Biomedical subjects

J Lafleur

Publications and source records attributed to J Lafleur.

16 recordsLinked to original sources

PubMed1995

Heterogeneity of contraction-induced effects in neurons of the cat dorsal spinocerebellar tract.

1. Clarke's column neurons of the dorsal spinocerebellar tract (DSCT) were recorded intracellularly in anaesthetized cats during weak sustained contractions of triceps surae (TS) produced by direct electrical stimulation of the muscle. 2. Of 145 DSCT neurons, 77 (53%) were contraction sensitive suggesting that information about weak contraction of a limited number of muscles is widely distributed among DSCT neurons. Four types of effects were observed in individual neurons during TS contractions. 3. In the first group of 11 DSCT neurons (14% of the contraction-sensitive cells), the effect was excitation persisting throughout the duration of contractions. These responses were ascribed to actions of afferents from contraction-activated tendon organs. 4. In a second group of 15 neurons (20% of the contraction-sensitive cells), quickly declining excitatory potentials were recorded during sustained TS contractions. By analogy with previous observations of contraction-induced effects in motoneurons, the decline of excitation might be explained by contraction-induced presynaptic inhibition of group I afferents in Clarke's column. 5. Declining inhibitions, resembling those previously observed in homonymous and synergic motoneurons, were recorded in 49% of contraction-sensitive DSCT neurons. This appears in keeping with the fact that interneurons mediating Ib inhibition to motoneurons project axon collaterals to DSCT neurons. Presynaptic inhibition of Ib fibres might therefore cause parallel reductions of inhibitory potentials in motoneurons and in DSCT neurons. 6. In a final group of 13 neurons, mixed excitatory and inhibitory effects were observed during TS contractions. Such DSCT neurons might monitor the excitability of Ib interneurons by integration of information about input to and output from these neurons. 7. The non-uniform patterns of DSCT responses to TS contractions suggest complex processing of information on ankle extensor activity in cerebellum. Phasic signalling of contraction onset is observed in many DSCT neurons while others carry messages about duration and strength of contraction.

Animals↗

PubMed1993

Declining inhibition in ipsi- and contralateral lumbar motoneurons during contractions of an ankle extensor muscle in the cat.

1. Motoneurons of pretibial ankle flexor and knee flexor and extensor muscles were recorded intracellularly in chloralose- or pentobarbitone-anesthetized cats during sustained submaximal contractions of either ipsi- or contralateral gastrocnemius medialis muscle (GM). 2. In a majority of ipsilateral motoneurons, a sustained GM contraction elicited inhibitory potentials that quickly subsided before the end of the contraction. An abrupt increase in contractile force could elicit a new series of inhibitory potentials, which declined again in spite of a maintained force level. 3. Contraction-induced effects were only exceptionally detected in contralateral triceps surae and plantaris motoneurons. In a small number of pretibial flexor and knee flexor and extensor motoneurons, declining inhibitions were observed during sustained contractions of the contralateral GM muscle. 4. At the onset of GM contractions, a variety of motoneurons uniformly receive inhibitory inputs that are quickly filtered out. Although the functional significance of this widespread initial inhibition remains to be elucidated, its rapid decline seems useful to allow subsequent recruitment of motor units as may be required for coordination of posture and movement. 5. Tendon organs are activated during muscle contraction, but it is not certain whether Ib inputs from GM can account for all the effects observed. Contribution of other afferents was considered and tested using a different experimental approach. The companion paper reports observations suggesting that effects elicited by group II afferents may cooperate in the contraction-induced inhibition of motoneurons.

Afferent Pathways↗

PubMed1993

Declining inhibition elicited in cat lumbar motoneurons by repetitive stimulation of group II muscle afferents.

1. The aim of the present experiments was to verify whether group II inputs from gastrocnemius medialis (GM) muscle could elicit declining inhibitions similar to those observed during GM contractions in a variety of lumbar motoneurons of the cat spinal cord. Motoneurons were recorded intracellularly in chloralose- or pentobarbitone-anesthetized preparations during electrical stimulation of GM nerve with repetitive trains. 2. With strengths in the group I range, repetitive stimulation evoked the usual Ia excitation in homonymous motoneurons and excitatory postsynaptic potential (EPSP) amplitudes remained constant throughout the stimulation sequence. In synergic plantaris motoneurons lacking an excitatory connection with Ia afferents from GM, the same stimulation, kept at a constant strength throughout the stimulation sequence, elicited rapidly decreasing inhibitory potentials reminiscent of those evoked by GM contractions. 3. In motoneurons of pretibial flexors, quadriceps, and posterior biceps-semitendinosus, the stimulation strength required to observe declining inhibitions resembling those produced by GM contractions was 4-8 times group I threshold, engaging group II in addition to group I fibers. 4. These results show that input from GM group II plus group I afferents can elicit inhibitory effects in a variety of motoneurons. Such observations support the hypothesis that messages from spindle secondary endings and/or nonspecific muscle receptors activated during contraction might contribute to the widespread inhibition caused by GM contractions. 5. Inasmuch as constant input in group II and group I afferents evoked declining inhibitory potentials, the origin of the decline must be central, which suggests that the rapid reduction of contraction-induced inhibitions also depended on a central mechanism.

Afferent Pathways↗

PubMed1992

Depolarization of Ib afferent axons in the cat spinal cord during homonymous muscle contraction.

1. Intra-axonal records from the intraspinal course of Ib and Ia afferent fibres innervating the gastrocnemius medialis muscle were obtained in chloralose or Nembutal-anaesthetized cats during submaximal contractions of the muscle. 2. Afferent fibres in continuity with their muscle of origin were functionally identified by their responses to muscle stretch or contraction. 3. In six out of eight Ib afferents, primary depolarizations (PADs) were recorded during contraction. They were independent of the presence of orthodromic impulses fired by tendon organs. 4. These observations support the assumption that the reduction of Ib autogenetic inhibition in homonymous and synergic motoneurones during GM contractions is due to presynaptic inhibition of transmission in Ib pathways.

Animals↗

PubMed1991

Retrospective cohort mortality study of cancer among sewage plant workers.

There is little known about the incidence of cancer among sewage workers. In this paper we examine findings from a retrospective cohort study of 487 white male sewer authority workers employed between January 1950 and October 1979. Vital status was ascertained for 93% of the cohort yielding a total of 6,886 person years. Total mortality from all causes was comparable to that of the general white male U.S. population (Standardized Mortality Ratio [SMR] = 0.91, 95% Confidence Interval [CI] = 0.77-1.07). The cohort was subdivided into those not exposed, and sewer workers who were exposed to sewage effluent, sludge, or wastewater containing chemicals including potential carcinogens. Among the nonexposed group, mortality from all causes was significantly low (SMR = 0.55, 95% CI = 0.33-0.88). Among the exposed sewer workers, mortality from all causes was not significantly different from that of the general white male U.S. population (SMR = 1.00, 95% CI = 0.84-1.19). Mortality from all cancers among exposed sewer workers was slightly higher than that of the general population (SMR = 1.19, 95% CI = 0.79-1.7). Statistically significant elevated mortality ratios were seen for cancer of the larynx (SMR = 7.93, 95% CI = 1.59-23.96), and cancer of the liver (SMR = 5.4, 95% CI = 1.10-16.05). Careful study of the medical and occupational histories of these cases suggested that larynx cancer was possibly work-related, while liver cancer was not. A group estimated to be the highest exposed, composed predominantly of operatives, had a higher directly adjusted death rate from all malignant neoplasms combined compared to all other workers (rate ratio = 1.64). These findings of increased risk of cancer among exposed sewage workers, especially operators, are based on small number of cases and should be interpreted with caution. Studies of larger cohorts are needed to clarify the risk of these cancers among sewage workers.

Adult↗

PubMed1990

Breathing pattern affects respiratory heat loss but not bronchoconstrictor response in asthma.

To determine whether changes in breathing pattern alone affect respiratory heat loss (RHL) and the constrictor response to cold dry gas hyperpnea in asthmatic subjects, we performed the following 2 part study: first we measured RHL in 8 asthmatic and 8 normal subjects during controlled eucapnic hyperpnea while they breathed at inspiratory to expiratory ratios (I/E) of 1:3, 3:1, and 2:2, and we recorded postchallenge forced expiratory volume in 1 sec (FEV1) in the asthmatic group; we then performed the same measurements in 8 asthmatic and 8 normal subjects at fixed target minute ventilation (VE) for tidal volumes of 0.2 X Forced vital capacity (FVC), 0.4 X FVC, and 0.6 X FVC by varying the target respiratory rate appropriately. Our results show that (1) increasing I/E ratio or tidal volume-frequency ratio (VT/f) at fixed VE produced small but statistically significant increases (p less than 0.05) in overall heat loss per unit volume of respired gas (RHL/VE) in both asthmatic and nonasthmatic subjects of 1-4 cal/L; (2) changes in breathing pattern alone did not affect bronchoconstrictor response as assessed by lack of change in slopes and intercepts of % delta FEV1 vs. RHL dose-response curves; and (3) the increase in RHL per unit volume of respired gas resulting from increasing VT/f ratios during cold gas hyperpnea was significantly greater in asthmatic than in nonasthmatic subjects. We conclude that changes in breathing pattern may affect overall RHL measured at the mouth, although the maximum effect of such changes in both asthmatic and nonasthmatic subjects is small (10-15%); that such changes do not significantly alter airway constrictor response in asthmatic persons; and (3) that the effects of changing breathing pattern on RHL may be more pronounced in asthmatic than nonasthmatic subjects, which suggests that the asthmatic group may be less able to adapt to factors that alter the magnitude and site of RHL.

Adult↗

PubMed1990

Reduction of Ib autogenetic inhibition in motoneurons during contractions of an ankle extensor muscle in the cat.

1. Triceps surae and plantaris (Pl) motoneurons were recorded intracellularly in chloralose or pentobarbital sodium (Nembutal)-anesthetized cats during unfused tetanic contractions of gastrocnemius medialis muscle (GM) produced by stimulating either a cut branch of the GM nerve or the muscle directly. 2. In alpha-motoneurons, during a series of GM twitches at 10/s, contraction-induced inhibitory potentials, probably the result of input from Golgi tendon organs (autogenetic inhibition), rapidly subsided before the end of the series. In contrast, excitatory potentials, probably the result of the activation of spindle primary endings during relaxation from contraction, persisted. 3. In gastrocnemius lateralis-soleus (GL-S) and Pl motoneurons lacking an excitatory connection with Ia afferents from GM, the sustained contraction of this muscle also elicited a declining inhibition. Rapid reduction of contraction-induced autogenetic inhibition was also observed in homonymous gamma-motoneurons. During unfused tetanic contractions lasting 0.5-4s, inhibitory potentials quickly subsided, but an abrupt increase in contractile force elicited a new series of decreasing inhibitory potentials. 4. The assumption that the inhibition induced by GM unfused tetanic contractions was due to activation of homonymous Ib afferents was supported by observations of the effects of electrical stimulation of the GM nerve. In Pl motoneurons lacking an excitatory connection with Ia afferents from GM, repetitive trains applied to the GM nerve, at a strength just above threshold for group I fibers, elicited rapidly declining inhibitory potentials similar to those produced by GM contraction. It was verified that during such stimulation, the amplitude of the group I afferent volleys did not decrease. 5. Reduction of contraction-induced Ib inhibition during sustained GM contraction was still present after a low spinalization of the preparation. As GM tendon organ discharges were verified to persist throughout prolonged contractions, the observed decline of autogenetic inhibition is likely to depend on a spinal mechanism, possibly involving presynaptic inhibition of Ib afferents and/or mutual inhibition of Ib-inhibitory interneurons.

Animals↗

PubMed1988

Dissociation of temperature-gradient and evaporative heat loss during cold gas hyperventilation in cold-induced asthma.

We examined temperature-gradient and evaporative energy losses during cold gas inhalation challenges in patients with exercise-induced asthma by using gases with similar water-carrying capacities but significantly different volume heat capacities. Seven subjects were asked to hyperventilate mixtures of 80% helium/20% oxygen (HeO2) or 80% sulfur hexafluoride/20% oxygen (SF6O2) for 5 min at a fixed target minute ventilation of 20 x FEV1 and an inspired gas temperature of 0 degrees C. Each subject equilibrated his or her lungs with the appropriate gas mixture prior to testing: PETCO2 and FIO2 were monitored and maintained at constant values (CO2 = 0.05; O2 = 0.20) by CO2 scrubbing and addition of compressed gas to the system. Gas composition, inspired and expired flow rates, and gas temperatures at the airway opening were recorded in real time using a computer-based data collection system that calculated respiratory heat loss on a per breath basis. Bronchoconstriction was quantitated using specific airway conductance measured before and serially after each challenge. The degree of bronchoconstriction correlated closely with evaporative respiratory heat loss (r = 0.658 p less than 0.05), but poorly with both temperature-gradient (r = 0.114, p greater than 0.20) and total (r = 0.268, p greater than 0.15) heat loss. These findings suggest that total respiratory heat loss is not the primary stimulus in exercise-induced asthma, and further suggest that total water loss, or focal heat/water loss, may be important in inducing bronchospasm in this subset of asthmatics.

Adult↗

PubMed1988

[Effects of partial unfused contractions of the gastrocnemius medialis muscle on homonymous and synergist motor neurons in cats].

Autogenetic inhibition of homonymous and synergist motoneurones can be elicited by very weak partial twitches of gastrocnemius medialis muscle, but during sustained contractions the amplitude of inhibitory post-synaptic potentials decreases quickly. A similar decrease also occurs during stronger contractions. The mechanism responsible for this decrease is still active in low spinal preparations. Pre-synaptic inhibition of Ib afferent fibres might contribute to this reduction of efficiency in the transmission of Ib afferent inputs to motoneurones.

Animals↗

PubMed1977

Haloperidol-induced dyskinesias in the monkey.

Haloperidol (0.25 mg/kg i.m.) was injected daily for 6 months in six normal monkeys. Over a 24 hour period, the following symptoms could be observed: akathisia, circling, akinesia, choreoathetoid and dystonic movements, oro-facial dyskinesias and postural tremor with or without harmaline. Six months after cessation of haloperidol, harmaline-induced postural tremor could still be observed in all animals and oro-facial abnormal movements, in one monkey. The neuropathologic study of the experimental material did not disclose any alteration of the central nervous system.

Animals↗

PubMed1974