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Biomedical subjects

R Katz

Publications and source records attributed to R Katz.

At least 307 records · Page 17Linked to original sources
PubMed1977

Influence of voluntary movement and posture on recurrent inhibition in human subjects.

Recurrent inhibition elicited by a conditioning H reflex is measured in normal man by the amount of inhibition of a test H reflex produced by motoneurones that have already given rise to the conditioning reflex. The recurrent inhibition of soleus motoneurones is lowered during a voluntary contraction of this muscle while it is enhanced during a voluntary contraction of its antagonist, the tibialis anterior, and not modified during a contraction of the quadriceps. This recurrent inhibition is also enhanced when the subject is standing without support. These changes in recurrent inhibition are thought to imply supraspinal mechanisms acting on Renshaw cells. The functional significance of these changes is discussed in relation to the recent finding in animals of recurrent depression of the transmission in the Ia inhibitory pathway.

Adult↗
PubMed1977

Comparison of aerosolized atropine sulfate and SCH 1000 on exercise-induced bronchospasm in children.

The new anticholinergic compound Sch 1000 (ipratropium bromide) has been reported to be an effective bronchodilator without significant atropine-like side effects. We evaluated the effectiveness of different doses of nebulized Sch 1000 (40 microgram and 80 microgram) aerosolized atropine sulfate (1 mg) and placebo in the prevention of exercise-induced bronchospasm (EIB) in 20 children with atopic bronchial asthma. A random, crossover double-blind protocol was used. Standard exercise on a cycloergometer was used to induce EIB. Pulmonary function was determined before and after drug administration and exercise. Following no treatment or placebo, exercise resulted in average reductions of 33% to 43% in plethysmographic specific airway conductance (SGaw), of 20% to 25% in forced expiratory volume in 1 sec (FEV1), and of 25% to 32% in maximal midexpiratory flow rate. Exercise following no treatment or placebo resulted in average increases of 23% to 30% in thoracic gas volume (Vtg). Prior to exercise atropine and either dose of Sch 1000 caused significant increases in SGaw (48% to 59%). After pretreatment with Sch 1000 or atropine, exercise caused SGaw to fall to values that were not significantly different from pretreatment medication values, but were significantly higher than values following exercise without pretreatment or after pretreatment with placebo. No significant differences were noted between the effects of atropine and Sch 1000 on EIB. We conclude that at the doses used atropine and Sch 1000 cause equivalent degrees of bronchodilation but neither drug specifically inhibits EIB.

Adolescent↗
PubMed1977

Application of the Free-Wilson technique to structurally related series of homologues. Quantitative structure-activity relationship studies of narcotic analgetics.

A series of benzomorphans with ED50 values determined in vivo by the hot-plate method in mice is analyzed by the modified Free-Wilson method. The QSAR yields 36 substituent constants (ai) with contributions to the overall activity in agreement with experimental data. Substituent constant values obtained for benzomorphans are used in calculating log (1/C) values for six morphinans. An excellent correlation is obtained (r = 0.95) between the six calculated and observed activities. The possibility of extending the Free-Wilson approach from one series of homologues to another is demonstrated.

Analgesics, Opioid↗
PubMed1977

Conditioning of H reflex by a preceding subthreshold tendon reflex stimulus.

The soleus H reflex excitability cycle has been studied using, as conditioning stimulus, a mechanical tap, subthreshold for the tendon reflex, which was applied either on the Achilles tendon, the short biceps tendon, or the quadriceps tendon. In all cases there was an early facilitation followed by a longlasting inhibition of the test H reflex. The same results were obtained in patients with a complete spinal cord section. Wherever the site of the conditioning stimulation, these modifications disappeared after ischaemia of the leg. It is concluded that the effects observed are due to the activation by the tendon tap of the Ia nerve fibres from the soleus muscle, and that the longlasting inhibition is probably due to a transmitter depletion.

Adult↗
PubMed1976

Strong association between B-lymphocyte group-2 specificity and asthma.

30 families in which at least one member has asthma were tested for five new specificities of B lymphocytes as well as for twenty-five HLA antigens. 41 other asthmatic patients were also tested. HLA-B8 was slightly less common than normal in the 71 patients with asthma and there was a trend towards an increased frequency of HLA-A2 in these patients. However, 88% of the 30 asthma patients had B lymphocyte group 2 compared with 24% of the 109 controls. This strong association between asthma and B lymphocyte group 2 was not completely paralleled by linkage with a postulated susceptibility gene of the HLA complex in 9 families whose members were investigated in detail.

Adult↗
PubMed1976

Excitability of human motoneurones after discharge in a conditioning reflex.

A new method of exploring the H reflex excitability cycle is proposed which permits the exploration of motoneurones that discharged in response to the conditioning shock. This is made possible by using a test stimulus supramaximal for the alpha motor fibres of the nerve, which causes a collision in the alpha fibres between the orthodromic conditioning reflex volley and the antidromic motor volley. As a result of this collision, a test reflex contraction appears in the EMG, due to motoneurones that have already discharged in the conditioning response. This method permits studies in human subjects of the poststimulus refractory period of motoneurones as well as the early inhibitory phenomena related to the conditioning stimulus and response. It is shown that during the initial period of the classical H reflex excitability cycle, the test shock explores only alpha motoneurones corresponding to a fringe of cells subliminally excited by the conditioning stimulus. The difference between the populations of motoneurones tested by the two methods explains the differences between the features of the cycles obtained.

Evoked Potentials↗
PubMed1976

Systematic evaluation of cellular radiosensitivity parameters.

Cellular radiosensitivity parameters of the track structure theory of Katz and co-workers are evaluated from a sum of squares minimizing computer program for nonlinear models. Based on these observations, suggestions are presented for efficient experiment design for the determination of these parameters from track-segment bombardments of high LET radiations.

Cell Survival↗
PubMed1975

RBE-dose relations for neutrons and pions.

From cellular radiosensitivity parameters and theoretical particle-energy spectra in tissue, of the secondary particles from neutron and negative pion irradiations, RBE-Dose relations have been calculated. The theoretical results are compared with clinical and radiobiological data for normal tissue, tumours and cells in culture. Formulae for calculation, cellular parameters and the needed properties of equivalent 'track-segment bombardments' are given, for several mammalian cells irradiated with pions and with neutrons of several energies.

Bone Marrow↗