Spinal Motor Circuits Research Articles

Rostrocaudal progression in the development of periodic spontaneous activity in fetal rat spinal motor circuits in vitro.

Rostrocaudal progression in the development of periodic spontaneous activity in fetal rat spinal motor circuits in vitro. Developmental changes in the periodic spontaneous bursts in cervical and lumbar ventral roots (VRs) were investigated using isolated spinal cord preparations obtained from rat fetuses at embryonic days (E) 13.5-18. 5. Spontaneous bursts were observed in the cervical VR at E13.5-17.5, and in the lumbar VR at E14.5-17.5. Bursts occurrence in the cervical and lumbar VRs was correlated in a 1:1 fashion at E14.5-16. 5. The bursts in the cervical VR preceded those in the lumbar VR at E14.5, but the latter came to precede the former by E16.5. The interval between spontaneous bursts in the lumbar VR was greatly prolonged after spinal cord transection at the midthoracic level at E14.5, whereas that in the cervical VR became significantly longer at E14.5-16.5. These results suggest that the dominant neuronal circuit initiating the spontaneous bursts shifts from cervical to lumbar region during this period. Bath application of a glutamate receptor antagonist, kynurenate (4 mM), had little effect on the spontaneous bursts in either cervical or lumbar VRs at E14.5-15.5. At E16.5, kynurenate abolished the spontaneous bursts in the cervical VR. Concomitant application of kynurenate and strychnine (5 microM), a glycine receptor antagonist, abolished all spontaneous bursts, suggesting that the major transmitter mediating the spontaneous bursts changes from glycine to glutamate in the cervical region by E16.5, but not in the lumbar region during this period.

Regulation of rhythmic movements by purinergic neurotransmitters in frog embryos.

Many rhythmic motor behaviours, including swimming, walking, scratching, swallowing, micturition and sexual climax, are episodic: even in the absence of sensory inputs they exhibit a gradual run-down in frequency before spontaneously terminating. We have investigated whether the purinergic transmitters, ATP and adenosine, control run- down of swimming in the Xenopus embryo. By using specific agonists and antagonists for the purinergic receptors, we have shown that ATP (or a related substance) is released during swimming and activates P2y receptors to reduce voltage-gated K+ currents and cause an increase in the excitability of the spinal motor circuits. Adenosine is also produced during motor activity, possibly through the actions of ectonucleotidases. The activation by adenosine of P1 receptors reduces the voltage-gated Ca(2+) currents, lowers excitability of the motor circuits, and so opposes the actions of ATP. A gradually changing balance between ATP and adenosine therefore seems to underlie the run-down of the motor pattern for swimming in Xenopus. We believe this to be the first time that ATP and adenosine have been found to be involved in motor pattern generation. The antagonistic interplay between these two transmitters may offer a general feedback mechanism that underlies run-down of all episodic motor patterns in vertebrates.

Monosynaptic reflexes during generalized spike and wave activity, provoked by intermittent photic stimulation

Achilles tendon (T) and Hoffmann (H) reflexes were evoked during spike and wave activity (SWA) in 6 patients with generalized epilepsy, selected on the basis of their photosensitivity. SWA was provoked by intermittent photic stimulation (IPS). It was demonstrated that monosynaptic reflex amplitudes were larger during SWA than at rest. Although IPS caused by itself a slight increase in amplitudes, there was an obvious difference from the larger increase during SWA. T reflexes showed a more explicit increment than H reflexes. The activity changes in the spinal motor circuits were nearly always present in the absence of any clinical manifestation of motor activity. The possible mechanisms are discussed.

The significance of cerebellar function for a reflex movement of the dogfish

An elevation of the pectoral fin generated reflexly by electrical stimulation of the fin was studied in decerebrate dogfish (Scyliorhinus) by recording the electromyogram from the levator muscle. This pectoral fin reflex had two components: a phasic lift of the fin lasting for 70–100 ms, followed by a sustained (tonic) elevation lasting for 500–1,000 ms or more. Ablation of the cerebellum resulted in a pronounced depression of the reflex which particularly affected the tonic component. Division of the brainstem at the level of the obex restored both components to the reflex and frequently led to spread of activity to other muscles. It is suggested that in this animal the brainstem generates a powerful tonic inhibitory drive directed at spinal motor circuits and that the cerebellum modulates precisely this inhibitory influence to permit effective and efficient movement.