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Postnatal differentiation of cell body volumes of spinal motoneurons innervating slow‐twitch and fast‐twitch muscles
Author(s) -
Sato Manabu,
Mizuno Noboru,
Konishi Akira
Publication year - 1977
Publication title -
journal of comparative neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.855
H-Index - 209
eISSN - 1096-9861
pISSN - 0021-9967
DOI - 10.1002/cne.901750104
Subject(s) - tonic (physiology) , biology , anatomy , horseradish peroxidase , hindlimb , motor neuron , soleus muscle , cell bodies , spinal cord , central nervous system , endocrinology , neuroscience , skeletal muscle , biochemistry , enzyme
Distribution of cell body volumes of motoneurons innervating the soleus (slow‐twitch or tonic) and medial gastrocnemius (fast‐twitch or phasic) muscles was examined in adult cats and a series of kittens ranging from one to 140 days in age. To identify the soleus (Sol) and the medial gastrocnemius (MG) motoneurons, each group of motoneurons was labeled differentially by utilizing retrograde axonal transport of horseradish peroxidase injected into the muscles. It was verified statistically that in the adult cat, the mean cell body volume of the Sol motoneurons was smaller than that of the MG motoneurons. Difference of the mean cell body volume between the Sol and MG motoneurons was found to be significant around the tenth postnatal day. The mean cell body volumes of both Sol and MG motoneurons increased mainly during the third to the seventh week after birth. After this period, increase of the cell body volume was relatively slight and in the fifth month after birth, some of the motoneurons still appeared to be growing. Our findings also suggested that the MG motoneurons may exhibit the adult pattern of distribution of cell body volume in an earlier postnatal stage than do the Sol motoneurons, and that differentiation of motoneurons into the gamma and alpha types may occur earlier than differentiation into the tonic and phasic types.