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The importance of activity in the post-natal development of nerve and muscle in the rat tail
Başlık:
The importance of activity in the post-natal development of nerve and muscle in the rat tail
Yazar:
Russell, Norman John Wilkie, author.
ISBN:
9780438060630
Yazar Ek Girişi:
Fiziksel Tanımlama:
1 electronic resource (185 pages)
Genel Not:
Source: Dissertation Abstracts International, Volume: 76-08C.
Advisors: Margaret Gladden.
Özet:
(1) The rat is born with a particularly immature neuromuscular system and is therefore ideally suited for experimental manipulation during the early stages of development. The terminal slips of the intertransverse caudal (ITC) muscles of male albino rats were tenotomised at birth, and these animals kept until eight weeks of age. (2) EMG recordings from the last slip of the ITC muscle of free- running 8-week-old animals showed that the normal muscle is phasically active. Acute tenotomy silenced the muscle, but the tendons of chronically tenotomised muscles had formed functional readhesions by eight weeks after birth since these muscles also exhibited phasic EMG patterns. Nevertheless, it is argued that tenotomy caused a reduction in the activity of both the sensory and the motor axons supplying these muscles during their early development. (3) The conduction velocities of axons supplying the last slip of the ITC muscle were measured. It was found that the distribution of conduction velocities to the normal muscle fell clearly into the well-defined classifications of Groups I, II, and III for afferent axons, and alpha and r for efferent axons. In contrast, the distribution of conduction velocities to tenotomised muscle was significantly different (Gladden and Russell 1975). Few axons were found with conduction velocities greater than about 36m/sec, whereas in normal animals axons were commonly found with conduction velocities up to 52m/sec. (4) By identifying the origins of single afferent axons from tenotomised muscle it was found that the redistribution of the conduction velocity histograms could not be simply explained by loss of the normally fastest conducting axons. Sensory receptors and their innervation survive muscle tenotomy during development, and it was shown that afferent axons from muscle spindle sensory endings and Golgi tendon organs remained functionally intact but with slower than normal conduction velocities. Similarly, the motor innervation remained intact after tenotomy, but all motor axons to tenotomised muscle were found with conduction velocities at the slow end of the normal alpha conduction velocity range. (5) This effect of tenotomy on axonal conduction velocity is limited to growing animals, since tenotomy of the same muscle for the same period in adult animals did not affect the distribution of conduction velocities. (6) The lack of impulse traffic, imposed by tenotomy during the growth period, may have limited the growth of axons supplying tenotomised muscle. To test this hypothesis it was necessary to reduce the impulse traffic in the nerves by another means. Therefore, the ITC muscles of young rats were deafferentated and the conduction velocities of the motor axons subsequently measured at 8 weeks of age. The slowing of the axonal conduction velocities of deafferentated alpha motoneurones was identical to that caused by tenotomy. As before, all alpha motor axons were found to conduct at the slow end of the normal alpha conduction velocity range. (7) These experiments are discussed with reference to activity- related manufacture and transport of structural materials within the neurone during its growth. It would appear that tenotomy and differentiation, by limiting the neuronal impulse traffic during development, has limited the capacity of neurones and their axons to undergo the normal dimensional increases by which they attain their adult functional characteristics. (8) The results of previous studies of disuse of synaptic connections in the adult spinal cord remain equivocal, and the developmental aspects have not been considered. With the present preparation, if neuronal growth had been altered by tenotomy, testing of the monosynaptic reflex should furnish information about these moto- neurones and the efficacy of their Group la synaptic input. However, it was established that the ITC muscle does not exhibit the classical monosynaptic reflex connections more commonly associated with the hind-limb musculature. This is discussed with reference to the fact that axial muscle motoneurones, of which the ITC is an example, have predominant inputs from the vestibular nuclei and contralateral muscles, and may not therefore be expected to exhibit ipsilateral monosynaptic reflexes.
Notlar:
School code: 0547
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Yer Numarası | Demirbaş Numarası | Shelf Location | Lokasyon / Statüsü / İade Tarihi |
---|---|---|---|
XX(684832.1) | 684832-1001 | Proquest E-Tez Koleksiyonu | Arıyor... |
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