Pyramidal tract of the cat: axon size and morphology

Biedenbach, M.A.; DeVito, J. L.; Brown, Anna

doi:10.1007/bf00239520

Cited by 27 publications

(26 citation statements)

References 24 publications

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“…The axonal morphology for small diameter unmyelinated and myelinated branched axons was based on the limited data that exists on the afferent connections to the STN, GP and ventrolateral thalamus (Biedenbach et al 1986;Kakei et al 2001;Kultas-Ilinsky et al 2003).…”

Section: Methodsmentioning

confidence: 99%

Antidromic propagation of action potentials in branched axons: implications for the mechanisms of action of deep brain stimulation

2007

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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.

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Section: Methodsmentioning

confidence: 99%

Antidromic propagation of action potentials in branched axons: implications for the mechanisms of action of deep brain stimulation

2007

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“…The thickest axons, which arise from the largest neurons, reach about 20 µm. In many tracts the distribution of axon diameters is highly skewed, such that thin axons are numerous and thick ones are rare (e.g., Biedenbach et al, 1986; Wang et al, 2008). This distribution, a basic feature of brain structure, has never been explained.…”

Section: Introductionmentioning

confidence: 99%

How the Optic Nerve Allocates Space, Energy Capacity, and Information

Perge¹,

Koch²,

Miller³

et al. 2009

Journal of Neuroscience

165

249

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Fiber tracts should use space and energy efficiently, because both resources constrain neural computation. We found for a myelinated tract (optic nerve) that astrocytes use nearly 30% of the space and Ͼ70% of the mitochondria, establishing the significance of astrocytes for the brain's space and energy budgets. Axons are mostly thin with a skewed distribution peaking at 0.7 m, near the lower limit set by channel noise. This distribution is matched closely by the distribution of mean firing rates measured under naturalistic conditions, suggesting that firing rate increases proportionally with axon diameter. In axons thicker than 0.7 m, mitochondria occupy a constant fraction of axonal volume-thus, mitochondrial volumes rise as the diameter squared. These results imply a law of diminishing returns: twice the information rate requires more than twice the space and energy capacity. We conclude that the optic nerve conserves space and energy by sending most information at low rates over fine axons with small terminal arbors and sending some information at higher rates over thicker axons with larger terminal arbors but only where more bits per second are needed for a specific purpose. Thicker axons seem to be needed, not for their greater conduction velocity (nor other intrinsic electrophysiological purpose), but instead to support larger terminal arbors and more active zones that transfer information synaptically at higher rates.

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“…We suggest that the probability of accurate tracking of structures smaller than this reduces with reducing structure diameter, though we have not rigorously tested this here. The diameter of axons of cortical neurons is typically reported to be in the range of 0.3-1 m (Rockland, 1995;Rockland and Knutson, 2001;Saint Marie and Peters, 1985;Schuz and Palm, 1989;Seguela et al, 1989), though axons with diameters around 0.1 m have been reported in cat and rat pyramidal tract (Biedenbach et al, 1986;Harding and Towe, 1985;Leenen et al, 1985) and axons as thick as 3 m have been reported for visual cortex (Rockland, 1995;Rockland and Knutson, 2001). More accurate tracking of fibres thinner than about 0.5 m may be achieved by acquiring images at higher magnification.…”

Section: Resolutionmentioning

confidence: 95%