Alterations in cat skeletal neuromuscular junctions following prolonged inactivity.

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SUMMARY1. The distributions of cholinesterase (ChE) activity and acetylcholine (ACh) receptors were studied in normal and denervated cat hind-limb fast-twitch skeletal muscles and in muscles contralateral to denervated muscles.2. On normal muscle fibres almost all receptors were confined to the immediately post-junctional membrane, although a perijunctional gradient of increased ACh receptor density was found on both fast-and slow-twitch fibres. After denervation, the extrajunctional ACh receptor density increased greatly and remained high for at least 10 months. Ectopic regions staining for ChE activity and having a high density of ACh receptors appeared in denervated muscle. The number of junctional ACh receptors decreased slowly after denervation, with a half-time of about 140 days.3. Fast-twitch muscles contralateral to denervated muscles also showed changes, including an increase in junctional size and a small but significant increase in extrajunctional ACh receptor density.

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Neuromuscular junctions and alpha‐bungarotoxin‐binding sites in denervated and contralateral cat skeletal muscles.

Steinbach¹

1981

Self Cite

“…The implication that inactivity changes the motoneuron-muscle fibre connectivity is based primarily on observations of the neuromuscular junction via endplate staining. Increases have been reported in the acetylcholine receptor density after SI (Eldridge et al 1981) and in 189 D. J. PIEROTTI AND OTHERS the branching of terminal axons after TTX treatment (Brown & Ironton, 1977). Caldwell & Ridge (1983) assessed increases in polyneuronal innervation in the lumbrical muscles in SI rats via both endplate staining and intracellular recordings of endplate potentials from muscle fibres.…”

Section: Discussionmentioning

confidence: 99%

Mechanical and morphological properties of chronically inactive cat tibialis anterior motor units.

Pierotti

Roy

Bodine

et al. 1991

SUMMARY1. The lumbar spinal cord was functionally isolated in ten cats by cord transection at the junctions of segments T12-T13 and L7-S1 and cutting bilaterally all dorsal roots between the two transections. Two 24 h EMG recording sessions were used to verify that muscles in the lower limb were virtually electrically silent. The cats were maintained in excellent health for 6 months.2. Six months after spinal cord isolation, an acute experiment was performed to isolate a single motor unit from the tibialis anterior of each hindlimb using ventral root splitting techniques. Each motor unit was characterized physiologically as either fast fatigable (FF, n = 11), fast fatigue resistant (FR, n = 4), fast intermediate (Fl, n = 2), or slow (S, n = 1), and repetitively stimulated to deplete the motor unit of its glycogen.3. Maximum tensions of the fast motor units were lower than mean maximum tensions of control, whereas the S motor unit remained within the range observed in controls. In general, the isometric contractile properties, as well as fatigability, were within the ranges for each of the motor unit types in control cats. The mean fibre cross-sectional areas of the fibres within the FR and FF motor units were 40 and 50 % smaller than control, while the mean fibre size of the fibres within the S motor unit was similar to control.4. Innervation ratios and specific tensions for all experimental motor units were within the ranges of those reported for tibialis anterior motor units in control cats. Thus, it appears that the decrease in maximum tension of the fast motor units was primarily related to a reduction in fibre size.5. The spatial distribution of the fibres within fast motor units of a spinally isolated cat, as measured by interfibre distances of the motor unit fibres, was similar to that reported for control tibialis anterior motor units.6. These data suggest that factors independent of activity play a prominent, if not dominant, role in maintaining the complement of motor unit types typical of adult cat muscles. In addition, normal innervation patterns appear to be maintained in the absence of activity. § To whom reprint requests should be sent. MS 8916 D. J. PIEROTTI AND OTHERS

“…This additional stimulus to extrajunctional ACh receptor production in denervated muscles should however be transitory, and if there were no trophic chemical then changes in paralysed and denervated preparations should eventually equalize. Prolonged paralyses have been carried out to see if this is so in baboons (Gilliatt, Westgaard & Williams, 1978), rats (Bray, Hubbard & Mills, 1979), frogs (Antony & Tonge, 1980) and cats (Eldridge, Liebhold & Steinbach, 1981), and differences between inactive and denervated muscles were still found. These results would seem to confirm finally the need to postulate a trophic agent in addition to activity and degeneration effects as one further means by which motor nerves control extrajunctional muscle properties.…”

Section: Introductionmentioning

confidence: 99%

Comparison of effects of denervation and botulinum toxin paralysis on muscle properties in mice

Brown

Hopkins

Keynes

1982

SUMMARY1. The properties of denervated and fully innervated but paralysed soleus and extensor digitorum longus (e.d.l.) muscles were compared in mice.2. Muscles were paralysed by single or repeated injections of botulinum toxin into the right lower leg. Contralateral muscles were denervated at the same time by sciatic nerve section. Muscles were excised 3-20 days later and direct and indirect isometric twitch and tetanic tensions measured in vitro. ACh sensitivity was assessed from isometric contractions to various concentrations of bath-applied ACh perchlorate.3. Denervated muscles as expected from the work of others developed sensitivity to ACh earlier and more rapidly than paralysed muscles. A transient peak of sensitivity was reached after 7 days of denervation in soleus and after 8 days in e.d.l. However 2 days later the sensitivity of muscles fully paralysed to nerve twitch and tetanic stimuli was not significantly different from that of denervated muscles.4. In both e.d.l. and soleus the direct tetanus/twitch ratios declined in paralysed and denervated muscles. The decline was initially more rapid in denervated than paralysed soleus, but the ratios for paralysed and denervated muscles were not significantly different after 10 days in either muscle. By this time there were no differences in the absolute strengths of the paralysed and denervated muscles.5. It is concluded that the ACh sensitivity and dynamic properties of fully paralysed mouse muscles become equal to those of denervated muscles once the acute effects associated with nerve degeneration are past. This result is consistent with the idea that normal neuronal control of extrajunctional mammalian skeletal muscle properties is mediated solely by means of activity.