Summating potential (SP) tuning curves (original) (raw)
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Electrophysiological measurements of the stria vascularis potentials in vivo
Hearing Research, 1987
Glass microelectrodes were introduced into the stria vascularis (SV) to measure the DC potential profile of the SV in vivo from its apical as well as basal side. The K+ concentration gradient in the lateral cochlear wall was measured by means of double barrel K+-selective microelectrodes. A positive potential 10.4* 6.3 mV higher than the endocochlear potential (EP) was found in the SV. In noise-exposed animals the positive potential found in the SV was 14.6k7.2 mV higher than the EP. K+ concentration observed during penetration into the SV was in the range of 50-100 mmol/l. Simultaneous measurement of the DC positive potential in the SV and EP showed a nearly parallel time course during anoxia with a tendency to increase the difference between the SV potential and the EP. The difference reached approximately 30 mV 20 min after the beginning of anoxia. It may be assumed that the electrogenic pump localized at the basolateral membrane of the marginal cell (MC) is a source of the positive potential inside the MC and is hence a source of the potential drop across the luminal side of the MC membrane. endocochlear potential, stria vascularis, basolateral membrane of marginal cell, electrogenic pump, noise, co&ear model
Positive endocochlear potential: Mechanism of production by marginal cells of stria vascularis
Hearing Research, 1987
The positive endocochlear potential (EP+) and high K+ concentration of the endolymph in the scala media of the mammalian cochlea are unusual. They have long been assumed to be due to a putative K-pump in the luminal membrane of the marginal cells of the stria vascularis, which were believed to have a negative internal potential. We show that the cell potential is more positive than the EP+, and that the ion pump is conventional Na,K-ATPase, probably in the basolateral membrane. The latter was determined from experiments in which the ionic environment of the strial cells was controlled by perfusion of the perilymphatic space of the cochlea, in the absence of vascular circulation.
Response of EP and cochlear blood flow to angiotensin II during hypoxic condition
Auris Nasus Larynx, 1998
To understand the importance of oxygen transport to the inner ear tissue, we studied, using guinea pigs, the relationship between endocochlear DC potential (EP) and cochlear blood flow (CoBF) under hypoxic conditions. 33 guinea pigs weighing 200-400 g were used. EP and CoBF were recorded from the basal turn of the cochlea. Hypoxia (10 min) was induced by inspiring a mixture gas (2-10% oxygen in nitrogen). By inducing hypoxia, the EP declined to a intermediate level of the positive range in a few minutes. In the midpoint of 10-min loading of hypoxia, Angiotensin II (1 vg/kg, 1 ml/kg) was infused in 60 s, resulting in raising of systemic blood pressure (BP). Responding to this, CoBF and EP showed generally transient elevations (DCoBF, DEP) in accordance with BP change. Obtained data were analyzed for the value of DEP/DCoBF, which means the sensitivity of EP to CoBF change. Distribution of the value of DEP/DCoBF was found to be in a correlation with the EP level just before Angiotensin II infusion (EPi). That is, the sensitivity of EP to CoBF change became greater as a intermediate level of EP (EPi) was lowered in the range from 70 to 100% of EPi. Among several factors, we thought the hyperactivity of glycolysis in the stria vascularis may occur in such a mild hypoxemic condition. In addition to this, it could be presumable that cyclic AMP in the stria vascularis may increase by the sympathetic stimulation during hypoxemia, and increased cyclic AMP may produce more EP with a given O 2 consumption.
A Model for Research on Cochlear Hypoxia
Laryngoscope, 1983
The vessels emerging from one side of the basilar artery are supplied exclusively by the homolateral vertebral artery. Since blood flow is laminar through the vertebrobasilar system, mixing between two sides does not normally occur. Based on this fact, an experi• mental model for research on cochlear hypoxia is proposed and described. The animal's own blood flow In the vertebral artery ls com• pletely replaced by a stream of poorly oxygenated blood injected retrogradely through the ipsilateral axillary artery. In this way, the territory supplied by the vessels emerging from this side of the basilar artery, including the ear, is rendered hypoxic. The changes in the cochlear action potentials induced by the reduced oxygen supply are recorded by a chronically implanted electrode and analyzed. An experimental model for research on cochlear hypoxia should take into consideration two aspects of the problem: 1. The method of reducing the oxygen supply to the ear; 2. The parameter chosen to objectivate the induced cochlear hypoxia. A long chain of events bring oxygen from the air to the tissue and to the mytochondria of the cells. These provide opportunities for the development of models for the study of the effects of oxygenation, but an ideal model has yet to be described. The requirements are numerous and difficult to procedure. The important ones are:
Hearing Research, 1998
The effects of changes in perilymphatic tonicity on the semicircular canal were investigated by combining the measurements of transepithelial potential and endolymphatic ionic composition in the isolated frog posterior canal with the electrophysiological assessment of synaptic activity and sensory spike firing at the posterior canal in the isolated intact labyrinth. In the isolated posterior canal, the endolymph was replaced by an endolymph-like solution of known composition, in the presence of basolateral perilymphlike solutions of normal (230 mosmol/kg), reduced (105 mosmol/kg, low NaCl) or increased osmolality (550 mosmol/kg, Na-Gluconate added). Altered perilymphatic tonicity did not produce significant changes in endolymphatic ionic concentrations during up to 5 min. In the presence of hypotonic perilymph, decreased osmolality, K and Cl concentrations were observed at 10 min. In the presence of hypertonic perilymph, the endolymphatic osmolality began to increase at 5 min and by 10 min Na concentration had also significantly increased. On decreasing the tonicity of the external solution an immediate decline was observed in transepithelial potential, whereas hypertonicity produced the opposite effect. In the intact frog labyrinth, mEPSPs and spike potentials were recorded from single fibers of the posterior nerve in normal Ringer's (240 mosmol/kg) as well as in solutions with modified tonicity. Hypotonic solutions consistently decreased and hypertonic solutions consistently increased mEPSP and spike frequencies, independent of the species whose concentration was altered. These effects ensued within 1^2 min after the start of perfusion with the test solutions. In particular, when the tonicity was changed by varying Na concentration the mean mEPSP rate was directly related to osmolality. Size histograms of synaptic potentials were well described by single log-normal distribution functions under all experimental conditions. Hypotonic solutions (105 mosmol/kg) markedly shifted the histograms to the left. Hypertonic solutions (380^550 mosmol/kg, NaCl or Na-Gluconate added) shifted the histograms to the right. Hypertonic solutions obtained by adding sucrose to normal Ringer's solution (final osmolality 550 mosmol/kg) increased mEPSP and spike rates, but did not display appreciable effects on mEPSP size. All effects on spike discharge and on mEPSP rate and size were rapidly reversible. In Ca-free, 10 mM EGTA, Ringer's solution, the sensory discharge was completely abolished and did not recover on making the solution hypertonic. These results indicate that perilymphatic solutions with altered tonicity produce small and slowly ensuing changes in the transepithelial parameters which may indirectly affect the sensory discharge rate, whereas relevant, early and reversible effects occur at the cytoneural junction. In particular, the modulation of mEPSP amplitude appears to be postsynaptic; the presynaptic effect on mEPSP rate of occurrence is presumably linked to local calcium levels, in agreement with previous results indicating that calcium inflow is required to sustain basal transmitter release in this preparation. z 1998 Elsevier Science B.V. All rights reserved.
Pfl�gers Archiv European Journal of Physiology, 1977
The endocochlear potential (EP), potassium K + concentration in the endolymph (e) and in the perilymph (Kp +) were measured in guinea-pigs during anoxia of different duration. Specific K § doublebarrel microelectrodes with liquid ion exchanger were used. The resting K § concentration in the endolymph was 146.8 + 9.2mM and in the perilymph 3.2 +_ 0.5 mM. The following time course of events was observed in the cochlea during anoxia: 40-50 s after the arrest of ventilation the K § concentration decreased by 0.1-0.2 mM in the scala vestibuli, which was time related to a rapid fall of EP to negative values. Perilymphatic K § started to increase in both scalae with a latency of 2-2.5 min, reaching a concentration of about 14 mM 60 min after the arrest of ventilation. The endolymphatic K § began to decrease after a latency of 2.5-3 min, and 60 min after the arrest of ventilation an 80~ concentration (average 112 mM K § was reached as compared to the initial value. From the comparison ofK + concentration changes with the experimental values of the negative EP, it may be assumed that the negative EP is mainly generated by the K § gradient between the perilymph and endolymph.
Hypoxic response of hypoglossal motoneurones in the in vivo cat
The Journal of Physiology, 1997
In current and voltage clamp, the effects of hypoxia were studied on resting and synaptic properties of hypoglossal motoneurones in barbiturate-anaesthetized adult cats. 2. Twenty-nine hypoglossal motoneurones with a mean membrane potential of-55 mV responded rapidly to acute hypoxia with a persistent membrane depolarization of about +17 mV. This depolarization correlated with the development of a persistent inward current of 0 3 nA at holding potentials close to resting membrane potential. 3. Superior laryngeal nerve (SLN) stimulation-evoked EPSPs were reduced in amplitude by, on average, 46%, while IPSP amplitude was reduced by 31 %. SLN stimulation-evoked EPSCs were reduced by 50-70%. 4. Extracellular application of adenosine (10 mm) hyperpolarized hypoglossal motoneurones by, on average, 5-6 mV, from a control value of-62 mV. SLN stimulation-evoked EPSPs decreased by 18 % and IPSPs decreased by 46 % during adenosine application. 5. Extracellular application of the KATP channel blocker glibenclamide led to a blockade of a persistent outward current and a significant increase of SLN stimulation-evoked EPSCs. 6. We conclude that hypoglossal motoneurones have a very low tolerance to hypoxia. They appear to be under metabolic stress even in normoxia and their capacity to activate protective potassium currents is limited when compared with other brainstem neurones. This may help to explain the rapid disturbance of hypoglossal function during energy depletion.
Cochlear potentials and their modulation by low-frequency sound in early endolymphatic hydrops
Hearing Research, 1988
Seventeen guinea pigs were unilaterally operated to produce endolymphatic hydrops. After 2 wk (9 animals) or 4 wk (8 animals), extracochlear electrophysiological responses to tone bursts of several frequencies were recorded in both the operated and non-operated ears. In addition, modulation by low-frequency (29 Hz sinusoidal bias) sound of the responses to 8 kHz tonebursts was measured. After the electrophysiological measurements, the animals were killed and examined histologically. Four weeks after the operation, cochlear microphonics in response to a 500 Hz tone burst and to the 29 Hz bias were significantly smaller in the operated ears. The summating potential showed a tendency to be larger in the operated ears. The compound action potential input-output curves for 2 kHz probes showed a small threshold shift accompanied by steep slopes, reminiscent of recruitment. Modulation of summating potentials by the low-frequency bias was smaller on the operated side. In most cochleae an endolymphatic hydrops was observed. Three cochleae showed a collapse of Reissner's membrane.
JARO-Journal of the …, 2010
Gerbils aged in quiet show a decline of the endocochlear potential (EP) and elevated auditory nerve compound action potential (CAP) thresholds. However, establishing a direct relationship between an age-related reduction in the EP and changes in the activities of primary auditory neurons is difficult owing to the complexity of age-related histological changes in the cochlea. To address this issue, we developed a young gerbil model of "metabolic" presbyacusis that uses an osmotic pump to deliver furosemide into the round window niche for 7 days, resulting in a chronically reduced EP. In this model, the only major histopathologic changes were restricted to the hook region of the cochlea and consisted of loss of strial intermediate cells and massive edema in the lateral wall. The morphological and physiological evidence suggests that the cochlea can adapt to furosemide application over time. The morphology of spiral ganglion cells and hair cells appeared normal throughout the cochlea. CAP responses and EP values in this model are similar to those of quiet-aged ears. The spontaneous activity of single auditory fibers (n= 188) was assessed in 15 young gerbils treated with furosemide for 7 days. The percentage of recorded low-spontaneous rate (SR) fibers at characteristic frequencies (CFs)≥6 kHz was significantly lower in furosemide-treated than in control ears. Recovery function tests of CAP responses after prior stimulation also showed a decline in activity of the low-SR population with CFs≥6 kHz in the treated cochleas. A similar loss in the activity of low-SR fiber has been previously shown in quiet-aged gerbils. These results suggest that dysfunction of the cochlear lateral wall and subsequent chronic reduction in the EP can directly affect the activity patterns of primary auditory neurons in a manner similar to that seen in aged gerbils.
Resonance, oscillation and the intrinsic frequency preferences of neurons
Trends in Neurosciences, 2000
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