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The influence of innervation on the differentiation of contractile speeds of developing chick muscles
Insights
Motor nerves determine muscle speed. Studies show that the nerve a muscle receives dictates its contractile speed and innervation pattern, not predetermined muscle fiber properties.
Area of Science:
- Muscle physiology
- Developmental biology
- Neuroscience
Background:
- Slow anterior latissimus dorsi (ALD) and fast posterior latissimus dorsi (PLD) muscles in chicks exhibit distinct contractile speeds.
- Muscle innervation occurs during embryonic development, preceding significant differentiation in contractile properties.
Purpose of the Study:
- To investigate the role of innervation in the differentiation of muscle contractile speeds.
- To determine if contractile characteristics are intrinsic to muscle fibers or influenced by neural input.
Main Methods:
- Comparative analysis of ALD and PLD muscle development and innervation timing.
- Cross-regeneration experiments involving minced ALD and PLD muscles in adult chicks.
- Histological examination of innervation patterns in regenerated muscles.
Main Results:
- Innervation precedes the divergence of contractile speeds between ALD and PLD muscles.
- Regenerated ALD innervated by a PLD nerve adopted fast muscle characteristics.
- Regenerated PLD innervated by an ALD nerve exhibited slow muscle properties.
- Histology revealed focal innervation in regenerated ALD and multiple innervation in regenerated PLD.
Conclusions:
- Muscle contractile speed is not a predetermined property of the muscle fiber.
- The motor nerve dictates both the contractile characteristics and the innervation pattern of developing muscles.
Abstract:
1. The role of innervation of the differentiation of contractile speeds was studied in the slow anterior latissimus dorsi (ALD) and fast posterior latissimus dorsi (PLD) muscle of the chick. 2. These muscles become innervated during the 12th and 15th day of embryonic development. At this time both muscles contract and relax extremely slowly and their contractile speeds are very similar. By the 18th day their contraction and relaxation becomes more rapid. It is at this time that the contractile characteristics of both muscles also become very different from each other, ALD being about 3 times slower than PLD. Thus innervation percedes differentiation of contractile speeds by several days. 3. The influence of innervation on the contractile characteristics of developing slow and fast muscles was studied during muscle regeneration in adults. When a slow ALD muscle was minced and implanted in place of a fast PLD the newly regenerated ALD became innervated by a PLD nerve and resembled a fast PLD. Conversely, when PLD muscles were minced and replaced ALD the regenerated PLD was innervated by ALD nerve and became slow. 4. Histological examination revealed that the regenerated ALD became focally innervated, and the regenerated PLD multiply innervated. 5. Thus, the contractile speeds are not predetermined properties of the muscle fibre. Both contractile characteristic and the pattern of innervation of developing muscles are determined by the motor nerve.