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B A Conway

Publications and source records attributed to B A Conway.

35 records · Page 2Linked to original sources
PubMed1995

Synchronization between motor cortex and spinal motoneuronal pool during the performance of a maintained motor task in man.

1. Simultaneous recordings of cortical activity, recorded as the magnetoencephalogram (MEG), and the electromyogram (EMG) of the ipsilateral and contralateral first dorsal interosseous muscles (1DI) were made during maintained voluntary contractions. 2. The MEG recorded from a localized region of the sensorimotor cortex of the dominant hemisphere was coherent with the EMG from the contralateral 1DI muscle over a limited band of frequencies. The peak coherence was confined largely within the beta range of cortical activity (13-35 Hz). Significant cortical activity at 10 Hz and 40-50 Hz was not correlated with motor output. The MEG and EMG from the ipsilateral 1DI muscle were uncorrelated at all frequencies. 3. Significant coherence between the MEG and the EMG was associated with synchronous behaviour between the MEG and EMG in the time domain. 4. The results demonstrate that synchronized cortical activity contributing to MEG activity within the beta range of frequencies during maintained voluntary contractions is coupled to motor output at frequencies of motor-unit activity associated with motor-unit synchronization. This observation provides further evidence for the involvement of cortical neurones in the generation of motor-unit synchronization. 5. We suggest that the coherence between MEG and contralateral EMG observed during maintained isometric contractions may provide an example of binding within the motor system.

Adult↗
PubMed1993

Detection of weak synaptic interactions between single Ia afferent and motor-unit spike trains in the decerebrate cat.

1. Spike trains from identified single Ia afferents from soleus and lateral gastrocnemius muscles were recorded (while 'in continuity' with the spinal cord) simultaneously with single-motor-unit EMG spike trains from the same muscles in decerebrate cats. 2. A total of 143 Ia afferent-motor-unit pairs were examined for the presence of correlated activity between the Ia afferent and motor-unit and between the motor-unit and Ia afferent. Four types of correlation were identified on the basis of the cross-intensity function estimated for individual Ia afferent-motor-unit pairs. These correlations were attributed to the absence or presence of a central Ia afferent-motoneurone interaction or a peripheral motor-unit-muscle spindle interaction. 3. In addition to the cross-correlation-based second-order cross-intensity function, third-order cumulants were defined and used further to investigate Ia afferent-motor-unit interactions. A third-order cumulant density-based approach to signal processing offers improved signal-to-noise ratios, compared with the traditional product density approach, for parameters characterizing certain kinds of linear processes as well as a description of non-linear interactions. Two classes of third-order relations were described. One class was associated with a strong central connection and the other with a weak central connection. 4. Third-order cumulants estimated for Ia afferent-motor-unit pairs with significant second-order central correlations were able to detect a period of decreased motoneuronal excitability. In addition, temporal summation prior to spike initiation could be identified in cases where the afferent discharge was suitably high. 5. Third-order cumulants estimated for Ia afferent-motor-unit pairs in which no significant second-order central correlation existed identified the presence of weak synaptic interactions. It is argued that these interactions result from the summation from the recorded Ia afferent discharge and other spontaneous synaptic inputs to the motoneurone. 6. The results of the second-order cross-intensity analysis of Ia afferent-motor-unit interactions, combined with those from the third-order cumulant density analysis, showed that 77% of the recorded afferents had a detectable influence on motor-unit behaviour. 7. The results of this study suggest that the third-order cumulant, based on the analysis of spike trains, will provide a useful tool for detecting synaptic interactions not found by the use of the second-order cross-correlation histogram alone, and may also be used to estimate the time course of post-spike depression in motoneurones, as well as other non-linear regions of motoneurone membrane trajectory.

Action Potentials↗
PubMed1993

Toward effective customer-supplier relationships.

Baxter Healthcare Corporation, a worldwide supplier to hospitals, has been using the principles of total quality management to improve their products and services as well as reshape relationships with customers. This article enumerates what suppliers and hospitals need in order to make mutually beneficial relationships possible and presents three examples of Baxter's work in this area.

Consumer Behavior↗
PubMed1992

Spinal locomotor activity in acutely spinalized cats induced by intrathecal application of noradrenaline.

In this study we present a method of intrathecal drug administration in the acute spinal cat. A thin tube introduced into the subarachnoid space below the spinal cord was used for local drug administration. Noradrenaline reduced short-latency and provoked long-latency reflexes following high threshold afferent stimulation. Topical application of noradrenaline to the spinal cord was also able to induce and maintain locomotion. Our results strengthen the notion that noradrenergic systems play an important role in motor control. In addition, the present report introduces a protocol in the acute spinal cat, which combine the benefits associated with direct application of drugs as used in vitro experiments with the advantages of using the well investigated in vivo cat spinal cord preparation.

Animals↗
PubMed1991

In vitro effects of dihydrotestosterone on granulosa cell production of estrogen and progesterone.

To investigate the direct effects of androgens on follicle development, intact, immature female rats were given 8 IU PMSG (0 hour) and four injections of either vehicle or dihydrotestosterone (DHT), 1 mg/kg body weight, at 0, 12, 24, and 36 hours after PMSG. Granulosa cells from small (less than 200 microns), medium (200 to 400 microns), and large (greater than 400 microns) follicles were isolated and cultured in the presence or absence of 0.5 microM DHT in vitro for 48 hours, and the medium was assayed for progesterone and estrogen. Results show that DHT caused an increase in progesterone accumulation in all granulosa cells, regardless of follicle size. However, DHT inhibited estrogen accumulation in granulosa cells from different-size follicles and the inhibition varied depending on the duration of androgen exposure in vivo. The inhibition of estrogen accumulation was seen in granulosa cells from small follicles without prior exposure to DHT in vivo, while an inhibition of estrogen accumulation was seen in granulosa cells from medium and large follicles exposed to DHT treatment in vivo. Taken together, the results of experiments with in vivo and/or in vitro DHT treatment show that the androgen increases granulosa cell progesterone synthesis regardless of follicle size. However, the estrogen accumulation by granulosa cell is dependent on follicle size and duration of DHT exposure.

Animals↗
PubMed1991

Flow cytometric analysis of granulosa cells from developing rat follicles.

Immature rats were treated with diethylstilboestrol (DES) or pregnant mares' serum gonadotropin (PMSG) and forward angle light-scatter (FALS) and 90 degrees light-scatter (90 degrees LS) signals were used to measure the size and the granularity (internal organization) of the granulosa cells, respectively. The results confirmed the presence of two major populations of granulosa cells in the ovaries of both groups of rats, with the same percentage of larger cells in both treatments (52.3% in DES, 49.5% in PMSG). Since DES treatment brings about granulosa cell growth while PMSG treatment causes growth and differentiation, it is evident that there is heterogeneity in granulosa cell sizes during different states of growth and differentiation. There was also heterogeneity in sizes of granulosa cells harvested from follicles of small (less than 210 microns), medium (210-420 microns) and large (greater than 420 microns) diameter. Quadrant analysis of granulosa cells in various fractions collected from Percoll gradients suggested an increase in granularity in the small and large granulosa cell populations. Cell cycle analysis of small and large granulosa cell populations collected from large follicles of rats treated with PMSG indicated that each population was distributed in G0/G1, S and G2/M phases. These results demonstrate that populations of small and large granulosa cells exist in rat ovarian follicles during various stages of growth and differentiation.

Animals↗
PubMed1991

Partners in quality: managing your suppliers.

Just expecting more from your supplier is not what partnership is about. We have had the experience where the quality improvement and partnership banner has been waved but the tone and spirit of the meeting did not encourage or support a joint quality improvement effort. Benefits will not be achieved until the wall truly begins to come apart and the relationship is built on mutual respect and trust. Data collection and open answers to questions often reveal embarrassing errors and obvious needs for improvements. As stated before, blame and finger-pointing must be replaced with a mutual commitment to asking and answering the question, "How can we improve?" As Dr. W. Edwards Deming has stated, "End the practice of awarding business on the basis of price tag. Instead, minimize total cost. Move toward a single supplier for any one item on a long-term relationship of loyalty and trust." The structured approach of a quality improvement process and the application of quality methods and techniques has proven useful in removing emotion and helping the team focus on the process rather than the people and the issues involved. Quality improvement methods are focused on achieving both customer and supplier goals--customer satisfaction, employee satisfaction, and operational efficiency and effectiveness. Our experience with Partners in Quality as well as our experience with the quality leadership process supports a recent quote in the Harvard Business Review: "Quality is not just a slogan...(it is) the most profitable way to run a business."

Commerce↗
PubMed1990

Effect of dihydrotestosterone on the growth and function of ovarian follicles in intact immature female rats primed with PMSG.

Intact, immature female rats were primed with PMSG and treated with 4 injections of DHT. DHT given at 0, 12, 24 and 36 h caused a significant decrease in the ovulation rate 72 h after the PMSG treatment. Concurrent treatment with oestrogen reversed the inhibitory effects of the androgen. The androgen effect was apparently exerted directly on the ovary since DHT did not alter the surge of LH and FSH which occurred at 58 h after PMSG treatment. The DHT inhibition of ovulation was observed in the treatment cycle as well as in subsequent cycles which followed a second PMSG injection. This finding suggests that intermediate size follicles were also adversely affected by the androgen. To confirm that androgen affects follicles of all size ranges, follicles less than 200 microns, 200-400 microns and greater than 400 microns in diameter were isolated from the ovaries of rats treated with PMSG and DHT or the vehicle. The follicles were isolated by density gradient separation of follicles followed by filtration with pre-calibrated Teflon sieves. In some experiments, granulosa cells were also harvested from isolated follicles. DHT treatment did not affect the numbers of follicles of any size but did reduce the oestrogen content of follicles of all sizes. Follicles from DHT-treated animals contained fewer granulosa cells and the cells from treated animals had lower aromatase activity than did cells from control rats. Taken together, these findings suggest that DHT reduces the ovulation rate by decreasing the number of granulosa cells/follicle and by altering the oestrogen synthetic abilities of the cells. All follicles, regardless of size, were sensitive to androgen treatment.

Animals↗
PubMed1989

A framework for the analysis of neuronal networks.

The object of this work is to consider the application of some methods of spike train analysis that are not widely known, and are concerned with the description of the interaction between spike trains and the determination of causal connections between them. The notation and terminology follow conventions established in the statistical literature. The examples given are based on in-continuity recordings of the spontaneous activity of single Ia afferents from the soleus muscle and single motor units from the same muscle. Cumulant densities are shown to be simple extensions of the traditional cross-correlation methods, and are useful in characterizing the pattern of activity in one spike train that influences that in another, and to reveal interactions between spike trains that would not be apparent from the correlation histogram alone. Parameters based on the Fourier transforms of the spike trains are shown to be useful in determining timing relations between them, and in inferring patterns of connectivity not possible by correlation methods alone.

Action Potentials↗
PubMed1988

Plateau potentials in alpha-motoneurones induced by intravenous injection of L-dopa and clonidine in the spinal cat.

1. Intracellular recordings were made from lumbar alpha-motoneurones in unanaesthetized decerebrate acute spinal cats. The response of motoneurones to direct current pulse injection or synaptic excitation was investigated following intravenous injection of L-beta-3,4-dihydroxyphenylalanine (L-DOPA, 20-120 mg/kg) alone, nialamide (10-50 mg/kg) and L-DOPA or clonidine (0.5-1 mg/kg). 2. The response properties of motoneurones were tested with rectangular and triangular current waveforms. Before L-DOPA treatment motoneuronal firing during a rectangular current pulse is characterized by an initial high firing frequency which rapidly decreases to a lower steady-state firing which is maintained only for the duration of the pulse. Following administration of L-DOPA an acceleration in firing frequency is apparent following the initial adaptation seen with rectangular current pulses. A transient after-depolarization or an after-discharge often followed the termination of the pulse. The frequency-current relation in response to a triangular current injection changed from a clockwise to a counter-clockwise hysteresis after L-DOPA treatment (i.e. after L-DOPA the firing frequency was higher for any given current during the descending phase than during the ascending phase of the triangular waveform). 3. Firing acceleration during and self-sustained firing after rectangular current pulses and counter-clockwise hysteresis of firing frequency with triangular current pulses are causally related to the presence of plateau potentials, which can be directly visualized after inactivation of the spikes. Plateau potentials in motoneurones could be generated by short-lasting intracellular depolarizing current pulses or brief excitatory synaptic inputs and terminated by short-lasting hyperpolarizing current pulses or brief inhibitory synaptic inputs. Plateau potentials were demonstrated in flexor and extensor motoneurones. 4. All bistable properties described in the preceding paragraphs following L-DOPA administration could also be seen after administration of the alpha-receptor agonist clonidine. 5. Slow rhythmic oscillations of the membrane potential (7.5-10 Hz) were seen superimposed on plateau potentials in a few cells after administration of L-DOPA and clonidine. The oscillations had an amplitude in the range 10-20 mV and represent the expression of an intrinsic property of the motoneurone. 6. It is demonstrated that plateau potentials in the motoneurones contribute to the late long-lasting reflexes observed in L-DOPA-treated spinal cats. 7. It is concluded that L-DOPA (and clonidine) change the response properties of the motoneurones in an analogous way to 5-hydroxy-DL-tryptophan (5-HTP).(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1987

Animal models for study of polycystic ovaries and ovarian atresia.

In the human, polycystic ovaries are generally accompanied by normal or elevated levels of serum LH, normal or slightly depressed FSH and by high levels of circulating estrogens and androgens. If the excess androgen secretion is reduced by one of several methods, ovulatory cycles are usually restored. Several animal model systems have been proposed for the study of the pathophysiology of the polycystic ovarian syndrome. These include neonatal androgenization, hCG administration to hypothyroid rats, injection of estradiol valerate and maintaining animals in constant light. In a model developed in this laboratory, pubertal or adult rats were treated with the weak androgen, dehydroepiandrosterone (DHA), to induce polycystic ovaries. This treatment also altered the blood levels of LH and FSH but the effect on gonadotropins and on the formation of the degenerative follicles was fully reversed following discontinuation of the androgen injections. The polycystic ovaries of the DHA-treated animals were steroidogenically more active than controls raising the possibility that the DHA was acting directly on the ovary in addition to an action on the pituitary-hypothalamus axis. In order to study the direct effect of androgens on the ovary, another animal model was developed in which immature, hypophysectomized rats were injected with pregnant mare serum gonadotropin (PMSG) to initiate follicular growth followed by a single injection of dihydrotestosterone (DHT). The androgen caused follicular atresia and decreased the number of ova shed in response to ovulation induction with hCG. The suppressive effects of DHT were entirely prevented by concomitant treatment with estradiol. The studies with DHT were continued using another batch of PMSG, but the DHT-induced increase in the rat of atresia and suppression of induced ovulation were no longer seen. However, when this same batch of PMSG was given with estrogen or with the antiandrogen flutamide, there was less atresia and the growth of follicles was actually enhanced. Based on these studies, it was postulated that the second batch of PMSG had greater LH activity than the first preparation and that the LH has stimulated endogenous androgen production. The ovarian follicles which appeared to be most susceptible to this DHT effect were small to medium in size and had a low capacity to synthesize estrogen. This possibility was confirmed in another animal model system in which immature rats were injected with PMSG and 4 separate injections of DHT and then sacrificed at several time points over the next 8 days.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1987

Proprioceptive input resets central locomotor rhythm in the spinal cat.

The reflex regulation of stepping is an important factor in adapting the step cycle to changes in the environment. The present experiments have examined the influence of muscle proprioceptors on centrally generated rhythmic locomotor activity in decerebrate unanesthetized cats with a spinal transection at Th12. Fictive locomotion, recorded as alternating activity in hindlimb flexor and extensor nerves, was induced by administration of nialamide (a monoamine oxidase inhibitor) and L-DOPA. Brief electrical stimulation of group I afferents from knee and ankle extensors were effective in resetting fictive locomotion in a coordinated fashion. An extensor group I volley delivered during a flexor burst would abruptly terminate the flexor activity and initiate an extensor burst. The same stimulus given during an extensor burst prolonged the extensor activity while delaying the appearance of the following flexor burst. Intracellular recordings from motoneurones revealed that these actions were mediated at premotoneuronal levels resulting from a distribution of inhibition to centres generating flexor bursts and excitation of centres generating extensor bursts. These results indicate that extensor group I afferents have access to central rhythm generators and suggest that this may be of importance in the reflex regulation of stepping. Experiments utilizing natural stimulation of muscle receptors demonstrate that the group I input to the rhythm generators arises mainly from Golgi tendon organ Ib afferents. Thus an increased load of limb extensors during the stance phase would enhance and prolong extensor activity while simultaneously delaying the transition to the swing phase of the step cycle.

Afferent Pathways↗
PubMed1987

Limb perfusion in the lower limb amputee--a comparative study using a laser Doppler flowmeter and a transcutaneous oxygen electrode.

Accurate and objective assessment of amputation level in the lower limb plays an important role in patient management. Laser Doppler flowmetry (LDF) is a new and noninvasive technique for skin blood flow measurement and has been used pre-operatively in 25 patients undergoing amputation for vascular disease and in five normal controls. Baseline flux measurements were made at room temperature on the medial aspect of legs and then again after local heating of the skin for five minutes. Transcutaneous oxygen measurements were made at the same site for comparison and amputation level in patients selected on this basis. Significant differences (p less than 0.001) in TcPO2 values were found between controls (10.9 +/- 0.5 kPa), below-knee (BK) amputees (6.0 +/- 1.5 kPa) and above-knee (AK) amputees (1.5 +/- 0.6 kPa). Baseline LDF flux did not differ significantly between any group. Heated flux values did however show a significant difference (p less than 0.005) between controls (52.4 +/- 23.5) and both BK (20.6 +/- 9.2) and AK groups (8.1 +/- 7.7) and also between the amputee groups. The relative increase in flux (heated flux/baseline flux) differed significantly between the BK (3.3 +/- 1.5) and AK (1.2 +/- 0.3) groups (p less than 0.001) and between these two and the controls (11.2 +/- 5.4) (p less than 0.001). The correlation between relative increase in flux and TcPO2 was 0.7 (p less than 0.001). It is concluded that laser Doppler flowmetry used in conjunction with thermal stressing could provide a quick, simple and non-invasive method for objectively determining amputation level in the lower limb.

Amputees↗
PubMed1986

Conditioning of crossed extensor reflex pathways by independent natural stimulation of labyrinth, neck and elbow joint afferents.

The present experiments demonstrated that labyrinth, neck and elbow joint afferents interact to influence the excitability of crossed extensor reflex pathways projecting to triceps brachii in decerebrate cats. Reflex excitability was dependent on head, neck and elbow position such that it was increased when the elbow was held at full flexion and either the head maintained side down or the neck rotated side up. Such interaction between these afferents is likely to be important in postural control.

Animals↗
PubMed1984

The participation of forelimb flexors in labyrinth and neck reflexes in the decerebrate cat.

The reflex behaviour of triceps and biceps brachii was assessed by EMG recordings during natural labyrinth or neck stimulation. Labyrinth reflexes resulting from changes in head position are antagonistic to those resulting from changes in neck position. Reflexes recorded from biceps were reciprocal to those recorded in ipsilateral triceps and symmetrical to those from contralateral triceps. A scheme of labyrinth and neck reflexes involving forelimb flexors is presented.

Animals↗