TY - JOUR
T1 - Phrenic motoneuron morphology during rapid diaphragm muscle growth
AU - Prakash, Y. S.
AU - Mantilla, Carlos B.
AU - Zhan, Wen Zhi
AU - Smithson, Kenneth G.
AU - Sieck, Gary C.
PY - 2000
Y1 - 2000
N2 - In the adult rat, there is a general correspondence between the sizes of motoneurons, motor units, and muscle fibers that has particular functional importance in motor control. During early postnatal development, after the establishment of singular innervation, there is rapid growth of diaphragm muscle (Dia(m)) fibers. In the present study, the association between Dia(m) fiber growth and changes in phrenic motoneuron size (both somal and dendritic) was evaluated from postnatal day 21 (D21) to adulthood. Phrenic motoneurons were retrogradely labeled with fluorescent tetramethylrhodamine dextran (3,000 MW), and motoneuron somal volumes and surface areas were measured using three-dimensional confocal microscopy. In separate animals, phrenic motoneurons retrogradely labeled with choleratoxin B-fragment were visualized using immunocytochemistry, and dendritic arborization was analyzed by camera lucida. Between D21 and adulthood, Dia(m) fiber cross-sectional area increased by ~164% overall, with the growth of type II fibers being disproportionate to that of type I fibers. There was also substantial growth of phrenic motoneurons (~360% increase in total surface area), during this same period, that was primarily attributable to an expansion of dendritic surface area. Comparison of the distribution of phrenic motoneuron surface areas between D21 and adults suggests the establishment of a bimodal distribution that may have functional significance for motor unit recruitment in the adult rat.
AB - In the adult rat, there is a general correspondence between the sizes of motoneurons, motor units, and muscle fibers that has particular functional importance in motor control. During early postnatal development, after the establishment of singular innervation, there is rapid growth of diaphragm muscle (Dia(m)) fibers. In the present study, the association between Dia(m) fiber growth and changes in phrenic motoneuron size (both somal and dendritic) was evaluated from postnatal day 21 (D21) to adulthood. Phrenic motoneurons were retrogradely labeled with fluorescent tetramethylrhodamine dextran (3,000 MW), and motoneuron somal volumes and surface areas were measured using three-dimensional confocal microscopy. In separate animals, phrenic motoneurons retrogradely labeled with choleratoxin B-fragment were visualized using immunocytochemistry, and dendritic arborization was analyzed by camera lucida. Between D21 and adulthood, Dia(m) fiber cross-sectional area increased by ~164% overall, with the growth of type II fibers being disproportionate to that of type I fibers. There was also substantial growth of phrenic motoneurons (~360% increase in total surface area), during this same period, that was primarily attributable to an expansion of dendritic surface area. Comparison of the distribution of phrenic motoneuron surface areas between D21 and adults suggests the establishment of a bimodal distribution that may have functional significance for motor unit recruitment in the adult rat.
KW - Cholera-toxin
KW - Confocal microscopy
KW - Immunocytochemistry
KW - Rat motor unit
KW - Recruitment
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U2 - 10.1152/jappl.2000.89.2.563
DO - 10.1152/jappl.2000.89.2.563
M3 - Article
C2 - 10926639
AN - SCOPUS:0033896478
SN - 8750-7587
VL - 89
SP - 563
EP - 572
JO - Journal of applied physiology
JF - Journal of applied physiology
IS - 2
ER -