Electrophysiological properties of spinal motoneurones of normal and dystrophic mice.

Abstract

SUMMARY1. The properties of spinal motoneurones of normal and dystrophic mice (129/ReJ) were examined with intracellular electrodes.2. The following parameters of spinal motoneurones showed no significant differences between normal and dystrophic mice: resting and action potentials, the amplitude and duration of after-hyperpolarization, rheobasic current for excitation, threshold for excitation of the somadendritic membrane (IS-SD inflexion) and input resistance.3. The changes in motoneurone properties observed 13-16 days after section of the sciatic nerve (axotomy) were similar in both normal and dystrophic mice.4. The axonal conduction velocity of motoneurones in dystrophic mice was about ten times slower than that in normal mice. The conduction velocity of the sciatic nerve was only about 25 % slower in dystrophic mice than in the normal animal. The estimated ventral root conduction velocity as well as the observed dorsal root conduction velocity in dystrophic mice was at least twenty times slower than that in normal mice.5. In dystrophic mice, spinal motoneurones often showed multiple discharges in response to single, antidromic stimuli. The site of initiation of multiple discharge was located in the motor axon rather than in the motoneurone cell body.6. In dystrophic mice, nerve impulses were transmitted from fibre to fibre ('cross-talk'). The site of impulse transmission among nerve fibres was near the distal portion of the spinal roots.7. Synaptic potentials and peripheral reflex discharges evoked by stimulation of the dorsal roots showed a longer latency and were more prolonged in dystrophic mice than in the control mice.

Ephaptic transmission between single nerve fibres in the spinal nerve roots of dystrophic mice.

“…Conduction velocity of nerve impulses is reduced in these spinal root fibres (Huizar, Kuno & Miyata, 1975;Rasminsky, Kearney, Aguayo & Bray, 1978); the finding that the mode of conduction in some of these fibres is continuous implies that at least some of the bare axons are electrically excitable (Rasminsky et al 1978).…”

“…Some of this ectopic activity is due to cross talk or ephaptic transmission between contiguous fibres within the spinal roots (Huizar et al 1975;Rasminsky, 1978a). Ephaptic transmission between mammalian axons also occurs as a transient phenomenon following acute injury of normal peripheral nerves (Granit, Leksell & Skoglund, 1944;Granit & Skoglund, 1945) and as a more stable phenomenon in experimental neuromas beginning about a month after nerve injury (Seltzer & Devor, 1979).…”

In Vivo Recordings of Bulbospinal Excitation in Adult Mouse Forelimb Motoneurons

“…A major difficulty for neurophysiological investigations has been to perform intracellular recordings from motoneurons in vivo in the adult mouse. Since the work by Kuno and colleagues (Huizar et al 1975;Kuno 1976) on the electrophysiological properties of spinal motoneurons in normal and dystrophic mice, no publications using intracellular recordings in vivo can be found in PubMed.…”

“…A major difficulty for neurophysiological investigations has been to perform intracellular recordings from motoneurons in vivo in the adult mouse. Since the work by Kuno and colleagues (Huizar et al 1975;Kuno 1976) on the electrophysiological properties of spinal motoneurons in normal and dystrophic mice, no publications using intracellular recordings in vivo can be found in PubMed.We have recently analyzed pyramidal excitation in the adult rat using intracellular recording from forelimb motoneurons (Alstermark et al 2004), and the work by Kuno and colleagues inspired us to attempt a similar analysis in the adult mouse. It will be shown that pyramidal stimulation evokes surprisingly weak excitation in forelimb motoneurons via the corticospinal pathway (different to rat) and that strong excitation is mediated via a fast reticulospinal pathway (similar to rat).…”

Simultaneous Intracellular Recording of a Lumbar Motoneuron and the Force Produced by its Motor Unit in the Adult Mouse <em>In vivo</em>

“…Until recently, only a few groups had managed to perform intracellular recordings of motoneurons in vivo [2][3][4] , including our team who published a new preparation which allowed us to obtain very stable recordings of motoneurons in vivo in adult mice 5,6 . However, these recordings were obtained in paralyzed animals, i.e.…”