Two Opposing Roles of 4-AP–Sensitive K+ Current in Initiation and Invasion of Spikes in Rat Mesencephalic Trigeminal Neurons

2006 ◽  
Vol 96 (4) ◽  
pp. 1887-1901 ◽  
Author(s):  
Mitsuru Saito ◽  
Yoshinaka Murai ◽  
Hajime Sato ◽  
Yong-Chul Bae ◽  
Tadashi Akaike ◽  
...  
Keyword(s):  
Current Pulse ◽  
Low Voltage ◽  
Initiation Site ◽  
Sensory Receptor ◽  
Trigeminal Neurons ◽  
K Current ◽  
Mesencephalic Trigeminal Neurons ◽  
Opposing Effects ◽  
Spike Initiation ◽  
Axonal Spikes

The axon initial segment plays important roles in spike initiation and invasion of axonal spikes into the soma. Among primary sensory neurons, those in the mesencephalic trigeminal nucleus (MTN) are exceptional in their ability to initiate soma spikes (S-spikes) in response to synaptic inputs, consequently displaying two kinds of S-spikes, one caused by invasion of an axonal spike arising from the sensory receptor and the other initiated by somatic inputs. We investigated where spikes are initiated in such MTN neurons and whether there are any differences between the two kinds of S-spikes. Simultaneous patch-clamp recordings from the soma and axon hillock revealed a spike-backpropagation from the spike-initiation site in the stem axon to the soma in response to 1-ms somatic current pulse, which disclosed the delayed emergence of S-spikes after the current-pulse offset. These initiated S-spikes were smaller in amplitude than S-spikes generated by stimulation of the stem axon; however, 4-AP (≤0.5 mM) eliminated the amplitude difference. Furthermore, 4-AP dramatically shortened the delay in spike initiation without affecting the spike-backpropagation time in the stem axon, whereas it substantially prolonged the refractory period of S-spikes arising from axonal-spike invasion without significantly affecting that of presumed axonal spikes. These observations suggest that 4-AP–sensitive K+ currents exert two opposing effects on S-spikes depending on their origins: suppression of spike initiation and facilitation of axonal-spike invasion at higher frequencies. Consistent with these findings, strong immunoreactivities for Kv1.1 and Kv1.6, among 4-AP–sensitive and low-voltage–activated Kv1 family examined, were detected in the soma but not in the stem axon of MTN neurons.

Arrangement and Connections of Mesencephalic Trigeminal Neurons in the Rat

1986 ◽  
Vol 127 (1) ◽  
pp. 7-15 ◽  
Author(s):  
J.T.M. Rokx ◽  
P.J.W. Jüch ◽  
J.D. van Willigen
Keyword(s):  
Trigeminal Neurons ◽  
Mesencephalic Trigeminal Neurons

scholarly journals Selective control of cortical axonal spikes by a slowly inactivating K+ current

2007 ◽  
Vol 104 (27) ◽  
pp. 11453-11458 ◽  
Author(s):  
Y. Shu ◽  
Y. Yu ◽  
J. Yang ◽  
D. A. McCormick
Keyword(s):  
Selective Control ◽  
K Current ◽  
Axonal Spikes

Multiple Modes of Action Potential Initiation and Propagation in Mitral Cell Primary Dendrite

2002 ◽  
Vol 88 (5) ◽  
pp. 2755-2764 ◽  
Author(s):  
Wei R. Chen ◽  
Gongyu Y. Shen ◽  
Gordon M. Shepherd ◽  
Michael L. Hines ◽  
Jens Midtgaard
Keyword(s):  
Action Potential ◽  
Primary Dendrite ◽  
Back Propagation ◽  
Olfactory Nerve ◽  
Mitral Cell ◽  
Initiation Site ◽  
Initiation And Propagation ◽  
Action Potential Initiation ◽  
Dendritic Spike ◽  
Spike Initiation

The mitral cell primary dendrite plays an important role in transmitting distal olfactory nerve input from olfactory glomerulus to the soma-axon initial segment. To understand how dendritic active properties are involved in this transmission, we have combined dual soma and dendritic patch recordings with computational modeling to analyze action-potential initiation and propagation in the primary dendrite. In response to depolarizing current injection or distal olfactory nerve input, fast Na+ action potentials were recorded along the entire length of the primary dendritic trunk. With weak-to-moderate olfactory nerve input, an action potential was initiated near the soma and then back-propagated into the primary dendrite. As olfactory nerve input increased, the initiation site suddenly shifted to the distal primary dendrite. Multi-compartmental modeling indicated that this abrupt shift of the spike-initiation site reflected an independent thresholding mechanism in the distal dendrite. When strong olfactory nerve excitation was paired with strong inhibition to the mitral cell basal secondary dendrites, a small fast prepotential was recorded at the soma, which indicated that an action potential was initiated in the distal primary dendrite but failed to propagate to the soma. As the inhibition became weaker, a “double-spike” was often observed at the dendritic recording site, corresponding to a single action potential at the soma. Simulation demonstrated that, in the course of forward propagation of the first dendritic spike, the action potential suddenly jumps from the middle of the dendrite to the axonal spike-initiation site, leaving the proximal part of primary dendrite unexcited by this initial dendritic spike. As Na+conductances in the proximal dendrite are not activated, they become available to support the back-propagation of the evoked somatic action potential to produce the second dendritic spike. In summary, the balance of spatially distributed excitatory and inhibitory inputs can dynamically switch the mitral cell firing among four different modes: axo-somatic initiation with back-propagation, dendritic initiation either with no forward propagation, forward propagation alone, or forward propagation followed by back-propagation.

Effect of Low-Voltage Electric Current Pulse on Semi-Solid Microstructure of Magnesium Alloy AZ91D

2011 ◽  
Vol 399-401 ◽  
pp. 1613-1619
Author(s):  
Quan Zhou ◽  
Le Ping Chen ◽  
Jian Yin
Keyword(s):  
Electric Current ◽  
Current Pulse ◽  
Low Voltage ◽  
Processing Parameters ◽  
Dynamic Factor ◽  
Semisolid Slurry ◽  
Az91d Alloy ◽  
Electric Current Pulse ◽  
Alloy Az91d ◽  
Semi Solid

The effect of discharging cycle, voltage, capacitance and time on solidified microstructure of semi-solid slurry of AZ91D alloy treated with Low-Voltage Electric Current Pulse(LVECP) was investigated in this paper. The experimental results show that primary grains of AZ91D alloy were refined apparently, the morphology dendrites of α-Mg were changed by electric current pulse and the nondendritic structure of semi-solid slurry of AZ91D alloy could be obtained with appropriate processing parameters. The decrease of discharging cycle and the increase of discharging voltage and time to prepare semisolid slurry by LVECP discharge promotes the formation of fine α-Mg grains. It is proposed that LVECP treatment created a new dynamic factor for nucleation so that the number of nuclei increased, which restrained the formation of large primary α-Mg dendrites and created a base to form spherical crystals of primary α-Mg. The stronger temperature fluctuation in the melt with many rosette primary α-Mg caused by LVECP discharge and the remelting of the secondary arm roots in the same time are the most important reasons for formation of spherical primary α-Mg grains.

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