PubMed Health⌕ Search

Biomedical subjects

J Jhamandas

Publications and source records attributed to J Jhamandas.

7 recordsLinked to original sources
PubMed1990

Motor unit numbers and contractile properties after spinal cord injury.

The number of motor units in the thenar muscle group was estimated in 11 patients with cervical spinal cord injuries. The surface electromyogram and twitch force, in response to maximal stimulation of the median nerve was divided by the average surface electromyogram and twitch of single units. The average single unit size was obtained by intramuscular microstimulation of motor nerve branches and by graded whole nerve stimulation, which provided three independent estimates, two based on the electromyogram and one based on force. The motor unit estimates from the patients covered a wide range. Some had essentially normal motor units both in numbers and contractile properties, while others had varying reductions in numbers of units. Those patients who showed a large reduction in motor unit numbers also had greatly enlarged units, which produced an average of up to sixfold the normal force. These enlarged units summed to produce maximal compound action potentials and twitches that were sometimes indistinguishable from normal. Magnetic resonance imaging scans of the cervical spine obtained from some patients provided independent evidence that patients with low motor unit counts had sustained direct injury to the anterior aspect of the spinal cord at the relevant segmental levels. Some patients showed a normal number of motor units long after the injury. No evidence of transneuronal degeneration could be demonstrated in the thenar group in these patients with the current techniques.

Adult↗
PubMed1987

Localization of luteinizing hormone-releasing hormone (LHRH) neurons that project to the median eminence.

The neuropeptide, luteinizing hormone-releasing hormone (LHRH), is released from nerve terminals in the median eminence and carried via the hypophysial portal system to the anterior pituitary, where it stimulates the release of gonadotropins. LHRH-containing neurons are located in many different regions of the rodent brain, including olfactory, septal, preoptic, and hypothalamic structures. Since those LHRH neurons that project to the median eminence form the final common pathway for the regulation of the pituitary/gonadal axis, we wished to determine which of these cell groups are afferent to this structure. A retrograde tracer, the lectin wheat germ agglutinin (WGA), was placed directly on the exposed surface of median eminence. Following survival times of 8-13 hr, brains were prepared for the dual immunocytochemical detection of WGA and LHRH. Approximately 50% of the LHRH neurons from the level of the septal nuclei caudalward were found to contain WGA immunoreactivity and therefore to project to the median eminence. The remaining single-labeled LHRH neurons were intermingled with the double-labeled cells. The 2 populations were not distinguishable from each other on either cytological or cytoarchitectonic criteria. Those LHRH neurons that were not retrogradely labeled following an injection of tracer into the median eminence are presumed to project to other regions of the central nervous system. We conclude that the LHRH neurons that are directly involved in the regulation of reproductive function are very heterogeneous, widely scattered in telencephalic and diencephalic regions.

Animals↗
PubMed1980

Long-term effects of axotomy on neural activity during cat locomotion.

1. Neural activity was recorded from cats during locomotion on a treadmill using electrodes in Silastic cuffs placed around the sciatic nerve and the lateral gastrocnemius-soleus, medial gastrocnemius, common peroneal and tibial nerve branches. Each branch gave characteristic patterns of activity which were studied before and after it was cut distal to the recording cuffs. Sensory and motor components were separated and measured using cross-correlation techniques. The amplitude of the cross-correlation peaks was compared with the amplitude of compound action potentials evoked by electrical stimulation and recorded from the same sites in the anaesthetized animal. 2. Sensory activity declined rapidly following axotomy and did not recover unless reinnervation occurred. Sensory activity even 5 months after nerve section and resuture had recovered to only a fraction of the control values. This reduction is attributed to a decline in the evoked compound potentials and to many fibres being unsuccessful in regenerating to appropriate sensory organs. 3. Motor activity declined more than could be accounted for by a decline in evoked potentials over the first month after axotomy. The extra reduction represents a decline in the number of impulses generated by alpha-motoneurones after axotomy. If regeneration was permitted, motor activity recovered to higher levels than did the evoked potentials for the whole nerve. Even if regeneration was prevented by nerve ligation, motoneurones continued to generate activity at a stable level over a period of months during which whole nerve compound potentials continued to decline. 4. The modulation of motor activity in ligated nerves during the step cycle was still appropriate to the required movement. Thus, activity recorded from severed nerves in human amputees may be useful in controlling powered artificial limbs. The persistence of motor activity may be responsible for the lesser degree of atrophy found in motor fibres than in sensory fibres following ligation (Hoffer, Stein & Gordon, 1979b).

Action Potentials↗
PubMed1978

Compound action potentials recorded from mammalian peripheral nerves following ligation or resuturing.

1. Cat hind limb peripheral nerves were fitted with cuff recording electrodes, and their distal portions were later cut and ligated to prevent regeneration. The compound action potential amplitude initially declined with a time constant between 1 and 2 months and then remained relatively unchanged for periods of more than a year. Similar but smaller changes were observed in the conduction velocity of the nerves which also stabilized after a few months. 2. In nerves that were cut and resutured to their distal stumps or sutured directly to nearby muscles, a recovery was observed. The time course was well fitted by an initial exponential decay with a similar time constant to that above, followed by an exponential recovery with a longer time constant (3-4 months). Nerve conduction, muscle potentials and twitch tension often recovered to control values, even when the amplitude of the nerve compound action potential remained depressed. 3. Thus, nerve fibres survive axotomy for long periods of time and continue to conduct action potentials, even if unable to regenerate to appropriate end-organs. When regeneration is permitted, a fraction of nerve fibres may reinnervate nearly all end-organs. The diameter and conduction velocity of these nerve fibres presumably increase toward control values, while other fibres remain subnormal in these parameters. 4. Factors in the design of cuff electrodes which determine the amplitude of compound action potentials are described in an Appendix.

Action Potentials↗
PubMed1977

Stable long-term recordings from cat peripheral nerves.

A procedure has been developed for the stable long-term recording of nerve signals in unanesthetized mammals, which should have wide application in basic research on the nervous system and also in clinical areas such as the derivation of control signals for powered prostheses. Methods are fully described for constructing devices consisting of (1) Silastic nerve cuffs containing three or more electrodes, (2) coiled leads insulated with Silastic which extend from the cuffs to an integrated circuit socket, (3) a vitreous carbon transcutaneous connector which surrounds the integrated circuit socket and makes a good interface with the skin. Neural activity has been recorded from mammalian nerves for many months during normal behaviour. The peak-to-peak amplitude and latency of the recorded compound action potentials remain stable and may continue at a constant level more or less indefinitely. A tripolar recording configuration between a central lead and the two end leads, which are connected together, permits good rejection of EMG signals from surrounding muscles. The amplitude of single unit potentials increases as the square of the conduction velocity of the nerve fibre. Thus, the largest nerve fibres will dominate the signals recorded during behaviour. The reasons for premature termination of a few experiments are given together with methods for overcoming these problems. For example, platinum-iridium electrodes remain relatively stable, whereas silver wires tend to fracture after being in an animal for several months. This and other relationships are discussed which permit an optimal design of nerve cuffs for a given recording situation.

Action Potentials↗
PubMed1975

Principles underlying new methods for chronic neural recording.

Chronic recording is possible from nerve fibers which have grown through holes in an insulating medium (regeneration electrodes) or which are enclosed by an insulating sheath (cuff electrodes). Use of three electrodes in a balanced configuration permits good rejection of electromyographic (EMG) signals and other sources of electrical interference (fluorescent lights, 60 Hz signals from the mains, etc.). Equations are derived and tested for predicting the amplitude and form of the signals expected for a given cuff length and diameter. These equations can be used to design electrode units optimally for a given application. Finally, the use of transformers permits the neural signals to be carefully matched to the recording apparatus and further optimizes the neural signal-to-noise and signal-to-EMG ratios. Use of these methods in several physiological and clinical applications, as well as potential abuses, are discussed.

Animals↗