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Dendritic orientation and branching distinguish a class of multifunctional turtle spinal interneurons.

Holmes JR, Berkowitz A - Front Neural Circuits (2014)

Bottom Line: These synaptic inputs can occur on distal dendrites and yet must remain effective at the soma.Here, we quantitatively investigated additional dendritic morphological characteristics of T neurons as compared to non-T neurons.We found that T neurons have less total dendritic length, a greater proportion of dendritic length in primary dendrites, and dendrites that are oriented more mediolaterally.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, University of Oklahoma Norman, OK, USA.

ABSTRACT
Spinal interneurons can integrate diverse propriospinal and supraspinal inputs that trigger or modulate locomotion and other limb movements. These synaptic inputs can occur on distal dendrites and yet must remain effective at the soma. Active dendritic conductances may amplify distal dendritic inputs, but appear to play a minimal role during scratching, at least. Another possibility is that spinal interneurons that integrate inputs on distal dendrites have unusually simple dendritic trees that effectively funnel current to the soma. We previously described a class of spinal interneurons, called transverse interneurons (or T neurons), in adult turtles. T neurons were defined as having dendrites that extend further in the transverse plane than rostrocaudally and a soma that extends further mediolaterally than rostrocaudally. T neurons are multifunctional, as they were activated during both swimming and scratching motor patterns. T neurons had higher peak firing rates and larger membrane potential oscillations during scratching than scratch-activated interneurons with different dendritic morphologies ("non-T" neurons). These characteristics make T neurons good candidates to play an important role in integrating diverse inputs and generating or relaying rhythmic motor patterns. Here, we quantitatively investigated additional dendritic morphological characteristics of T neurons as compared to non-T neurons. We found that T neurons have less total dendritic length, a greater proportion of dendritic length in primary dendrites, and dendrites that are oriented more mediolaterally. Thus, T neuron dendritic trees extend far mediolaterally, yet are unusually simple, which may help channel synaptic current from distal dendrites in the lateral and ventral funiculi to the soma. In combination with T neuron physiological properties, these dendritic properties may help integrate supraspinal and propriospinal inputs and generate and/or modulate rhythmic limb movements.

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Examples of Sholl analyses for three T neurons (A–C, blue), three non-T neurons (D–F, red), and (G) the superimposed means (+ SD) for all T neurons (blue; n = 17) and non-T neurons (red; n = 14). Dendritic intersections were measured every 10 µm from the soma.
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Figure 4: Examples of Sholl analyses for three T neurons (A–C, blue), three non-T neurons (D–F, red), and (G) the superimposed means (+ SD) for all T neurons (blue; n = 17) and non-T neurons (red; n = 14). Dendritic intersections were measured every 10 µm from the soma.

Mentions: An additional method of characterizing dendritic branching is via Sholl analysis, which measures the number of intersections between dendritic branches and concentric circles of increasing radii surrounding the soma (Sholl, 1953; Binley et al., 2014). Figure 4 shows Sholl analyses of example T neurons (Figures 4A–C, blue) and non-T neurons (Figures 4D–F, red). The example T neurons had a peak of dendritic branching 50–100 µm from the soma, while the non-T neurons had a broader peak and/or a second peak ~200 µm from the soma. In these examples, T neuron branching ended within 600 µm of the soma, while non-T neuron branching could continue beyond 1 mm (Figures 4E,F).


Dendritic orientation and branching distinguish a class of multifunctional turtle spinal interneurons.

Holmes JR, Berkowitz A - Front Neural Circuits (2014)

Examples of Sholl analyses for three T neurons (A–C, blue), three non-T neurons (D–F, red), and (G) the superimposed means (+ SD) for all T neurons (blue; n = 17) and non-T neurons (red; n = 14). Dendritic intersections were measured every 10 µm from the soma.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4230039&req=5

Figure 4: Examples of Sholl analyses for three T neurons (A–C, blue), three non-T neurons (D–F, red), and (G) the superimposed means (+ SD) for all T neurons (blue; n = 17) and non-T neurons (red; n = 14). Dendritic intersections were measured every 10 µm from the soma.
Mentions: An additional method of characterizing dendritic branching is via Sholl analysis, which measures the number of intersections between dendritic branches and concentric circles of increasing radii surrounding the soma (Sholl, 1953; Binley et al., 2014). Figure 4 shows Sholl analyses of example T neurons (Figures 4A–C, blue) and non-T neurons (Figures 4D–F, red). The example T neurons had a peak of dendritic branching 50–100 µm from the soma, while the non-T neurons had a broader peak and/or a second peak ~200 µm from the soma. In these examples, T neuron branching ended within 600 µm of the soma, while non-T neuron branching could continue beyond 1 mm (Figures 4E,F).

Bottom Line: These synaptic inputs can occur on distal dendrites and yet must remain effective at the soma.Here, we quantitatively investigated additional dendritic morphological characteristics of T neurons as compared to non-T neurons.We found that T neurons have less total dendritic length, a greater proportion of dendritic length in primary dendrites, and dendrites that are oriented more mediolaterally.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, University of Oklahoma Norman, OK, USA.

ABSTRACT
Spinal interneurons can integrate diverse propriospinal and supraspinal inputs that trigger or modulate locomotion and other limb movements. These synaptic inputs can occur on distal dendrites and yet must remain effective at the soma. Active dendritic conductances may amplify distal dendritic inputs, but appear to play a minimal role during scratching, at least. Another possibility is that spinal interneurons that integrate inputs on distal dendrites have unusually simple dendritic trees that effectively funnel current to the soma. We previously described a class of spinal interneurons, called transverse interneurons (or T neurons), in adult turtles. T neurons were defined as having dendrites that extend further in the transverse plane than rostrocaudally and a soma that extends further mediolaterally than rostrocaudally. T neurons are multifunctional, as they were activated during both swimming and scratching motor patterns. T neurons had higher peak firing rates and larger membrane potential oscillations during scratching than scratch-activated interneurons with different dendritic morphologies ("non-T" neurons). These characteristics make T neurons good candidates to play an important role in integrating diverse inputs and generating or relaying rhythmic motor patterns. Here, we quantitatively investigated additional dendritic morphological characteristics of T neurons as compared to non-T neurons. We found that T neurons have less total dendritic length, a greater proportion of dendritic length in primary dendrites, and dendrites that are oriented more mediolaterally. Thus, T neuron dendritic trees extend far mediolaterally, yet are unusually simple, which may help channel synaptic current from distal dendrites in the lateral and ventral funiculi to the soma. In combination with T neuron physiological properties, these dendritic properties may help integrate supraspinal and propriospinal inputs and generate and/or modulate rhythmic limb movements.

Show MeSH