Elektronenmikroskopische Untersuchungen am Diaphragma der Maus nach einseitiger Phrenikotomie

127

Signs of Schwann cell encroachment into the synaptic cleft were readily found and large areas of post-junctional membrane apposed only by Schwann cell were evident. 4. It is suggested that the mechanics of the process of synapse elimination in neonates is similar to that occurring during degeneration in the denervated adult. Transmission failure occurs abruptly at the supernumerary endings and they are disposed of by the Schwann cell.

“…Nickel & Waser, 1968;Miledi & Slater, 1970). Degeneration-like features were not found in a recent morphological study of developing rat soleus (Korneliussen .…”

Section: Discussionmentioning

confidence: 82%

Reduction of multiaxonal innervation at the neuromuscular junction of the rat during development.

Rosenthal¹,

Taraskevich²

1977

127

“…A similar formation and subsequent loss of synapses occurs on the initial axon segment of motoneurones during development (Conradi & Skoglund, 1969) and this loss of synapses is accompanied by the engulfing of terminal boutons on the initial segment by glial cell processes (Ronnevi & Conradi, 1974). The denervated endplate is similarly engulfed by the terminal Schwann cell (Nickel & Waser, 1968;Miledi & Slater, 1968;Lillman-Rauch, 1971;Manolov, 1974), as are degenerating boutons on motoneurones by glial cells following dorsal root section (Conradi, 1969). It is possible then that synapses are removed from the surface of the myofibres during development because of a refractory message from the muscle and that the unwanted terminals are then engulfed and phagocytosed by the terminal Schwann cells.…”

Section: Discussionmentioning

confidence: 88%

The formation of synapses in amphibian striated muscle during development.

Bennett¹,

Pettigrew²

1975

103

SUMMARY1. A study has been made of the formation of synapses in developing reinnervated and cross-reinnervated amphibian twitch muscles which receive either a focal (iliofibularis) or a distributed (sartorius) innervation from 'en plaque' nerve terminals using histological, ultrastructural and electrophysiological techniques.2. During the development of the tadpole through metamorphosis to the adult frog, the sartorius myofibres increased in length at about twice the rate of the iliofibularis myofibres, due to a fast rate of growth at their insertions on to the pelvic tendon.3 5. Reinnervation or cross-reinnervation of the sartorius and the iliofibularis muscles in adults or at a late stage of development simply reconstituted the normal focal and distributed innervation patterns of the muscles, as found in the control muscles of the contralateral and unoperated legs.6. These observations on synapse formation in amphibia are consistent M. R. BENNETT AND A. G. PETTIGREW with the hypothesis that during development the axon making the initial synaptic contact on the muscle cells induces a property over a length of muscle membrane adjacent to this site which makes it refractory to synapse formation; thus during reinnervation or cross-reinnervation of adult muscles this refractory property constrains synapse formation to these sites.

“…Schwann cells were never seen in contact with denervated synaptic folds (n = 14) although none of the muscles were examined at times shorter than 5 weeks after denervation, a considerable time after the Schwann cells have previously been reported to migrate from above the folds in mammals (Bauer, Blumberg & Zacks, 1962;Nickel & Waser, 1968;Miledi & Slater, 1968;LUillman-Rauch, 1971 (Li, Shy & Wells, 1957;Thesleff, 1963). Bursts of action potential firing sometimes occurred coincident with insertion of the micro-electrode, but more frequently action potentials were generated at regular intervals (frequency range 05-20 Hz in different cells), the activity resembling that recorded from pace-maker tissue in the heart (Weidmann, 1956).…”

Section: Resultsmentioning

confidence: 99%

“…The arrangement of the intramuscular nerve branches in reinnervated muscle is often quite unlike the normal, except after simple crushing of the nerve close to the muscle (Gutmann and Young, 1944 (Edds, 1950;Aitken, 1965) is involved, as the cell migrates from this site after a few days of denervation (Nickel & Waser, 1968;Luillman-Rauch, 1971). It follows that the reinnervation of the old end-plates must occur as a consequence of some property of the muscle fibre at the end-plate which favours the formation of synapses (Young, 1942;Gutmann & Young, 1944).…”

Section: Discussionmentioning

confidence: 99%

The formation of synapses in reinnervated mammalian striated muscle

Bennett¹,

McLachlan²,

Taylor³

1973

118

SUMMARY1. The hemidiaphragm of the adult rabbit has a single band of endplates running around the middle of the muscle. A study has been made of the formation of synapses during spontaneous reinnervation of this muscle, using histological, ultrastructural and electrophysiological techniques.2. Following spontaneous reinnervation, silver-stained nerve terminals were found in association with cholinesterase-stained end-plates only in the region of the muscle corresponding to the original innervation band. 3. The regenerated nerve terminals were observed with the electronmicroscope in positions overlying or adjacent to the old synaptic folds.4. Spontaneous miniature end-plate potentials and evoked synaptic potentials were recorded only in the middle of the muscle fibres after remnervation. 5. The growth of the regenerating axons was not oriented towards the end-plate zone but followed muscle fibres and blood vessels in random directions.6. It is concluded that, in adult mammalian striated muscle, the old end-plate region is preferentially reinnervated as a consequence of some special property of the muscle fibre at this site.