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  • 1
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A transmission electron microscope operating with a cold field emission source has been modified to facilitate differential phase contrast mapping and applied to the observation of microscopic magnetic features appearing in recorded longitudinal media. After describing the design and performance of the scanning Lorentz electron microscope, as we call it, results on the observation of bit patterns delineated on Co-based sputtered longitudinal media are presented. Relations of observed bit profiles to macroscopic magnetic properties of media and to device performance are discussed. Then, magnetization fluctuation on a scale of magnetic crystallites constituting the medium is examined. Also given is an account of a stray field effect inherent in hard magnetic materials.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 81 (1990), S. 581-588 
    ISSN: 1432-1106
    Keywords: Dorsal cochlear nucleus ; Microiontophoretic application ; GABA sensitive neuron ; Single unit Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary It is well known that the superficial layers of the dorsal cochlear nucleus (DCN) are rich in GABAergic neurons. We investigated the effects of topical application of GABA receptor agonists and/or antagonists upon the auditory response properties of DCN neurons in rats anesthetized with alpha chloralose-urethane. Auditory stimuli consisted of 20 ms tone bursts presented in a free field. Response properties of DCN neurons were studied before and during iontophoretic application of GABA, bicuculline methiodide (BIC) and muscimol (MUS) alone and GABA with MUS or BIC through triple barrel electrodes glued to the recording microelectrode. Of 68 DCN neurons studied, 27 were sensitive to topical application of the GABA agonists or antagonist. In these neurons, BIC enhanced spontaneous activity as well as auditory responses and decreased the Q-30 quality factor values. MUS reduced auditory responses. BIC often increased the width of the tuning curve but GABA and/or MUS reduced it. Without drug application, GABA sensitive neurons tended to have longer response latencies and larger tuning widths at 30 dB above threshold as well as larger Q-30 values as compared with neurons that were insensitive to GABA. These findings suggest that: 1) GABAergic neurons determine the width of the tuning curve in neurons with GABA receptors by curtailing the excitatory response area, and 2) such neurons receive tonic inhibition from intrinsic GABAergic neurons.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 50 (1983), S. 359-366 
    ISSN: 1432-1106
    Keywords: Ambiguous motoneurons ; Ultrasonic vocalization ; Unitary discharges ; Respiration ; Ventral division
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Unit discharges associated with ultrasonic vocalization were recorded from the rat medullary region including the nucleus ambiguous (NA). Three types of units were distinguished: ultrasound-related (US), expiration (EXP) and inspiration (INSP) units. Both US and EXP units discharged with tonic bursts mostly prior to ultrasounds. US units were silent during respiration while EXP units discharged synchronously with expiration. During ultrasonic vocalization INSP units suppressed their discharges which were otherwise synchronized with inspiration. Histological examination revealed that US and EXP units were recorded from the ventral division of the NA and the adjacent medullary region where the NA contained large cells and the adjacent region consisted of small cells. These results suggest that both US and EXP units are NA motoneurons responsible for ultrasound emission. EXP units were always supplied with respiratory afferents while US units were not.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 75 (1989), S. 381-389 
    ISSN: 1432-1106
    Keywords: Dorsal cochlear nucleus ; Tonotopical organization ; Unitary discharges ; Sidebands ; Pure tone burst ; Rats
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Pure tone burst stimulation was used to study discharge properties and tonotopic organization in the dorsal cochlear nucleus (DCN) of rats anesthetized with alpha-chloralose urethane. An animal's head was fixed with a fine nail embedded in the skull in order to prevent the head from moving. Unit discharges of DCN neurons were recorded with micropipettes filled with fast green dye. Free field pure tone bursts were presented using a ribbon tweeter; it delivered stimuli at a maximum SPL of 96 dB. Electrode tracks were reconstructed through subsequent histological examinations. A total of 429 units were sampled in 51 animals. Of these, 230 units (54%) responded to tone bursts higher than 20 kHz with a mean latency of 6.3 ms. Tonotopical organization was clearly evident throughout the mediolateral axis of the DCN; high frequencies were represented medially and low frequencies laterally. Nearly constant frequencies were represented along the dorsoventral axis and no systematic organization was observed along the rostrocaudal extension of the DCN. When tuning curves were measured in DCN neurons with excitatory and inhibitory responses, we found that inhibitory sidebands were usually located in a frequency range higher or lower than the excitatory response area and sometimes partially overlapped with it.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1432-1106
    Keywords: Nucleus ambiguus ; Oropharyngeal swallow ; Vocalization ; Ventral medullary swallowing center ; Larynx ; Monkey
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Extracellular recordings were made from the nucleus ambiguus in three conscious Macaca nemestrina monkeys during spontaneous vocalizations and swallows. The temporal relationship of neuronal activity to swallowing was inferred through correlation with the thyroarytenoid electromyographic (EMG) activity. Videofluoroscopic analysis of a fourth monkey during swallows of barium-impregnated fruit juice established the temporal relationship between swallowing and thyroarytenoid EMG activity. Of 691 cells recorded from the nucleus ambiguus and its adjacent area, the neuronal activity of 80 cells showed modulation during swallowing. Sixty-two cells were classified as “active” cells, with increased activity in relation to swallowing, while 18 cells were classified as “suppressed” cells, with tonic activity that reduced with swallowing. A continuum of latency was seen between the onset of modulation of these cells and the onset of swallowing, from “early” before the swallow to “late” after the swallow onset with most of the cells (44 cells) showing modulation near the onset of the swallow. A majority (37) of the 62 active swallowing-related cells also discharged with vocalization, but they demonstrated a lower discharge frequency and a longer burst duration during swallowing. Of the 18 suppressed swallowing-related cells, 11 cells discharged phasically with the respiratory cycle and may be a part of the ventral medullary respiratory center. This chronic awake primate model would preserve the many sensory inputs that may modify the oropharyngeal swallow and may better approximate human physiology.
    Type of Medium: Electronic Resource
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