This study of the fine structure of sciatic nerve branches in normal old cats provides evidence indicating that segmental demyelination may account, in part, for the significant decrease with age in the mean axonal conduction velocity in these hindlimb nerves. Fibers of different diameters exhibited focal abnormalities of their myelin sheath. Lipid-like droplets and granulo-vacuolar debris were present in distended portions of the inner adaxonal rim and in the outer cytoplasmic compartment of the Schwann cell. These inclusions extended into the cytoplasm of the paranodal myelin loops and clefts of Schmidt-Lantermann. There also occurred disruption of the axoglial junctions and separation of the myelin loops from the paranodal axolemma which widens the nodes of Ranvier. Complete disruption of one or more contiguous segments of the myelin sheath was produced by interlamellar splitting and ballooning along the major dense and intraperiod lines. Axonal degeneration occurred less frequently and was not present in all hindlimb nerves.

Aging↗

PubMedDate not supplied

Active electrophysiological properties of spinal motoneurons in aged cats following axotomy.

The present study was designed to examine the effects of the aging process on the response of motoneurons to axotomy. Accordingly, in aged cats using intracellular recording techniques, the electrophysiological properties of axotomized lumbar spinal cord motoneurons were compared with those of control (nonaxotomized) motoneurons. In motoneurons that were subjected to axotomy, there was a reduction in axonal conduction velocity compared to that exhibited by control motoneurons. In addition, there were a number of changes in the configuration of the action potential following axotomy. The amplitude of the spike and the overshoot increased as did the slope of the soma-dendritic spike, whereas the delay between the initial segment and the soma-dendritic spikes decreased. The duration of the action potential's afterhyperpolarization increased; its amplitude remained unaffected although the calculated afterhyperpolarization current decreased. Following the spike, most of the axotomized motoneurons exhibited hyperpolarization undershoots and delayed depolarizations. Axotomized motoneurons exhibited a small decrease in the membrane potential and a reduction in the rheobasic current compared to control cells. The changes in the frequency distribution of axonal conduction velocity, afterhyperpolarization duration, afterhyperpolarization current and rheobase measurements suggest that aged motoneurons dedifferentiated following axotomy. These results indicate that axotomy, in aged motoneurons, results in the disruption of a variety of electrophysiological parameters and that the specific patterns of the responses that occur in axotomized motoneurons of adult cats also emerge in axotomized motoneurons of aged animals.

Action Potentials↗

PubMedDate not supplied

Central neural components of the autonomic nervous system.

Explore the source record for details and available documents.

Aggression↗