Interspecific Polymorphism of DEP1 Genes and the Spike Shape in Wheats

Although action potentials propagate along axons in an all-or-none manner, subthreshold membrane potential fluctuations at the soma affect neurotransmitter release from synaptic boutons. An important mechanism underlying analog–digital modulation is depolarization-mediated inactivation of presynaptic Kv1-family potassium channels, leading to action potential broadening and increased calcium influx. Previous studies have relied heavily on recordings from blebs formed after axon transection, which may exaggerate the passive propagation of somatic depolarization. We recorded instead from small boutons supplied by intact axons identified with scanning ion conductance microscopy in primary hippocampal cultures and asked how distinct potassium channels interact in determining the basal spike width and its modulation by subthreshold somatic depolarization. Pharmacological or genetic deletion of Kv1.1 broadened presynaptic spikes without preventing further prolongation by brief depolarizing somatic prepulses. A heterozygous mouse model of episodic ataxia type 1 harboring a dominant Kv1.1 mutation had a similar broadening effect on basal spike shape as deletion of Kv1.1; however, spike modulation by somatic prepulses was abolished. These results argue that the Kv1.1 subunit is not necessary for subthreshold modulation of spike width. However, a disease-associated mutant subunit prevents the interplay of analog and digital transmission, possibly by disrupting the normal stoichiometry of presynaptic potassium channels.

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Anatomic patterning in the expression of vestibulosympathetic reflexes

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.2000.279.1.r109 ◽

2000 ◽

Vol 279 (1) ◽

pp. R109-R117 ◽

Cited By ~ 31

Author(s):

I. A. Kerman ◽

B. J. Yates ◽

R. M. McAllen

Keyword(s):

Relative Proportion ◽

Vestibular Stimulation ◽

Nerve Fibers ◽

Spike Shape ◽

The Face ◽

Nerve Fascicle ◽

The Difference ◽

Vestibulosympathetic Reflexes

To investigate the possibility that expression of vestibulosympathetic reflexes (VSR) is related to a nerve's anatomic location rather than its target organ, we compared VSR recorded from the same type of postganglionic fiber [muscle vasoconstrictor (MVC)] located at three different rostrocaudal levels: hindlimb, forelimb, and face. Experiments were performed on chloralose-anesthetized cats, and vestibular afferents were stimulated electrically. Single MVC unit activity was extracted by spike shape analysis of few-fiber recordings, and unit discrimination was confirmed by autocorrelation. Poststimulus time histogram analysis revealed that about half of the neurons were initially inhibited by vestibular stimulation (type 1 response), whereas the other MVC fibers were initially strongly excited (type 2 response). MVC units with types 1 and 2 responses were present in the same nerve fascicle. Barosensitivity was equivalent in the two groups, but fibers showing type 1 responses fired significantly faster than those giving type 2 responses (0.29 ± 0.04 vs. 0.20 ± 0.02 Hz). Nerve fibers with type 1 responses were most common in the hindlimb (21 of 29 units) and least common in the face (2 of 11 units), the difference in relative proportion being significant ( P < 0.05, χ2 test). These results support the hypothesis that VSR are anatomically patterned.

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Theoretical analysis of parameters leading to frequency modulation along an inhomogeneous axon

Journal of Neurophysiology ◽

10.1152/jn.1976.39.4.909 ◽

1976 ◽

Vol 39 (4) ◽

pp. 909-923 ◽

Cited By ~ 56

Author(s):

I. Parnas ◽

S. Hochstein ◽

H. Parnas

Keyword(s):

Potassium Concentration ◽

Single Step ◽

Repetitive Firing ◽

Extracellular Potassium ◽

Pass Filter ◽

Low Pass Filter ◽

Extracellular Potassium Concentration ◽

Spike Shape ◽

Single Spike ◽

Low Pass

1. Theoretical computations were conducted on a computer model of a segmented, nonhomogeneous axon to understand the mechanism of frequency block of conduction. 2. The model is based on the Hodgkin-Huxley equations modified in several ways to better describe the cockroach axon. We used cockroach parameters where available. 3. The increase in fiber radius was spread over a series of segments to approximate a taper. We found that a taper allows a larger overall increase in fiber diameter than a single step to be successfully passed. 4. We studied effects on a train of impulses. The modified equations included effects due to changes in extracellular potassium concentration resulting from the repetitive firing of the axon. 5. An increase in diameter which allows a single spike to pass blocks the subsequent impulses in a train at the taper if potassium concentration variability is introduced. This could explain the low-pass filter characteristics of axon constrictions. 6. Results of the model fit well with the experiemental spike shape and height. Data were computed for the refractory period and its dependence on the taper parameters.

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ROMK1 (Kir1.1) Causes Apoptosis and Chronic Silencing of Hippocampal Neurons

Journal of Neurophysiology ◽

10.1152/jn.2000.84.2.1062 ◽

2000 ◽

Vol 84 (2) ◽

pp. 1062-1075 ◽

Cited By ~ 62

Author(s):

H. Nadeau ◽

S. McKinney ◽

D. J. Anderson ◽

H. A. Lester

Keyword(s):

Cell Death ◽

Hippocampal Neurons ◽

Fluorescent Protein ◽

Input Resistance ◽

Firing Frequency ◽

Compensatory Mechanisms ◽

Spike Shape ◽

Infected Cells ◽

Green Fluorescent ◽

Potential Threshold

Lentiviral vectors were constructed to express the weakly rectifying kidney K+ channel ROMK1 (Kir1.1), either fused to enhanced green fluorescent protein (EGFP) or as a bicistronic message (ROMK1-CITE-EGFP). The channel was stably expressed in cultured rat hippocampal neurons. Infected cells were maintained for 2–4 wk without decrease in expression level or evidence of viral toxicity, although 15.4 mM external KCl was required to prevent apoptosis of neurons expressing functional ROMK1. No other trophic agents tested could prevent cell death, which was probably caused by K+loss. This cell death did not occur in glia, which were able to support ROMK1 expression indefinitely. Functional ROMK1, quantified as the nonnative inward current at −144 mV in 5.4 mM external K+blockable by 500 μM Ba2+, ranged from 1 to 40 pA/pF. Infected neurons exhibited a Ba2+-induced depolarization of 7 ± 2 mV relative to matched EGFP-infected controls, as well as a 30% decrease in input resistance and a shift in action potential threshold of 2.6 ± 0.5 mV. This led to a shift in the relation between injected current and firing frequency, without changes in spike shape, size, or timing. This shift, which quantifies silencing as a function of ROMK1 expression, was predicted from Hodgkin-Huxley models. No cellular compensatory mechanisms in response to expression of ROMK1 were identified, making ROMK1 potentially useful for transgenic studies of silencing and neurodegeneration, although its lethality in normal K+ has implications for the use of K+ channels in gene therapy.

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Genetic variability of spelt factor gene in Triticum and Aegilops species

BMC Plant Biology ◽

10.1186/s12870-020-02536-8 ◽

2020 ◽

Vol 20 (S1) ◽

Author(s):

Valeriya Vavilova ◽

Irina Konopatskaia ◽

Alexandr Blinov ◽

Elena Ya. Kondratenko ◽

Yuliya V. Kruchinina ◽

...

Keyword(s):

Phylogenetic Relationships ◽

Chinese Spring ◽

Stop Codon ◽

Aegilops Tauschii ◽

Premature Stop Codon ◽

Gene Sequences ◽

D Genome ◽

Factor Gene ◽

Spike Shape ◽

Wide Range

Abstract Background Threshability, rachis fragility and spike shape are critical traits for the domestication and evolution of wheat, determining the crop yield and efficiency of the harvest. Spelt factor gene Q controls a wide range of domestication-related traits in polyploid wheats, including those mentioned above. The main goal of the present study was to characterise the Q gene for uninvestigated accessions of wheats, including four endemics, and Aegilops accessions, and to analyze the species evolution based on differences in Q gene sequences. Results We have studied the spike morphology for 15 accessions of wheat species, including four endemics, namely Triticum macha, T. tibetanum, T. aestivum ssp. petropavlovskyi and T. spelta ssp. yunnanense, and 24 Aegilops accessions, which are donors of B and D genomes for polyploid wheat. The Q-5A, q-5D and q-5S genes were investigated, and a novel allele of the Q-5A gene was found in accessions of T. tibetanum (KU510 and KU515). This allele was similar to the Q allele of T. aestivum cv. Chinese Spring but had an insertion 161 bp in length within exon 5. This insertion led to a frameshift and premature stop codon formation. Thus, the T. tibetanum have spelt spikes, which is probably determined by the gene Tg, rather than Q. We determined the variability within the q-5D genes among hexaploid wheat and their D genome donor Aegilops tauschii. Moreover, we studied the accessions C21–5129, KU-2074, and K-1100 of Ae. tauschii ssp. strangulata, which could be involved in the origin of hexaploid wheats. Conclusions The variability and phylogenetic relationships of the Q gene sequences studied allowed us to clarify the relationships between species of the genus Triticum and to predict the donor of the D genome among the Ae. tauschii accessions. Ae. tauschii ssp. strangulata accessions C21–5129, KU-2074 and K-1100 are the most interesting among the analysed accessions, since their partial sequence of q-5D is identical to the q-5D of T. aestivum cv. Chinese Spring. This result indicates that the donor is Ae. tauschii ssp. strangulata but not Ae. tauschii ssp. tauschii. Our analysis allowed us to clarify the phylogenetic relationships in the genus Triticum.

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Physiological characterization of a rare subpopulation of doublet-spiking neurons in the ferret lateral geniculate nucleus

Journal of Neurophysiology ◽

10.1152/jn.00191.2020 ◽

2020 ◽

Vol 124 (2) ◽

pp. 432-442

Author(s):

Allison J. Murphy ◽

J. Michael Hasse ◽

Farran Briggs

Keyword(s):

Retinal Ganglion Cells ◽

Ganglion Cells ◽

Visual Response ◽

Retinal Ganglion ◽

Visual Responses ◽

Response Properties ◽

Physiological Characterization ◽

Visual Thalamus ◽

Spike Shape

Interest in visual system homologies across species has recently increased. Across species, retinas contain diverse retinal ganglion cells including cells with unusual visual response properties. It is unclear whether rare retinal ganglion cells in carnivores project to and drive similarly unique visual responses in the visual thalamus. We discovered a rare subpopulation of thalamic neurons defined by unique spike shape and visual response properties, suggesting that nonstandard visual computations are common to many species.

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Changes in Na+ Channel Currents of Rat Dorsal Root Ganglion Neurons Following Axotomy and Axotomy-Induced Autotomy

Journal of Neurophysiology ◽

10.1152/jn.00913.2001 ◽

2002 ◽

Vol 88 (5) ◽

pp. 2518-2529 ◽

Cited By ~ 60

Author(s):

Fuad A. Abdulla ◽

Peter A. Smith

Keyword(s):

Dorsal Root ◽

Dorsal Root Ganglion Neurons ◽

Small Cells ◽

Na Channel ◽

Spike Shape ◽

Cell Recording ◽

Ganglion Neurons ◽

Induced Changes ◽

Excitability Of Neurons ◽

Channel Currents

Section of rat sciatic nerve (axotomy) increases the excitability of neurons in the L4–L5 dorsal root ganglia (DRG). These changes are more pronounced in animals that exhibit a self-mutilatory behavior known as autotomy. We used whole cell recording to examine changes in the tetrodotoxin-sensitive (TTX-S) and the tetrodotoxin-resistant (TTX-R) components of sodium channel currents ( I Na) that may contribute to axotomy-induced increases in excitability. Cells were initially divided on the basis of size into “large,” “medium,” and “small” groups. TTX-S I Na predominated in “large” cells, whereas TTX-R I Napredominated in some, but not all “small cells.” “Small” cells were therefore subdivided into “small-slow” cells, which predominately exhibited TTX-R I Na and “small fast” cells that exhibited more TTX-S I Na. In contrast to results obtained in other laboratories, where slightly different experimental procedures were used, we found that axotomy increased TTX-R and/or TTX-S I Na and slowed inactivation. The effects were greatest in “small-slow” cells and least in “large” cells. The changes promoted by axotomy were expressed more clearly in animals that exhibited autotomy. Also, the presence of autotomy correlated with a shift in the properties of I Na in “large” rather than “small-slow,” putative nociceptive cells. These trends parallel previous observations on axotomy-induced increases in excitability, spike height, and spike width that are also greatest in “small” cells and least in “large” cells. In addition, the presence of autotomy correlates with an increase in excitability of “large” rather than “small” cells. Increases in TTX-R and TTX-S I Na thus coincide with axotomy-induced increases in excitability and alterations in spike shape across the whole population of sensory neurons. Injury-induced changes of this type are likely associated with the onset of chronic pain in humans.

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Characterization of Voltage-Dependent Ca2+ Currents in Identified Drosophila Motoneurons In Situ

Journal of Neurophysiology ◽

10.1152/jn.90464.2008 ◽

2008 ◽

Vol 100 (2) ◽

pp. 868-878 ◽

Cited By ~ 39

Author(s):

Jason W. Worrell ◽

Richard B. Levine

Keyword(s):

Neurotransmitter Release ◽

Cell Voltage ◽

Drosophila Genome ◽

Whole Cell ◽

Spike Shape ◽

Voltage Dependent ◽

Targeted Expression ◽

Firing Properties

Voltage-dependent Ca2+ channels contribute to neurotransmitter release, integration of synaptic information, and gene regulation within neurons. Thus understanding where diverse Ca2+ channels are expressed is an important step toward understanding neuronal function within a network. Drosophila provides a useful model for exploring the function of voltage-dependent Ca2+ channels in an intact system, but Ca2+ currents within the central processes of Drosophila neurons in situ have not been well described. The aim of this study was to characterize voltage-dependent Ca2+ currents in situ from identified larval motoneurons. Whole cell recordings from the somata of identified motoneurons revealed a significant influence of extracellular Ca2+ on spike shape and firing rate. Using whole cell voltage clamp, along with blockers of Na+ and K+ channels, a Ca2+-dependent inward current was isolated. The Drosophila genome contains three genes with homology to vertebrate voltage-dependent Ca2+ channels: Dmca1A, Dmca1D, and Dmα1G. We used mutants of Dmca1A and Dmca1D as well as targeted expression of an RNAi transgene to Dmca1D to determine the genes responsible for the voltage-dependent Ca2+ current recorded from two identified motoneurons. Our results implicate Dmca1D as the major contributor to the voltage-dependent Ca2+ current recorded from the somatodendritic processes of motoneurons, whereas Dmca1A has previously been localized to the presynaptic terminal where it is essential for neurotransmitter release. Altered firing properties in cells from both Dmca1D and Dmca1A mutants indicate a role for both genes in shaping firing properties.

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