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Biomedical subjects

I C Bruce

Publications and source records attributed to I C Bruce.

14 recordsLinked to original sources
PubMed1997

Mechanical properties of foods responsible for resisting food breakdown in the human mouth.

The fragmentation of foods (breakage function) was measured in five humans on "bagged' single particles of 28 foods from three food groups. The change in the square root of the specific surface of the particles (the specific surface being the area of particle silhouettes, measured by image analysis, divided by original particle volume) produced by one bite, averaged for all participants, was inversely linearly related to the square root of the toughness of the foods divided by the square root of their Young's moduli(r = -0.86; p < 0.00001). This relation is predicted by an analysis based on food fragmentation within a limited jaw displacement. Thus, resistance to jaw movement appears to provide sensory information on the deformation fracture and fragmentation of foods. It is believed that this is the first time that a relation between the breakage of food particles by the teeth and their material properties has been found, and the finding has considerable implications for human masticatory studies, for the analysis of dentition and diet in mammals and for texture studies in food science.

Adult↗
PubMed1996

Vagal hyperactivity in stress induced gastric ulceration in rats.

Indirect evidence suggests that stress ulceration is provoked by vagal hyperactivity. However, direct evidence of hypervagal activity during stress conditions is lacking. Experiments were designed to directly measure vagal activity under different stress conditions in rats. Starvation stress for 48 h did not change the mean amplitude of action potentials, but their frequency was significantly decreased. Restraint stress at 22 degrees C increased vagal activity, both amplitude and frequency, in the first 60 min; these responses were markedly enhanced by cold (4 degrees C) and persisted for at least 2 h. Starvation for 48 h did not induce any gastric mucosal lesions. Restraint alone produced petechiae in the gastric mucosa, but cold restraint induced severe haemorrhagic ulcers. It is concluded that cold restraint stress provokes a prolonged vagal hyperactivity, which is one of the causative factors for gastric ulceration.

Animals↗
PubMed1994

Electromyographic assessment of non-functional masseter muscle in an awake animal model.

Non-functional activities, such as bruxism, have been implicated in the development of temporomandibular disorders (TMD). It would be of value to have an animal model in which to investigate the processes underlying such disorders. The aim of this study was to determine the electromyographic (EMG) characteristics of experimentally induced, non-functional activity in the jaw-closing muscles of awake, behaving rats and how the EMG characteristics differed from those found under normal conditions. In the same animals, chronic EMG recordings were made prior to and following the insertion of an occlusal cap, which induced non-functional activity. A characteristic EMG pattern was found only during non-functional activity. The durations and amplitudes of the EMG bursts during this activity were significantly different statistically from those found in the same animals under normal conditions.

Animals↗
PubMed1991

A multimodal neurophysiological assessment in terminal renal failure.

A prospective multimodal neurophysiological study was conducted on 36 patients with end-stage renal failure, 16 of whom subsequently underwent renal transplantation (TR). Nerve conduction study and somatosensory evoked potentials revealed that peripheral conduction deficit, often subclinical, was the commonest abnormality, and TR resulted in substantial improvement. Visual evoked potentials demonstrated subclinical impairment, which did not improve after TR. The brainstem auditory evoked potentials were essentially normal and unaffected by TR.

Brain Stem↗
PubMed1984

A technique for recording from single neurons in the spinal cord of the awake cat.

A means of recording activity from single neurons in the spinal cord of the awake cat over periods of several weeks is described. The method combines elements of the chronically implanted well technique used in recording from supraspinal structures, with a novel method for reversibly stabilizing the vertebral column in a detachable 'outrigger' device. Between recording sessions, the animal is therefore freely mobile, its vertebral column again flexible. This preparation allows exploration of 1 cm2 of the spinal cord to all depths, and single neurons can be held for periods of 30 min to 2 h. The activity of primary afferents, intraspinal interneurons and motoneurons can be identified and their responses quantified during limb movement by combining ancillary techniques with the stabilization method.

Animals↗
PubMed1984

Defective utilization of sensory input as the basis for bradykinesia, rigidity and decreased movement repertoire in Parkinson's disease: a hypothesis.

From a review of the anatomical relationships and single unit activity in the components of the basal ganglia related to limb movement, it is concluded that the major outflow from basal ganglia circuits is via the motor cortex (area 4). Recent results of recording from area 4 neurons revealed that they preferentially "encode" the higher derivatives of movement, i.e. acceleration and jerk. In the parkinsonian (PK) patient and in the monkeys treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), EMG responses to imposed loads show a markedly increased gain of the "M2" component which depends upon the integrity of area 4 and which correlates with the severity of PK rigidity. The above observations are considered, along with those of others (demonstrating prolonged movement times, a decreased "repertoire" of voluntary movements fractionation of voluntary movements, inability in tracking movements without visual input, and failure to improve performance in PK's) in relation to a model of the interactions between sensory input and motor programs. Using this model, it is hypothesized that the above PK movement deficits, as well as rigidity, can be accounted for by abnormal processing of the mechanoreceptor sensory input utilized in the generation and execution of movements. The MPTP treated monkey is suggested as a model in which to directly test the hypothesis.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed1983

Postnatal dendritic development in motoneurons: evaluation by a Monte Carlo technique.

A Monte Carlo method was used to quantitate the dendritic characteristics of horseradish peroxidase-injected lumbar motoneurons (MNs) from kittens 44 to 73 days old (during the postnatal interval when motor cortical input/output linkages mature) and compared with those from adults. All of the 6 MNs analyzed were within the same range of somal sizes (40-61 micron) and dendritic domain volumes. However, two-dimensional distributions of dendritic diameter versus distance from the soma revealed that in the youngest MNs' (44 and 51 days) most dendritic processes (82 and 84%) were less than 2 micron in diameter, and had no dendrites greater than 5 micron. The adult MNs had large dendrites (20 and 24% were greater than 5 mu), while the kittens of intermediate age (66 and 73 days) exhibited both adult-like (6 and 13% greater than 5 micron) and immature (48 and 73% less than 2 micron) characteristics. "Hit probabilities" calculated from the Monte Carlo data suggest that immature MNs' dendrites may present denser targets per unit volume for ingrowing growth cones than adult MNs, and may facilitate the probability of contact with appropriate afferent axons.

Animals↗
PubMed1981

Descending projections to the cervical spinal cord in the developing kitten.

The distribution of neurons filled by retrograde axonal transport of horseradish peroxidase from the cervical enlargement is described in kittens prior to and following the time of appearance of mature alpha-motoneuron responses to motor cortical stimulation (at 107-111 days gestational age; about 41 days postnatally). Cortex and brainstem reconstructions of the distributions of filled neurons demonstrate a well-defined, discrete projection from cortical area 4 to spinal cord segments C3 to C8, both in mature and immature (20 and 24 days postnatal) animals. In addition, appropriate rubrospinal, reticulospinal and vestibulospinal projections were present at all ages studied.

Animals↗
PubMed1981

Comment: a schema for the interactions between motor programs and sensory input.

In this overview we utilize and extend a model, originally developed for "command interneuron" control of the generation of motor programs, to discuss the roles sensory inputs play in movement control. To provide a conceptual framework, we present a modular schematic of the motor control and sensory processing apparatus of an hypothetical nervous system. In the schematic, "subroutines" (basic units of motor programs) are seen as "playing out" through switching and sequencing networks to "driver neurons." The "driver neurons" then activate motoneurons to execute the programmed movements. Five modes of interaction between motor programs and sensory input are considered using examples from invertebrate and vertebrate neuronal circuitry. These modes of interaction occur at the following locations: (1) the "program selector," to initiate a motor program; (2) the "motor subroutine directory," advancing the program to the next subroutine; (3) the "driver neurons" and motoneurons, where the "gain" of subroutine instructions can be modulated; (4) the "motor programmer," which monitors programs in progress and provides for program development and updating; and (5) the "driver neurons" themselves, which control sensory processing by "selecting" the appropriate sensory inputs for the program in progress. Mode 5 is illustrated in more detail through a consideration of the modification of stretch receptor input by "extensor" and "flexor" command interneurones in the circuitry controlling postural movements of the crayfish abdomen.

Humans↗
PubMed1980

Synchronous development of motor cortical output to different muscles in the kitten.

Previous observations indicate that the output linkages from motor cortex (area 4) to triceps brachii motoneurons develop relatively late in the postnatal kitten. Responses in multiple, simultaneously-recorded EMG's from facial, forelimb and proximal hindlimb musculature to intracortical microstimulation appear over gestational days 107-111 (about 41 days postnatally). Thus, output from the motor cortex to alpha motoneurons develops in a synchronous, rather than a sequential manner across the area 4 homunculi.

Aging↗
PubMed1980

Sequential output-input maturation of kitten motor cortex.

Average response histograms of the responses of single cortical neurons to imposed forelimb displacements in the kitten were utilized to quantify: (1) Background activity, (2) excitatory response latency, (3) percentage responding neurons, and (4) synaptic effectiveness. Motor cortical neuronal responses to the input did not attain adult values until 55--65 days of age, while adult-like responses were found in somatosensory cortical neurons as early as 9 days postnatally. Motor cortical output to alpha-motoneurons innervating triceps brachii, as tested by intracortical and subcortical microstimulation, first appeared over an interval ranging from 37--45 days postnatally. Thus, motor cortical responses to forelimb mechanoreceptors develop after completion of the output linkages from motor cortex to forelimb motoneurons and, though the motor cortex can output at 45 days, motor cortical functions requiring somatosensory feedback cannot be operative until about 60 days. This system provides a discrete and "late" maturing model in which to study the postnatal development of neuronal networks underlying normal and abnormal motor behavior.

Afferent Pathways↗
PubMedDate not supplied

Reversal of long-latency reflexes in first dorsal interosseous during a force-tracking task.

Cutaneous reflexes in response to electrical stimulation of the index finger were recorded from first dorsal interosseous (1DI) at specified force levels under three conditions: during a static posture and during the incremental and decremental phases of a sinusoidal, force-tracking task. Under static conditions, while 1DI generated a steady force [10, 20 or 30% maximum voluntary contraction (MVC)], four reflex components could be identified: E1, I1, E2 and I2. The amplitudes of these components were measured as the subjects tracked a 0.5 Hz sine wave by gradually changing the force output of 1DI between zero and 40% MVC. E1 and I1 showed minimal changes from the static condition, while activity during the E2 period was inhibitory during the incremental phase and excitatory during the decremental phase of tracking. Abrupt switching from inhibition to excitation during the E2 period occurred around the transition from incremental to decremental force. Activity during the I2 period was less markedly modulated than that during E2. Reflex reversal during the E2 interval may function to reduce the rate of change of force under conditions requiring precise force-control.

Adolescent↗