Restoration of dysgenic muscle contraction and calcium channel function by co-culture with normal spinal cord neurons

El Manira, A. and N. Bussières. Calcium channel subtypes in lamprey sensory and motor neurons. J. Neurophysiol. 78: 1334–1340, 1997. Pharmacologically distinct calcium channels have been characterized in dissociated cutaneous sensory neurons and motoneurons of the larval lamprey spinal cord. To enable cell identification, sensory dorsal cells and motoneurons were selectively labeled with fluorescein-coupled dextran amine in the intact spinal cord in vitro before dissociation. Calcium channels present in sensory dorsal cells, motoneurons, and other spinal cord neurons were characterized with the use of whole cell voltage-clamp recordings and specific calcium channel agonist and antagonists. The results show that a transient low-voltage-activated (LVA) calcium current was present in a proportion of sensory dorsal cells but not in motoneurons, whereas high-voltage-activated (HVA) calcium currents were seen in all neurons recorded. The different components of HVA current were dissected pharmacologically and similar results were obtained for both dorsal cells and motoneurons. The N-type calcium channel antagonist ω-conotoxin-GVIA(ω-CgTx) blocked >70% of the HVA current. A large part of the ω-CgTx block was reversed after washout of the toxin. The L-type calcium channel antagonist nimodipine blocked ∼15% of the total HVA current. The dihydropyridine agonist (±)-BayK 8644 markedly increased the amplitude of the calcium channel current. The BayK-potentiated current was not affected by ω-CgTx, indicating that the reversibility of the ω-CgTx effect is not due to a blockade of L-type channels. Simultaneous application of ω-CgTx and nimodipine left ∼15% of the HVA calcium channel current, a small part of which was blocked by the P/Q-type channel antagonist ω-agatoxin-IVA. In the presence of the three antagonists, the persistent residual current (∼10%) was completely blocked by cadmium. Our results provide evidence for the existence of HVA calcium channels of the N, L, and P/Q types and other HVA calcium channels in lamprey sensory neurons and motoneurons. In addition, certain types of neurons express LVA calcium channels.

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Trans-spinal direct current enhances corticospinal output and stimulation-evoked release of glutamate analog, D-2,3-3H-aspartic acid

Journal of Applied Physiology ◽

10.1152/japplphysiol.00967.2011 ◽

2012 ◽

Vol 112 (9) ◽

pp. 1576-1592 ◽

Cited By ~ 32

Author(s):

Zaghloul Ahmed ◽

Andrzej Wieraszko

Keyword(s):

Spinal Cord ◽

Muscle Contraction ◽

Direct Current ◽

Neuronal Excitability ◽

Spinal Cord Injuries ◽

Low Frequency ◽

Motor Units ◽

Spinal Cord Neurons ◽

Muscle Actions

Trans-spinal direct current (tsDC) stimulation is a modulator of spinal excitability and can influence cortically elicited muscle contraction in a polarity-dependent fashion. When combined with low-frequency repetitive cortical stimulation, cathodal tsDC [tsDC(−)] produces a long-term facilitation of cortically elicited muscle actions. We investigated the ability of this combined stimulation paradigm to facilitate cortically elicited muscle actions in spinal cord-injured and noninjured animals. The effect of tsDC—applied alone or in combination with repetitive spinal stimulation (rSS) on the release of the glutamate analog, D-2,3-3H-aspartate (D-Asp), from spinal cord preparations in vitro—was also tested. In noninjured animals, tsDC (−2 mA) reproducibly potentiated cortically elicited contractions of contralateral and ipsilateral muscles tested at various levels of baseline muscle contraction forces. Cortically elicited muscle responses in animals with contusive and hemisectioned spinal cord injuries (SCIs) were similarly potentiated. The combined paradigm of stimulation caused long-lasting potentiation of cortically elicited bilateral muscle contraction in injured and noninjured animals. Additional analysis suggests that at higher baseline forces, tsDC(−) application does not increase the rising slope of the muscle contraction but causes repeated firing of the same motor units. Both cathodal and anodal stimulations induced a significant increase of D-Asp release in vitro. The effect of the combined paradigm of stimulation (tsDC and rSS) on the concentration of extracellular D-Asp was polarity dependent. These results indicate that tsDC can powerfully modulate the responsiveness of spinal cord neurons. The results obtained from the in vitro preparation suggest that the changes in neuronal excitability were correlated with an increased concentration of extracellular glutamate. The combined paradigm of stimulation, used in our experiments, could be noninvasively applied to restore motor control in humans with SCI.

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Effects of ω-Agatoxin IVA, a P-Type Calcium Channel Antagonist, on the Development of Spinal Neuronal Hyperexcitability Caused by Knee Inflammation in Rats

Journal of Neurophysiology ◽

10.1152/jn.1999.81.6.2620 ◽

1999 ◽

Vol 81 (6) ◽

pp. 2620-2626 ◽

Cited By ~ 17

Author(s):

Johannes Nebe ◽

Andrea Ebersberger ◽

Horacio Vanegas ◽

Hans-Georg Schaible

Keyword(s):

Spinal Cord ◽

Knee Joint ◽

Calcium Channels ◽

Calcium Channel ◽

Calcium Channel Antagonist ◽

Dynamic Range ◽

Control Group ◽

Spinal Cord Neurons ◽

Neuronal Hyperexcitability ◽

P Type

Effects of ω-agatoxin IVA, a P-type calcium channel antagonist, on the development of spinal neuronal hyperexcitability caused by knee inflammation in rats. Both N- and P-type high-threshold calcium channels are located presynaptically in the CNS and are involved in the release of transmitters. To investigate the importance of P-type calcium channels in the generation of inflammation-evoked hyperexcitability of spinal cord neurons, electrophysiological recordings were made from wide-dynamic-range neurons with input from the knee joint in the anesthetized rat. The responses of each neuron to innocuous and noxious pressure onto the knee and the ankle were continuously assessed before and during the development of an inflammation in the knee joint induced by the injections of K/C into the joint cavity. The specific antagonist at P-type calcium channels ω-agatoxin was administered into a 30-μl trough on the spinal cord surface above the recorded neuron. In most neurons the application of ω-agatoxin before induction of inflammation slightly enhanced the responses to pressure onto the knee and ankle or left them unchanged. Two different protocols were then followed. In the control group (13 rats) only Tyrode was administered to the spinal cord during and after induction of inflammation. In these neurons the responses to mechanical stimuli applied to both the inflamed knee and to the noninflamed ankle showed a significant increase over 4 h. In the experimental group (12 rats) ω-agatoxin was applied during knee injection and in five 15-min periods up to 180 min after kaolin. This prevented the increase of the neuronal responses to innocuous pressure onto the knee and to innocuous and noxious pressure onto the ankle; only the responses to noxious pressure onto the knee were significantly enhanced during development of inflammation. Thus the development of inflammation-evoked hyperexcitability was attenuated by ω-agatoxin, and this suggests that P-type calcium channels in the spinal cord are involved in the generation of inflammation-evoked hyperexcitability of spinal cord neurons. Finally, when ω-agatoxin was administered to the spinal cord 4 h after the kaolin injection, i.e., when inflammation-evoked hyperexcitability was fully established, the responses to innocuous and noxious pressure onto the knee were reduced by 20–30% on average. The shift in the effect of ω-agatoxin, from slight facilitation or no change of the responses before inflammation to inhibition in the state of hyperexcitability, indicates that P-type calcium channels are important for excitatory synaptic transmission involved in the maintenance of inflammation-evoked hyperexcitability.

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