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March 1969

Histochemical and Contractile Properties in the Cross-Innervated Guinea Pig Soleus Muscle

Author Affiliations

Bethesda, Md; Montreal; Bethesda, Md
From the National Institute of Neurological Diseases and Stroke, National Institutes of Health, US Public Health Service, Department of Health, Education, and Welfare, Laboratory of Neurophysiology (Dr. Robbins), and Medical Neurology Branch (Dr. Engel). Dr. Karpati is a Postdoctoral Research Fellow of the Muscular Dystrophy Association of Canada. His current address is Montreal Neurological Institute, 3801 University St, Montreal.

Arch Neurol. 1969;20(3):318-329. doi:10.1001/archneur.1969.00480090106015

THE soleus muscle of the adult guinea pig is well suited for a quantitative investigation of both histochemical and physiological consequences of cross-innervation: (1) Histochemically, it contains only type I extrafusal muscle fibers, as determined with the myofibrillar adenosine triphosphatase (ATPase) reaction, whereas in all other species studied (cat, rat, mouse, rabbit, or dog) it contains a variable number of type II fibers.1 (Histochemical type I fibers contain high activity of most oxidative enzymes and low activity of myofibrillar ATPase and amylophosphorylase; type II fibers have opposite relative activities.) (2) Physiologically it is a typical "slow" twitch muscle. (3) It is possible to reinnervate the denervated soleus by nerves which normally innervate histochemically "mixed" and physiologically "fast" muscles, after which a variable number of type II muscle fibers appear.2

We have studied both the degree of "speeding" and the relative proportion of type II fibers after cross-innervation.3

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