Properties of fast and slow alpha motoneurones following motor reinnervation

Abstract

SUMMARY1. The properties of medial gastrocnemius (fast alpha) and soleus (slow alpha) motoneurones ofthe cat were examined with intracellular electrodes 33-154 days after self-or cross-union of the muscle nerves.2. The original properties of fast and slow alpha motoneurones measured in terms of the axonal conduction velocity, the duration of after-hyperpolarization and the overshoot amplitude were restored at least in part after self-union of the muscle nerves.3. Slow alpha motoneurones recovered their original properties whether the muscle nerve was united to the original, slow red muscle or to the fast pale muscle. In two animals, some of the fast muscle fibres seemed to be doubly innervated by both fast and slow alpha motoneurones.4. The degree of restoration of the original motoneurone properties was closely related to the degree of motor reinnervation of the muscle.5. At a given stage of motor reinnervation, the degree of recovery of the motoneurone properties was approximately the same regardless of the presence or absence of functional motor connexions of the motoneurone under study.6. When the dorsal root ganglia were removed immediately before selfunion of the muscle nerves, recovery of the conduction velocity of motoneurones was impeded without significant effect upon the process of motor reinnervation or upon recovery of the overshoot amplitude and the duration of after-hyperpolarization.7. It is concluded that the 'dedifferentiated' properties of fast and slow alpha motoneurones after nerve section may be 'redifferentiated' following motor reinnervation to any muscle. The possible signal for restoration of the motoneurone properties is discussed.

Enhancement of synaptic function in cat motoneurones during peripheral sensory regeneration

“…1) was about 2 weeks faster than that following reunion of a sectioned muscle nerve (see Fig. 5 in Kuno et al 1974). …”

Changes in the dendritic geometry of mouse superior cervical ganglion cells following postganglionic axotomy

“…The most conventional explanation of other axotomy-induced changes is loss of trophic support from the periphery (Cragg, 1970;Lieberman, 197 1;Kuno et al, 1974;Purves, 1975Purves, , 1976Mendell et al, 1976). For sympathetic neurons, the protein NGF appears to play an important part in this regulation (Hendry, 1975;Purves and Nja, 1976;Nja and Purves, 1978; see also Purves and Lichtman, 1978;Purves and Nja, 1978;Levi-Montalcini and Aloe, 1983;Thoenen and Edgar, 1985).…”

Presumptive Renshaw cells contain decreased calbindin during recovery from sciatic nerve lesions.

“…Peripheral nerve lesions are known to induce several morphological (16), biochemical (20)(21)(22)(23), and physiological (17)(18)(19) changes in a-motoneurons. The alterations in a-motoneuron physiological properties seen after sciatic nerve lesions are known to be reversible upon target reinnervation (33)(34)(35) and have been ascribed primarily to the loss of functional contact with the muscular targets, since they can be reproduced by the intramuscular administration of botulinum toxin (36) and are not prevented by chronic electric stimulation (37). The major functional changes in a-motoneurons after peripheral nerve lesions include reduced action-potential amplitude, decreased after-hyperpolarization duration, decreased axonalconduction velocity (17,19), and reduction of intramedullary axon collaterals originating from the axotomized motoneurons (38).…”