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J F Iles

Publications and source records attributed to J F Iles.

12 recordsLinked to original sources
PubMed1992

Vestibular-evoked postural reactions in man and modulation of transmission in spinal reflex pathways.

1. The effects of galvanic stimulation of the vestibular apparatus (with electrodes on the mastoid processes) have been studied in standing human subjects. With the head turned to one side, subjects swayed towards the anode. 2. Forwards sway was preceded by electromyographic (EMG) activity in quadriceps and tibialis anterior muscles. Backwards sway was preceded by EMG activity in soleus and hamstring muscles. 3. Using the method of H reflex conditioning, forward sway was found to be preceded by inhibition of soleus motoneurones. 4. Interaction between the vestibular-evoked inhibition of soleus motoneurones preceding forwards sway and peripheral reflex inhibition was examined by a spatial facilitation method. 5. Interaction was found between vestibular-evoked inhibition and Ia reciprocal, group I non-reciprocal and group Ia-Ia presynaptic inhibitory pathways. It is concluded that vestibular signals converge on spinal interneurones subserving these inhibitory actions. 6. A 'decoupling' of soleus motoneurons and soleus-coupled Renshaw cells was found in the period of soleus activation preceding backwards sway.

Adult↗
PubMed1992

Cortical modulation of transmission in spinal reflex pathways of man.

1. The motor actions in the lower limb of transcranial electrical stimulation of the motor cortex have been studied in sitting human subjects. 2. Cortical stimulation induced a short latency inhibition of H reflexes evoked in soleus motoneurones both at rest and during small voluntary contractions of soleus. 3. Spatial interaction between cortical inhibition of soleus motoneurons and inhibition evoked through identified spinal reflex machinery was investigated. 4. Interactions were found between cortically evoked inhibition and spinal Ia reciprocal inhibition, group I non-reciprocal inhibition and higher threshold components of longer latency reciprocal inhibition (D1 and D2 inhibitions). 5. Interactions were facilitatory when cortical and spinal inhibitory actions were weak and reversed to occlusion when both actions were strong. 6. It is concluded that the corticospinal pathway converges on the interneurones which subserve Ia reciprocal, group I non-reciprocal, D1 and D2 inhibition of soleus motoneurones. 7. No significant interaction was found under the present experimental conditions between cortical stimulation and group Ia-Ia presynaptic inhibition of soleus afferents. 8. The statistical significance of spatial interactions observed with H reflex conditioning was investigated using a control experiment.

Adult↗
PubMed1990

Reflex actions of knee joint afferents during contraction of the human quadriceps.

(1) The spinal reflex actions of afferents stimulated by knee joint distension have been investigated in man. (2) Cannulation of the knee and infusion of saline raised intra-articular pressure, especially during quadriceps contraction. High pressures did not induce any sensation of pain. Pressure was taken as an index of joint proprioceptor activation. (3) Increased pressure progressively depressed the quadriceps H-reflex, both at rest and during quadriceps contraction. There was no indication of a threshold pressure for this inhibitory action. (4) It is concluded that joint distension inhibits quadriceps motoneurons through spinal pathways that still operate during voluntary contraction. These pathways could thus contribute to pathological weakness after joint injury. (5) Joint distension produced spatial facilitation of non-reciprocal inhibition of quadriceps H-reflexes from afferents in the tibial nerve.

Adult↗
PubMed1979

Synaptic transmission: ion concentration changes in the synaptic cleft.

Currents flowing through the postsynaptic membrane of an active synapse will tend to change the concentrations of ions in the synaptic cleft. Published experimental data are used to predict (a) the sodium and potassium concentration changes in the cleft at the frog neuromuscular junction, and (b) the sodium depletion in the cleft under a Ia synaptic bouton on a cat motoneuron. Significant concentration changes are predicted at both synapses. These changes will contribute to the time dependence of the observed current and will cause the reversal potential of the current to be time dependent. At the frog neuromuscular junction, the time course of the endplate current has been shown previously to depend on the magnitude of the current flowing (at a given potential). We attribute this to changes of the cleft ion concentration. The time dependent changes of the endplate current reversal potential that we predict for the neuromuscular junction are probably too small to be detected. This is because the effects of sodium depletion and potassium accumulation on the reversal potential almost cancel. We predict that near the reversal potential small currents of complex time course will remain, i.e. no true reversl potential exists. Such currents have previously been experimentally. At the cat Ia synapse, the synaptic current is predicted to deplete a significant fraction of the available extracellular sodium ions. Consequently, the magnitude of the synaptic current should be relatively independent of the number of postsynaptic channels activated, and of the membrane potental, as has previously been found experimentally.

Animals↗
PubMed1977

Responses in human pretibial muscles to sudden stretch and to nerve stimulation.

Electromyograms have been recorded from the human tibialis anterior muscle during voluntary contraction. The accessibility of the nerve to this muscle (common peroneal) has permitted a comparison of reflex responses to low threshold electrical stimulation of the nerve with those to stretch of the muscle itself. Nerve stimulation elicited a reflex at monosynaptic latency (V1 at 28-29 ms) and a second response (V2 at 50-52 ms). A tendon tap induced two responses (M1 at 29 ms and M2 at 50 ms). The responses to a 'ramp' stretch were similar. The homology of V1 with M1, and of V2 with M2 is discussed. V2 and M2 probably correspond to the 'transcortical' reflexes described from other muscles. Neither V1, V2, M1 nor M2 were influenced by anaesthesia of the foot. M1 and M2 were both reduced in amplitude by a selective gamma-efferent block produced by local anaesthetic in the common peroneal nerve. It is concluded, that muscle spindles are the receptors predominantly responsible for M2 ('transcortical') responses. The amplitudes of M1 and M2, but not V1 and V2 were augmented by prior instruction to 'resist' the stimulus. This is interpreted as evidence for voluntary modulation of gamma-efferent activity at a constant force of contraction.

Anesthesia↗
PubMed1976

Organization of motoneurones in the prothoracic ganglion of the cockroach Periplaneta americana (L.).

The location within the prothoracic ganglion of neurone somata with axons in identified peripheral nerves is examined by the cobalt iontophoresis technique. Axons are filled with cobalt by diffusion through their cut ends and the cobalt is then precipitated as the black sulphide inside the neurone. It is assumed that neurones with axons in peripheral nerves and somata in central ganglia are either motor or neuro-secretory. Fifteen nerves are examined and maps of the location of somata with axons in each nerve are presented. The axon distribution in peripheral nerves of three common inhibitory neurones is described. Dendritic morphology of one common inhibitory neurone and two coxal depressor motoneurones is illustrated. It is proposed that some individual neurones can be reliably identified from their soma dimensions and location within the ganglion. The number of motoneurones with somata in the prothoracic ganglion and their homology with cells in the other thoracic ganglia are discussed.

Animals↗
PubMed1976

Effects of glutamate and sulphur containing amino acids on ammonia toxicity and methionine sulphoximine convulsions in mice.

Arginine and large doses of glutamate (greater than 500 mg/kg) were found to reduce ammonia toxicity transiently in mice. Smaller doses of glutamate (greater than or equal to 200 mg/kg) were effective when administered with glucose. Cysteic acid, homocysteine and methionine, but not taurine reduced ammonia toxicity. All 4 amino acids reduced the number of convulsions induced by methionine sulphoximine. It is proposed that taurine has a general anticonvulsant action and that cysteic acid, homocysteine and methionine may have a specific effect on the action of ammonia on the central nervous system.

Amino Acids, Sulfur↗
PubMed1976

Central terminations of muscle afferents on motoneurones in the cat spinal cord.

Intraspinal branches of primary afferent axons in the cat lumbar cord have been revealed by filling then with cobalt, followed by precipitation as cobalt sulphide and silver intensification. 2. Primary afferent collaterals which reached the ventral horn were myelinated and had axon diameters of around 2 mum. Up to four (mean 1) side branches occurred at nodes within the ventral horn. The finest branches were less than 1 mum in diameter. 3. The finest branches formed synaptic boutons on nerve cells. The total observed association between one afferent and a motoneurone (synaptic structure) consisted of up to six boutons (mean 1-85). The boutons constituting a synaptic structure were usually located close together on the soma or dendrites, but sometimes were spread along more than 60 mum of dendrite. It was assumed that these monosynaptic structures on moto-neurones were formed by muscle spindle afferents. 4. There was no correlation between the total contact area of a synaptic structure and its location on a motoneurone. 5. A computer model of the motoneurone was used to investigate the effect of multiple synaptic contact on electrophysiological estimates of synaptic location. It was concluded that the observed spread of boutons making up a synaptic structure would not significantly affect distance allocation of distal synapses but could lead to some proximal dendrite structures being incorrectly classified as somatic.

Animals↗