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Biomedical subjects

T Lømo

Publications and source records attributed to T Lømo.

44 records · Page 3Linked to original sources
PubMed1980

Effects of chronic nerve conduction block on formation of neuromuscular junctions and junctional AChE in the rat.

The development of ectopic n.m.j.s. between the transplanted superficial fibular nerve and the soleus muscle has been studied in adult rats. Impulse conduction in the sciatic nerve was blocked chronically and synapse formation between the blocked fibular nerve and the paralysed soleus was compared with synapse formation between non-blocked fibular nerves and denervated soleus muscles. Nerves with conduction block readily made new n.m.j.s. Thus 6 and 10--14 days after the onset of the block the number of newly innervated muscle fibres, the percentage of innervated fibres responding with action potentials and the frequency of m.e.p.p.s. at new junctions were comparable to that observed during innervation by non-blocked nerves. Muscle fibres innervated by both the original soleus nerve and the foreign fibular nerve were regularly encountered in the impulse blocked preparations. Junctions formed by impulse blocked fibular nerves had either no or very little AChE activity 10--15 days after the onset of the block. The evidence for this was 1) weak staining for CHE; 2) prolonged rise time and 1/2 decay time of m.e.p.p.s; 3) positive correlation between m.e.p.p. amplitude and 1/2 decay time and 4) insensitivity to anticholinesterases. In contrast, junctions formed by non-blocked fibular nerves had strong AChE activity by these criteria at corresponding times. AChE activity at the original soleus endplates was much reduced 10--15 days after the onset of conduction block.

Acetylcholinesterase↗
PubMed1980

Acetylcholine sensitivity of developing ectopic nerve-muscle junctions in adult rat soleus muscles.

1. The development of junctional ACh sensitivity has been studied during the formation of ectopic nerve-muscle junctions (n.m.j.s) between the superficial fibular nerve and the denervated soleus muscle of adult rats. 2. When the soleus nerve was cut 2 weeks or more after implanting the fibular nerve, spontaneous m.e.p.p.s and evoked e.p.p.s were first detected in the vicinity of the fibular nerve sprouts 2.5-3 days later. At this time, peaks of local ACh sensitivity greater than the high level of extrajunctional sensitivity induced by denervation were found near the sprouts of the fibular nerve. 3. During the first week of foreign innervation, the extrajunctional sensitivity of the newly innervated muscle fibres fell, but the peaks of sensitivity in the region of the fibular nerve sprouts persisted. Many of these peaks occurred at sites of transmitter release from the fibular nerve terminals. Each innervated fibre had from 1-8 such peaks. 4. When the fibular nerve was cut 2 days or more after cutting the soleus nerve peaks of ACh sensitivity persisted in the region of the degenerated foreign nerve terminals even if the extrajunctional sensitivity was abolished by direct electrical stimulation of the muscle starting soon after cutting the fibular nerve. 5. When the fibular nerve was left intact, more than half of the peaks of sensitivity formed initially in the region of the foreign nerve sprouts had disappeared 2-3 weeks after cutting the soleus nerve. 6. We conclude that during the formation of ectopic n.m.j.s in adult rat muscle the foreign nerve terminals bring about two types of long-lasting change in the distribution and stability of the underlying ACh sensitivity in the muscle fibre membrane; an increase and stabilization of sensitivity at sites of transmitter release which occurs by the time functional transmission at the newly formed n.m.j.s can be detected, and a loss of sensitivity at some of the sites which takes place about 1-2 weeks later.

Acetylcholine↗
PubMed1980

Control of junctional acetylcholinesterase by neural and muscular influences in the rat.

1. The development of AChE at ectopic neuromuscular junctions forming between a transplanted foreign nerve (the superficial fibular nerve) and the denervated soleus muscle has been studied in adult rats. 2. Junctional AChE activity began to appear in the vicinity of the fibular nerve sprouts 6-7 days after section of the soleus nerve and 3-4 days after the onset of transmission. 3. No histochemically detectable AChE appeared when the fibular nerve was cut 0-4 days after the soleus nerve had been cut. 4. Direct electrical stimulation of the denervated soleus muscle caused plaques of true AChE, as determined by inhibitor studies, to appear in muscles where the fibular nerve had been cut 2-4 days after the soleus nerve but not in muscles where the two nerves had been cut at the same time. The plaques appeared only in the vicinity of fibular nerve sprouts and coincided with newly formed but stable peaks of ACh sensitivity. Local application of Neostigmine prolonged and increased the depolarising response evoked by pulses of ACh at these sites. 5. In muscles where the fibular nerve was intact the AChE plaques changed gradually over a few weeks from an immature appearance to a mature appearance characteristic of normal end-plates. In stimulated muscles where the fibular nerve had been cut the plaques stained intensely but remained morphologically immature. 6. We conclude (1) that muscle activity is important for the appearance of AChE at developing neuromuscular junctions and (2) that AChE accumulates only at sites on the muscle surface where the nerve fibres have left a 'trace' upon contact with the muscle fibres. These traces form quickly and persist after nerve-muscle interaction of as little as 2 days. The muscle appears as a major source of junctional AChE since stimulation of the muscle induces intense AChE activity in muscles where the nerve has degenerated.

Acetylcholine↗
PubMed1978

Control of acetylcholine sensitivity and synapse formation by muscle activity.

1. The formation of ectopic junctions between the 'foreign' superficial fibular nerve and the soleus muscle of adult rats, and its relation to changes in extrajunctional sensitivity to acetylcholine (ACh), has been studied by denervating the muscle 3-6 weeks after implanting the foreign nerve. 2. The earliest signs of nerve-muscle transmission were seen 2.5-3 days after denervation, in those fibres where the extrajunctional ACh sensitivity first reached its full post-denervation level. The number of innervated fibres continued to increase throughout the first week after denervation until 70-100% of fibres underlying the foreign nerve growth were innervated. 3. Direct stimulation of muscles with chronically implanted electrodes from the time of denervation prevents the formation of functional neuromuscular junctions (n.m.j.s). If stimulation begins 2 or 4 days after denervation, some functional n.m.j.s are formed which can be detected 7-9 days after denervation, though not as many as in the absence of stimulation. 4. Direct stimulation of muscles from the time of denervation prevents the development of detectable extrajunctional ACh sensitivity. If stimulation begins 2 days after denervation nearly maximal sensitivity develops during the third day and then rapidly declines to undetectable levels by the beginning of the eight day after denervation.

Acetylcholine↗
PubMedDate not supplied

Firing patterns of motor units in normal rats.

Skeletal muscles consist of motor units which may differ considerably in contractile properties and types of usage. Some units participate mainly in relatively rare, quick movements and contract rapidly and are easily fatigued (type FF); others contribute to the maintenance of posture and hence contract slowly and are fatigue-resistant (type S), while others are both fast and fatigue-resistant (type FR). Our understanding of motor control mechanisms and the dependence of contractile properties on usage would be enhanced if more quantitative information were available concerning the firing patterns of individual motor units during normal motor behaviour. Therefore, we have made continuous recordings for extended periods from single motor units in the fast extensor digitorum longus (edl) and the slow soleus (sol) muscle of freely moving adult rats. By counting the total number of discharges for each unit, and by determining the distributions of interspike intervals and the duration of the individual impulse trains, we have obtained information about firing rate, amount of use, modulation of muscle force and tonic and phasic behaviour for 16 motor units. We now report that these units fall into three classes apparently corresponding to type FF and FR in the edl muscle and type S in the soleus muscle.

Action Potentials↗