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Do nerve impulses penetrate terminal arborizations? A pre-presynaptic control mechanism
1Division of Physiology, UMDS, St Thomas's Hospital, London, UK.
Trends in Neurosciences
|February 1, 1995
Summary
Action potentials may not reach all axon terminals in spinal afferents. A GABA-operated chloride shunt can block impulses, but antagonists relieve this blockade, suggesting proximal axonal control.
Area of Science:
- Neuroscience
- Cellular Neuroscience
- Axonal Physiology
Background:
- Spinal afferent fibers exhibit extensive arborizations, with some regions lacking responsive cells.
- Action potential propagation in myelinated fibers can be modulated by specific mechanisms.
Purpose of the Study:
- To investigate whether action potentials reliably reach all terminals of parent axons.
- To explore the role of GABA-operated chloride shunts in modulating impulse propagation in spinal afferents.
Main Methods:
- Electrophysiological recordings in spinal afferents.
- Utilizing antagonists of GABAA receptors to study impulse propagation.
- Examining the effects of GABA-operated chloride shunts on action potential conduction.
Main Results:
- Many spinal afferent fibers possess terminal arborizations extending beyond responsive areas.
- Impulse propagation fails in long-range myelinated fibers when a GABA-operated Cl- shunt is active.
- Blocking the GABA-operated chloride shunt with antagonists restores impulse propagation.
Conclusions:
- A GABA-operated chloride shunt mechanism in terminals can prevent action potentials from reaching distal axon branches.
- An additional control mechanism, located proximally in the axon, may regulate which parts of the terminal arborization influence postsynaptic cells.