neurophysiol. 80: 1647–1652, 1998. We examined the effects of mechanical stress, induced by a stream of bath solution, on evoked action potentials, electrical excitability, and Ca2+ currents in rat dorsal root ganglion neurons in culture with the use of the whole cell patch-clamp technique. Action-potential duration was altered reversibly by flow in 39% of the 51 neurons tested, but membrane potential and excitability were unaffected. The flow-induced increases and decreases in action-potential duration were consistent with the different effects of flow on two types of Ca2+ channel, determined by voltage-clamp recordings of Ba2+ currents. Current through ω-conotoxin–sensitive (N-type) Ca2+ channels increased by an estimated 74% with flow, corresponding to 23% increase in the total high voltage–activated current, whereas current through low-threshold voltage-activated (T-type) channels decreased by 14%. We conclude that modulation of voltage-activated Ca2+ currents constitutes a route by which mechanical events can regulate Ca2+ influx in sensory neurons.

scholarly journals Acute corneal epithelial debridement unmasks the corneal stromal nerve responses to ocular stimulation in rats: implications for abnormal sensations of the eye

2017 ◽  
Vol 117 (5) ◽  
pp. 1935-1947 ◽  
Author(s):  
Harumitsu Hirata ◽  
Kamila Mizerska ◽  
Valentina Dallacasagrande ◽  
Victor H. Guaiquil ◽  
Mark I. Rosenblatt
Keyword(s):  
Epithelial Cell ◽  
Sensory Information ◽  
Sensory Transduction ◽  
High Threshold ◽  
Nerve Terminals ◽  
Transduction Mechanisms ◽  
Cell Layers ◽  
Cold Sensitive ◽  
Low Threshold ◽  
Ganglion Neurons

It is widely accepted that the mechanisms for transducing sensory information reside in the nerve terminals. Occasionally, however, studies have appeared demonstrating that similar mechanisms may exist in the axon to which these terminals are connected. We examined this issue in the cornea, where nerve terminals in the epithelial cell layers are easily accessible for debridement, leaving the underlying stromal (axonal) nerves undisturbed. In isoflurane-anesthetized rats, we recorded extracellularly from single trigeminal ganglion neurons innervating the cornea that are excited by ocular dryness and cooling: low-threshold (<2°C cooling) and high-threshold (>2°C) cold-sensitive plus dry-sensitive neurons playing possible roles in tearing and ocular pain. We found that the responses in both types of neurons to dryness, wetness, and menthol stimuli were effectively abolished by the debridement, indicating that their transduction mechanisms lie in the nerve terminals. However, some responses to the cold, heat, and hyperosmolar stimuli in low-threshold cold-sensitive plus dry-sensitive neurons still remained. Surprisingly, the responses to heat in approximately half of the neurons were augmented after the debridement. We were also able to evoke these residual responses and follow the trajectory of the stromal nerves, which we subsequently confirmed histologically. The residual responses always disappeared when the stromal nerves were cut at the limbus, suggesting that the additional transduction mechanisms for these sensory modalities originated most likely in stromal nerves. The functional significance of these residual and enhanced responses from stromal nerves may be related to the abnormal sensations observed in ocular disease. NEW & NOTEWORTHY In addition to the traditional view that the sensory transduction mechanisms exist in the nerve terminals, we report here that the proximal axons (stromal nerves in the cornea from which these nerve terminals originate) may also be capable of transducing sensory information. We arrived at this conclusion by removing the epithelial cell layers of the cornea in which the nerve terminals reside but leaving the underlying stromal nerves undisturbed.

Mormyromast electroreceptor organs and their afferent fibers in mormyrid fish. III. Physiological differences between two morphological types of fibers

1990 ◽  
Vol 63 (2) ◽  
pp. 319-332 ◽  
Author(s):  
C. C. Bell
Keyword(s):  
Tuning Curve ◽  
Conditioning Stimulus ◽  
Receptor Potential ◽  
Sensory Cells ◽  
High Threshold ◽  
Afferent Fibers ◽  
Mormyrid Fish ◽  
Spike Number ◽  
Low Threshold ◽  
Physiological Differences

1. Mormyromast electroreceptor organs in electric fish of the family Mormyridae have two types of separately innervated sensory cells, the A and B sensory cells of Szabo and Wersall. The first paper in this series showed anatomically that afferent fibers from the two types of sensory cell terminate centrally in separate zones of the electrosensory lateral line lobe (ELL), fibers from A cells terminating in the medial zone and fibers from B cells terminating in the dorsolateral zone. The goal of the present study was to determine the physiological differences between the two morphologically distinct types of mormyromast afferent fibers. 2. The present study has two parts. In the first part, mormyromast fibers were recorded near their central terminals in the two mormyromast zones of ELL. In the second part, mormyromast fibers were recorded from a peripheral electrosensory nerve. In both parts, various electrosensory stimuli were delivered and voltage thresholds were measured at the electroreceptor. 3. In the first part of the study, mormyromast fibers terminating in the two central zones were found to be different in their thresholds and in the maximum number of spikes evoked by a single stimulus. Afferent fibers terminating in the medial zone, which arise from A sensory cells, had higher thresholds and smaller maximum spike numbers than fibers terminating in the dorsolateral zone, which arise from B sensory cells. 4. In the second part of the study, the same two groups of fibers--one group with a high threshold and a small maximum spike number, and a second group with a low threshold and a large maximum spike number--were identified in extracellular recordings from a peripheral electrosensory nerve. The thresholds of the two groups were quite distinct, allowing the fibers to be divided into high- and low-threshold groups, which most likely represent the fibers from the A and B sensory cells, respectively. 5. The high- and low-threshold groups of fibers recorded from peripheral nerve were found to be different in a number of additional properties besides threshold and maximum spike number. Additional differences were found in the following properties: strength-duration curve, correlation with a receptor potential recorded at the electroreceptor, tuning curve, and short latency facilitation by a conditioning stimulus. Thus there appear to be several physiological differences between mormyromast afferent fibers from A and B sensory cells, in addition to the differences in threshold and spike number.(ABSTRACT TRUNCATED AT 400 WORDS)

Development of Potassium Conductances in Perinatal Rat Phrenic Motoneurons

2000 ◽  
Vol 83 (6) ◽  
pp. 3497-3508 ◽  
Author(s):  
Miguel Martin-Caraballo ◽  
John J. Greer
Keyword(s):  
Action Potential ◽  
Potassium Currents ◽  
Perinatal Period ◽  
Repetitive Firing ◽  
Respiratory Drive ◽  
Calcium Dependent ◽  
Phrenic Motoneurons ◽  
Potential Shape ◽  
Potassium Conductances ◽  
Firing Properties

Prior to the inception of inspiratory synaptic drive transmission from medullary respiratory centers, rat phrenic motoneurons (PMNs) have action potential and repetitive firing characteristics typical of immature embryonic motoneurons. During the period spanning from when respiratory bulbospinal and segmental afferent synaptic connections are formed at embryonic day 17 ( E17) through to birth (gestational period is ∼21 days), a pronounced transformation of PMN electrophysiological properties occurs. In this study, we test the hypothesis that the elaboration of action potential afterpotentials and the resulting changes in repetitive firing properties are due in large part to developmental changes in PMN potassium conductances. Ionic conductances were measured via whole cell patch recordings using a cervical slice-phrenic nerve preparation isolated from perinatal rats. Voltage- and current-clamp recordings revealed that PMNs expressed outward rectifier ( I KV) and A-type potassium currents that regulated PMN action potential and repetitive firing properties throughout the perinatal period. There was an age-dependent leftward shift in the activation voltage and a decrease in the time-to-peak of I KV during the period from E16 through to birth. The most dramatic change during the perinatal period was the increase in calcium-activated potassium currents after the inception of inspiratory drive transmission at E17. Block of the maxi-type calcium-dependent potassium conductance caused a significant increase in action potential duration and a suppression of the fast afterhyperpolarizing potential. Block of the small conductance calcium-dependent potassium channels resulted in a marked suppression of the medium afterhyperpolarizing potential and an increase in the repetitive firing frequency. In conclusion, the increase in calcium-mediated potassium conductances are in large part responsible for the marked transformation in action potential shape and firing properties of PMNs from the time between the inception of fetal respiratory drive transmission and birth.

Benzolamide inhibits low-threshold calcium currents in hippocampal pyramidal neurons

1995 ◽  
Vol 74 (6) ◽  
pp. 2774-2777 ◽  
Author(s):  
J. A. Gottfried ◽  
M. Chesler
Keyword(s):  
Carbonic Anhydrase ◽  
Pyramidal Neurons ◽  
Hippocampal Slices ◽  
Pyramidal Cells ◽  
Calcium Currents ◽  
Dorsal Root Ganglion Neurons ◽  
High Threshold ◽  
Low Threshold ◽  
Ganglion Neurons ◽  
Ca Currents

1. Benzolamide is a poorly permeant sulfonamide inhibitor of the enzyme carbonic anhydrase. We studied the effect of benzolamide on low-threshold (LT) Ca currents in neonatal hippocampal CAl neurons. 2. In hippocampal slices, benzolamide (2-10 microM) inhibited the LT current 30-75% in voltage-clamped CAl pyramidal cells (n = 6). In slices bathed in N-2-hydroxypiperazine-N'-2-ethane-sulfonic acid (HEPES)-buffered Ringer, benzolamide also reduced the LT current, indicating that the action of the drug was not bicarbonate dependent. 3. Benzolamide inhibited LT Ca currents 20-75% in acutely dissociated CAl neurons in HEPES (n = 18): inhibition was 36 +/- 8% (mean +/- SE; n = 7) and 50 +/- 8% (n = 7) at 10 and 50 microM benzolamide, respectively. By contrast, high-threshold calcium currents recorded in CAl pyramidal cells (n = 18) and dorsal root ganglion neurons (n = 4) were virtually unaffected by benzolamide. 4. These results indicate that benzolamide inhibits LT Ca channels in central neurons and suggest caution in the use of this agent to inhibit extracellular carbonic anhydrase in excitable tissues.

Quantitative Analysis of Firing Properties of Pyramidal Neurons From Layer 5 of Rat Sensorimotor Cortex

1997 ◽  
Vol 77 (5) ◽  
pp. 2484-2498 ◽  
Author(s):  
Peter Schwindt ◽  
Jennifer A. O'Brien ◽  
Wayne Crill
Keyword(s):  
Firing Rate ◽  
Sensorimotor Cortex ◽  
Pyramidal Neurons ◽  
Repetitive Firing ◽  
High Threshold ◽  
Tonic Firing ◽  
Current Step ◽  
Low Threshold ◽  
Current Steps ◽  
Firing Properties

Schwindt, Peter, Jennifer A. O'Brien, and Wayne Crill. Quantitative analysis of firing properties of pyramidal neurons from layer 5 of rat sensorimotor cortex. J. Neurophysiol. 77: 2484–2498, 1997. Quantitative aspects of repetitive firing evoked by injected current steps and ramps were studied in layer 5 pyramidal neurons in brain slices of rat sensorimotor cortex to answer the following questions. Do the tonic firing properties of burst-firing and regular-spiking (nonbursting) neurons differ significantly? Does burst firing denote a discrete class of neurons or represent a continuum of firing properties? Is firing rate during the burst of action potentials related to stimulus amplitude? What aspect of the stimulus might the initial firing rate code? How stable are a neuron's firing properties over time? All recorded neurons fired tonically to a long-lasting current above a minimum value, and the tonic firing properties of most neurons were quite similar irrespective of their initial response to a current step. Only a group of high-resistance neurons had significantly different tonic firing properties. When slow current ramps (rising between 0.5 and ≈20 nA/s) were applied, the relation between firing rate and current during the ramp was very similar to the relation between tonic firing rate and current obtained from long-lasting current steps. Low-resistance cells exhibited three distinct initial responses to a current step: fast adaptation, high-threshold bursts, and low-threshold bursts, observed in 54, 28, and 10% of recorded cells, respectively. High-resistance cells exhibited a distinctive slow adaptation of firing rate. Slowly adapting, fast-adapting (FA), and high-threshold burster (HTB) neurons exhibited no adaptation near the minimum current that evoked repetitive firing ( I o). FA and HTB cells exhibited two-spike adaptation to a final tonic firing rate during currents up to 1.6 times I o. Only a higher current (2.1 times I o) evoked a burst in HTB cells, whereas a burst was evoked at I o in the low-threshold burster cells. In most cells analyzed, the initial firing rate, whatever its nature, increased monotonically with current step amplitude. The response to fast current ramps indicated that firing rate during adaptation or bursting may code rate of change of current. Repeated measurements during long-duration impalements indicated that both transient and tonic firing properties are stable over time. We discuss how the different tonic firing properties of large and small pyramidal neurons could be more important functionally than the different transient responses (burst/nonburst) of the large neurons. We conclude that the large neurons would perform a better linear transduction of time-varying synaptic current that reaches their somata. We compare the responses evoked by somatically injected current with those evoked by dendritic glutamate iontophoresis in previous studies.

scholarly journals Role of Intrinsic Properties in Drosophila Motoneuron Recruitment During Fictive Crawling

2010 ◽  
Vol 104 (3) ◽  
pp. 1257-1266 ◽  
Author(s):  
Jennifer E. Schaefer ◽  
Jason W. Worrell ◽  
Richard B. Levine
Keyword(s):  
Resting Membrane Potential ◽  
High Threshold ◽  
Intrinsic Properties ◽  
Whole Cell ◽  
Whole Cell Patch Clamp ◽  
Drosophila Larvae ◽  
Low Threshold ◽  
Evoked Activity

Motoneurons in most organisms conserve a division into low-threshold and high-threshold types that are responsible for generating powerful and precise movements. Drosophila 1b and 1s motoneurons may be analogous to low-threshold and high-threshold neurons, respectively, based on data obtained at the neuromuscular junction, although there is little information available on intrinsic properties or recruitment during behavior. Therefore in situ whole cell patch-clamp recordings were used to compare parameters of 1b and 1s motoneurons in Drosophila larvae. We find that resting membrane potential, voltage threshold, and delay-to-spike distinguish 1b from 1s motoneurons. The longer delay-to-spike in 1s motoneurons is a result of the shal-encoded A-type K+ current. Functional differences between 1b and 1s motoneurons are behaviorally relevant because a higher threshold and longer delay-to-spike are observed in MNISN-1s in pairwise whole cell recordings of synaptically evoked activity during bouts of fictive locomotion.

Sign in / Sign up

Export Citation Format

Share Document