| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Centre for Neuroscience, University of Alberta, Edmonton, Alberta, Canada
Submitted 31 March 2006; accepted in final form 31 May 2006
The spinal cord and spinal motoneurons are densely innervated by terminals of serotonin (5-HT) and norepinephrine (NE) neurons arising mostly from the brain stem, but also from intrinsic spinal neurons. Even after long-term spinal transection (chronic spinal), significant amounts (10%) of 5-HT and NE (monoamines) remain caudal to the injury. To determine the role of such endogenous monoamines, we blocked their action with monoamine receptor antagonists and measured changes in the sodium currents and firing in motoneurons. We focused on persistent sodium currents (Na PIC) and sodium spike properties because they are critical for enabling repetitive firing in motoneurons and are facilitated by monoamines. Intracellular recordings were made from motoneurons in the sacrocaudal spinal cord of normal and chronic spinal rats (2 mo postsacral transection) with the whole sacrocaudal cord acutely removed and maintained in vitro (cords from normal rats termed acute spinal). Acute and chronic spinal rats had TTX-sensitive Na PICs that were respectively 0.62 ± 0.76 and 1.60 ± 1.04 nA, with mean onset voltages of –63.0 ± 5.6 and –64.1 ± 5.4 mV, measured with slow voltage ramps. Application of 5-HT2A, 5-HT2C, and 
1-NE receptor antagonists (ketanserin, RS 102221, and WB 4101, respectively) significantly reduced the Na PICs, and a combined application of these three monoamine antagonists completely eliminated the Na PIC, in both acute and chronic spinal rats. Likewise, reduction of presynaptic transmitter release (including 5-HT and NE) with long-term application of cadmium also eliminated the Na PIC. Associated with the elimination of the Na PIC in monoamine antagonists, the motoneurons lost their ability to fire during slow current ramps. At this point, the spike evoked by antidromic stimulation was not affected, suggesting that activation of the transient sodium current was not impaired. However, the spike evoked after a slow ramp depolarization was slightly reduced in height and rate-of-rise, suggesting decreased sodium channel availability as a result of increased channel inactivation. These results suggest that endogenous monoamine receptor activation is critical for enabling the Na PIC and decreasing sodium channel inactivation, ultimately enabling steady repetitive firing in both normal and chronic spinal rats.
This article has been cited by other articles:
|
|
 |
|
  C.J. Heckman, M. Johnson, C. Mottram, and J. Schuster Persistent Inward Currents in Spinal Motoneurons and Their Influence on Human Motoneuron Firing Patterns Neuroscientist, June 1, 2008; 14(3): 264 - 275. [Abstract] [PDF]
|
|
|
|
 |
|
 J. A. Norton, D. J. Bennett, M. E. Knash, K. C. Murray, and M. A. Gorassini Changes in sensory-evoked synaptic activation of motoneurons after spinal cord injury in man Brain, June 1, 2008; 131(6): 1478 - 1491. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 P. K. Rose The control of motoneurone activity: getting all of the players on the same stage J. Physiol., March 15, 2008; 586(6): 1463 - 1463. [Full Text] [PDF]
|
|
|
|
 |
|
 W. M. St.-John and J. C. Leiter Maintenance of gasping and restoration of eupnea after hypoxia is impaired following blockers of {alpha}1-adrenergic receptors and serotonin 5-HT2 receptors J Appl Physiol, March 1, 2008; 104(3): 665 - 673. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
C. J. Heckman, A. S. Hyngstrom, and M. D. Johnson Active properties of motoneurone dendrites: diffuse descending neuromodulation, focused local inhibition J. Physiol., March 1, 2008; 586(5): 1225 - 1231. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 D. J. Bennett Demystifying Spasticity: Reply to Dietz J Neurophysiol, February 1, 2008; 99(2): 1041 - 1043. [Full Text] [PDF]
|
|
|
|
|
|
D. C. Button, J. M. Kalmar, K. Gardiner, T. Marqueste, H. Zhong, R. R. Roy, V. R. Edgerton, and P. F. Gardiner Does elimination of afferent input modify the changes in rat motoneurone properties that occur following chronic spinal cord transection? J. Physiol., January 15, 2008; 586(2): 529 - 544. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 M. Manuel, C. Meunier, M. Donnet, and D. Zytnicki Resonant or Not, Two Amplification Modes of Proprioceptive Inputs by Persistent Inward Currents in Spinal Motoneurons J. Neurosci., November 21, 2007; 27(47): 12977 - 12988. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. M. ElBasiouny and V. K. Mushahwar Suppressing the excitability of spinal motoneurons by extracellularly applied electrical fields: insights from computer simulations J Appl Physiol, November 1, 2007; 103(5): 1824 - 1836. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. Diaz-Rios, D. A. Dombeck, W. W. Webb, and R. M. Harris-Warrick Serotonin Modulates Dendritic Calcium Influx in Commissural Interneurons in the Mouse Spinal Locomotor Network J Neurophysiol, October 1, 2007; 98(4): 2157 - 2167. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
V. A. L. Toppin, M. B. Harris, A. M. Kober, J. C. Leiter, and W. M. St.-John Persistence of eupnea and gasping following blockade of both serotonin type 1 and 2 receptors in the in situ juvenile rat preparation J Appl Physiol, July 1, 2007; 103(1): 220 - 227. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. C. Dean, L. M. Yates, and D. F. Collins Turning on the central contribution to contractions evoked by neuromuscular electrical stimulation J Appl Physiol, July 1, 2007; 103(1): 170 - 176. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. M. Rank, X. Li, D. J. Bennett, and M. A. Gorassini Role of Endogenous Release of Norepinephrine in Muscle Spasms After Chronic Spinal Cord Injury J Neurophysiol, May 1, 2007; 97(5): 3166 - 3180. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
N. P. Cramer, Y. Li, and A. Keller The Whisking Rhythm Generator: A Novel Mammalian Network for the Generation of Movement J Neurophysiol, March 1, 2007; 97(3): 2148 - 2158. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
X. Li, K. Murray, P. J. Harvey, E. W. Ballou, and D. J. Bennett Serotonin Facilitates a Persistent Calcium Current in Motoneurons of Rats With and Without Chronic Spinal Cord Injury J Neurophysiol, February 1, 2007; 97(2): 1236 - 1246. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
P. J. Harvey, Y. Li, X. Li, and D. J. Bennett Persistent Sodium Currents and Repetitive Firing in Motoneurons of the Sacrocaudal Spinal Cord of Adult Rats J Neurophysiol, September 1, 2006; 96(3): 1141 - 1157. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
P. J. Harvey, X. Li, Y. Li, and D. J. Bennett 5-HT2 Receptor Activation Facilitates a Persistent Sodium Current and Repetitive Firing in Spinal Motoneurons of Rats With and Without Chronic Spinal Cord Injury J Neurophysiol, September 1, 2006; 96(3): 1158 - 1170. [Abstract] [Full Text] [PDF]
|
|
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| Visit Other APS Journals Online |
