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Functional organization of locomotor interneurons in the ventral lumbar spinal cord of the newborn rat.

Antri M, Mellen N, Cazalets JR - PLoS ONE (2011)

Bottom Line: Moreover, L1 segment lesioning induced the most important changes in the locomotor activity in comparison with lesions at the T13 or L2 segments.However, no lesions led to selective disruption of either flexor or extensor output.In addition, this study found no evidence of functional parcellation of locomotor interneurons into flexor and extensor pools at the dorsal-ventral midline of the lumbar spinal cord of the rat.

View Article: PubMed Central - PubMed

Affiliation: Université de Bordeaux, Centre National de la Recherche Scientifique, Institut des Neurosciences Cognitives et Intégratives d'Aquitaine, Unité Mixte de Recherche 5287, Bordeaux, France. myriam.antri@gmail.com

ABSTRACT
Although the mammalian locomotor CPG has been localized to the lumbar spinal cord, the functional-anatomical organization of flexor and extensor interneurons has not been characterized. Here, we tested the hypothesis that flexor and extensor interneuronal networks for walking are physically segregated in the lumbar spinal cord. For this purpose, we performed optical recordings and lesion experiments from a horizontally sectioned lumbar spinal cord isolated from neonate rats. This ventral hemi spinal cord preparation produces well-organized fictive locomotion when superfused with 5-HT/NMDA. The dorsal surface of the preparation was visualized using the Ca(2+) indicator fluo-4 AM, while simultaneously monitoring motor output at ventral roots L2 and L5. Using calcium imaging, we provided a general mapping view of the interneurons that maintained a stable phase relationship with motor output. We showed that the dorsal surface of L1 segment contains a higher density of locomotor rhythmic cells than the other segments. Moreover, L1 segment lesioning induced the most important changes in the locomotor activity in comparison with lesions at the T13 or L2 segments. However, no lesions led to selective disruption of either flexor or extensor output. In addition, this study found no evidence of functional parcellation of locomotor interneurons into flexor and extensor pools at the dorsal-ventral midline of the lumbar spinal cord of the rat.

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Lesion experiments.A, Photomicrographs of a ventral SC preparation (top) and its corresponding transverse section (bottom) showing an example of electrocoagulation of a restricted region located at the T13 segment level (magnification 4×; scale bar = 300 µm). B, Schematic drawing presenting all microlesions performed from T12 to L2 segments. The thick circles represent the first lesion (n = 21) whereas the thin circles represent the second lesion n = 16/21). The right and left dashed lines delineate the grey and white matter. The lesion size is expressed as a percentage of SC size (central canal set to 0). C, Lesion effects on locomotor activity. (C1), Extracellular recordings of L2 and L5 VRs before and after a lesion at the L1 level. The arrow represents the onset of locomotor recovery. (C2), Time course of the motor period 1 min before (control) and after a lesion at the T13 level (circles), the L1 level (triangles) and L2 level (squares). The onset of recovery is indicated by successive arrows for each lesion. D, Lesion effect on duration of locomotor activity disruption (D1), motor period (D2), and burst area (D3) of microlesions performed at different SC level (T13-L1-L2). The black circles indicate the first microlesions and the grey triangles illustrate the second microlesions.
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pone-0020529-g003: Lesion experiments.A, Photomicrographs of a ventral SC preparation (top) and its corresponding transverse section (bottom) showing an example of electrocoagulation of a restricted region located at the T13 segment level (magnification 4×; scale bar = 300 µm). B, Schematic drawing presenting all microlesions performed from T12 to L2 segments. The thick circles represent the first lesion (n = 21) whereas the thin circles represent the second lesion n = 16/21). The right and left dashed lines delineate the grey and white matter. The lesion size is expressed as a percentage of SC size (central canal set to 0). C, Lesion effects on locomotor activity. (C1), Extracellular recordings of L2 and L5 VRs before and after a lesion at the L1 level. The arrow represents the onset of locomotor recovery. (C2), Time course of the motor period 1 min before (control) and after a lesion at the T13 level (circles), the L1 level (triangles) and L2 level (squares). The onset of recovery is indicated by successive arrows for each lesion. D, Lesion effect on duration of locomotor activity disruption (D1), motor period (D2), and burst area (D3) of microlesions performed at different SC level (T13-L1-L2). The black circles indicate the first microlesions and the grey triangles illustrate the second microlesions.

Mentions: To test whether anatomical segregation of neurons controlling flexor and extensor-related-activity exist more deeply in the tissue, we performed microlesion experiments (n = 21; Figure 3A) and investigated whether localized lesions induced selective disruption of either flexor or extensor motor output. Figure 3B illustrates the rosto-caudal and the medio-lateral location of the lesions. The size of the lesions (thick black circles = first lesion, thin black circles = second lesion, mean diameter = 208±6 µm) is expressed as a percentage of each SC thickness. The mean lesion depth measured in all spinal cord was 329±26 µm. The lesions' effect on locomotor activity was dependent on lesion location (Figure 3C and D). Typical examples of the effect of different lesions on the L2 motor period are illustrated in Figure 3C. The arrows indicate the recovery of locomotor activity for each lesion (T13, L2 and L1 lesion). A lesion performed at the T13 segment induced a short disruption of activity (mean = 29.3±17.8 sec, n = 4, Figure 3C2 black arrow, and Figure 3D1, T13 level). In contrast, lesions performed at the L1 and L2 segments blocked the locomotor activity for a longer period of time (Figure 3D1, L1 mean = 273.3±71.4 sec, n = 9; L2 mean = 137.3±37.5 sec, n = 8). The period and area of L2 VRs bursts were measured at the onset of the alternating activity recovery (Figure 3D2 and D3). In all cases, no change or a slight acceleration of the locomotor rhythm was observed following lesions at the T13 (mean = −10.4±6.2% of the output motor period, n = 4) and L2 level (mean = −3.1±3.4% of the output motor period, n = 8; Figure 3D2). In contrast, in 5 out of 9 cases of lesions at the L1 level induced a short or a long-lasting increase in locomotor period (mean = +41.2±20.6%) whereas the other 4 cases induced nothing or a slight acceleration of the motor period (mean = −6±3.6%). For all levels of lesion, burst area was reduced (mean = −27.6±18.5% for T13 lesions; mean = −37.3±11.9% for L1 lesions and mean = −48.2±25.9% for L2 lesions; Figure 3D3). Furthermore, there was no relationship between the size of the lesion and i) the duration of locomotor disruption ii) the motor period, and iii) the burst area (one-way ANOVA, p>0.05). Interestingly, the second lesion did not induce a greater effect than the first lesion on locomotor activity (grey triangles, Figure 3D1–3).


Functional organization of locomotor interneurons in the ventral lumbar spinal cord of the newborn rat.

Antri M, Mellen N, Cazalets JR - PLoS ONE (2011)

Lesion experiments.A, Photomicrographs of a ventral SC preparation (top) and its corresponding transverse section (bottom) showing an example of electrocoagulation of a restricted region located at the T13 segment level (magnification 4×; scale bar = 300 µm). B, Schematic drawing presenting all microlesions performed from T12 to L2 segments. The thick circles represent the first lesion (n = 21) whereas the thin circles represent the second lesion n = 16/21). The right and left dashed lines delineate the grey and white matter. The lesion size is expressed as a percentage of SC size (central canal set to 0). C, Lesion effects on locomotor activity. (C1), Extracellular recordings of L2 and L5 VRs before and after a lesion at the L1 level. The arrow represents the onset of locomotor recovery. (C2), Time course of the motor period 1 min before (control) and after a lesion at the T13 level (circles), the L1 level (triangles) and L2 level (squares). The onset of recovery is indicated by successive arrows for each lesion. D, Lesion effect on duration of locomotor activity disruption (D1), motor period (D2), and burst area (D3) of microlesions performed at different SC level (T13-L1-L2). The black circles indicate the first microlesions and the grey triangles illustrate the second microlesions.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3117791&req=5

pone-0020529-g003: Lesion experiments.A, Photomicrographs of a ventral SC preparation (top) and its corresponding transverse section (bottom) showing an example of electrocoagulation of a restricted region located at the T13 segment level (magnification 4×; scale bar = 300 µm). B, Schematic drawing presenting all microlesions performed from T12 to L2 segments. The thick circles represent the first lesion (n = 21) whereas the thin circles represent the second lesion n = 16/21). The right and left dashed lines delineate the grey and white matter. The lesion size is expressed as a percentage of SC size (central canal set to 0). C, Lesion effects on locomotor activity. (C1), Extracellular recordings of L2 and L5 VRs before and after a lesion at the L1 level. The arrow represents the onset of locomotor recovery. (C2), Time course of the motor period 1 min before (control) and after a lesion at the T13 level (circles), the L1 level (triangles) and L2 level (squares). The onset of recovery is indicated by successive arrows for each lesion. D, Lesion effect on duration of locomotor activity disruption (D1), motor period (D2), and burst area (D3) of microlesions performed at different SC level (T13-L1-L2). The black circles indicate the first microlesions and the grey triangles illustrate the second microlesions.
Mentions: To test whether anatomical segregation of neurons controlling flexor and extensor-related-activity exist more deeply in the tissue, we performed microlesion experiments (n = 21; Figure 3A) and investigated whether localized lesions induced selective disruption of either flexor or extensor motor output. Figure 3B illustrates the rosto-caudal and the medio-lateral location of the lesions. The size of the lesions (thick black circles = first lesion, thin black circles = second lesion, mean diameter = 208±6 µm) is expressed as a percentage of each SC thickness. The mean lesion depth measured in all spinal cord was 329±26 µm. The lesions' effect on locomotor activity was dependent on lesion location (Figure 3C and D). Typical examples of the effect of different lesions on the L2 motor period are illustrated in Figure 3C. The arrows indicate the recovery of locomotor activity for each lesion (T13, L2 and L1 lesion). A lesion performed at the T13 segment induced a short disruption of activity (mean = 29.3±17.8 sec, n = 4, Figure 3C2 black arrow, and Figure 3D1, T13 level). In contrast, lesions performed at the L1 and L2 segments blocked the locomotor activity for a longer period of time (Figure 3D1, L1 mean = 273.3±71.4 sec, n = 9; L2 mean = 137.3±37.5 sec, n = 8). The period and area of L2 VRs bursts were measured at the onset of the alternating activity recovery (Figure 3D2 and D3). In all cases, no change or a slight acceleration of the locomotor rhythm was observed following lesions at the T13 (mean = −10.4±6.2% of the output motor period, n = 4) and L2 level (mean = −3.1±3.4% of the output motor period, n = 8; Figure 3D2). In contrast, in 5 out of 9 cases of lesions at the L1 level induced a short or a long-lasting increase in locomotor period (mean = +41.2±20.6%) whereas the other 4 cases induced nothing or a slight acceleration of the motor period (mean = −6±3.6%). For all levels of lesion, burst area was reduced (mean = −27.6±18.5% for T13 lesions; mean = −37.3±11.9% for L1 lesions and mean = −48.2±25.9% for L2 lesions; Figure 3D3). Furthermore, there was no relationship between the size of the lesion and i) the duration of locomotor disruption ii) the motor period, and iii) the burst area (one-way ANOVA, p>0.05). Interestingly, the second lesion did not induce a greater effect than the first lesion on locomotor activity (grey triangles, Figure 3D1–3).

Bottom Line: Moreover, L1 segment lesioning induced the most important changes in the locomotor activity in comparison with lesions at the T13 or L2 segments.However, no lesions led to selective disruption of either flexor or extensor output.In addition, this study found no evidence of functional parcellation of locomotor interneurons into flexor and extensor pools at the dorsal-ventral midline of the lumbar spinal cord of the rat.

View Article: PubMed Central - PubMed

Affiliation: Université de Bordeaux, Centre National de la Recherche Scientifique, Institut des Neurosciences Cognitives et Intégratives d'Aquitaine, Unité Mixte de Recherche 5287, Bordeaux, France. myriam.antri@gmail.com

ABSTRACT
Although the mammalian locomotor CPG has been localized to the lumbar spinal cord, the functional-anatomical organization of flexor and extensor interneurons has not been characterized. Here, we tested the hypothesis that flexor and extensor interneuronal networks for walking are physically segregated in the lumbar spinal cord. For this purpose, we performed optical recordings and lesion experiments from a horizontally sectioned lumbar spinal cord isolated from neonate rats. This ventral hemi spinal cord preparation produces well-organized fictive locomotion when superfused with 5-HT/NMDA. The dorsal surface of the preparation was visualized using the Ca(2+) indicator fluo-4 AM, while simultaneously monitoring motor output at ventral roots L2 and L5. Using calcium imaging, we provided a general mapping view of the interneurons that maintained a stable phase relationship with motor output. We showed that the dorsal surface of L1 segment contains a higher density of locomotor rhythmic cells than the other segments. Moreover, L1 segment lesioning induced the most important changes in the locomotor activity in comparison with lesions at the T13 or L2 segments. However, no lesions led to selective disruption of either flexor or extensor output. In addition, this study found no evidence of functional parcellation of locomotor interneurons into flexor and extensor pools at the dorsal-ventral midline of the lumbar spinal cord of the rat.

Show MeSH