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Somato-dendritic morphology and dendritic signal transfer properties differentiate between fore- and hindlimb innervating motoneurons in the frog Rana esculenta.

Stelescu A, Sümegi J, Wéber I, Birinyi A, Wolf E - BMC Neurosci (2012)

Bottom Line: On the other hand no segregation was observed by the steady-state current transfer except under high background activity.We found size-dependent and size-independent differences in morphology and electrical structure of the limb moving motoneurons based on their spinal segmental location in frogs.Location specificity of locomotor networks is therefore partly due to segmental differences in motoneurons driving fore-, and hindlimbs.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Anatomy, Histology and Embryology, Faculty of Medicine, Medical and Health Science Center, University of Debrecen, Nagyerdei krt 98, Debrecen, H-4032, Hungary.

ABSTRACT

Background: The location specific motor pattern generation properties of the spinal cord along its rostro-caudal axis have been demonstrated. However, it is still unclear that these differences are due to the different spinal interneuronal networks underlying locomotions or there are also segmental differences in motoneurons innervating different limbs. Frogs use their fore- and hindlimbs differently during jumping and swimming. Therefore we hypothesized that limb innervating motoneurons, located in the cervical and lumbar spinal cord, are different in their morphology and dendritic signal transfer properties. The test of this hypothesis what we report here.

Results: Discriminant analysis classified segmental origin of the intracellularly labeled and three-dimensionally reconstructed motoneurons 100% correctly based on twelve morphological variables. Somata of lumbar motoneurons were rounder; the dendrites had bigger total length, more branches with higher branching orders and different spatial distributions of branch points. The ventro-medial extent of cervical dendrites was bigger than in lumbar motoneurons. Computational models of the motoneurons showed that dendritic signal transfer properties were also different in the two groups of motoneurons. Whether log attenuations were higher or lower in cervical than in lumbar motoneurons depended on the proximity of dendritic input to the soma. To investigate dendritic voltage and current transfer properties imposed by dendritic architecture rather than by neuronal size we used standardized distributions of transfer variables. We introduced a novel combination of cluster analysis and homogeneity indexes to quantify segmental segregation tendencies of motoneurons based on their dendritic transfer properties. A segregation tendency of cervical and lumbar motoneurons was detected by the rates of steady-state and transient voltage-amplitude transfers from dendrites to soma at all levels of synaptic background activities, modeled by varying the specific dendritic membrane resistance. On the other hand no segregation was observed by the steady-state current transfer except under high background activity.

Conclusions: We found size-dependent and size-independent differences in morphology and electrical structure of the limb moving motoneurons based on their spinal segmental location in frogs. Location specificity of locomotor networks is therefore partly due to segmental differences in motoneurons driving fore-, and hindlimbs.

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Related in: MedlinePlus

Sample cluster formations represented by dendrogram and similarity level (dashed line) at last order clusters. In calculation of homogeneity indexes measuring segmental homogeneities of MNs in the biggest two clusters (last order clustering and Peterson’s indexes), the ratios of MNs from the lumbar (L) and cervical (C) segments were considered in each cluster. See Methods for more details.
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Figure 2: Sample cluster formations represented by dendrogram and similarity level (dashed line) at last order clusters. In calculation of homogeneity indexes measuring segmental homogeneities of MNs in the biggest two clusters (last order clustering and Peterson’s indexes), the ratios of MNs from the lumbar (L) and cervical (C) segments were considered in each cluster. See Methods for more details.

Mentions: The cluster analysis was used with Euclidean distance metric and with two different agglomerative algorithms, the Ward’s and the Pair group methods. In the beginning of the agglomerative analysis all MNs were separated and later they were united step by step to form clusters with increasing numbers of MNs. In each consecutive agglomerative step, when further MNs or clusters of MNs were fused, the fusion occurs at increasing distances (at decreasing similarity levels). The hierarchy of agglomerative steps may be represented by a tree-like structure called dendrogram (see Figure 2 for a sample), where the smallest branches correspond to the individual MNs. During such agglomerative cluster formations, the last meaningful step is the situation when all MNs belong to two clusters just before joining all of them to a single cluster. This step with two clusters comprising all MNs what we will call last order clustering throughout this paper. Cluster formations were analyzed at this level.


Somato-dendritic morphology and dendritic signal transfer properties differentiate between fore- and hindlimb innervating motoneurons in the frog Rana esculenta.

Stelescu A, Sümegi J, Wéber I, Birinyi A, Wolf E - BMC Neurosci (2012)

Sample cluster formations represented by dendrogram and similarity level (dashed line) at last order clusters. In calculation of homogeneity indexes measuring segmental homogeneities of MNs in the biggest two clusters (last order clustering and Peterson’s indexes), the ratios of MNs from the lumbar (L) and cervical (C) segments were considered in each cluster. See Methods for more details.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3472316&req=5

Figure 2: Sample cluster formations represented by dendrogram and similarity level (dashed line) at last order clusters. In calculation of homogeneity indexes measuring segmental homogeneities of MNs in the biggest two clusters (last order clustering and Peterson’s indexes), the ratios of MNs from the lumbar (L) and cervical (C) segments were considered in each cluster. See Methods for more details.
Mentions: The cluster analysis was used with Euclidean distance metric and with two different agglomerative algorithms, the Ward’s and the Pair group methods. In the beginning of the agglomerative analysis all MNs were separated and later they were united step by step to form clusters with increasing numbers of MNs. In each consecutive agglomerative step, when further MNs or clusters of MNs were fused, the fusion occurs at increasing distances (at decreasing similarity levels). The hierarchy of agglomerative steps may be represented by a tree-like structure called dendrogram (see Figure 2 for a sample), where the smallest branches correspond to the individual MNs. During such agglomerative cluster formations, the last meaningful step is the situation when all MNs belong to two clusters just before joining all of them to a single cluster. This step with two clusters comprising all MNs what we will call last order clustering throughout this paper. Cluster formations were analyzed at this level.

Bottom Line: On the other hand no segregation was observed by the steady-state current transfer except under high background activity.We found size-dependent and size-independent differences in morphology and electrical structure of the limb moving motoneurons based on their spinal segmental location in frogs.Location specificity of locomotor networks is therefore partly due to segmental differences in motoneurons driving fore-, and hindlimbs.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Anatomy, Histology and Embryology, Faculty of Medicine, Medical and Health Science Center, University of Debrecen, Nagyerdei krt 98, Debrecen, H-4032, Hungary.

ABSTRACT

Background: The location specific motor pattern generation properties of the spinal cord along its rostro-caudal axis have been demonstrated. However, it is still unclear that these differences are due to the different spinal interneuronal networks underlying locomotions or there are also segmental differences in motoneurons innervating different limbs. Frogs use their fore- and hindlimbs differently during jumping and swimming. Therefore we hypothesized that limb innervating motoneurons, located in the cervical and lumbar spinal cord, are different in their morphology and dendritic signal transfer properties. The test of this hypothesis what we report here.

Results: Discriminant analysis classified segmental origin of the intracellularly labeled and three-dimensionally reconstructed motoneurons 100% correctly based on twelve morphological variables. Somata of lumbar motoneurons were rounder; the dendrites had bigger total length, more branches with higher branching orders and different spatial distributions of branch points. The ventro-medial extent of cervical dendrites was bigger than in lumbar motoneurons. Computational models of the motoneurons showed that dendritic signal transfer properties were also different in the two groups of motoneurons. Whether log attenuations were higher or lower in cervical than in lumbar motoneurons depended on the proximity of dendritic input to the soma. To investigate dendritic voltage and current transfer properties imposed by dendritic architecture rather than by neuronal size we used standardized distributions of transfer variables. We introduced a novel combination of cluster analysis and homogeneity indexes to quantify segmental segregation tendencies of motoneurons based on their dendritic transfer properties. A segregation tendency of cervical and lumbar motoneurons was detected by the rates of steady-state and transient voltage-amplitude transfers from dendrites to soma at all levels of synaptic background activities, modeled by varying the specific dendritic membrane resistance. On the other hand no segregation was observed by the steady-state current transfer except under high background activity.

Conclusions: We found size-dependent and size-independent differences in morphology and electrical structure of the limb moving motoneurons based on their spinal segmental location in frogs. Location specificity of locomotor networks is therefore partly due to segmental differences in motoneurons driving fore-, and hindlimbs.

Show MeSH
Related in: MedlinePlus