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Biomedical subjects

S Grillner

Publications and source records attributed to S Grillner.

At least 199 records · Page 11Linked to original sources
PubMed1985

N-Methyl-D-aspartate (NMDA), kainate and quisqualate receptors and the generation of fictive locomotion in the lamprey spinal cord.

The motor pattern underlying swimming can be elicited in an in vitro preparation of the lamprey spinal cord by applying excitatory amino acids in the bath activating N-methyl-D-aspartate (NMDA) receptors and kainate receptors, but not quisqualate receptors. L-DOPA exerts a weak rythmogenic effect due to an action on kainate receptors. The kainate-induced rhythm is unchanged when a NMDA receptor antagonist is applied (2APV) and the N-methyl-aspartate-induced fictive locomotion can occur when kainate receptors are blocked (PDA). The burst frequency of the NMA-induced activity (dose range 30-5000 microM) is wide and ranges from 0.05-0.1 Hz up to 2.5-4 Hz, while the kainate-induced activity (dose range 7-30 microM) ranges from 0.5-1 Hz up to 4-8 Hz. This frequency range overlaps largely with that of the intact swimming animal. The findings further consolidate that NMDA receptors are efficient and demonstrates that kainate can also be effective in inducing fictive locomotion, and also that activation of either receptor type is sufficient. It has previously been shown that fictive locomotion elicited via sensory stimuli is depressed by NMDA and kainate receptor antagonists. It is suggested that these effects, presumably via aspartate and/or glutamate actions, are exerted on the input stage of interneuronal network.

Animals↗
PubMed1985

Dorsal and ventral myotome motoneurons and their input during fictive locomotion in lamprey.

Motoneurons supplying the dorsal and ventral parts of the myotome in the lamprey are shown to have different morphological characteristics; furthermore, their pattern of activation during fictive locomotion may differ considerably. Intracellular recordings from motoneurons were performed in an in vitro spinal cord-myotome preparation from segments rostral to the fins. The location of the contracting muscle fibers in the myotome could be observed directly in the dissection microscope during intracellular stimulation of the motoneuron. The motoneurons were injected with Lucifer Yellow, an intracellular dye, and were subsequently reconstructed, sometimes in both a horizontal and a transverse plane. Motoneurons supplying the ventral third of the myotome had a dense, fan-like, dendritic tree and ramifications near the midline. In contrast, motoneurons supplying the dorsal third of the myotome had a more widespread and less dense dendritic tree, with few ramifications near the midline. Some motoneurons supplying the most ventral or dorsal part of the myotome had contralateral dendrites crossing in the ventral commissure and ramifying near contralateral large, reticulospinal Müller fibers. The differences in morphology may indicate that these motoneurons receive different descending inputs. This may be related to the need for an effective control in the dorsoventral plane during righting and steering responses. During fictive locomotion elicited in the isolated spinal cord by bath-applied N-methyl-aspartate, pairs of motoneurons were recorded which subsequently were identified and characterized by intracellular injections of Lucifer Yellow.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Activation of 'fictive swimming' by electrical microstimulation of brainstem locomotor regions in an in vitro preparation of the lamprey central nervous system.

Electrical microstimulation of specific areas of the brainstem in an in vitro preparation of the lamprey CNS elicits coordinated swimming motor activity recorded in spinal ventral roots. Swimming motor activity could be graded in intensity by variations in stimulus current. This 'brainstem locomotor region' extends from the mesencephalon, near the torus semicircularis, caudally through the rhombencephalon in parallel strips about 200-300 micron lateral to the midline.

Adaptation, Physiological↗
PubMed1984

The edge cell, a possible intraspinal mechanoreceptor.

In the lateral edge of the "white matter" in the lamprey spinal cord, there is a group of nerve cells referred to as edge cells. The results of a combined physiological, light microscopical, and electron microscopical study suggest that these cells serve as intraspinal mechanoreceptors. Edge cells are depolarized on stretch of the lateral margin of the spinal cord, and they have nestlike ramifications in this region oriented in a rostrocaudal plane. These cells exhibit a close structural similarity with the crayfish stretch receptor.

Animals↗
PubMed1984

The effect of dorsal root transection on the efferent motor pattern in the cat's hindlimb during locomotion.

Mesencephalic cats can walk on a treadmill if the midbrain locomotor region is stimulated. The motor pattern of different hindlimb muscles is similar to that of th intact cat. The present experiments in the mesencephalic preparation test if the complex motor pattern in one hindlimb is causally dependent on the afferent signals arising in the same limb during walking. The electromyographical activity and the movement pattern during locomotion were compared before and after transecting all dorsal root fibres originating from one hindlimb. Flexor and extensor muscles at different joints may retain their general pattern after the dorsal root transection. This applies also to muscles such as the knee flexors, which have a short and early flexor burst and a second burst during the extension phase, and the short toe dorsiflexor , which has an early burst in the transition between flexor and extensor activity. After the dorsal root transection the pattern of activity may become more variable and it can even break down altogether. The present results demonstrate that the central nervous system devoid of phasic afferent inflow from one hindlimb can produce a complex motor output to this limb rather than a motor pattern degraded to a simple alternation between flexors and extensors.

Adaptation, Physiological↗
PubMed1984

Phasic variations of extracellular potassium during fictive swimming in the lamprey spinal cord in vitro.

The lamprey spinal cord in vitro can generate the motor pattern underlying locomotion, which can be recorded with suction electrodes in the ventral roots. To test if the extracellular level of potassium changed during rhythmic activity, potassium-sensitive microelectrodes were used to systematically (every 25 micrometers) explore the level of extracellular potassium [K+]e in different loci in the transverse plane of the spinal cord. During fictive locomotion the baseline level of [K+] increased with 0.08-0.4 mM in the grey matter. As a rule phasic variations of up to 0.2 mM, correlated to each ventral root burst, were superimposed on the tonic deviation of [K+]e. Changes in this range may cause a moderate depolarization of the spinal neurones and might also affect other neuronal functions including the rhythm-generating circuits.

Animals↗
PubMed1983

Initiation and sensory gating of 'fictive' swimming and withdrawal responses in an in vitro preparation of the lamprey spinal cord.

An in vitro preparation has been developed in which the caudal part of the lamprey spinal cord (resting on the notochord) is still innervating the tail fin. Mechanical stimulation of the tail fin elicits ventral root activity that would normally lead to an initial body flexure (tail fin withdrawal) followed by escape swimming. These patterns of ventral root activity are correlated with motor activity and movements elicited by a similar tail fin stimulus in intact and spinal lampreys. The ascending control systems activated by tail fin stimulation consists of long axons which project for at least 20 segments, and are not dependent on propagation through local circuits in the gray matter. Sensory input activated by passive bending of the notochord/spinal cord in the in vitro preparation gates the tail fin withdrawal motor activity, such that tail fin stimulation elicits ventral root bursts on the same side as the direction of bending. This new in vitro preparation survives for several days and will provide new opportunities to study the normal initiation and coordination of two different patterns of behavior, swimming and withdrawal.

Animals↗
PubMed1983

Peripheral control of the cat's step cycle. II. Entrainment of the central pattern generators for locomotion by sinusoidal hip movements during "fictive locomotion.".

Acute low spinal and curarized cats injected with noradrenergic agonists i.v. can elicit an efferent burst pattern which can be recorded in muscle nerve filaments and can be referred to as "fictive locomotion". This study investigates the effect that feedback, arising from movements in the hip joint, can exert on the central network generating fictive locomotion. The central network is uncoupled from generating any active movements by curarization. The motor pattern could be entrained by applying sinusoidal hip movements, even when a very extensive denervation of the leg had been performed leaving only some of the muscles around the hip and the hip joint innervated. During flexion movements, efferents to different flexor muscles became active and during movements in the reverse direction (extension), efferents to extensors were active. With an increasing movement frequency the onsets of both flexor and extensor bursts were delayed in the movement cycle. The duration of the extensor bursts varied markedly with the movement cycle, whereas pure flexors changed less in burst duration. The frequency within which the efferent burst activity was entrained in a strict 1:1 relation to the movement varied between 5 to 70% above and below the resting burst period. In preparations with a narrow 1:1 range, a "relative coordination" was encountered outside this range. The flexor burst duration was in these cases dependent on where in the hip movement cycle the bursts appeared.

4-Aminopyridine↗
PubMed1982

Mechanosensitive neurons in the spinal cord of the lamprey.

'Fictive locomotion' in the lamprey in vitro spinal cord-notochord preparation can be entrained by side to side movements of the spinal cord-notochord which mimic swimming movements even after transection of dorsal and ventral roots. This study provides direct evidence of mechanosensitive neurons intrinsic to the spinal cord. Neurons with axons located in the lateral aspect of the spinal cord discharge in response to moderate bending movements of the spinal cord. Movements of this amplitude will inevitably occur during normal swimming.

Animals↗
PubMed1982

On peripheral control mechanisms acting on the central pattern generators for swimming in the dogfish.

When sinusoidal movements were artificially imposed on the tail region of the curarized spinal dogfish during "fictive locomotion' the coordinated burst pattern recorded in the ventral roots was effectively entrained to follow movement frequencies above as well as below the resting rate. The entrainment was characterized by: (1) a broad range of effective movement frequencies and amplitudes (down to a few degrees); (2) frequency-dependent timing of entrained bursts to the movement; (3) constant burst durations at low and moderate frequencies; (4) incomplete entrainment in response to high or low movement frequencies combined with a low amplitude; (5) entrainment was still present when mean position of movement was displaced laterally; (6) effects persisted when the tail region was devoid of skin and muscle tissue. Entrainment effects may be explained by the activation of stretch receptors on either side of the vertebral column-spinal cord, exciting the presumed central pattern generators (CPGs) in the hemisegments ipsilateral to the stretch, while inhibiting the contralateral CPGs.

Action Potentials↗
PubMed1981

Entrainment of the spinal pattern generators for swimming by mechano-sensitive elements in the lamprey spinal cord in vitro.

Imposed sinusoidal bending of a mobile region of the curarized spinal cord/notochord preparation of the lamprey results in phase-locking (i.e. 'entrainment') of the 'fictive swimming' motor pattern (recording in ventral roots) to the bending movements. This entrainment phenomenon occurs both with intact ventral and dorsal roots and with all roots cut (i.e. a completely isolated spinal cord). It is proposed that mechano-sensitive elements within the spinal cord contribute in part to the entrainment.

Animals↗
PubMed1981

Peripheral control of the cat's step cycle. I. Phase dependent effects of ramp-movements of the hip during "fictive locomotion".

Acute spinal and curarized cats can generate "fictive locomotor activity" after an i.v. injection of Nialamid followed by 4-AP and L-DOPA. The efferent burst activity to flexors and extensors can be recorded in peripheral nerve filaments. Ramp-formed movements were applied in the hip at constant angular velocity in different phases of the spontaneous efferent burst activity. The cycle duration was markedly influenced. A flexion or an extension ramp applied in the early part of the "step-cycle" (during flexor activity) will prolong the cycle duration, but in the later part of the cycle instead a marked shortening effect will occur. The transition from a prolongation to a shortening is very steep for the extensive-ramps, with a subsequent gradual increase from a shortening to a lengthening of the cycle. This type of phase response curve expresses a potent peripheral modulatory effect on the central pattern generator. A ramp movement (flexion or extension) applied in the beginning of the flexor burst will reinforce the flexor activity. In the end of the flexor burst instead there is a directional sensitivity with positive feedback, resulting in an excitation of the flexor activity for flexion ramps, but a depression of the flexor activity for extension-ramps. Extension-ramps also show a position dependent effect which enhances the response in the flexors for more extended hip positions.

Animals↗