The regression of synapses formed by a foreign nerve in a mature axolotl striated muscle

Selective reinnervation of skeletal muscle in the newt Triturus cristatus.

“…Dennis, personal communication) and their estimations of the quantal content of e.p.p.s evoked by stimulation of the foreign nerve were very similar to ours. In contrast to these findings however, Bennett et al (1979) were unable to find any difference between the quantal contents of e.p.p.s evoked by stimulation of a transplanted foreign nerve and the original nerve in the forelimb of the axolotl. However, an important difference in their study was that they suppressed neuromuscular transmission with low [Ca].…”

“…high [Mg]0 Ringer solution in order to obtain m.e.p.p.s and sub-threshold e.p.p.s on which a binomial analysis was performed. One possible explanation for why we observed differences between the quantal content of e.p.p.s whereas Bennett et al (1979) In the present study the reason for the abnormally low quantal content of e.p.p.s evoked in biceps during stimulation of the implanted nerve was not established. One possible explanation was that the foreign synapses could have been formed ectopically and therefore taken longer to mature than those formed by the original nerve if it had reinnervated its old synaptic gutters.…”

“…Direct (Cass, Sutton & Mark, 1973;Bennett & Raftos, 1977; Dennis & Yip, 1978;Wigston, 1980). Although suppression of transmission at inappropriate neuromuscular junctions has been consistently observed in urodeles, it is generally accepted that this is a slow process and that individual muscle fibres may remain innervated by both foreign and original nerves for some time before transmission at the foreign synapses finally fails (Dennis & Yip, 1978;Bennett, McGrath & Davey, 1979;Wigston, 1980). A paradoxical feature of the persistence of foreign synapses during the reinnervation of skeletal muscle in the newt is that the movements ofthe limb are always essentially normal without any evidence of synkinesia.…”

Synaptic strength as a function of motor unit size in the normal frog sartorius.

“…It is not clear, however, whether axonal diameter is an intrinsic neuronal feature determining the number of terminal branches and motor unit size, or rather a response to some peripheral advantage over other axons and consequently more trophic feed-back from muscles of a substance analogous to nerve growth factor (Brown, Jansen & Van Essen, 1976;Hollyday & Hamburger, 1976;Betz, Caldwell & Ribchester, 1980;Oppenheim, 1981 (Grinnell, Letinsky & Rheuben, 1979 Nudell & Grinnell, 1983). Many other instances of competitive interaction between terminals on multiply innervated amphibian fibres have been reported (Dennis & Yip, 1978;Wigston, 1980;Bennett, McGrath & Davey, 1979; see reviews by Mark, 1980; In contrast to the sartorius, the fibres of the cutaneous pectoris muscle each have only one end-plate site. Consistent with the concept of competitive regulation of synaptic strength, the cutaneous pectoris junctions are of higher efficacy than those of the sartorius (see Introduction) and the occurrence of very small motor units with large tetanus/twitch ratios is rare (L. 0.…”

Competition between segmental nerves at end‐plates in rat gastrocnemius muscle during loss of polyneuronal innervation.

“…This suppression suggests that the formation of synapses by motor axons is favoured in some parts of a muscle over others, depending on the position of the motoneurones in the spinal cord. There is evidence that transmission from foreign nerves is not as effective as that from native nerves in axolotl muscle (Holder, Mills & Tonge, 1982) and that the foreign synapses can be completely suppressed following return of the native nerves (Dennis & Yip, 1978;Bennett, McGrath & Davey, 1979). If the segmental nerves to an axolotl muscle are cut, the topographical projection onto the muscle is re-established on reinnervation, after a transient period in which inappropriate connexions are formed and then eliminated (Cass & Mark, 1975;Bennett & McGrath, 1980).…”