[Integrated medical practice. Which models make sense?].
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Germany↗
Biomedical subjects
W Plassmann
Publications and source records attributed to W Plassmann.
Vestibular responses of flocculus and vestibular nuclei neurons in mice (B6CBA). Variation of stimulus amplitude and frequency.
Vestibular nuclei (Vn) neurons and floccular Purkinje (P) cells of unanesthetized paralyzed mice (B6CBA) responding to horizontal angular acceleration in the dark (type I and type II neurons) were studied by extracellular recordings with micropipettes while varying either the frequency (and velocity) or the amplitude (and velocity) of the sinusoidal rotation, keeping the respective third parameter constant. Phase and sensitivity were analyzed by a Fourier analysis and a "best sine fitting" program. Recording sites were localized by means of small iontophoretically applied horseradish peroxidase markings. The neuronal response amplitude at fundamental frequency (determined from peristimulus time histograms) increased with the frequency and amplitude of the sinusoidal rotation for both Vn and floccular neurons (0.05-0.5 Hz; +/- 60 degrees amplitude). Stimulus frequency/response amplitude and stimulus amplitude/response amplitude curves of floccular neurons were distinctly lower in magnitude than those of Vn neurons (P < 0.01) Accordingly, the sensitivity (re velocity) curves of Vn neurons and P cells differed in magnitude significantly (decreasing slightly with increasing stimulus frequency and amplitude in Vn neurons and more or less independent of stimulus parameters in floccular P cells). Response amplitudes of type I and type II neurons did not differ from each other. Phase advance relative to head angular velocity in the midfrequency range in Vn neurons was very small, indicating a head velocity signal carried by the Vn neurons. In floccular P cells phase advance was only small at 0.1 Hz (amplitude +/- 35 degrees), but increased with augmenting frequency to 140 degrees at 0.5 Hz. With a constant stimulus frequency (0.3 Hz) and varied stimulus amplitude, phase advance was 90 degrees at +/- 20 degrees amplitude and 60 degrees amplitude. Data are shown for the first time in which both the stimulus frequency and the stimulus amplitude have been varied in the same species and in the same neurons. The results demonstrate that the single data are in general well within the range of those found in other species, but they demonstrate further that phase behavior is dependent on the stimulus paradigm. The data provide the basis for comparative studies with mutant mice.
Animals↗
Low-frequency sensitivity in a gerbilline rodent, Pachyuromys duprasi.
The contribution of the bulla to low-frequency hearing capability was studied in the gerbilline rodent Pachyuromys duprasi. In the frequency range of 0.6-3 kHz, the sound pressure behind the tympanic membrane is higher than the pressure in the meatus acusticus externus near the eardrum. Gradual augmentation of frequencies above 0.6 kHz gives rise to steadily increasing phase lag in the bulla relative to that in the meatus. Severing of the incudostapedial joint yields results indicating that the phase difference between meatus and bulla is caused by resonance properties of the bulla and resistance in the cochlea. Both destruction of the bulla and stiffening of the pars flaccida tympani lead to a sound pressure decrease in the frequency range around 2 kHz. This drop is accompanied by an amplitude decrease of the same magnitude in the cochlear microphonic potentials. These results support the hypothesis that the bulla functions like a Helmholtz resonator in the frequency range of 1-3 kHz, improving sound transduction to the cochlea. These experimental findings, in conjunction with theoretical considerations involving bulla volume, orifice area of the resonator, and resonance frequency of the bulla, suggest that the theoretically required area of the resonator's orifice is, in fact, of the same magnitude as the area of the pars flaccida tympani. The middle-ear system of P. duprasi thus consists of a resonating bulla in which the area of the pars flaccida tympani constitutes the resonator's opening towards the meatus and in which the pars tensa tympani functions as a pressure gradient receiver, due to phase differences caused by the resistance of the cochlea and by the resonance properties of the bulla. By these functional principles the peripheral auditory system of P. duprasi is capable of low-frequency perception despite the smallness of its structures. The middle ear in P. duprasi thus represents a prime example of a strategy: the dimensional constraints derived from a general bauplan for the peripheral auditory system have here been overcome.
Animals↗
Electrosensory activity in the telencephalon of the axolotl.
Electrical shock of the anterior lateral line nerve evokes slow wave potentials in the contralateral corpus striatum and bilaterally in the medial pallium of the telencephalon of axolotls. The onset latency of the evoked response in the medial pallium (70 ms) is considerably longer than that of the corpus striatum (46 ms). Quasi-natural stimuli, such as weak uniform electric fields (100 microV/cm) or water drops striking the surface of the water surrounding the axolotls elicited evoked potentials or multiple unit activity in the corpus striatum but not in the medial pallium. Striatal responses to weak electric fields have a threshold of approximately 50 microV/cm and habituate at rates higher than 1 every 10 s. Multiple-unit responses in the medial pallium were elicited only by gentle strokes to the snout with a brush, and it is possible that trigeminal fibers were inadvertently stimulated in the nerve shock cases. The discovery that the corpus striatum is a major telencephalic target of electrosensory information rather than the medial pallium as reported in elasmobranch fishes, suggests that there are additional electrosensory telencephalic centers in elasmobranchs and/or that homologous nuclei of the midbrain or thalamus have evolved different projections.
Action Potentials↗
The cochlea in gerbilline rodents.
The inner ears of 5 different gerbil species are compared on the basis of cochlear microphonic recordings, serial sections and computerized quantitative reconstructions of the cochleae and their specific morphological structures. The hearing range of most gerbils is below 20 kHz. Some species are extremely sensitive in the frequency range of 1-4 kHz. This special sensitivity is reflected in, among other features, the following cochlear structures and their suggested functions: (1) the rapid width increase of the basilar membrane in the basal portion of the cochlea provides additional space for the representation of lower frequencies at the expense of higher frequencies; (2) the large hyaline mass and the cells of Claudius and Hensen in the medial and apical portions of the cochlea influence the vibratory properties of the cochlear partition, and (3) the specialized structures of the cochlea may be an adaptation to the acoustical environment in arid habitats.
Adaptation, Biological↗
Coding of amplitude-modulated tones in the central auditory system of catfish.
In the catfish central acoustic system information is coded by two subsets of units. Type I units show little or no adaptation, type II units adapt rapidly, and some units are transitional, showing moderate adaptation. The two groups of units also respond differently when exposed to sinusoidal amplitude modulation of the signal's carrier frequency. The tonic, less readily adapting type I units code over an intensity range of about 30 dB, are fairly insensitive to intensity changes, and follow stimulus envelopes of 60 Hz and less. They apparently discharge in response to the actual intensity of the signal rather than in response to something in its temporal pattern. The onset-sensitive, fast-adapting type II units on the other hand are restricted to an intensity range of only 10 dB, show greater sensitivity to intensity changes, and are capable of following the temporal pattern of amplitude-modulated stimuli exceeding 100 Hz. These units appear to code the temporal changes in the stimulus intensity irrespective of the absolute intensity of the signal.
Adaptation, Physiological↗
Sensory modality interdependence in the octaval system of an elasmobranch.
Vibration-sensitive units with labyrinth input are studied in the medullary magnocellular region, and in the mesencephalic torus semicircularis and oculomotor nucleus of the thornback ray. Neuronal activity is recorded during delivery of vibratory and acoustic stimuli, and during presentation of static tilt and sinusoidal pitch movement. These stimulation procedures are subsequently combined in order to gain some insight into the potential biological function of these units. The units described fall into three categories. The first group (called VIB I) are highly sensitive to vibration. They project to the torus semicircularis and are probably activated by the macula neglecta. Their responses to vibratory shocks or acoustic click sounds are not affected by simultaneous presentation of static tilt or movement of pitch. However, if exposed to a background of vibration, these units yield responses phase-locked to sinusoidal pitch; they respond poorly to pitch alone or even fail to do so at all without simultaneous delivery of vibration. Since it is uncertain exactly which natural stimuli excite these units, their biological function is still unclear. The units of the second group (VIB II) are less sensitive to vibration, project to the oculomotor nucleus, and possibly receive input from the anterior two thirds of the macula sacculi and/or the lacinia utriculi. The units respond to both tilt and pitch, provided that continuous vibration is delivered at the same time. Unlike the preceding class, their responses to vibratory bursts and acoustic clicks are suppressed during presentation of pitch and static tilt. It is suggested that this type of unit is more likely to be used for vestibular input of tilt and pitch rather than for vibratory and acoustic information. The third group of units (VIB III) is least sensitive to vibration. These units appear to receive input from the macula utriculi and/or the posterior third of the macula sacculi. They discharge poorly during vibratory stimulation, and are able to respond to pitch even without simultaneous delivery of vibration. Their responses to vibratory stimulation are enhanced by static tilt. Apparently, these units are involved in the processing of vestibular input.
Animals↗
Central projections of the octaval system in the thornback ray Platyrhinoidis triseriata.
Octaval nerve centers are studied at medullary and mesencephalic levels after electrical stimulation of the VIIIth nerve and selected brain areas. Recording of evoked potentials shows that primary afferent input is relayed to the anterior, magnocellular, and descending octaval nuclei in the medulla as well as to the cerebellar auricle. The three medullary nuclei project to their contralateral homologues via second-order commissural fibers. Both the ipsi- and contralateral anterior and magnocellular nuclei pass on information via secondary neurons to the oculomotor area and the torus semicircularis in the midbrain.
Animals↗