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Biomedical subjects

M L Walsh

Publications and source records attributed to M L Walsh.

At least 19 recordsLinked to original sources
PubMed2000

Control of the wrist joint in humans.

As one considers changes in motor activity from lower mammals to higher primates, one of the major changes one observes lies in the cortical control of forelimb muscles. There has been a shift from disynaptic control of spinal motoneurons in, for example, the cat, to a greater and greater percentage of monosynaptic control of hand and forelimb motoneurons in the primate. In spite of the species and evolutionary changes in the synaptic connections of the corticospinal tract, it appears that the interneurons identified in the cat are retained in the monkey and human. These interneurons, under the influence of descending pathways, modulate the output of motoneuron pools. Perhaps the control of these interneurons has also changed towards finer control of movement, as has been suggested by recent studies in the monkey. Whether in cat or human, the recruitment pattern for motor units is the same; the change from disynaptic to monosynaptic connections has not changed the recruitment pattern of muscles. Differences in the recruitment patterns of muscles may lie in the finer control of inputs to motoneurons in the primate. This review seeks to integrate the current knowledge of the mechanisms involved in the motor control of the wrist joint and especially in the recruitment patterns of the muscles. These motor control mechanisms include the biomechanics of the wrist joint, recruitment patterns of wrist muscles, interneurons and spinal cord circuits in the cervical regions mediating the output of spinal motoneurons, and the supraspinal control of these muscles.

Biomechanical Phenomena↗
PubMed2000

Whole body fatigue and critical power: a physiological interpretation.

Critical power (CP) is a fundamental concept describing fatigue and exhaustion. The main physiological determinant of CP is the ability to utilise oxygen. This in turn is dependent primarily on diffusion distance. During exercise, many different tissue systems must increase their metabolic demand. It is argued that each tissue system, such as cardiac, respiratory and leg muscles, has their own CP. Cardiac muscle has the greatest CP relative to its maximum power because it has the shortest diffusion distances. Respiratory muscle also has a substantially higher relative CP than leg muscle. The higher relative CPs of cardiac and respiratory muscle are due in part to the homeostatic functions these tissues provide. This built in protective design can be disrupted in certain conditions such as hypoxia. During high intensity exercise, fatigue and ensuing exhaustion will occur if any contributing physiological system functions above its CP.

Cell Respiration↗
PubMed1999

Effect of endurance training on blood lactate clearance after maximal exercise.

The aim of this study was to measure serial changes in the rate of blood lactate clearance (gamma2) in response to sequential periods of training and detraining in four male triathletes aged 22-44 years. There were two major phases of training and taper, each lasting 4-5 weeks (training 1 = 5 weeks, taper 1 = 2 weeks, training 2 = 4 weeks and taper 2 = 2 weeks), in preparation for a triathlon competition. The training stimulus absorbed by each subject was carefully quantified from the duration and intensity of the training exercise. A serial weekly measure of each trainee's physical response to training was evaluated as the peak power, termed a 'criterion performance', developed by a subject during a 30 W x min(-1) ramp cycle ergometer test to exhaustion each week. During 30 min of recovery after this test, 13 samples of venous blood were drawn sequentially from a subject to measure the blood lactate recovery curve. The rate constant of blood lactate clearance was estimated by a non-linear least-squares regression technique. In addition, the concurrent time to peak lactate concentration and the peak lactate concentration were also estimated to help define changing lactate kinetics. The criterion performance generally declined throughout each period of incremental training and improved during each taper period, rising iteratively in this way to be clearly above baseline by the end of the second taper. The blood lactate clearance rate increased transiently in early training before declining from the middle of the first training period to the middle of the first taper; thereafter, gamma2 increased above baseline in each trainee throughout the remaining first taper and the major portion of the second training period, decreasing only in the final criterion performance test. The time to peak lactate declined from baseline throughout all phases of training and taper. Peak blood lactate increased in all subjects to the end of the first taper before declining by the end of the second training period, rising again to baseline levels during the second taper. The change in gamma2 was examined relative to the work rate achieved in cycle ergometry above an initial baseline score (deltaCP) and against concurrent peak blood lactate. There was a clear upward shift in gamma2 above baseline throughout the first and second training and taper in two subjects; this was less clear in the remaining two subjects, each of whom had a lower deltaCP. We conclude that this indicates improved lactate clearance, manifest by the change in gamma2 induced by endurance training.

Adult↗
PubMed1995

Task-dependent factors in fatigue of human voluntary contractions.

This chapter explores the hypothesis that fatigue is not caused uniquely by any common set of factors, but rather that the amount of stress placed on each site depends on the type of exercise from which fatigue develops. Evidence supporting this idea is presented by comparing results from various studies in which fatigue was caused by different exercise protocols. However, the way in which human endurance capacity changes with the type or intensity of the task performed suggest a unitary process. Thus, perhaps the neuromuscular system as a whole is so well adjusted that any task-related additional impairment at one site is compensated by corresponding functional improvements at others. We suggest that nature has had a long time in which to "get it right".

Exercise↗
PubMed1995

The influence of inspired oxygen on the oxygen uptake response to ramp exercise.

The relation between VO2 and work rate (WR) was examined in seven male subjects who performed ramp (1 W.3s-1) two-legged cycle ergometry to exhaustion while inspiring either hypoxic (12% O2), normoxic (21% O2), or hyperoxic (40% O2) air. The anaerobic threshold was estimated from respiratory gas exchange threshold (RGET). Prior to the RGET, the delta VO2/delta WR was greater under normoxic [mean (SD); 10.19(1.04) ml O2.min-1.W-1] and hyperoxic [10.44 (0.72)] conditions compared with hypoxia [9.34 (0.89)]. Above the RGET, the delta VO2/delta WR for hypoxia [8.91 (0.63)], normoxia [10.40 (0.77)], and hyperoxia [11.08 (0.48)] were all significantly different from each other. These data indicated that for two-legged, cycle, ramp ergometry in normoxia below the RGET, both the delta VO2/delta WR and response time was constant. Above the RGET, the normoxic VO2 response was the net result of a declining delta VO2/delta WR and a longer response time to the unsteady state character of a ramp exercise protocol.

Adult↗
PubMed1995

Aggression is attenuated by ovariectomy in pregnant female rats given progesterone and estradiol replacement to maintain pregnancy.

Female rats were tested for aggression toward an unfamiliar female conspecific 13 days following the beginning of cohabitation with a male. Forty-eight hours later, half of the females that displayed aggression were ovariectomized. To maintain pregnancy, they were also given Silastic implants of estradiol (1-mm tube) and progesterone (6 tubes, 30-mm long; Dow-Corning tubing #602-305) sufficient to maintain pregnancy but at lower levels than those normally present. Control females were given a sham ovariectomy and implanted with empty tubes. Each animal received a second aggression test at 48 h following surgery and a third test, 3 days following the second. Hormone implants successfully maintained pregnancy and supported the normal development of the pups. However, Ovariectomized females with hormone implants did not spontaneously give birth. Ovariectomized females displayed less aggression than their sham-ovariectomized counterparts at the second and third aggression tests. The difference was due to an increasing level of aggression by the control but not the experimental animals. These results are consistent with other evidence that circulating gonadal hormones influence the onset of maternal aggression in the female rat.

Aggression↗
PubMed1995

Aggression in the lactating female rat: the normal decline is not dependent on the physical development of the pups.

Female rats that had been assessed for aggression on two occasions during pregnancy were also assessed for aggressiveness toward an unfamiliar adult female on days 5, 12, and 19 of lactation. Each female had its litter of pups exchanged for another litter on days 10 and 17 following parturition. Half of the females received pups that were 2 days old. The other half received pups of the same age as those taken away. Aggression by females of the two groups declined at a similar rate during the period of lactation. Retrieval of a group of seven 6-day-old pups following the last aggression test was present in females whose litter had been replaced with 2-day-old pups but not in females whose litter had been replaced with same-age pups. Lactation was maintained in all females during the three weeks following parturition but declined to a level that was not sufficient to maintain growth following the normal 21 day lactation period. A single set of biological or stimulus variables does not maintain all aspects of maternal behavior. Physical and behavioral maturation of the pups does not appear responsible for the decline in maternal aggression during the final two weeks of lactation.

Age Factors↗
PubMed1995

Motor unit activity during isometric and concentric-eccentric contractions of the human first dorsal interosseus muscle.

1. Motor unit activity was recorded with intramuscular fine wire electrodes during isometric, concentric, and eccentric activity in the human first dorsal interosseus muscle. Twenty-one units from 11 subjects were sampled. 2. During isotonic cycles of shortening and lengthening, 18 of 21 units were recruited during the concentric phase, increased their discharge rates as the concentric movement progressed, then decreased their discharge rate during the eccentric phase, and were derecruited. 3. A different pattern of recruitment was observed in recordings from three units. These units were recruited during the eccentric phase, at a time when other units were decreasing their discharge rate or being derecruited. In two of the units selectively recruited during the eccentric phase, it was possible to determine their isometric thresholds, which were higher than those of units exhibiting the more common pattern of recruitment. 4. For two of the three units exhibiting selective recruitment during eccentric contraction, the unit was recorded simultaneously with different pairs of recording wires separated by 5-10 mm. Each discharge of these units was detected by both electrodes, making it unlikely that movement artifact was responsible for the initiation or cessation of discharge. 5. The recruitment patterns observed suggest that changes in the type or distribution of synaptic inputs to motoneurons during movement can, in some instances, override pre- and postsynaptic factors that shape recruitment order in isometric conditions.

Adolescent↗
PubMed1994

Statistical evidence consistent with two lactate turnpoints during ramp exercise.

A number of studies have identified the existence of two ventilation thresholds during ramp or incremental exercise to exhaustion on the cycle ergometer. This study was undertaken to investigate whether two threshold turnpoints could be identified in blood lactate concentration data collected at such times. Five trained athletes provided serial blood samples on several occasions each during a 3-month period of training. Blood lactate concentration was analysed by fitting models with no, one or two turnpoints. Ordinary residuals from the first two models were often found to exhibit an oscillatory behaviour consistent with the existence of two turnpoints in lactate concentration. A comparative analysis of goodness of fit of these models revealed that the model with two turnpoints was significantly better than either of the simpler models. This suggests that two transitions exist, which divide the time domain for blood lactate concentration in ramp exercise into three regions. These two transitions may correspond to the two ventilation thresholds.

Adult↗
PubMed1993

Influence of combined estradiol and testosterone implants on the aggressiveness of nonaggressive female rats.

Female rats that had been cohabiting with a sterile male or with another female for 6 weeks were tested for aggression toward an unfamiliar female once each week for 3 weeks. Females that were not aggressive as a result of cohabitation with a sterile male were ovariectomized. Half were implanted with a Silastic tube containing estradiol (1 mm long hormone-filled space) and a tube containing testosterone (5 mm long hormone-filled space). The other half were implanted with empty tubes. All females that had been cohabiting with another female were ovariectomized and implanted with an estradiol- and a testosterone-filled tube. Three additional weekly tests of aggression were given beginning 1 week postoperatively. Females given hormone replacement displayed only a slight increase in aggression postoperatively. Females not given hormone replacement declined in aggressiveness. These results indicate that hormone replacement levels sufficient to maintain aggression in highly aggressive females following ovariectomy are not sufficient to produce a high level of aggression in females that have not become aggressive following cohabitation with a sterile male or that have been cohabiting with another female.

Aggression↗
PubMed1993

Aggression by a female rat cohabiting with a sterile male declines within 27 h following ovariectomy.

Females that had become aggressive as a result of cohabiting with a sterile male were ovariectomized and implanted with empty Silastic tubes. Control groups were either sham ovariectomized or ovariectomized and implanted with Silastic tubes providing replacement levels of estradiol and testosterone. Twenty-seven hours following surgery, all animals were tested for aggressiveness toward an unfamiliar female rat. The aggression of ovariectomized females without hormone replacement declined to a minimal level postoperatively and was significantly lower than that of sham-ovariectomized females or ovariectomized females with estradiol and testosterone replacement. Both sham-ovariectomized females and ovariectomized females given hormone replacement displayed a level of aggression close to that observed preoperatively. The aggression of a female rat cohabiting with a sterile male appears to be highly sensitive to the removal of gonadal hormones. This corresponds with observations made on pregnant females and contrasts with those made on lactating females.

Aggression↗
PubMed1993

Aggression in humans: what is its biological foundation?

Although human aggression is frequently inferred to parallel aggression based on testosterone in nonprimate mammals, there is little concrete support for this position. High- and low-aggression individuals do not consistently differ in serum testosterone. Aggression does not change at puberty when testosterone levels increase. Aggression does not increase in hypogonadal males (or females) when exogenous testosterone is administered to support sexual activity. Similarly, there are no reports that aggression increases in hirsute females even though testosterone levels may rise to 200% above normal. Conversely, castration or antiandrogen administration to human males is not associated with a consistent decrease in aggression. Finally, changes in human aggression associated with neuropathology are not consistent with current knowledge of the neural basis of testosterone-dependent aggression. In contrast, human aggression does have a substantial number of features in common with defensive aggression seen in nonprimate mammals. It is present at all age levels, is displayed by both males and females, is directed at both males and females, and is not dependent on seasonal changes in hormone levels or experiential events such as sexual activity. As would be expected from current knowledge of the neural system controlling defensive aggression, aggression in humans increases with tumors in the medial hypothalamus and septal region, and with seizure activity in the amygdala. It decreases with lesions in the amygdala. The inference that human aggression has its roots in the defensive aggression of nonprimate mammals is in general agreement with evidence on the consistency of human aggressiveness over age, with similarities in male and female aggressiveness in laboratory studies, and with observations that some neurological disturbances contribute to criminal violence. This evidence suggests that human aggression has its biological roots in the defensive aggression of nonprimate mammals and not in hormone-dependent aggression based on testosterone.

Aggression↗
PubMed1992

Cohabitation with a sterile male facilitates the development of retrieval behavior in nulliparous female rats exposed to pups.

Female rats were housed with a sterile male or another female. After 3 weeks, half of the females that had been housed with a female were rehoused with an intact male. At the end of 6 weeks female or sterile male cagemates were removed. Intact male cagemates and pups were removed 3 to 12 h following parturition. All females were tested for retrieval of three unfamiliar pups placed in their cage on the day following removal of their cagemate. Three unfamiliar pups were placed with each female and the female's behavior observed for 10 min. Observations were made in this way for 13 days or until the female retrieved all three pups within the 10-min interval. Pups were left with the female on days they were not retrieved. Females housed with a sterile male reached criterion for pup retrieval in 2.9 days, significantly fewer days than were required for females housed with another female (6.6 days) but significantly more than were required for a postpartum female (0.8 days). By demonstrating that cohabitation with a male fosters the development of retrieval, these results support evidence from the study of aggressive behavior that pseudopregnancy facilitates the development of behaviors associated with pregnancy and lactation.

Aggression↗
PubMed1992

Interaction of estradiol, testosterone, and progesterone in the modulation of hormone-dependent aggression in the female rat.

Female rats that had become aggressive as a result of cohabiting with a sterile male were ovariectomized and implanted with Silastic tubes of estradiol, testosterone, and progesterone, estradiol and testosterone alone, or with empty tubes. The implants were designed to model serum concentrations present during the last week of pregnancy (estradiol, 0.06 ng/ml; testosterone, 2.6 ng/ml; progesterone, 70 ng/ml). Following a test of aggression 1 week postoperatively, estradiol and testosterone implants were replaced with ones designed to maintain the lower hormone levels present following parturition (0.02 ng/ml; 0.6 ng/ml, respectively). Progesterone was not replaced. At the first aggression test, females with estradiol and testosterone alone displayed significantly more aggression than females with these hormones plus progesterone. Both groups were more aggressive than females without hormone replacement. Following the exchange of large implants for small ones, females that previously had progesterone increased in aggression while females that previously had only estradiol and testosterone decreased in aggression. Both groups continued to be more aggressive than the group without hormone replacement. High serum progesterone present near the end of pregnancy appears to moderate the expression of aggression supported by estradiol and testosterone. Conversely, progesterone's decline at parturition appears to produce a rebound facilitation of aggression even though serum estradiol and testosterone simultaneously decline.

Aggression↗
PubMed1992

Ovariectomy does not attenuate aggression by primiparous lactating female rats.

Nulliparous female hooded rats were allowed to cohabit with a sexually active male in a large living cage. Aggression toward an unfamiliar female was assessed during the second and third week of pregnancy. Within 12 to 24 h following parturition females were ovariectomized (n = 7) or sham-ovariectomized (n = 6) in a manner that balanced previous aggression scores. Aggression was assessed at 48 h following ovariectomy and at three weekly intervals thereafter. Ovariectomized and sham-ovariectomized females did not differ in the number of attacks, number of bites, duration of on-top, or frequency of piloerection on any test day following parturition. These results indicate that circulating levels of ovarian steroids do not influence the level of aggression by a primiparous lactating female toward an unfamiliar female conspecific.

Aggression↗