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Biomedical subjects

Z Hasan

Publications and source records attributed to Z Hasan.

At least 55 records · Page 3Linked to original sources
PubMed1989

Epilepsy and photosensitivity.

In a series of 2053 cases of epilepsy studied 3.9% were found to have some form of photosensitive epilepsy. The mean age of onset was 14.9 years for males, 11.8 years for females. In the age group of 6-10 years there was a definite male preponderance. In 48.2% cases the seizures were caused by watching television and in 7.4% they were precipitated by sunlight or electric lights. Primary generalized tonic clonic seizures were seen in 44.4% cases and 34.6% had secondary generalized seizures. E.E.G. was normal in 60% cases, while 18.8% had nonspecific dysrhythmias, 2.1% hypersynchronization during the interictal period with spike and sharp wave complexes. A family history of photosensitive epilepsy was present in 14.1% cases.

Adolescent↗
PubMed1989

Trace element studies in Karachi populations. Part III: Blood copper, zinc, magnesium and lead levels in psychiatric patients with disturbed behaviour.

Blood levels of copper, zinc, magnesium and lead were determined in 29 males and 15 females suffering from disturbed behaviour. As far as we could ascertain they were under no medication and belonged to low income groups. Male patients had significantly higher levels than female patients for zinc (0.05 greater than P greater than 0.01) but there was no sexual difference for magnesium or copper. In patients copper and lead levels were higher than for normals (P less than 0.01), but no difference could be found for Mg and Zn. At least one metal abnormality was observed in 19 (65.5%) of the males and 9 (60.0%) of the female patients.

Copper↗
PubMed1988

Anticollagen antibody responses in DBA/1 (H-2q) mice associated with type II collagen-induced arthritis and the effect of pregnancy.

We have previously shown that DBA/1 mice immunized with heterologous type II collagen showed remission of the subsequent collagen-induced arthritis (CIA) when pregnant, but experienced exacerbation postpartum. Measurement of anticollagen antibody (aCa) responses by ELISA in primiparous mice immunized at day 1 of pregnancy revealed no significant difference compared to aCa titres in virgin animals, apart from slightly increased titres following the primary immunisation. When mice received collagen challenge during early pregnancy, however, the date at which maximal antibody titres was reached was delayed by 5 days. Pregnancy initiated following the intraperitoneal boost caused a ten-fold suppression in aCa titres with a rise post-partum. Measurements of aCa levels in individuals which showed fetal resorption indicated that suppression of humoral responses was dependent on the presence of a viable conceptus. Antibody titres declined in all animals after a period of time, which was more prolonged in multigravidae where aCa titres were higher than in nulliparous and primiparous mice. The results show that although pregnancy alters aCa responses during the course of gestation, no long-term modification of humoral immunity occurs, an observation in agreement with the clinical findings in these mice and in humans.

Animals↗
PubMed1987

Antagonist muscle activity during human forearm movements under varying kinematic and loading conditions.

During the performance of unidirectional, single-joint movements it is known that muscle activation is not confined to the agonist, but is generally seen in the antagonist as well, appearing as a burst of antagonist activity if the movement is quite rapid. We have studied the integral over time of antagonist electromyographic activity (Eant) during forearm movements encompassing a wide range of movement speeds, amplitudes and inertial loads, with two intents: first, to provide an empirical description of the dependence of Eant on kinematic and loading parameters which would be valid over a several hundred-fold range of Eant; and second, to test the hypothesis that Eant is related to the torque necessary for braking the movement. With respect to the first aim, we found that for all subjects Eant was correlated with a simple algebraic expression dependent upon peak velocity, movement amplitude and total moment of inertia, when each of these movement parameters was varied either singly or in combination. Although a more complex algebraic expression, in which exponents for each parameter were optimized for a given subject, provided marginally better correlations with Eant, we prefer the simpler expression on the grounds that it provides similar correlations without requiring a different form for each subject. With respect to the second aim of the study, the braking hypothesis was supported by the fact that the simple expression could be interpreted as representing the average net torque required for braking. However, in experiments in which an external torque was provided to assist in braking, antagonist muscle activity was not reduced as much as would be expected if provision of braking torque was the sole function of antagonist activity. We conclude that: (1) antagonist activity varies with kinematic parameters and inertial load in accordance with the requirements for braking the limb, but (2) the activity may in fact provide a multiple of the torque that is required for braking alone, with excess activity presumably offset by concurrent agonist activity. Possible roles of such cocontraction are discussed.

Adolescent↗
PubMed1986

Relative activation of two human elbow flexors under isometric conditions: a cautionary note concerning flexor equivalence.

We examined the electromyographic (EMG) activity of two human elbow-flexor muscles, biceps brachii and brachioradialis, during isometric contractions. The task required subjects to match the EMG level of one of the muscles (the control muscle) to one of four target levels (5, 10, 15, or 20% of maximum) at various elbow angles. A new technique was developed for the target-matching task. The activity of the other muscle (the test muscle) was simultaneously recorded during the task. For the notion of flexor equivalence to be supported, the EMG levels for the two muscles should have covaried. This was not the case. The results revealed three features: (1) while the control-muscle EMG remained constant across joint angles, the test-muscle EMG varied with joint angle, and the trend of this variation differed among subjects; (2) in nine out of ten subjects the trend of test-muscle EMG variation with joint angle was reversed when the other muscle served as the test muscle; and (3) the test-muscle EMG associated with the four target levels was subject-, muscle-, and angle-dependent. These results caution against the generalization of the flexor equivalent concept to isometric conditions. In particular, the activity of one muscle is not a reliable indicator of the activity of other muscles subserving the same joint action.

Computers↗
PubMed1986

Optimized movement trajectories and joint stiffness in unperturbed, inertially loaded movements.

An attempt is made to integrate theoretically the mechanical, electromyographic, and psychophysical lines of inquiry into the control of movement by investigating the significance of joint stiffness in the reduction of effort. Attention is focused on single-joint, unperturbed movements of specified duration performed from one specified position to another in the presence of an inertial load. A theoretical measure of the sense of effort is formulated in the light of psychophysical observations and mechanical considerations. This measure is such that it is increased by reciprocal changes in the central drives to opposing sets of muscles, as well as by enhancement of joint stiffness. Mathematical analysis of the interplay of these factors reveals that, in any given condition, the minimization of this measure of effort necessitates a particular value of joint stiffness and a particular trajectory of movement. The predicted stiffness and trajectory are shown to be in quantitative agreement with available observations. In addition, the conditions in which a higher value of stiffness is predicted to be advantageous for reducing the effort are shown to be the conditions that are known to promote greater coactivation of the agonist and antagonist muscles. It is concluded that the seemingly wasteful coactivation may serve to optimize the stiffness. The stiffness, therefore, need not be viewed simply as a means of resisting imposed perturbations, but as a means of reducing the alterations in the central drives necessary for the performance of movement, thereby reducing the effort.

Animals↗
PubMed1986

Recording of spindle afferent discharge during hindlimb movements in spinalized turtles.

The feasibility of spindle afferent recording during naturally or electrically induced hindlimb movements is demonstrated in the case of spinalized, decapitated turtles. Since these recordings are obtained from fine filaments of exposed dorsal roots, it is possible for the experimenter to select the afferents of interest. This feasibility, together with the fact that spinally generated movements are readily exhibited, make the turtle an attractive animal for the study of spinal motor control mechanisms.

Action Potentials↗
PubMed1985

Effects of phenytoin on field bursts of rat hippocampal slices in low-calcium solutions.

Recurring bursts of population spikes, a simple model of epileptiform activity, can be produced by exposing slices of rat hippocampus to saline containing 0.2 mM [Ca2+] and 4.0 mM [Mg2+], at which concentration chemical synaptic activity is blocked. Phenytoin at 7.3-73 microM shortened the duration of these bursts. At 73 microM the bursts were slowed and often eliminated. This model appears to be more sensitive to the action of phenytoin than the penicillin model of epileptiform bursting.

Animals↗
PubMed1985

Isometric torque-angle relationship and movement-related activity of human elbow flexors: implications for the equilibrium-point hypothesis.

Since the moment arms for the elbow-flexor muscles are longest at intermediate positions of the elbow and shorter at the extremes of the range of motion, it was expected that the elbow torque would also show a peak at an intermediate angle provided the activity of the flexor muscles remained constant. We measured the isometric elbow torque at different elbow angles while the subject attempted to keep constant the electromyographic activity (EMG) of the brachioradialis muscle. The torque-angle relationship thus obtained exhibited a peak, as expected, but the shape of the relationship varied widely among subjects. This was due in part to differences in the variation of the biceps brachii EMG with elbow angle among the different subjects. The implications of these observations for the equilibrium-point hypothesis of movement were investigated as follows. The subject performed elbow movements in the presence of an external torque (which tended to extend the elbow joint) provided by a weight-and-pulley arrangement. We found in the case of flexion movements that invariably there was a transient increase in flexor EMG, as would seem necessary for initiating the movement. However, the steady-state EMG after the movement could be greater or less than the pre-movement EMG. Specifically, the least flexor EMG was required for equilibrium in the intermediate range of elbow angles, compared to the extremes of the range of motion. The EMG-angle relationship, however, varied with the muscle and the subject. The observation that the directions of change in the transient and the steady-state EMG are independent of each other militates against the generality of the equilibrium-point hypothesis. However, a form of the hypothesis which includes the effects of the stretch reflex is not contradicted by this observation.

Arm↗
PubMed1984

Time course of the effects of trimethyltin on limbic evoked potentials and distribution of tin in blood and brain in the rat.

The averaged evoked potential technique was used to determine the sequence and relative effects of a single dose of trimethyltin (TMT) on the neurophysiologic functioning of two limbic system pathways, selected for study because they are known to show TMT-induced pathologic changes. Adult female rats were implanted with bipolar electrodes in the olfactory or prepyriform cortex (PPC), dentate gyrus (DG) and distal CA3 subfield of the hippocampus. Evoked potentials were elicited in the DG by stimulation of the PPC, and in CA3 by stimulation of the mossy fiber system which originates in dentate granule cells. TMT chloride was administered po in a single 7.5 mg/kg dose in water to 9 implanted rats. A parallel group of 6 implanted rats served as a control group. No changes in potentials were noted 24 hr after TMT, but some effects appeared at 48 hr. Amplitudes of potentials elicited in the DG were greatly potentiated between 2-7 days after TMT with peak effects between 4-6 days, followed by a marked decline in amplitude of the response. At the same time, recordings of spontaneous electrical activity did not reveal marked abnormalities such as electrographic seizure waves. Amplitude of the CA3 response began to decline 3 days after TMT and by 3 weeks was markedly depressed. Average amplitudes of the same responses in the control group remained within 12 percent of pretreatment values for the 20 days of the study. Tin levels in whole brain were lowest at 24 hr, doubled at 48 hr, then doubled again at 4 days when peak levels were reached. Values remained high in both blood and brain and at 20 days were still 66 percent of peak levels. Thus, the delay in onset of effects of TMT on evoked potentials may be related to the slow entry of tin into brain, presumably because of high affinity binding to hemoglobin in blood, as reported by others. Also, the time of peak potentiating effects on potentials evoked in the DG correlated well with the time of peak levels of tin in brain.

Animals↗
PubMed1983

A model of spindle afferent response to muscle stretch.

1. A unified model of the properties of stretch responses of mammalian spindle endings is proposed. This model encompasses the disparity between sensitivity of spindle endings to small and to large stretch of the muscle as well as the disparity in their dynamic responsiveness for different amplitudes of stretch. 2. In the model the mechanical properties of intrafusal fibers include a property akin to friction, which is hypothesized on the basis of reported observations on amphibian muscle. Transducer and encoder processes are modeled in the light of recent observations on isolated spindles. The model involves five unknown parameters whose values are selected by reference to certain reported observations on deefferented primary and secondary endings. The model can be used to predict responses to length changes of arbitrary time course. 3. Predicted responses to large ramp-and-hold stretch are quantitatively comparable to observations over a wide range of stretch velocities. The quantities compared include the increment in response during ramp stretch as well as the dynamic index, which is a measure of adaptation at stretch plateau. 4. At a fixed frequency of sinusoidal stretch, the relation between amplitudes of stretch and response is predicted in quantitative agreement with measurements. As the frequency of stretch is decreased, the predicted phase lead decreases and then increases, while the sensitivity decreases monotonically, in accord with observations. 5. In the model the high sensitivity for small stretch is not specific to any particular length of the muscle. When stretch is large, the region of high sensitivity is gradually reestablished at the new length, a phenomenon referred to as resetting. The dynamic response to a large stretch can be seen as arising, for the most part, from the dynamic process of resetting. 6. The influences of static or dynamic fusimotor activation on stretch responses of the primary ending are simulated by modifying the parameter values in the model. The modifications are such that static (dynamic) fusimotor activity speeds up (slows down) the resetting of the high-sensitivity region. The predictions mimic qualitatively the observed fusimotor effects not only on the response to large ramp stretch but also the contrasting effects seen with smaller, sinusoidal stretch.

Animals↗
PubMed1981

Prolonged time course for vibratory suppression of stretch reflex in the decerebrate cat.

We studied the effects of longitudinal tendon vibration on the stretch reflex of the soleus and gastrocnemius muscles in 11 decerebrate cats. Vibration was applied at amplitudes (40-80 micrometer) and frequencies (120-250 HZ) sufficient to provide a strong tonic vibration reflex. In keeping with previous reports, we found that during an established tonic vibration reflex, the force and emg response to superimposed ramp and hold stretch are largely suppressed. This suppression is most obvious during the dynamic phase of stretch where it gives rise to a complex force response resembling that of active areflexic muscle. If stretch initiation is delayed until after vibration is terminated, the suppressed effects of vibration persist for 5 s or more. These suppressive effects are marked in the first 200 ms, and then decay gradually over the ensuing time period, paralleling the decline in emg and force which follows vibration offset. Simultaneous recordings from homonymous Ia afferents showed that this suppression persists even though the stretch responsiveness of primary spindle endings has returned to normal immediately following the end of vibration. When stretch is initiated shortly after vibration commences, the suppressive effects are first evident at 50-100 ms latency, but are not well established until 1 s or more after vibration onset. Tests of monosynaptic transmission using small amplitude tendon taps or electrical stimulation of synergist nerves to activate Ia fibers revealed that reductions in the magnitude of the response following vibration are usually modest (12% mean reduction at 50 ms, n = 5), and they are quite sensitive to the initial level of excitation of the motoneuron pool. These reductions were also rather shortlived, being largely completed within 500 ms of vibration offset. Although the relative contributions of presynaptic and postsynaptic inhibition are not readily dissociated in this type of experiment, it is likely that the magnitude of presynaptic inhibition is quite small. We argue that the effects of vibration on the stretch reflex are best explained by invoking an excitatory autogenetic projection from Ia interneurons to extensor motor neurons, which lies in parallel with the Ia monosynaptic projection. In order to account for the vibratory suppression, we propose that these interneurons are driven to saturation by vibration. When vibration ceases, the discharge rate of these interneurons declines with a prolonged time-course that coincides with the recovery of stretch responsiveness. This recovery would contribute to the return of stretch reflex force.

Animals↗