Biomedical subjects
Publications and source records attributed to J Kimm.
We present the case of a 23-year-old woman with cerebrospinal fluid eosinophilia and myelopathy caused by Toxocara canis and describe the clinical and thoracic MR findings. An enhancing thoracic spinal cord lesion which was shown on MR resolved after an interval of 140 days with partial resolution of the patient's symptoms.
We observed several differences between the dynamics of the vestibulo-ocular reflex (VOR) in rabbits and in human subjects. In the rabbit the "apparent time constant" (time required for the slow phase velocity to reach 37% of the initial value) of postrotatory nystagmus (PRN) increased and the low-frequency phase lead of sinusoidal perrotatory nystagmus decreased with increasing stimulus velocity. In human subjects these measurements did not change with stimulus velocity (for the range of 15 to 120 deg/s). The pattern of PRN decay in the rabbit usually appeared linear whereas in human subjects the decay was usually exponential. After the largest stimulus (120 deg/s) PRN reversals occurred in human subjects but not in rabbits. These differences can be explained on the basis of a simple nonlinearity (saturation of a feedback pathway) present in the rabbit but not in the human VOR.
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Intracellular recordings were made in the VIIIth nerve of the bullfrog (Rana catesbiana) to measure the membrane characteristics and obtain records of spontaneous and evoked spike activity of primary semicircular canal afferents. Physiological stimulation of the canals was achieved by rotating the preparation on a servomotor driven turntable with the animals' head centered in the rotational axis. The responses of each neuron to sinusoidal rotations at frequencies of 0.05Hz, 0.5Hz and for impulsive accelerations of 400 deg/sec2 were obtained. Membrane characteristics measured included the cell resting and action potential amplitude, and spike-activation threshold for applied currents. Physiologically characterized neurons were injected with horseradish peroxidase by applying pneumatic pressure and/or iontophoretic currents to the micropipettes containing 5% HRP in 1 M KCI. Following survival times of 12--48 h, the VIIIth nerve and attached vestibular end organ was removed for histochemical processing using a diaminobenzidine procedure to visualize the HRP reaction product. Light microscopy was used to discern the anatomical features of the neurons and to trace their peripheral dendritic trajectories from the ganglion to their termination(s) in the crista. Our studies have revealed that the bullfrog's primary vestibular afferents are characterized by a broad range of soma and axon diameters which correspond to an equally broad range of spontaneous and evoked activity characteristics. The largest neurons had more irregular spontaneous firing rates and consistently exhibited the greatest gain and smallest phase shifts with respect to head acceleration. These neurons consistently terminated at or near the central region of the crista. On the other hand, the smallest neurons were characterized by having the most regular spontaneous discharge patterns, the lowest gains, and greatest phase shifts with respect to head acceleration. Our findings are thus consistent with the view that the anatomical features of the primary vestibular neurons are important in determining the neuron's physiological characteristics. In terms of response dynamics our observations indicate that the receptors in the frog's crista ampullaris are heterogeneous and differentially sensitive to a wide range of stimulus frequencies.
We performed a brainstem evoked response (BSER) study to evaluate the extent to which electrical stimulation of the cochlea was conducted centrally by facial, vestibular, and cochlear nerves. Short-term experiments were performed in three monkeys: via a postauricular approach to the round window, a molded Silastic multielectrode prosthesis was placed in the scala tympani. The BSER was recorded to threshold and suprathreshold biphasic electrical pulses delivered to the implant electrodes. A middle cranial fossa dissection was then carried out, exposing the nerves of the internal auditory canal from above. Facial and vestibular neurotomy had no significant effect on BSER, while cochlear nerve section abolished the response. In one animal, blunt pressure on the cochlear nerve caused a reversible loss of electrically evoked BSER. Electrically evoked BSER probably depends on propagated impulses in the cochlear nerve.
Auditory thresholds were determined in rabbits by a classically conditioned nicitating membrane response established with a tone-conditioned stimulus and a shock-unconditioned stimulus. The audiograms obtained were comparable in shape and sensitivity to threshold curves measured for a variety of small mammals by other conditioning techniques. This procedure provides a quick and efficient method for measuring hearing sensitivity in a restrained preparation that permits precise stimulus control as well as providing an ideal situation for a variety of physiological studies of hearing in an awake, behaving animal.
Hyperactive vestibular response in a patient was documented with electronystagmography (ENG). The patient's symptoms were relieved for a year following placement of a shunt from the saccus endolymphaticus to the subarachnoid space. Recurring symptoms were relieved for three years by cryosurgery to the hyperactive labyrinth. Activity of the involved labyrinth was shown on electronystagmography to be hyperactive when the patient was symptomatic and normal or hypoactive when the patient was asymptomatic.
The effect of electrical stimulation of the cochlea on vestibular response was monitored in six rhesus monkeys. Eye movements and single-unit activity from the vestibular portion of the eighth nerve, vestibular nuclei, reticular formation, and abducens nucleus were observed while electrical stimulation was delivered through an implanted cochlear prosthesis. In one animal of this series, neural activity from the inferior colliculus and cochlear nuclear complex was also recorded. Electrical stimulation elicited eye-movement responses in only one animal. In the animals from which single-unit activity was recorded, no positive vestibular effects were noted. In one animal of this study, responses were elicited from auditory structures by relatively low intensities of electrical stimulation.
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Single units in the brain stem were recorded in the awake monkey during concomitant adequate vestibular stimulation, eye movement, and electrical stimulation of the fastigial nucleus in areas that produce short-latency horizontal saccades. Forty-eight percent of the recorded brain stem cells were associated with eye movements; 40% respond only to head rotation; and the remainder are unrelated to either. The activity of the majority of the eye movement-related cells was similar for spontaneously and fastigially evoked saccades. The activity of the head rotation and unrelated cells show no consistent relationship to fastigial stimulation.
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1. The activity of single units in the vestibular nerve was recorded in alert monkeys in stationary positions and during horizontal sinusoidal angular rotations at frequencies from 0.10 to 4.0 Hz. 2. All units encountered had a spontaneous discharge rate which varied from 48.61 to 178.25 spikes/sec. The regularity of firing for each unit also varied. 3. To ipsilateral rotation of the animal the units responded with an increase in firing rate. Rotations in the opposite direction decreased the firing rate relative to the spontaneous discharge rate. The unit response was indicative of imposed velocity rather than acceleration or position. The harmonic distortion of the unit response was not a function of frequency of oscillation. For 43 units at 0.78 Hz the harmonic distortion averaged 23.9%. 4. There was some correlation between the regularity of spontaneous discharge of each unit and the degree of diminished phase lag at higher frequencies of oscillation. Those units with the most irregular spontaneous discharge patterns were most likely to exhibit a diminishing phase lag re:acceleration as frequency of oscillation increased beyond 0.5 Hz. 5. No unit activity related to eye movements was encountered in the vestibular nerve.
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Single units were recorded from the vestibular nuclei of unanesthetized monkeys that were rotated in the horizontal plane while simultaneously pressing individual buttons in a controlled array which turned with hem. Using this behavioral paradigm, it was possible to 1) determine the relationship of unit discharge to eye movements measured by the DC-coupled electrooculogram and calibrated by the button-press task, and 2) determine the relationship of unit discharge to horizontal acceleration, either with or without the compensatory eye movements evoked by vestibular stimulation. Based on their responses during vestibular stimulation and/or eye movements, neurons in the vestibular nuclei (77% of our sample was in the medial nucleus) could be divided into four groups...