Sprouting of active nerve terminals in partially inactive muscles of the XXXX .

@entity3734 @entity1022 @entity16 @entity4957 @entity51154 @entity35 @entity616
1. Certain muscles in the hind foot of @entity35 were partially paralysed by applying tetrodotoxin to part of their motor innervation. In these muscles motor nerve sprouting occurred from the terminals of the unblocked axons. The extent of sprouting was compared with that seen in totally paralysed and in partially denervated muscles. 2. Action potentials were blocked in the medial and lateral plantar nerves of adult @entity35 for 5-13 days by continuous superfusion with a solution containing @entity1022 . The drug was delivered through a tube and nerve cuff from an osmotic pump placed intraperitoneally. Control experiments showed that @entity616 was complete and that signs of @entity16 were absent in the animals included in the study. 3. Two muscles (the second lumbrical and flexor digitorum brevis), which received innervation only from the medial plantar nerve, were totally paralysed by the @entity616 . Two different muscles (the fourth lumbrical and flexor digitorum quinti brevis) were only partially paralysed, since they received their innervation from the @entity4957 and, in addition, from the sural nerve which was not blocked. One day before the final experiment, the @entity4957 was cut, and its terminals degenerated. Thus in the partially paralysed muscles only the unblocked terminals from the sural nerve remained. These terminals were observed after staining with @entity51154 and @entity3734 . Similarly, terminals from the medial plantar nerve were examined in the totally blocked muscles from the same animal. 4. In other experiments, muscles were partially denervated by cutting the @entity4957 in order to compare effects of @entity616 and nerve section. 5. Sprouting occurred under all three conditions. Active terminals in the muscles partially paralysed for 5-7 days sprouted to the same extent as terminals in muscles totally blocked during the same period: about 35% of the terminals had sprouts, and their average length was about 13 micron. Sprouting was more pronounced in partially denervated muscles: about 65% of the terminals had sprouts and they averaged 24 micron in length. Collateral (preterminal) sprouts were seen only after partial denervation. 6. Physiological and histological observations suggested that sprouts in paralysed muscles, unlike those in partially denervated muscles, seldom if ever made new synapses on neighbouring muscle fibres, even after 12-13 days of @entity616 . 7. The results show that inactive muscle fibres cause active nerve terminals on neighbouring fibres to sprout, perhaps by releasing a diffusible, sprout-promoting factor, which is part of the stimulus for motor nerve sprouting in partially denervated muscles.
