Postnatal loss of axons in normal rat sciatic nerve

Jenq, Chung Bii; Chung, Kevin K.; Coggeshall, R.E.

doi:10.1016/0304-3959(87)90095-9

Cited by 10 publications

(10 citation statements)

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“…In our own work, we have shown a significant postnatal decrease in the number of axons in dorsal roots, sciatic nerve, and dorsolateral fasciculus (Lissauer's tract), and these decreases have taken place much later than the normal prenatal death among neuronal populations that give rise to these axons (Chung and Coggeshall, 1984;Hulsebosch et al, 1986;Jenq et al, 1986). A difficulty with Lissauer's tract, however, is that its ventral border is difficult to recognize in newborn animals; thus one of the reasons for the present study is to determine changes in axon numbers in one of the large funiculi of the spinal white matter, where the boundaries are clear even in the newborn.…”

Section: Discussionmentioning

confidence: 99%

Postnatal development of the rat dorsal funiculus

Ks¹,

Coggeshall²

1987

J. Neurosci.

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The present study shows that there are approximately 21,000 axons in the neonatal rat dorsal funiculus, as compared to 26,000 in 2-week-old animals. We attribute this increase primarily to arriving corticospinal fibers. In adult animals, however, there are approximately 15,000 axons. This is a decline of 58% from the 2 week level, and the decrease is proportionately similar in the corticospinal area and the dorsal funiculus proper. Thus, axon numbers decline in later postnatal development, and since the decline seems to be well past the time of the histogenetic death of the cells that give rise to these axons, we propose that the loss is not caused by the death of neurons. This is further evidence that a reduction in axon numbers not accompanied by cell death is a widespread phenomenon in mammalian postnatal neural development. We infer that the mechanism of axon loss is a reduction in axon branching and that its function is to sharpen synaptic connections.

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Section: Discussionmentioning

confidence: 99%

Postnatal development of the rat dorsal funiculus

Ks¹,

Coggeshall²

1987

J. Neurosci.

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“…He arrived at this conclusion by comparing peraxon oxygen consumption for C fibers, which are unmyelinated, with an estimated value for myelinated axons obtained by dividing the oxygen consumption of whole sciatic nerve (Brink et al, 1952) by the total number of axons (Dunn, 1909;Gasser and Erlanger, 1927). However, anatomical work since that time has established that two-thirds of the axons in adult sciatic nerve are unmyelinated (Jenq et al 1986). Thus, in both C fibers and sciatic nerve, oxygen consumption is likely to be dominated by contributions from unmyelinated axons, leaving the claim unsupported.…”

Section: Discussionmentioning

confidence: 99%

Functional Trade-Offs in White Matter Axonal Scaling

et al. 2008

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The brains of large mammals have lower rates of metabolism than those of small mammals, but the functional consequences of this scaling are not well understood. An attractive target for analysis is axons, whose size, speed and energy consumption are straightforwardly related. Here we show that from shrews to whales, the composition of white matter shifts from compact, slow-conducting, and energetically expensive unmyelinated axons to large, fast-conducting, and energetically inexpensive myelinated axons. The fastest axons have conduction times of 1-5 ms across the neocortex and Ͻ1 ms from the eye to the brain, suggesting that in select sets of communicating fibers, large brains reduce transmission delays and metabolic firing costs at the expense of increased volume. Delays and potential imprecision in cross-brain conduction times are especially great in unmyelinated axons, which may transmit information via firing rate rather than precise spike timing. In neocortex, axon size distributions can account for the scaling of per-volume metabolic rate and suggest a maximum supportable firing rate, averaged across all axons, of 7 Ϯ 2 Hz. Axon size distributions also account for the scaling of white matter volume with respect to brain size. The heterogeneous white matter composition found in large brains thus reflects a metabolically constrained trade-off that reduces both volume and conduction time.

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“…Two recent studies employing counts of all neurones in the ventral horn have shown that there is no post-natal death in the lumbar spinal cord of the mouse (Lance-Jones, 1982) or in the brachial or lumbar cord of the rat (Oppenheim, 1986). Third, counts of large, myelinated axons in the ventral roots are subject to errors resulting from the presence of sensory or preganglionic sympathetic axons within the ventral roots and from the post-natal elimination of axon collaterals in the absence of any cell death (Jenq, Chung & Coggeshall, 1986). Counts of axons in muscle nerves remove some of these objections; such counts in the rabbit soleus (Bixby & Van Essen, 1979) and rat gluteus muscle (Hardman & Brown, 1985) have shown no post-natal loss.…”

Section: Extent Of Polyneuronal Innervation and Time Course Of Synapsmentioning

confidence: 99%

Synaptic rearrangements and alterations in motor unit properties in neonatal rat extensor digitorum longus muscle.

Balice-Gordon

Thompson

1988

The Journal of Physiology

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SUMMARY1. We have used in vitro intracellular recordings and measurements of the contractile properties of single motor units to examine the changes in muscle innervation occurring during the post-natal development of a fast-twitch muscle in the hindlimb of the rat, the extensor digitorum longus (EDL).2. Intracellular recordings of end-plate potentials evoked in response to graded stimulation of the nerve supply to the muscle indicate that during the first day after birth, each muscle fibre receives synaptic input from at least two motoneurones and that some muscle fibres receive as many as six such inputs. With subsequent development, most of this polyneuronal innervation is eliminated: the first singly innervated fibres are encountered on day 3; by day 18 fewer than 5 % of the fibres remain polyneuronally innervated. These results show that there are quantitative differences in post-natal synapse elimination in EDL compared to its well-studied counterpart, the soleus. Although the great majority of fibres in both muscles become singly innervated at about 18 days, the first singly innervated fibres appear at least a week earlier in the EDL. None the less, synapses are lost from EDL at about half the rate they are lost from soleus.3. The number of motor units, determined by counting the number of twitch increments produced by graded stimulation of ventral root filaments teased to contain only a few EDL motor axons, remains unchanged from an average of fortyone from post-natal day 1 to day 17. In addition, the number of muscle fibres counted in muscle cross-sections stained with an anti-myosin antibody increases less than 10 % from birth to adulthood. Therefore, synapse elimination in EDL occurs with a largely constant population of muscle fibres as well as motoneurones.4. Measurements of tensions generated by single motor units indicate that the average size of a motor unit declines from 6f8 % of the muscle fibres at day 1 to 2-3 % at 17 days. This result indicates that each motoneurone, on average, comes to innervate threefold fewer muscle fibres. Motor units derived from each of the spinal segments innervating the muscle undergo equivalent reductions in motor unit size, indicating that there is no segmental disproportion to synapse elimination in this

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Postnatal loss of axons in normal rat sciatic nerve

Cited by 10 publications

References 0 publications

Postnatal development of the rat dorsal funiculus

Postnatal development of the rat dorsal funiculus

Functional Trade-Offs in White Matter Axonal Scaling

Synaptic rearrangements and alterations in motor unit properties in neonatal rat extensor digitorum longus muscle.

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