Asymmetry in Signal Propagation between the Soma and Dendrites Plays a Key Role in Determining Dendritic Excitability in Motoneurons
Figure 1
Characterization of voltage attenuation property of the dendrites.
(A) – (E). Morphologies of the motoneurons in the left column and the three voltage attenuation (VA) factors measured at all distances (Dpath) from the soma (VASDDC in black, VASDAC in gray and VADSDC in purple) in the right column. A single exponential function (exp(-Dpath/λ)) was used to fit the VASDDC (λ = 2678.7, 3085.6, 2763.7, 1945.5 and 2156.4 for A–E) and VASDAC (λ = 420.1, 437.1, 402.3, 373.1 and 464.7 for A–E), and a modified Boltzmann equation (1/[1−exp(−α1/α2)+exp((Dpath−α1)/α2)]) for VADSDC (α1& α2 = 1020.8&307.7, 635.2&439.5, 327.9&469.6, 374.2&504.8 and 861.9&268.3 for A–E). Note that purple solid lines represents the VADSDC between the soma and all points in the dendrites at the same distance (i.e. point-to-all) whereas purple dotted lines (exp(-Dpath/λ) where λ = 225, 143.6, 118.5, 144, 193.7 for A–E) for the VADSDC between the soma and a single point along the path of all individual dendritic trees from the soma (i.e. point-to-point). (F). The VADSDC was measured in six type identified anatomically reconstructed motoneurons while varying the input resistance (RN) from 0.4 to 4.0 MΩ. The α1 (the distance at which the VADSDC dropped to 50%) parameter was more sensitive to changes in RN compared with α2 parameter (a measure of the slope of the curve at α1). The insets show examples of the VADSDC curves at extreme RN values of 0.4 and 4.0 MΩ. Note that the distribution of points (α1, α2) at the same RN is not type specific (e.g. gray and black filled circles for FR-type motoneurons). S, FR and FF indicate slow twitch, fast twitch and fatigue resistant, and fast twitch and fast fatigable motoneuron type respectively.
