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Biomedical subjects

H G Ross

Publications and source records attributed to H G Ross.

At least 19 recordsLinked to original sources
PubMed1992

Presynaptic dopaminergic inhibition of the spinal reflex in rats.

Dopaminergic influence on spinal monosynaptic transmission was examined in rats. Monosynaptic mass reflex (MMR) was recorded from the ventral root L6 following supramaximal stimulation (0.2 Hz; 0.1 ms) to the ipsilateral dorsal root L6 in spinalized rat under pentobarbitone sodium (40 mg/kg, i.p.) anaesthesia. MMR was inhibited by intravenous administration of the dopaminergic agonist, apomorphine (50-200 ug/kg) in a dose-dependent manner. The attenuatory effect of apomorphine (200 ug/kg i.v.) on the reflex could be reversed by the dopaminergic antagonist haloperidol (0.5 mg/kg, i.v.). Under tetanic stimulation (200 Hz; 15s), the pretetanic relative inhibition induced by apomorphine (200 ug/kg, i.v.) was increased only for a short period immediately after the cessation of tetanic stimulation. The results indicate existence of presynaptic dopamine receptors on the afferent terminals converging on the motoneurone which may functionally modulate the spinal motor output.

Animals↗
PubMed1987

Inhibitory connections of ipsilateral semicircular canal afferents onto Renshaw cells in the lumbar spinal cord of the cat.

1. In intercollicularly decerebrate cats, the excitability of lumbar spinal Renshaw cells (tested by single shocks to ventral roots and deafferented muscle nerves) decreased for 600-1000 ms after conditioning electrical stimulation of ipsilateral semicircular canal nerves. 2. Conditioning stimulation of posterior canal afferents and combined stimulation of anterior and lateral canal afferents were equally effective in causing inhibition of Renshaw cells. No significant differences were observed for Renshaw cells excitable from hind-limb flexor or extensor nerves. 3. Inhibition appeared when one to five stimuli were applied to the canal afferents and arrived at the spinal segmental level 11-15 ms after the onset of conditioning stimulation. 4. Evidence is adduced to suggest that the inhibitory effects on Renshaw cells following stimulation of semicircular canal afferents were mediated directly, i.e. they were not caused by alterations of motoneurone activity. 5. Excitation of Renshaw cells due to stimulation of the canal afferents was rarely observed; it could not be excluded that it was secondary to motoneurone discharges. 6. It is suggested that vestibular inhibition of Renshaw cells ensure a high gain of hind-limb alpha-motoneurones during postural adjustments following a massive disturbance of body equilibrium.

Action Potentials↗
PubMed1984

Chronic inflammatory polyneuropathy. Reduction of nerve conduction velocities in monkeys by systemic passive transfer of immunoglobulin G.

In chronic (relapsing) inflammatory polyneuropathy (CRIP), successful treatment with plasma exchange has led to the concept of pathogenic humoral factors. In 6 patients with CRIP, 5 of whom improved after plasma exchange, the potential pathogenic role of circulating immunoglobulin (Ig) fractions was tested by applying the systemic passive transfer model to marmoset monkeys. After continuous treatment with intramuscular injections for 2-8 weeks, monkeys injected with the crude immunoglobulin fractions or with purified IgG from 5 of the 6 patients showed a significant and partially reversible reduction of the motor nerve conduction velocity (mean 34%, P less than 0.001) when compared with pre-treatment values. In control animals the reduction was 4%. Morphological examination revealed only minor ultrastructural changes of the myelin sheath. Immunocytochemistry revealed that human IgG was able to cross the blood-nerve barrier. It is concluded that the circulating IgG-fraction of patients with CRIP contains a factor that may contribute to the disordered nerve function after crossing the blood-nerve barrier. It may be the removal of this particular factor which is responsible for the rapid recovery of nerve conduction in patients after plasma exchange.

Animals↗
PubMed1983

Movement programming depends on understanding of behavioral requirements.

Use of programmed movements seems to depend on comprehension of the required behavior of which the movements are part. Once this understanding becomes evident by correct behavior, smooth movement take-offs and landings are programmed together. Monkeys were trained to perform a step-tracking task that required accurate self-paced elbow movements of moderate speed. Behavioral aspects of the task, such as correct successive movement directions and timing, were all learned at about the same rates. Use of programmed movements however, increased only after these behavioral requirements had been learned to near the 50% level, i.e., the beginning of behavioral sureness. Movements were programmed as a whole, accelerations together with decelerations, from earliest training onwards.

Animals↗
PubMed1982

Participation of the principal olivary nucleus in neocerebellar motor control.

A new method for reversible cooling of the inferior olivary nucleus has been used in chronically prepared monkeys. Local olivary cooling depressed discharge of complex spikes of Purkinje cells in contralateral cerebellar cortex. Selective cooling of the principal olive (lateral and dorsal lamellae) produced movement oscillations at about 3-5 Hz of the contralateral arm during cooling in a monkey trained to make prescribed arm movements in the horizontal plane. The effects resemble those of dentate dysfunction. Selective cooling of the dorsal accessory olive and/or the overlying reticular formation, in 3 monkeys, produced during cooling a tendency for postural drift of the contralateral arm and for reduction of its movement amplitudes. These changes tended to vary together according to the degree of cooling. Arm oscillations did not occur. It is concluded that climbing fiber projections from the principal olivary nucleus are essential in the primate for optimal neocerebellar control of arm movements.

Animals↗
PubMed1982

Dynamic properties of Renshaw cells: equivalence of responses to step changes in recruitment and discharge frequency of motor axons.

In decerebrate cats, the dynamic responses of Renshaw cells to step changes in input were determined separately both for changes in the number of alpha-axons excited and for changes in the frequency at which they were stimulated. Together, these two input variables to the Renshaw cells describe the level of activity in the motor output from the spinal cord. In either case, the dynamic responses of the interneurons depend only on their static activity before and after an input step occurs, but are otherwise indistinguishable. This favors the interpretation that the two input variables are equivalent under dynamic conditions, i.e., Renshaw cells respond to total motor output.

Animals↗
PubMed1980

X-ray controlled implantation of the brain stem.

Using X-rays to improve accuracy of stereotaxic implantation of the brain stem of Macaca irus monkeys overcomes the problems of moveable brain stem and inaccurate fixation in the stereotaxic frame. The method is independent of standard atlases and correct ear bar fixation. The key to the method is the establishment of a nomogram which relates the implantation target to bony landmarks. The nomogram is established by X-ray contrast studies which outline the brain stem, the implantation target in the brain stem being decided by superimposed histology. This target is nomographically related to bony landmarks seen both on the contrast X-ray and on a plain X-ray taken later at implantation with the monkey in the stereotaxic frame. Being able to locate the target on this plain X-ray, and having included on the X-ray a metal marker, the stereotaxic coordinates of which are known, the distance can be measured (allowing for X-ray magnification) between target and stereotaxic marker and thus one computes the target coordinates. Accuracy of implantation according to these coordinates is monitored with further plain X-rays.

Animals↗
PubMed1978

Rat isolated phrenic nerve-diaphragm preparation for pharmacological study of muscle spindle afferent activity: effect of oxotremorine.

1. Muscle spindle afferent discharges exhibiting an approximately linear length-frequency relation could be recorded from the phrenic nerve in the isolated phrenic nerve-diaphragm preparation of the rat. 2. Muscle spindle afferent discharges could be identified by their characteristic "spindle pause" during muscle contraction and by their response to succinylcholine. 3. Cholinergic influence on spontaneous and stretch-induced afferent discharges was indicated by the augmentation produced by physostigmine and acetylcholine. (+)-Tubocurarine, but not atropine, prevented this augmentation indicating the presence of curariform cholinoceptors in muscle spindles. 4. Acetylcholine did not appear to be involved in the genesis of spindle afferent discharges as incubation with hemicholinium-3 and (+)-tubocurarine failed to affect the rate of spontaneous and stretch-induced spindle discharges. 5. Oxotremorine markedly increased the rate of spontaneous and stretch-induced spindle afferent discharges and this effect was prevented in the presence of hemicholinium-3 and (+)-tubocurarine. 6. These results with oxotremorine are of interest in connection with the observation that muscle spindle afferents and hyperactive in Parkinsonian patients.

Animals↗
PubMed1977

[Urinary tract infection after gynecologic surgery (author's transl)].

In a prospective research study, 119 (female) patients were examined with regards to the occurence of bacteriuria six days after abdominal or vaginal operations of benignous gynecologic disease. Prior to operation, in 7% of the patients a urinary tract infection was already present. Subsequent to operation, 36% got an urinary tract infection within the first six days. From the correlation between urinary tract infection and age of patient, type and uration of operation, a probability catalogue for post-operative urinary tract infections is deducted. The high infection rates, especially in patients beyond 55 years of age, speak in favour of a chemoprophylaxis, especially for such patients.

Adult↗
PubMed1976

[Indications and results of cerclage in cervical incompetence (author's transl)].

The results of 79 cerclage operations in gestation are reported. The rate of abortion increased in cases of more severe symptomatics: firstly, without labour and bleeding: 83 p.c. successful operations; secondly, with labour: 77 p.c.; thirdly, bleeding and without labour: 70p.c.; and lastly, with labour and bleeding: 40p.c. Before treatment with tocolytic pharmaca was possible, the period of gestation time could not successfully be prolonged if labour had started. With tocolytic pharmaca 56p.c. patients of this group gave birth to a living child. The rate of premature children was 23p.c. Cerclage operations were most successful after the 25th week of gestation. When applied before the 16th week of gestation, the success rate was below 69p.c. Treatment with tocolytic pharmaca increased the indication for cerclage operations. Cerclage operations together with tocolytic treatment are indicated in cases where labour and bleeding occur in gestation.

Female↗
PubMed1976

Effect of oxotremorine on the response of antidromically activated Renshaw cells in decerebrate cats.

In intercollicular decerebrate cats, some of which were made spinal in addition, the effect of oxotremorine (intravenous injection, 10-30 mug/kg) was tested on antidromically activated Renshaw cells. Methylatropine premedication prevented the otherwise often fatal drop in blood pressure; ipsilateral dorsal roots L6-S1 and contralateral hindlimb nerves were cut to exclude segmental receptor interference. During supramaximal stimulation of ventral root L7 or the gastrocnemius nerves, an increase of activity ranging from 10-110% was observed. The drug occasionally evoked spontaneous discharges in Renshaw cells, or enhanced activity already present. Alpha motoneuron activity decreased in most cases. The interaction of oxotremorine with atropine and eserine was also investigated on Renshaw cells. Our results suggest that one of the effects of oxotremorine may be a disbalance between motor output and recurrent inhibition.

Animals↗
PubMed1975

Neurochemical changes in the cat's spinal cord due to orthodromic tetanic stimuli. I: phospholipids.

Posttetanic potentiation of monosynaptic reflexes has been used as a paradigm for neuronal plasticity. The explanation for this phenomenon is an increased responsiveness of the synaptic junctions. This would basically require chemical changes of the nervous structures involved. The ventral horn area of the spinal cord was therefore analyzed neurochemically. The determination of the phospholipids revealed an alteration of their composition. Sphingomyelin, phosphatidylcholine and phosphatidylinositide/serine behaved differently, whereas phosphatidylethanolamine and the total phospholipid content remained unchanged.

Animals↗