Response of developing rat fast muscles to partial denervation

Connold, A.L.; fisher, T.J.; Maudarbocus, S.; Vrbová, Gerta

doi:10.1016/0306-4522(92)90199-c

Cited by 16 publications

(5 citation statements)

References 24 publications

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“…Because axotomy at P 14 caused severe motoneuronal death, these data suggest that SNB motoneurons that survive developmental axotomy at P 14 expand their terminal arbors to innervate more muscle fibers than normal. This is consistent with reports that adult motoneurons can expand their terminal arbors (Thompson and Jansen, 1977;Brown and Ironton, 1978), and that developing motoneurons can maintain expanded terminal arbors after partial denervation (Thompson and Jansen, 1977;Betz et al, 1980;Fladby and Jansen, 1987;Gates and Ridge, 1992; but see Connold et al, 1992). Moreover, it is possible that surviving SNB motoneurons maintain less polyneuronal innervation of LA fibers than is normally seen in adult LA muscle, resulting in less overlap between motor units.…”

Section: Discussionsupporting

confidence: 90%

“…During early postnatal development, mammalian motoneurons experience a net loss of synaptic terminals (Redfern, 1970;Brown et al, 1976;reviewed by Purves and Lichtman, 1980;Jansen and Fladby, 1990), they do not sprout following partial denervation of the target (Brown et al, 1976;Thompson and Jansen, 1977;Betz et al, 1980;Connold et al, 1992), and they cannot survive direct axonal injury (Romanes, 1946;Schmalbruch, 1984;Snider and Thanedar, 1989;Pollin et al, 1991;reviewed by Lowrie and Vrbova, 1992). The mechanisms underlying each process are undoubtedly complex.…”

Section: Discussionmentioning

confidence: 99%

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Axotomy of developing rat spinal motoneurons: Cell survival, soma size, muscle recovery, and the influence of testosterone

Lubischer

Arnold

1995

J. Neurobiol.

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During the period of synapse elimination, motoneurons are impaired in their ability to generate or regenerate axonal branches: following partial denervation of their target muscle, young motoneurons do not sprout to nearby denervated fibers and after axonal injury, they fail to reinnervate the muscle. In the rat levator ani (LA) muscle, which is innervated by motoneurons in the spinal nucleus of the bulbocavernosus (SNB), synapse elimination ends relatively late in development and can be regulated by testosterone. We took advantage of this system to determine if the end of synapse elimination and the development of regenerative capabilities by motoneurons share a common mechanism, or, alternatively, if these two events can be dissociated in time. Axotomy on or before postnatal day 14 (P14) caused the death of SNB motoneurons. By P21, toward the end of synapse elimination in the LA muscle, SNB motoneurons had developed the ability to survive axonal injury. Altering testosterone levels by castration on P7 followed by 4 weeks of either testosterone propionate or control injections did not change the ability of SNB motoneurons to survive axonal injury during development, although these same treatments alter the time course of synapse elimination in the LA muscle. Thus, we dissociated the inability of SNB motoneurons to recover from axonal injury from their developmental elimination of synaptic terminals. We also measured the effect of early axotomy on motoneuronal soma size and on target muscle weight. Axotomy on P14 caused a long-lasting decrease in the soma size of surviving SNB motoneurons, whereas motoneurons axotomized on P28 recovered their normal soma size. Axotomy on or before P7 caused severe atrophy of the target muscles, matching the extensive loss of motoneurons. However, target muscle recovery after axotomy on P14 was as good as recovery after axotomy at later ages, despite greater motoneuronal death after axotomy on P14. This result may reflect an increase in motor unit size, a decrease in polyneuronal innervation by SNB motoneurons that survive axotomy on P14, or a combination of the two.

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Section: Discussionsupporting

confidence: 90%

Section: Discussionmentioning

confidence: 99%

Axotomy of developing rat spinal motoneurons: Cell survival, soma size, muscle recovery, and the influence of testosterone

Lubischer

Arnold

1995

J. Neurobiol.

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“…Nevertheless in spite of the removal of axons that might compete with the terminals of the remaining L5 axons, the force output of their MUs decreased. In the study of Connold et al (1992), no increase of MU sizes was seen in rats partially denervated at 5 days, and MU size was similar to that of control EDL muscles, whereas the present results show that in animals operated on at 3 days the MU force output, and probably size, was smaller than normal. This indicates that partial denervation has a more deleterious effect on muscle recovery in younger animals and that the ability of MUs to achieve a larger force output depends on the age at which the partial denervation is carried out.…”

Section: Behavioural Observations and Locomotor Changescontrasting

confidence: 81%

“…Indeed, when the muscles that were partially denervated at 5 days were examined 2-6 months later, their MUs had a territory that was no greater than that of control muscles that had not been operated on. This was in contrast to EDL muscles where partial denervation was carried out at 18-20 days of age causing an almost 2-fold expansion of their MUs (Connold, Fisher, Maudarbocus & Vrbova', 1992). Since at 5 days, MU territory of the EDL is already retracting (Balice-Gordon & Thompson, 1988), it is possible that even after partial denervation at this stage axons continue to withdraw their synapses and are unable to maintain their expanded peripheral field, or expand it again so as to re-occupy the denervated muscle fibres.…”

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confidence: 66%

The effect of partial denervation of developing rats fast muscles on their motor unit properties.

Tyč¹,

Vrbová²

1995

The Journal of Physiology

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1. The effects of partial denervation on motor units of the fast twitch extensor digitorum longus (EDL) muscle of the rat were studied. 2. Partial denervation was performed by surgically removing 2-4 mm of the L4 ventral ramus in 3-and 18-day-old Wistar rats. Two to three months later, EMG activity, contractile properties and muscle fibre types were analysed. 3. After partial denervation the EDL muscle became significantly more active, particularly in the animals operated on at 3 days. The amount of activity during periods of rest was up to 4 times that of the control EDL muscle. 4. The maximum tetanic tension developed by the EDL muscles 2 months after partial denervation at 3 days was only 11 + 1.01 % (S.E.M., n = 18) of the control. In animals operated on at 18 days this value was larger, i.e. 44 + 3-46% (S.E.M., n= 12). The low force output of animals operated on at 3 days was also reflected in the low mean motor unit (MU) force output which was only 69 + 5-82 % (S.E.M., n = 17) of the contralateral control muscle. In contrast the force generated by MUs of rats operated on at 18 days was larger than that of control muscles, i.e. 151 + 13-05% (S.E.M., n = 11). The number of MUs was 6 + 0-32 (S.E.M., n = 19) in rats operated on at 3 days and 12 + 0-83 (S.E.M., n = 14) in rats operated on at 18 days. 5. The speed of contraction decreased and the resistance to fatigue increased. These changes were greater in animals operated on at 3 days. The proportion of muscle fibres reacting with antibody against slow myosin showed a significant increase, especially in the group of animals operated on at 3 days.

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“…Two days later 1 mg silicone implants containing either nifedipine (30 jug) and NaCl (380 ,sg) or NaCl only were inserted alongside the soleus muscle on the operated side. Ten weeks later all animals were anaesthetized using chloral hydrate intraperitoneally (1 ml (100 g body weight)-') and bilateral soleus muscles prepared for isometric tension recording and assessment of motor unit size (MUS) as described by Connold et al (1992).…”

mentioning

confidence: 99%

Muscle Contraction

1995

The Journal of Physiology

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Response of developing rat fast muscles to partial denervation

Cited by 16 publications

References 24 publications

Axotomy of developing rat spinal motoneurons: Cell survival, soma size, muscle recovery, and the influence of testosterone

Axotomy of developing rat spinal motoneurons: Cell survival, soma size, muscle recovery, and the influence of testosterone

The effect of partial denervation of developing rats fast muscles on their motor unit properties.

Muscle Contraction

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