Impulse propagation over tactile and kinaesthetic sensory axons to central target neurones of the cuneate nucleus in cat.

School of Medical Sciences, University of New South Wales, Sydney 2052, Australia.
The Journal of Physiology (Impact Factor: 4.38). 08/2003; 550(Pt 2):553-62. DOI: 10.1113/jphysiol.2002.037002
Source: PubMed

ABSTRACT Paired, simultaneous recordings were made in anaesthetized cats from the peripheral and central axons of individual tactile and kinaesthetic sensory fibres. The aim was to determine whether failure of spike propagation occurred at any of the three major axonal branch points in the path to their cuneate target neurones, and whether propagation failure may contribute, along with synaptic transmission failures, to limitations in transmission security observed for the cuneate synaptic relay. No evidence for propagation failure was found at the two major axonal branch points prior to the cuneate nucleus, namely, the T-junction at the dorsal root ganglion, and the major branch point near the cord entry point, even for the highest impulse rates (approximately 400 impulses s(-1)) at which these fibres could be driven. However, at the highest impulse rates there was evidence at the central, intra-cuneate recording site of switching between two states in the terminal axonal spike configuration. This appears to reflect a sporadic propagation failure into one of the terminal branches of the sensory axon. In conclusion, it appears that central impulse propagation over group II sensory axons occurs with complete security through branch points within the dorsal root ganglion and at the spinal cord entry zone. However, at high rates of afferent drive, terminal axonal propagation failure may contribute to the observed decline in transmission security within the cuneate synaptic relay.

  • [Show abstract] [Hide abstract]
    ABSTRACT: Electrical stimulation of the central nervous system creates both orthodromically propagating action potentials, by stimulation of local cells and passing axons, and antidromically propagating action potentials, by stimulation of presynaptic axons and terminals. Our aim was to understand how antidromic action potentials navigate through complex arborizations, such as those of thalamic and basal ganglia afferents-sites of electrical activation during deep brain stimulation. We developed computational models to study the propagation of antidromic action potentials past the bifurcation in branched axons. In both unmyelinated and myelinated branched axons, when the diameters of each axon branch remained under a specific threshold (set by the antidromic geometric ratio), antidromic propagation occurred robustly; action potentials traveled both antidromically into the primary segment as well as "re-orthodromically" into the terminal secondary segment. Propagation occurred across a broad range of stimulation frequencies, axon segment geometries, and concentrations of extracellular potassium, but was strongly dependent on the geometry of the node of Ranvier at the axonal bifurcation. Thus, antidromic activation of axon terminals can, through axon collaterals, lead to widespread activation or inhibition of targets remote from the site of stimulation. These effects should be included when interpreting the results of functional imaging or evoked potential studies on the mechanisms of action of DBS.
    Journal of Computational Neuroscience 03/2008; 24(1):81-93. · 2.44 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The present series of experiments was designed to examine, in the anesthetized cat, the extent to which the synaptic efficacy of knee joint afferents is modified during the state of central sensitization produced by the injection of capsaicin into the hindlimb plantar cushion. We found that the intradermic injection of capsaicin increased the N2 and N3 components of the focal potentials produced by stimulation of intermediate and high threshold myelinated fibers in the posterior articular nerve (PAN), respectively. This facilitation lasted several hours, had about the same time course as the paw inflammation and was more evident for the N2 and N3 potentials recorded within the intermediate zone in the L6 than in the L7 spinal segments. The capsaicin-induced facilitation of the N2 focal potentials, which are assumed to be generated by activation of fibers signaling joint position, suggests that nociception may affect the processing of proprioceptive and somato-sensory information and, probably also, movement. In addition, the increased effectiveness of these afferents could activate, besides neurons in the intermediate region, neurons located in the more superficial layers of the dorsal horn. As a consequence, normal joint movements could produce pain representing a secondary hyperalgesia. The capsaicin-induced increased efficacy of the PAN afferents producing the N3 focal potentials, together with the reduced post-activation depression that follows high frequency autogenetic stimulation of these afferents, could further contribute to the pain sensation from non-inflamed joints during skin inflammation in humans. The persistence, after capsaicin, of the inhibitory effects produced by stimulation of cutaneous nerves innervating non-inflamed skin regions may account for the reported reduction of the articular pain sensations produced by trans-cutaneous stimulation.
    Experimental Brain Research 06/2008; 187(1):71-84. · 2.22 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: A preparation is described in which it is possible to selectively activate and monitor the activity of the individual periosteal afferent nerve fibres arising from the humerus bone of the cat. The nerve is a fine branch of the median nerve that accompanies the small artery and vein that enter the nutrient foramen of the humerus. By freeing this fine nerve from nearby tissue over a length of approximately 1-2 cm and placing it over a silver hook recording electrode, it becomes possible to identify and monitor electrophysiologically, the impulse activity of individual periosteal afferent fibres activated by focal mechanical stimulation of the periosteum. With this preparation it will be possible to examine the central actions and security of transmission at central synaptic targets for single, small-diameter afferent fibres arising from bone.
    Journal of Neuroscience Methods 10/2006; 156(1-2):140-4. · 2.11 Impact Factor

Full-text (2 Sources)

Available from
Jun 3, 2014