Hi Rizwan,

Have a look on this very classic paper if can find some answers from it!

All the best,

Vuokko

Med Sci Sports. 1975 Fall;7(3):185-98.

Mechanism of work-induced hypertrophy of skeletal muscle.

Goldberg AL, Etlinger JD, Goldspink DF, Jablecki C.

Abstract

Skeletal muscle can undergo rapid growth in response to a sudden increase in work load. For example, the rat soleus muscle increases in weight by 40% within six days after the tendon of the synergistic gastrocnemius is sectioned. Such growth of the overworked muscle involves an enlargement of muscle fibers and occasional longitudinal splitting. Hypertrophy leads to greater maximal tension development, although decreased contraction time and reduced contractility have also been reported. Unlike normal developmental growth, work-induced hypertrophy can be induced in hypophysectomized or diabetic animals. This process thus appears independent of growth hormone and insulin as well as testosterone and thyroid hormones. Hypertrophy of the soleus can also be induced in fasting animals, in which there is a generalized muscle wasting. Thus muscular activity takes precedence over endocrine influences on muscle size. The increase in muscle weight reflects an increase in protein, especially sarcoplasmic protein, and results from greater protein synthesis and reduced protein breakdown. Within several hours after operation, the hypertrophying soleus shows more rapid uptake of certain amino acids and synthesis of phosphatidyl-inositol. By 8 hours, protein synthesis is enhanced. RNA synthesis also increases, and hypertrophy can be prevented with actinomycin D. Nuclear DNA synthesis also increases on the second day after operation and leads to a greater DNA content. The significance of the increased RNA and DNA synthesis is not clear, since most of it occurs in interstitial and satellite cells. The proliferation of the non-muscle cells seems linked to the growth of the muscle fibers; in addition, factors causing muscle atrophy (e.g. denervation) decrease DNA synthesis by such cells. In order to define more precisely the early events in hypertrophy, the effects of contractile activity were studied in rat muscles in vitro. Electrical stimulation enhanced active transport of certain amino acids within an hour, and the magnitude of this effect depended on the amount of contractile activity. Stimulation or passive stretch of the soleus or diaphragm also retarded protein degradation. Presumably these effects of mechanical activity contribute to the changes occuring during hypertrophy in vivo. However, under the same conditions, or even after more prolonged stimulation, no change in rates of protein synthesis was detected. These findings with passive tension in vitro are particularly interesting, since passive stretch has been reported to retard atrophy or to induce hypertrophy of denervated muscle in vivo. It is suggested that increased tension development (either passive or active) is the critical event in initiating compensatory growth.

Hi Vuokko

 thanks for this very classic paper, I went through it and am still wondering what and where can it go wrong ? I feel something very fundamental is wrong somewhere but what it is ?

 I checked atlases of mouse anatomy and I identify the plantaris correctly.

 and I have been visiting mice everyday to check their activity pattern and they look normal and active. still no hypertrophy ? 

Dear Rizwan,

Did you check the innervation of the plantaris muscle after the operation?

Best regards, Willem

Dear Rizwan,

I agree with Willem, it's easy to damage both innervation and vascular supply of the plantaris muscle especially if you try to separate the gastrocnemius from the plantaris all the way up to the joint. What I do is that when I see the gastrocnemius/plantaris interface I stop trying to separate the muscles and instead I cut with a pair of scissors, aiming slightly diagonally, trying to remove as much of the gastrocnemius as I can but without interfering with the plantaris. The result looks somewhat like a ski slope when observed from the side.

Good luck with the procedure

Best regards

Ferdinand 

Dear Willem and Ferdinand, 

 Many thanks for the suggestion, I guess this might be the problem. I have been removing much of the gastrocnemius all the way close to the knee, and I might be cutting nerve or blood supply to plantaris.

Online literature and atlases do not give much tracking of the blood/nerve supply to plantaris. But I feel the problem might be solved, I will do another mouse later today to see if it responds better.

Loads of thanks, 

-- Rizwan

Rizwan,

   I'm curious to know if you ever solved the problems you were having with this model. In C57 mice we typically see a very large increase in muscle weight, but fiber CSA does not change very much (type IIa increase, but type IIb do not, type IIx response is moderate). Instead we see a very large increase in fiber number. We also only remove about 1/2 of the gastroc, basically up to the point of where it becomes firmly attached to the plantaris. Would love to hear a response.

Troy Hornberger

Troy, 

 I apologize for delay, I missed your post and rarely log in here. 

 We have just sacrificed some ablated mice (C57 WT, and SOD1-/-) and see a good amount of hypertrophy. Your finding of fiber hyperplasia as prime contributor to muscle hypertrophy is very fascinating, so as the type IIa vs IIb hypertrophic response. I will come back to you with our findings as soon as we have some data. :)

 My wishes, and sorry again. :)

 -- Rizwan 

Val,

  Our traditional model involves removing all of the soleus and about the distal 2/3rd of the gastroc. However, I do not think that removing this much tissue is necessary and probably causes to much overload. Just removing the soleus and about the distal 1/4 of the gastroc is more than sufficient to induce a large increase in muscle mass. 

I am a bit confused, but what is the rationale that cutting 2/3 of the gastroc compared to 1/4 will result in a stronger overload. At least in the longitudinal direction, the plantaris will carry all of the load as long as the muscle facia is separated and the gastroc tendon is cut?

I can't say for sure, but I suspect that there is still a large degree of lateral force transmission between the gastroc and the fascia that surrounds the plantaris. Regardless of the cause, we definitely see larger increases in plantaris mass when we cut away more of the gastroc.

And you are sure that this increase in mass is not due to inflammation or other type of damage resulting from cutting of the blood supply or massive bleeding from the gastroc, extensive forming of connective tissue etc? Is this larger increase in mass also reflected in an increased force production and/or muscle fiber cross-sectional area?