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Biomedical subjects

J C Montgomery

Publications and source records attributed to J C Montgomery.

At least 55 records · Page 3Linked to original sources
PubMed1985

Projection of secondary vestibular neurons to the abducens nucleus in the carpet shark Cephaloscyllium isabella.

The abducens nucleus in carpet sharks is not a discrete delimited nucleus, as the dendrites of the motoneurons extend into the reticular formation and the medial longitudinal fasciculus. Injections of horseradish peroxidase (HRP) designed to trace the inputs to these neurons are therefore difficult to confine to this system alone. Despite this problem a consistent finding from injection of HRP in the area of the abducens nucleus is the retrograde labelling of a column of cells in the contralateral octaval nuclei. The column of cells is predominantly in the ventral portion of the descending octaval nucleus, but does straddle the entrance of nerve VIII, extending into the caudal part of the ascending octaval nucleus. Labelled cells correspond in location and morphology to those cells receiving input from horizontal canal afferent fibers, confirming the trineuronal nature of the horizontal vestibulo-ocular reflex arc in elasmobranch fishes.

Abducens Nerve↗
PubMed1985

Oculomotor function at low temperature: antarctic versus temperate fish.

The peripheral oculomotor system can be modelled as a first order linear system (Montgomery, 1983), and hence specified by its characteristic frequency and 'd.c.' gain. These parameters can be determined by recording eye movements produced by stimulation of the abducens nerve with sinusoidally modulated pulse trains, and compare well with those independently derived from the relationship between motoneurone firing and spontaneous eye movement. Characteristic frequency and gain of the peripheral oculomotor system were determined for two species of antarctic teleost and one temperate species, to examine temperature compensation within a complete motor output pathway. Compared with low temperature function in temperate fish, the characteristic frequency is clearly temperature compensated in antarctic fish, which explains in part the observed temperature compensation of their rapid eye movement. The 'd.c.' gain of the peripheral oculomotor system is inversely related to temperature, providing an automatic compensation for possible reductions in central nervous system output and sensory gain at low temperature.

Animals↗
PubMed1984

Volunteers.

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Female↗
PubMed1984

The structure of the external rectus eye muscles of the carpet shark Cephaloscyllium isabella.

The external rectus muscles of the carpet shark Cephaloscyllium isabella contain two types of muscle fibre. A core of large white fibres which have regular myofibrils with extensive sarcoplasmic reticulum, triads located at the Z disc and a pronounced H band and M line. Mitochondria are frequent but tend to be smaller and less abundant than mitochondria of the smaller red fibre type. The red fibres which surround the central region are rich in mitochondria, have little sarcoplasmic reticulum and triads which are infrequent and dispersed. Sarcomere banding of red fibres is characterised by a faint H band and M line while the Z disc is thick in comparison with that found on the white muscle fibre sarcomere.

Animals↗
PubMed1983

Central projections of vestibular afferents from the horizontal semicircular canal in the carpet shark Cephaloscyllium isabella.

This study utilizes anterograde axonal transport of cobaltous-lysine and conventional silver-staining techniques to study the central projections of the horizontal semicircular canal branch of the VIII nerve within the vestibular nuclei of the carpet shark Cephaloscyllium isabella. Two major terminating axon fields were observed, one caudal and one rostral to the entrance of the VIII nerve, corresponding to the ventral vestibular nucleus and superior vestibular nucleus, respectively. Both fields appear to be located within the ventral portion of the nuclei indicating an apparent subdivision of the VIII nerve projections within the brainstem. The resolution of the sensitive cobalt tracer indicates the presence of both dendritic and pericellular termination of these primary afferent fibres. In the area immediately caudal to the entrance of the VIII nerve a number of labelled primary afferent fibres project to the ventral region of the intermediate nucleus. Other fibres follow the visceral sensory root VII and terminate proximal to the sulcus limitans of His within the dendritic field of the neurons of the nucleus magnocellularis. Some fibres turn ventromedially from the main group of the ascending fibres and terminate in the area of the inferior reticular formation.

Afferent Pathways↗
PubMed1983

The abducens nucleus in the carpet shark Cephaloscyllium isabella.

This study utilizes retrograde axonal transport of cobaltous-lysine, and conventional silver and Golgi staining techniques to study the abducens motor nucleus innervating the external rectus muscle of the carpet shark. The nucleus consists of 300-400 motoneurons located immediately ventrolateral to the medial longitudinal fasciculus (MLF), distributed over about 1.25 mm in a rostrocaudal direction at the level of exit of the VI nerve. The axons of the motoneurons form seven or eight discrete ventrally directed fascicles which, having exited from the brainstem, group together to form the abducens (VI) nerve. The motoneurons are on average about 16 micron in diameter, are bipolar, and their dendrites have a transverse orientation. Typically one set of dendrites penetrates the MLF and the other set extends ventrally into the reticular formation.

Abducens Nerve↗
PubMed1983

The effects of lowered temperature on spontaneous eye movements in a teleost fish.

A new opto-electronic method has been used to measure spontaneous eye movements in a lightly restrained unanaesthetized marine teleost fish (Parore). The normal scanning pattern of eye movement is similar to that previously described in goldfish. The effects of cooling on eye movements were investigated by 2 degrees C step changes down from ambient temperature (13-14 degrees C). Lowered temperature altered the scanning pattern, decreased saccade velocity, increased mean saccade amplitude and impaired the ability of the fish to hold the eye stationary between saccades. All eye movements stopped at temperatures around 6 degrees C, but could be restored by subsequent warming.

Animals↗
PubMed1983

Eye movement dynamics in the dogfish.

A method is described of obtaining the relationship between electrical stimulation of the abducens nerve and horizontal eye movement in the dogfish. The stump of the VIth nerve was stimulated intracranially in a fish in which the brain had been removed, but in which the circulation remained intact, and the gills were perfused with sea water. Horizontal rotation of the eye was monitored with an opto-electronic movement detector. Eye rotation was linearly related to stimulus frequency in the 0-20 Hz range, and was maximal at frequencies above 40 Hz. Stimulation of the VIth nerve, with a pulse train whose frequency was modulated sinusoidally between 0 and 20 Hz, produced sinusoidal eye movements. The frequency response of the system approximates a first order low pass filter with a characteristic frequency of 0.23 Hz, and an additional phase lag equivalent to a time delay of approximately 50 ms.

Abducens Nerve↗
PubMed1982

Community and job satisfactions: an argument for reciprocal influence based on the principle of stimulus generalization.

The principle of stimulus generalization provided the underlying argument for a test of hypotheses regarding the association of community and job satisfactions and a critique of related theory and research. Two-stage least squares (2SLS) analysis made possible the examination of reciprocal causation, a notion inherent in the theoretical argument. Data were obtained from 276 employees of a Western U.S. coal mine as part of a work attitudes survey. The 2SLS analysis indicated a significant impact of community satisfaction on job satisfaction and an effect of borderline significance of job on community satisfaction. Theory-based correlational comparisons were made on groups of employees residing in four distinct communities, high and low tenure groups, males and females, and different levels in the mine's hierarchy. The pattern of correlations was generally consistent with predictions, but significance tests for differences yielded equivocal support. When considered in the context of previous studies, the data upheld a reciprocal causal model and the explanatory principle of stimulus generalization for understanding the relation of community and job satisfactions. Sample characteristics necessitate cautious interpretation and the model per se might best be viewed as a heuristic framework for more definitive research.

Adult↗
PubMed1982

Functional organization of the dogfish vestibulocerebellum.

Electrophysiological and light microscopical studies were made on the dogfish vestibulocerebellum. The cell types, estimates of their numbers, and the organization of this part of the cerebellum are described and compared with the other lobes of the elasmobranch cerebellum. Electrophysiological study of the inputs to this region from the VIIIth nerves indicates that primary afferent fibres from the VIIIth nerve project to the ipsilateral granule cell layer.

Afferent Pathways↗
PubMed1981

Origin of the parallel fibers in the cerebellar crest overlying the intermediate nucleus of the elasmobranch hindbrain.

This study utilizes anterograde transport of horseradish peroxidase (HRP), Golgi staining, and electrophysiological techniques to demonstrate the origin of the parallel fibers which constitute the molecular layer overlying the intermediate nucleus of the dogfish hindbrain. The parallel fibers are shown to arise from granule cells of the auricle. The majority come from the granular area of the lower leaf of the auricles, which is termed the lateral granule cell area of the auricle. A band of parallel fibers at the ventrolateral extent of the molecular layer arises from the ipsilateral and contralateral granule cell layers of the upper leaf of the auricle. The functional continuity of the molecular layer between vestibular and lateral-liner areas may provide an additional basis for interactions between these two sense modalities.

Action Potentials↗
PubMed1981

A Vibrio cholerae infection in a transient teamster.

An illness indistinguishable clinically from classical cholera but caused by a non-cholera vibrio occurred in an over-the-road truck driver. The infecting organism was not finally identified as Vibrio cholera, Smith serotype 113 toxin positive, until 4 weeks after his hospital discharge. Hospital laboratories in most parts of the United States are unlikely to identify Vibrio cholerae in stool cultures unless specifically requested to do so. If one recognizes the chronic cholera carriers have been documented, that small epidemics do occur in unlikely places, and the lack of evidence that toxigenic V. cholerae 01 differs from toxigenic V. cholerae non-01 in these two respects, then the potential for epidemics in the United States is real.

Cholera↗
PubMed1979

Organization of vestibular afferents to the vestibular nuclei of the dogfish.

Electrophysiological and light microscopical studies were made on the vestibular area of the dogfish hindbrain. Three vestibular nuclei were distinguished: the superior nucleus (VES), the magnocellularis nucleus (VEM), and the ventral nucleus (VEV). The distribution of field potentials evoked in the hindbrain by stimulation of nerve VIII confirms the location and extent of the vestibular nuclei. It also raises the possibility of a direct contralateral projection of vestibular nerve fibres. Unit studies confirm the interpretation of the field potentials and provide evidence of mono- and polysynaptic activation of vestibular nuclear neurons by vestibular afferents.

Animals↗