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Biomedical subjects

J K Jansen

Publications and source records attributed to J K Jansen.

At least 37 records · Page 2Linked to original sources
PubMed1977

The specificity of re-innervation by identified sensory and motor neurons in the leech.

Re-innervation of skin and muscle by identified sensory and motor neurons in segmental ganglia of the leech was studied using physiological techniques. After lesions of peripheral nerves, sensory axons which re-innervated the skin always regained sensitivity to their original stimulus modality (touch, pressure or noxious stimuli). Motor neurons invariably re-innervated the appropriate type of body wall muscle, such as longitudinal or circular muscle layers. Both sensory and motor axons usually returned to the appropriate region of the body wall (dorsal, lateral, or ventral) when regenerating after a nerve crush or cut. This capacity was lost, however, when growth along old nerve branches was prevented by evulsing long segments of the nerve. Re-innervation usually occurred by way of growth of new axons all the way to the periphery, but in a few cases reconnection with the surviving distal segment of the original axon had taken place. The specificity of re-innervation can be accounted for by a combination of selective growth along appropriate nerve branches and specific interactions with target tissues.

Action Potentials↗
PubMed1976

Morphological aspects of the elimination of polyneuronal innervation of skeletal muscle fibres in newborn rats.

The ultrastructure of neuromuscular junctions of rat soleus muscles 1-40 days postnatally was examined for possible morphological correlates of the transient polyneuronal innervation which is present in newborn rats. Several vesicle-laden profiles of terminal axons are seen to contact each muscle fiber up to 8 days postnatally. Axon terminals often lie close together, without Schwann cell intervention. Between days 8 and 16 the number of profiles of terminals on each muscle fibre is reduced, and both Schwann cells and ridge-like extensions of muscle fibre cytoplasm intervene between and separate axon terminals. No signs of degenerating intramuscular axons or axon terminals could be found. It is suggested that the redundant terminals are eliminated by retraction into the parent axons. This process is apparently accomplished without any morphological signs of degeneration.

Animals↗
PubMed1976

Polyneuronal innervation of skeletal muscle in new-born rats and its elimination during maturation.

1. The events taking place during the elimination of polyneuronal innervation in the soleus muscle of new-born rats have been studied using a combination of electrophysiological and anatomical techniques. 2. Each immature muscle fibre is supplied by two or more motor axons which converge on to a single end-plate. There was no sign of electrical coupling between muscle fibres receiving multiple synaptic inputs. By the end of the second week after birth virtually all muscle fibres are innervated by only a single motor axon. 3. The average tension produced by individual motor units, measured in terms of the percentage of the total muscle twitch tension, declined dramatically during the first 2 weeks after birth. During this period there was no significant change in the number of motor neurones innervating the soleus muscle. Thus, the disappearance of polyneuronal innervation reflects a decrease in the number of peripheral synapses made by each motor neurone. 4. The decline in motor unit size was delayed, but not ultimately prevented, by the early surgical removal of all but a few motor axons to the soleus muscle. This procedure also caused a delay in the removal of polyneuronal innervation involving the remaining motor units. 5. Following a crush of the soleus nerve in neonatal animals, regenerating axons usually returned to the original end-plates. Polyneuronal innervation was extensive at early stages of re-innervation and it disappeared during the second week after birth just as in normal muscles. 6. Cross-innervation of neonatal muscles by an implanted foreign nerve caused a rapid disappearance of cholinesterase at denervated original end-plates and in most fibres prevented re-innervation by the original nerve. In the small proportion of fibres that did become innervated through both the foreign and original nerves the end-plates were more than 1 mm apart, and both foreign and original nerve end-plates could persist indefinitely. 7. Many cross-innervated fibres received multiple inputs through the foreign nerve. Some foreign end-plates were separated by distances ranging up to 1 mm. Polyneuronal innervation through the foreign nerve was completely eliminated during maturation but over a slightly longer period than in normal muscles. Apparently the elimination process can act over a distance up to but not much more than 1 mm. 8. These observations suggest that there are several factors influencing the elimination of redundant inputs in immature muscles. Individual motor neurones appear to have an inherent tendency to withdraw the majority of their original complement of peripheral terminals. The determination of which particular synapses are to survive, however, seems to be made in the periphery by a selection among all the synapses that innervate a limited region of each muscle fibre. There may be a competitive interaction among synapses in which those belonging to smaller motor units are less likely to be eliminated, thereby leading to a relatively uniform size of the motor units in the soleus.

Animals↗
PubMed1976

Interaction between foreign and original nerves innervating gill muscles in fish.

Foreign somatic motor nerves were made to innervate denervated gill muscles of the perch. The foreign innervation remained functional after reinnervation by the original nerve. Intracellular recordings showed that individual muscle fibers could be activated by both foreign and original neurons. Extensive foreign innervation appeared to inhibit the ability of the original nerve to reinnervate its own muscle. These studies provide evidence for a functional coexistence of appropriate and inappropriate innervation and show that foreign synapses need not be repressed by the "correct" nerve.

Animals↗
PubMed1975

A multisomatic axon in the central nervous system of the leech.

There is one particularly large axon in the medial bundle of the nerve cord of the leech. It extends along the entire length of the cord and is connected to a single cell body in each ganglion. The cell bodies in adjacent ganglia are tightly electrically coupled, and dye injected into one cell body can diffuse along the axon and into the cell body of the next ganglion. If the nerve cord is cut between two ganglia, neither end of the axon degenerates. Repair of the axon appears to occur by end-to-end fusion.

Action Potentials↗
PubMed1975

The interaction between foreign and original motor nerves innervating the soleus muscle of rats.

1. The fibular nerve was transplanted on to the soleus muscle of the rats. Interruption of the original soleus nerve then permitted cross-innervation, and subsequently, over a period of weeks, re-innervation by the original nerve. 2. Individual muscle fibres were often innervated by both the original and the foreign nerve. The original and foreign end-plates were located in separate regions of the muscle. There were no indications that the original nerve could displace or repress the foreign innervation. 3. The extent of re-innervation by the original nerve depended upon the method of denervation. A single crush of the nerve was followed by virtually complete re-innervation, even of muscle fibres already innervated by the foreign nerve. When re-innervation was delayed by resection of a segment of the nerve only muscle fibres without foreign nerve innervation were re-innervated. Denervation by a simple nerve cut gave an intermediate result. 4. Re-innervation by the original nerve can take place without measurable extrajunctional sensitivity to ACh. 5. The original end-plate region could retain high and localized sensitivity to ACh for several months despite degeneration of its motor nerve terminal and activity of the muscle fibre. 6. Established foreign end-plates were re-innervated by the foreign nerve on muscle fibres with intact original innervation. 7. The factors controlling synapse formation in skeletal muscles are discussed.

Acetylcholine↗
PubMed1975

Re-innervation of rat skeleton muscle in the presence of alpha-bungarotoxin.

1. The possible role of acetylcholine (ACh) receptors in controlling neuromuscular synapse formation was studied by blocking the receptors with alpha-bungarotoxin during re-innervationf the rat diaphragm. Anaesthetized and artificially respirated rats were perfused with toxin throughout the 3-day period when most re-innervation was shown to take place (from day 4 to day 6 after a nerve crush). 2. The toxin treatment blocked about 99.9% of both junctional and extrajunctional ACh receptors, thereby eliminating virtually all end-plate potentials. However, a low level of ACh sensitivity returned to the muscle after several hours of washing, and small end-plate potentials were then recorded from the majority of fibres on the side that previously had been denervated. The degree of re-innervation was nearly as great as that seen in control denervated muscles that had not been treated with toxin. 3. The presence of bungarotoxin during re-innervation did not significantly affect either the appearance of newly formed synapses in the light microscope or the amount of transmitter they released during nerve stimulation. 4. Double innervation, which was not seen in normal muscles, was found in about 10-15% of re-innervated fibres in both the untreated and toxin-treated preparations. This suggests that some of the synapses formed during re-innervation may have been made over what previously had been extrajunctional membrane. 5. It is therefore unlikely that the ACh receptor, or at least that part of the receptor to which bungarotoxin binds, plays a direct role in controlling the process of synapse formation in mammalian skeletal muscle...

Animals↗
PubMed1974

Persistent modification of synaptic interactions between sensory and motor nerve cells following discrete lesions in the central nervous system of the leech.

We have examined changes that develop in the synaptic interactions of sensory and motor nerve cells following surgical lesions to the central nervous system of the leech. In one type of operation an individual ganglion was isolated from the rest of the nervous system by severing all the incoming and outgoing fibres. During the next few weeks, marked changes appeared in synaptic interactions.1. In chronically isolated ganglia inhibitory potentials were recorded in the motoneurone which raises the skin into ridges (the AE cell) following impulses in sensory neurones that respond to pressure (P) or noxious (N) stimuli. In contrast the same AE cell in ganglia taken from normal animals shows excitatory synaptic potentials when the P or N sensory cells are stimulated.2. Another altered synaptic interaction in ganglia isolated by lesions was that between sensory cells responding to touch and a motoneurone that supplies longitudinal muscles (L cell). Instead of the pure, electrical coupling potential seen normally, a large, additional chemically mediated excitatory potential was also apparent.3. Some of the changes in synaptic interactions were not restricted to synapses within the isolated ganglion, but appeared gradually over the following year in successive ganglia along the length of the ventral nerve cord.4. Indirect evidence suggests that the altered synaptic potentials that became conspicuous after operations are also present but smaller and obscured in normal animals.5. It is concluded that some synapses in the leech nervous system are more readily changed than others by cutting the connectives. Furthermore, these changes influence in a predictable manner the way in which the animal behaves in response to mechanical stimuli.

Action Potentials↗