Ephaptic interactions between myelinated nerve fibres of rodent peripheral nerves

Abstract

We report evidence that ephaptic interactions may occur between intact mammalian myelinated nerve fibres and not only between demyelinated or damaged mammalian nerve fibres or nerve cells as analysed in previous studies. The ephaptic interactions were investigated between nerve fibres traversing the lumbar dorsal roots and between bundles of fibres in the sciatic nerve in anaesthetized rats in vivo. The interactions were estimated by comparing the excitability of nerve fibres originating from one of the hindlimb nerves (peroneal or sural) under control conditions and when the stimulation of these fibres was combined with stimulation of another nerve (tibial). An increase in nerve volleys recorded from group I muscle afferents in the peroneal nerve and of the fastest skin afferents in the sural nerve was used as a measure of the increase in the excitability. The excitability of these fibres was increased during a fraction of a millisecond, coinciding with the period of passage of nerve impulses evoked by the conditioning stimulation of the tibial nerve. The degree of the increase was comparable to the increases in the excitability evoked by 1–2 min lasting fibre polarization. Ephaptic interactions were found to be more potent and with longer lasting after‐effects within the dorsal roots than within the sciatic nerve. We postulate that ephaptic interactions may result in the synchronization of information forwarded via neighbouring afferent nerve fibres prior to their entry into the spinal cord and thereby securing the propagation of nerve impulses across branching points within the spinal grey matter.

Fictive Scratching Patterns in Brain Cortex-Ablated, Midcollicular Decerebrate, and Spinal Cats

“…The excitability of these fibers increased coincident with the nerve impulses evoked by a conditioning stimulation. The increase in the excitability lasted 1-2 min (Bolzoni and Jankowska, 2019). We do not know whether there is an ephaptic connection between MG, PB, and FHL Ia afferent fibers.…”

“…It is not known whether there is a synaptic connection between PB Ia afferents and FHL MG motoneurons. Ephaptic interactions between nerve fibers traversing the lumbar dorsal roots under control conditions and with nerve fiber stimulation have been demonstrated (Bolzoni and Jankowska, 2019). The excitability of these fibers increased coincident with the nerve impulses evoked by a conditioning stimulation.…”

Neonatal Mice Spinal Cord Interneurons Sending Axons in Dorsal Roots

“…Thus, antidromic activity could have an origin other than PAD, and consequently, other functions. Ephaptic interaction in afferent bers could also produce antidromic ring (18).…”

Augmentation of neural activity in peripheral nerve of sheep using 6 kHz subthreshold currents

“…These interactions can improve synchrony of activity within populations of neural cells or triggering of neural activity in subthreshold cells, and may be induced either by naturally occurring physiological effects [17][18][19] or by artificially increasing excitability using chemicals [20,21] and subthreshold electrical current [18,22,23]. In myelinated nerve fibres, modelling studies predict ephaptic interactions alter the propagation velocities of action potentials in neighboring active fibres which improves synchrony [24][25][26][27], and an in vivo study on rat showed increased activity in response to an electrical stimulus when it was temporally coupled with a compound action potential (CAP) [28]. Increasing synchrony and localized triggering of new action potentials in peripheral nerves using a subthreshold current presents an exciting prospect because such a paradigm could improve the signal to noise ratio in peripheral nerve interfaces, aid physical rehabilitation after spinal cord injury and stroke, and provide insight into mechanisms of subthreshold current neuromodulation therapies.…”