Isometric contractions of motor units in self‐reinnervated fast and slow twitch muscles of the cat

100

SUMMARY1. Nerve and muscle properties were studied in single motor units of triceps surae muscles in the cat using chronic recording techniques and intramuscular microstimulation. Recordings were made before and at intervals up to 18 months after a nerve was sectioned and sutured either to its distal stump (nerve-nerve suture) or to a muscle directly (nerve-muscle suture). Thus, each nerve and muscle served as its own control for recovery after reinnervation.2. Following a delay all muscles recovered their preoperative tension after nerve-nerve suture with a single exponential having a time constant of 1-2 months. Only half the muscles recovered their preoperative tensions after nerve-muscle sutures. Muscles which did not recover fully also had a slower time course of recovery.3. The estimated number of motor units did not increase significantly later than 2 months after nerve section and suture. Further recovery of muscle tension is due to increased unit tension, rather than increasing numbers of reinnervated motor units. Unit tension recovered completely in all muscles, but did not become enlarged, even when muscles apparently remained partially denervated.4. The latency of compound nerve potentials often recovered completely, although the amplitude of the potential remained depressed. Single motor axonal potentials recovered to control levels after reinnervation of muscle with a time constant similar to that for the recovery of motor unit tension. Therefore, two distinct populations of motor axons contribute to the compound potential: reinnervating axons whose size recovers fully, and disconnected axons which remain atrophic. Incomplete recovery of the compound potential amplitude mainly results from a failure of all axons to remake peripheral connexions.5. Thus, formation of functional nerve-muscle connexions completely reverses the effects of axotomy on nerve and muscle. Reinnervated motor units recovered their preoperative size, whether or not much of the muscle remained denervated.

Section: Discussionmentioning

confidence: 99%

Time course and extent of recovery in reinnervated motor units of cat triceps surae muscles

Gordon

1982

100

“…One drawback to the proposal ofthis possibility is that relevant signals cannot be specified in concrete terms. Bagust & Lewis (1974) have noted that impulse conduction along many reunited motor nerve fibres fails to cross a neuroma at the site of suture even six months after the selfunion operation. However, the conduction velocity of these motor fibres was within the range found for those motor axons which had functional connexions with the muscle (Bagust & Lewis, 1974).…”

Section: Methodsmentioning

confidence: 99%

“…Bagust & Lewis (1974) have noted that impulse conduction along many reunited motor nerve fibres fails to cross a neuroma at the site of suture even six months after the selfunion operation. However, the conduction velocity of these motor fibres was within the range found for those motor axons which had functional connexions with the muscle (Bagust & Lewis, 1974). It has been proposed that the original properties of motoneurones may be restored following the formation of neuromas at the central ends of the cut peripheral nerves (Watson, 1968;Cragg, 1970).…”

Section: Methodsmentioning

confidence: 99%

Properties of fast and slow alpha motoneurones following motor reinnervation

Kuno¹,

Miyata²,

Muñoz-Martínez³

1974

SUMMARY1. The properties of medial gastrocnemius (fast alpha) and soleus (slow alpha) motoneurones ofthe cat were examined with intracellular electrodes 33-154 days after self-or cross-union of the muscle nerves.2. The original properties of fast and slow alpha motoneurones measured in terms of the axonal conduction velocity, the duration of after-hyperpolarization and the overshoot amplitude were restored at least in part after self-union of the muscle nerves.3. Slow alpha motoneurones recovered their original properties whether the muscle nerve was united to the original, slow red muscle or to the fast pale muscle. In two animals, some of the fast muscle fibres seemed to be doubly innervated by both fast and slow alpha motoneurones.4. The degree of restoration of the original motoneurone properties was closely related to the degree of motor reinnervation of the muscle.5. At a given stage of motor reinnervation, the degree of recovery of the motoneurone properties was approximately the same regardless of the presence or absence of functional motor connexions of the motoneurone under study.6. When the dorsal root ganglia were removed immediately before selfunion of the muscle nerves, recovery of the conduction velocity of motoneurones was impeded without significant effect upon the process of motor reinnervation or upon recovery of the overshoot amplitude and the duration of after-hyperpolarization.7. It is concluded that the 'dedifferentiated' properties of fast and slow alpha motoneurones after nerve section may be 'redifferentiated' following motor reinnervation to any muscle. The possible signal for restoration of the motoneurone properties is discussed.

“…Injuries in peripheral nerve fibres result in a reduction of conduction velocity proximal to the lesion (Acheson, Lee & Morison, 1942;Gutmann & Holubar, 1951;Eccles & McIntyre, 1953; Eccles, Krnjevic & Miledi, 1959;Kiraly & Krnjevic, 1959;Cragg & Thomas, 1961;Aitken & Thomas, 1962;Bagust & Lewis, 1974; Kuno, Miyata & Munioz-Martinez, 1974;Mendell, Munson & Scott, 1976;Schmidt & Stefani, 1976). The reduced conduction velocity appears to be associated with a decrease in axon diameter (Greenman, 1913;Gutmann & Sanders, 1943;Gutmann & Holuba6, 1951;Cragg & Thomas, 1961;Aitken & Thomas, 1962).…”

Section: Introductionmentioning

confidence: 99%

Membrane properties and conduction velocity in sensory neurones following central or peripheral axotomy

Czéh¹,

Kudo²,

Kuno³

1977

SUMMARY1. The properties of dorsal root ganglion cells in the lumbosacral segments were examined with intracellular electrodes about 3 weeks after section of the central (dorsal roots) or peripheral processes in the cat.2. Chronic section of the peripheral nerve in the hind limb resulted in a reduction in conduction velocity of both the central and peripheral processes of sensory neurones.3. Sensory neurones arising from the triceps surae and plantaris muscles were subject to 'disuse' conditions for about 3 weeks by section of the ventral roots combined with severance of the Achilles tendon. Under such conditions, the central and peripheral conduction velocities of these sensory neurones tended to decrease, but the decrease was significantly less than that following peripheral nerve section.4. Chronic section of the dorsal roots produced no significant changes in conduction velocity of the central processes of muscle sensory neurones but caused a significant increase in the peripheral conduction velocity.5. The only electrophysiological property of dorsal root ganglion cells which altered following axotomy was the time-dependent membrane rectification in response to hyperpolarizing current pulses. The rectification characteristics were modified by chronic section of the peripheral nerve but not by chronic section of the dorsal root.6. It is concluded that injuries in nerve fibres per se do not necessarily result in a decrease of their conduction velocity and that a decrease in their conduction velocity is associated with changes in the properties of the cell bodies.7. It is suggested that a decrease in conduction velocity following nerve section may require the participation of changes in the neurone cell body.