Biology subjects

Jankowska, E.

Publications and source records attributed to Jankowska, E..

2 recordsLinked to original sources

bioRxiv2024

Modulation of sensory input to the spinal cord by peripheral afferent fibres. Searching for relays

A long-lasting GABA-dependent increase in the excitability of afferent fibres, and thus modulation of the sensory input to the spinal cord, may be evoked by epidural polarization. However, the direct effects of fibre polarization are short-lasting and the sustained increase in their excitability appears to be secondary to the release of GABA from nearby astrocytes. We have now investigated whether the modulation of spinal sensory input by stimulation of a peripheral nerve, previously attributed to synaptically evoked intraspinal field potentials, is evoked in a similar way. However, as neither its dependence on GABA nor its relays have been investigated, we addressed the question of whether the increase in the excitability of epidurally stimulated afferent fibres following a peripheral nerve stimulation does or does not depend on GABA and whether it might be mediated by astrocytes. The effects of conditioning stimulation of the tibial nerve were evaluated from changes in the excitability of both group I and group II muscle afferents, estimated from action potentials recorded in peripheral nerves and in field potentials recorded in the dorsal horn respectively in acute experiments on deeply anaesthetized rats. The excitability of the afferents was increased by stimulation of group II and/or cutaneous but not group I muscle afferents. The effects were significantly weakened by blocking GABA channels by gabazine, and by astrocyte toxin L-alpha-aminoadipic acid (L-AAA), indicating that the excitability of both group I and group II afferent fibres may be modulated by GABAergic astrocytes, the new role played by astrocytes.

neuroscience↗

bioRxiv2024

Modulation of input to the spinal cord; contribution of GABA released by interneurons and glial cells by polarization at the entry of sensory information

Modulation of input from primary afferent fibres has long been examined at the level of the first relay neurons of these fibres. However, recent studies reveal that input to the spinal cord may also be modulated before action potentials in intraspinal collaterals of afferent fibres reach their target neurons, even at the level of the very entry of afferent fibres to the spinal grey matter. Such modulation greatly depends on the actions of GABA via extrasynaptic membrane receptors. In the reported study we hypothesized that the increase in excitability of afferent fibres following epidural polarization close to the site where collaterals of afferent fibres leave the dorsal columns is due to the release of GABA from two sources: not only terminals of GABAergic interneurons but also glial cells. We present evidence, primo, that GABA from both these sources contributes to a long-lasting increase in the excitability and a shortening of the refractory period of epidurally stimulated afferents fibres and, secondo, that effects of epidural polarization on GABA-containing terminals of GABAergic interneurons and on glial cells are more critical for these changes than direct effects on the stimulated fibres. The experiments were carried out in deeply anaesthetized rats in which changes in compound action potentials evoked in hindlimb peripheral nerves by dorsal column stimulation were used as a measure of the excitability of afferent fibres. The study throws new light on the modulation of input to spinal networks but also on mechanisms underlying the restoration of spinal functions.

neuroscience↗