Factors determining the variation of the afterhyperpolarization duration in cat lumbar α-motoneurons

doi:10.1016/0006-8993(85)90053-8

Brain Research

Volume 326, Issue 2, 11 February 1985, Pages 392-395

https://doi.org/10.1016/0006-8993(85)90053-8 Get rights and content

Abstract

The duration of the afterhyperpolarization (AHP) in cat spinal α-motoneurons varies systematically with motoneurone type, being shorter in motoneurones projecting to fast-contracting muscle units. Recent experiments have shown that the AHP duration is correlated with the amount of sag found in the voltage response to injected constant current pulses. Using a model of the sag process, the present study shows that this correlated is likely to be causal to a substantial extent. Short AHP durations in fast motoneurones may thus be as much, or more, a consequence of a more developed sag process than of faster kinetics of the K conductance process underlying the AHP. This notion is also supported by the experimental observation of a decreased amount of sag and a prolonged AHP duration after axotomy.

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Cited by (19)

Retrograde response in axotomized motoneurons: Nitric oxide as a key player in triggering reversion toward a dedifferentiated phenotype
2014, Neuroscience
Citation Excerpt :
Altogether, these results suggest that decreases in recruitment threshold and disorganization of the recruitment pattern in the injured motor pool are mediated by the action of NO synthesized by the induced nNOS acting via sGC. The recruitment order of a motor pool is mainly determined by intrinsic membrane properties, although synaptic input arrangement and afferent activity could finally adjust threshold range or recruitment gain (Gustafsson and Pinter, 1985; Heckman and Binder, 1993; Cope and Sokoloff, 1999). In our model, axonal injury induces a prominent increase in RN in neonatal HMNs and the loss of excitatory synaptic terminals on both adult and neonatal HMNs (Sumner, 1975; Moreno-Lopez and González-Forero, 2006; Sunico et al., 2010).
The adult brain retains a considerable capacity to functionally reorganize its circuits, which mainly relies on the prevalence of three basic processes that confer plastic potential: synaptic plasticity, plastic changes in intrinsic excitability and, in certain central nervous system (CNS) regions, also neurogenesis. Experimental models of peripheral nerve injury have provided a useful paradigm for studying injury-induced mechanisms of central plasticity. In particular, axotomy of somatic motoneurons triggers a robust retrograde reaction in the CNS, characterized by the expression of plastic changes affecting motoneurons, their synaptic inputs and surrounding glia. Axotomized motoneurons undergo a reprograming of their gene expression and biosynthetic machineries which produce cell components required for axonal regrowth and lead them to resume a functionally dedifferentiated phenotype characterized by the removal of afferent synaptic contacts, atrophy of dendritic arbors and an enhanced somato-dendritic excitability. Although experimental research has provided valuable clues to unravel many basic aspects of this central response, we are still lacking detailed information on the cellular/molecular mechanisms underlying its expression. It becomes clear, however, that the state-switch must be orchestrated by motoneuron-derived signals produced under the direction of the re-activated growth program. Our group has identified the highly reactive gas nitric oxide (NO) as one of these signals, by providing robust evidence for its key role to induce synapse elimination and increases in intrinsic excitability following motor axon damage. We have elucidated operational principles of the NO-triggered downstream transduction pathways mediating each of these changes. Our findings further demonstrate that de novo NO synthesis is not only “necessary” but also “sufficient” to promote the expression of at least some of the features that reflect reversion toward a dedifferentiated state in axotomized adult motoneurons.
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The spinal cord is engaged in a wide variety of functions including generation of motor acts, coding of sensory information and autonomic control. The intrinsic electrophysiological properties of spinal neurones represent a fundamental building block of the spinal circuits executing these tasks. The intrinsic response properties of spinal neurones – determined by the particular set and distribution of voltage sensitive channels and their dynamic non-linear interactions – show a high degree of functional specialisation as reflected by the differences of intrinsic response patterns in different cell types. Specialised, cell specific electrophysiological phenotypes gradually differentiate during development and are continuously adjusted in the adult animal by metabotropic synaptic interactions and activity-dependent plasticity to meet a broad range of functional demands.
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Research reportFactors determining the variation of the afterhyperpolarization duration in cat lumbar α-motoneurons

Abstract

Brain Research

Brain Research

Afterhyperpolarization conductance time course in lumbar motoneurones of the cat

Acta physiol. scand.

Motor unit types of cat triceps surae muscle

J. Physiol. (Lond.)

The electrical properties of the motoneurone membrane

J. Physiol. (Lond.)

The action potential of the alpha motoneurones supplying fast and slow muscles

J. Physiol. (Lond.)

Research report
Factors determining the variation of the afterhyperpolarization duration in cat lumbar α-motoneurons