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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 six T neuron dendritic trees (A–F), with dendritic branches color-coded by branch order. Vertical lines indicate borders of gray matter. 1°, primary; 2°, secondary, etc. R, rostral; C, caudal; M, medial; L, lateral; VF, ventral funiculus; VH, ventral horn; LF, lateral funiculus.
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Figure 1: Examples of six T neuron dendritic trees (A–F), with dendritic branches color-coded by branch order. Vertical lines indicate borders of gray matter. 1°, primary; 2°, secondary, etc. R, rostral; C, caudal; M, medial; L, lateral; VF, ventral funiculus; VH, ventral horn; LF, lateral funiculus.

Mentions: Figure 1 shows six examples of T neuron morphologies, with dendritic segments color-coded by whether they were primary, secondary, etc. These examples were chosen to illustrate both the range of dendritic characteristics of T neurons and the features T neurons have in common. T neuron dendritic trees were relatively simple. Most dendritic segments appeared to be oriented more mediolaterally than rostrocaudally. There appeared to be relatively little branching of the dendrites, even though the labeled dendrites were typically several hundred µm long. Thus, a relatively large proportion of the dendrites appeared to be primary (red, in Figure 1) and a relatively small proportion appeared to be high-order dendrites (brown for >5th-order dendrites in Figure 1).


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

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

Examples of six T neuron dendritic trees (A–F), with dendritic branches color-coded by branch order. Vertical lines indicate borders of gray matter. 1°, primary; 2°, secondary, etc. R, rostral; C, caudal; M, medial; L, lateral; VF, ventral funiculus; VH, ventral horn; LF, lateral funiculus.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 1: Examples of six T neuron dendritic trees (A–F), with dendritic branches color-coded by branch order. Vertical lines indicate borders of gray matter. 1°, primary; 2°, secondary, etc. R, rostral; C, caudal; M, medial; L, lateral; VF, ventral funiculus; VH, ventral horn; LF, lateral funiculus.
Mentions: Figure 1 shows six examples of T neuron morphologies, with dendritic segments color-coded by whether they were primary, secondary, etc. These examples were chosen to illustrate both the range of dendritic characteristics of T neurons and the features T neurons have in common. T neuron dendritic trees were relatively simple. Most dendritic segments appeared to be oriented more mediolaterally than rostrocaudally. There appeared to be relatively little branching of the dendrites, even though the labeled dendrites were typically several hundred µm long. Thus, a relatively large proportion of the dendrites appeared to be primary (red, in Figure 1) and a relatively small proportion appeared to be high-order dendrites (brown for >5th-order dendrites in Figure 1).

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