AP Responses Research Articles

Rate-versus-intensity functions and related AP responses in normal and pathological guinea pig and human cochleas.

Cochlear fiber discharge rate-versus-intensity functions, across frequency, have been measured in pathological guinea pig cochleas (ototoxic antibiotic poisoning) and compared with the normal animal. The frequency dependence of the slopes of these functions is reduced in cochlear pathology which results in minimum threshold elevations of more than 50 dB, i.e., there is a reduction in this frequency dependent nonlinearity. The rate functions at characteristic frequency (CF) become abnormally steep (e.g., 4--5 spikes/s/dB compared with a normal 1--2 spikes/s/dB), and comparable to those of the low-frequency tail region of normal cochlear fibers. The CF dynamic range is reduced from 30--40 to 10--15 dB in cochlear pathology. The fiber study has been confirmed by (and has confirmed) a method of indirect measurement of rate functions from AP suppression-versus-intensity functions using a pure-tone forward masking paradigm [Abbas and Gorga, J. Acoust. Soc. Am. 69, 492--499 (1981)]. This method has been used in normal and pathological guinea pigs, and the results parallel the single fiber study. In addition, AP suppression functions, across frequency, have been obtained in human subjects with (near) normal hearing thresholds, and in patients with sensorineural hearing loss of cochlear origin, during transtympanic electrocochleography. The AP suppression curves in pathology indicate, as for the animal studies, a loss of the frequency dependency of the rate function slopes, and predict steep rate functions at CF (and thus reduced dynamic range) in cochlear deafness. The findings are related to loudness recruitment.

内リンパのう閉鎖および内リンパのう吸引による聴神経複合電位（ＡＰ），加重電位（ＳＰ），か牛マイクロホン電位（ＣＭ）の変化

The changes of AP, SP and CM were investigated in accordance with the grade of endolymphatic hydrops which was produced by endolymphatic sac obliteration in the guinea pigs. Also, AP, SP and CM were measured in animals in which the endolymphatic sac was suctioned. The results obtained were as follows:1. In animals with a minimum endolymphatic hydrops, a super-normal AP and CM responses were obtained in a few eases.2. With the increase of endolymphatic hydrops, CMs were reduced, where as APs at intensive stimulation were relatively well preserved.3. With the increase of endolymphatic hydrops, the potentials of positive SP were reduced, and a few cases showed the potential change to be a negative SP.4. With the increase of endolymphatic hydrops, the AP latency was increased.5. In endolymphatic sac suction, AP and CM responses at intensive stimulation were well preserved. A slight endolymphatic hydrops was observed. The potential of positive SP was reduced, and a few cases showed the change to cause a negative SP.6. In this series of experiments, the degeneration of the organ of Corti was hardly seen under the light microscope. It is suggested that polarity of positive SP observed in control was influenced to deflect towards negative SP by the increase of endolymphatic hydrops and the change of the biochemical component of the inner ear fluids.

Electrocochleographical Findings in the Cases with Inner Ear Syphilis

Pathophysiology and prognosis of hearing acuity in 16 ears of 10 cases with inner ear syphilis were studied by the transtympanic electrode technique of electrocochleography.The results were obtained as follows:The improvement of hearing acuity after steroid therapy was obtained at low frequency range on audiogram. These cases showed a well defined AP, a dominant-SP and remarkable CM response at 0.5kHz. It was speculated that there may be endolymphatic hydrops and the reversible change of hair cells at low frequency area of the cochlea.On the other hand, in the cases showing slight improvement of hearing acuity, both AP and CM responses shwed a low out-put potential which suggests a reversible change or organic damage of the hair cells or cochlear nevre.

Atrial inotropic responses to brief vagal stimuli: frequency-force interactions.

The effect of brief vagal stimulus burst on atrial contractile force was assessed in paced- and unpaced-heart preparations by recording the changes in pressure (AP) generated in a balloon in the right atrial appendage or by a miniature strain gauge on the atrium. One and 3 stimuli per vagal burst depressed AP up to 62 and 90%, respectively. The response varied with the time in the cardiac cycle at which the stimulus was given. Identical stimuli produced a greater inotropic depression at longer cardiac cycle durations. The differences between the magnitudes of the AP responses at two different mean heart rates were relatively constant when the stimulus intensity was increased from 1 to 99 stimuli per burst. A low-level stimulus caused a greater depression in contractile force when the heart rate was allowed to change than with the identical stimulus when the heart was paced, although this difference in paced- and unpaced-heart responses tended to disappear when the stimulus intensity (burst width) was increased. The composite frequency-force relationship was relatively flat over normal heart periods, but fell off by 15-20% at the extremes. The present results show an unexpected interaction between the vagal inotropic effect and the frequency-force relationship such that a given vagal stimulus causes a greater depression of atrial contractile force at lower heart rates.

AP and SP Responses in Guinea Pig, Rabbit and Cat

AP and SP responses were investigated by the single electrode technique.The recording sites were the round window, mid-portion of the bony wall of cochlea, the apical portion of the cochlea and bony wall of the hypotympanum.One cycle of sound stimuli at 8kHz, 4kHz, 1kHz and 0.5kHz was used and the sounds were given from 50cm lateral to the tested ear.The tone bursts with duration of 30msec were used as measurement of SP.The results obtained were as follows:The highest value of AP out-put potential was obtained by the round window recording. The highest value of AP out-put potential was obtained by the stimulation of one cycle of 4kHz and 8kHz.The positive SP as seen in the round window recording changed to a decreased positive SP or negative SP at the recording sites except the round window.The SP induced by a tone burst from the round window showed the positive SP at high frequency and the negative SP at low frequency.These results will contribute to the research on the single electrode recording of AP and SP responses in these animals.

Quantitative Evaluation of Nitromin Ototoxicity and Analysis of Compound Action Potential Responses in Electrocochleography in Guinea Pig Cochlea

Quantitative evaluation of Nitromin ototoxicity was examined in guinea pigs given one dose of the drug intravenously. Pathological changes in the cochlear sensory hair cells were then observed under a light microscope following surface preparation after cold phosphate-buffered 2% osmic acid solution fixation. Possibility of frequency specificity of tone pip electrocochleography and modification of input-output functions of cochlear whole-nerve action potentials in absence of outer hair cells were studied by examining the relationship between the degree of outer hair cell damage and the cochlear AP responses.I) Degree of outer hair cell damage:At the initial stage, the degeneration of the outer hair cells were the most extensive in the basal turn, and least in the third turn. With the advance of degenerative changes, the damage in the lower turns proceeded rapidly and became more extensive than that in the apical turns.The outer hair cells in the first row were significantly more vulnerable in each coil. However, at the initial stage, the outer hair cells in the fourth coil were more vulnerable in the third than the first row.II) Cochlear AP responses in guinea pigs treated with drugs:Both the prolongation of minimum latency and increase in the width of the AP-SP wave form complex of AP responses to low-frequency (1, 2KHz) tone pip were more prominent than to high-frequency (4, 8KHz) one.Decrease of the maximum amplitude of AP responses to low-frequency (0.5, 1, 2KHz) tone pip was greater than to high-frequency (4, 8KHz) one, comparing each decrease of that with the degree of the outer hair cell damage in respective coils. Therefore, changes of each parameter at high intensities indicated the decrease of the number and the degree of synchronization of the activity of the auditory units located in the lower turns, especially in the basal turn, regardless of the frequency of the stimulation tone.The elevation of the threshold of AP response to each frequency tone pip was comparatively correlative with the degree of outer hair cell damage in each coil, respectively.For the input-output curves of AP responses to 4 and 8KHz tone pips, the L-curve disappeared according to the advancement of the degenerative changes, after which the maximum output of the H-curve decreased respectively to 22.9% and 24.1% of each average output in the normal group, despite the finding that almost all the inner hair cells survived. Accordingly, it was considered that the outer-hair-cell units had a significant influence on the synchronous firing of the inner radial fibers connecting to the inner hair cell system, though the L-response and the H-response component mainly depended on the auditory units originating in the outer and inner hair cells, respectively.At higher intensities, the polarity of SP as the earlier fraction of AP-SP wave form complex, changed to negative with 4 and 8KHz tone pips and click stimulations in case of severe outer hair cell damage in the lower turns.

AP responses in forward-masking paradigms and their relationship to responses of auditory-nerve fibers.

The amplitude of N1 peak of whole-nerve AP was measured in cats using a tone-burst probe with tonal maskers in a forward-masking paradigm. Experiments examined the effects of masker level, frequency, and duration (Tm), as well as interstimulus interval (delta t). Results are consistent with the interpretation that amplitude of N1 reflects activity of a limited group of fibers with CF near the probe frequency. For single fibers, decrement in discharge rate (relative to an unmasked condition) is dependent upon rate to the masker [Smith, Neurophys. 40 (1977)]. For the AP, decrement in probe-elicited amplitude should reflect the rate to masker in those fibers excited by the probe. Thus measurements of N1 decrement versus masker frequency and level are similar to single unit rate versus level functions. Since decrement in N1 reflects amount of adaptation, increasing Tm decreases probe response. N1 amplitude as a function of Tm thus resembles PST histograms of nerve fibers. Finally, plots of N1 amplitude as a function of delta t are interpreted as a measure of recovery from adaptation.

AP responses in forward‐masking paradigms and their relationship to responses of auditory‐nerve fibers

AP responses in forward‐masking paradigms and their relationship to responses of auditory‐nerve fibers

The development of some peripheral and central auditory responses in the neonatal cat

The development of cochlear nerve action potential thresholds at different frequencies (AP audiograms) and inferior colliculus (IC) single unit thresholds and tuning was examined in barbiturate-anaesthetized kittens. AP thresholds decreased over the whole frequency spectrum during the first 5 weeks of life. Threshold to high-frequency stimulation remained higher in 7-week-old animals than in adults. These results are in contrast to previous reports which have suggested that the AP response and gross cochlear anatomy are mature by the end of the second week. These differences may be due to the fact that the AP audiogram technique provides a measure of the activity of discrete regions along the cochlear partition. IC units in animals younger than 3.5 weeks had significantly elevated thresholds and broader tuning than those of the adult cat. Comparison of AP audiogram and IC unit thresholds in the adult revealed that these indices show similar frequency-dependent sensitivity. The slower maturation revealed by the AP audiogram may be due to the greater number and/or synchrony of cochlear nerve discharges needed to produce the gross AP. If this were the case, perception of suprathreshold sounds might not develop as quickly as thresholds for sound detection.

Electrocochleographic study of sudden deafness.

By performing electrochleography (AP, SP and CM) on 34 patients with sudden deafness, it was thought that the pathophysiology of this disease could be deduced. The various waveform patterns of AP and SP responses obtained in cases of sudden deafness were classified into the following types: 1) AP high response; 2) decreased AP high response; 3) AP low response; 4) dominant -SP; 5) -SP or +SP; and 6) AP, SP no response. The cases showing the type of dominant -SP and AP high response had satisfactory prognoses. In these cases the sensory epithelium and the cochlear nerve seemed to indicate a reversible condition being affected by the temporary functional block. Furthermore, it seemed to indicate that the neural regions related to the source of AP(N1) response were impaired in cases in which CM were recorded at normal response threshold in spite of the absence of AP(N1) response. In the unsatisfactory prognosis cases with decreased AP high response, AP low response and AP, SP no response in which only the extremely low or depressed CM responses could be recorded, it seemed that the sensory epithelium and the cochlear nerve were affected permanently, although the degree of impairment varied.

Electrocochleographical Odservation of Deafness Caused by Head Trauma

We made electrocochleographical examinations on 11 cases of hearing loss due to head trauma. These cases were tested with the trans-tympanic technique using 0.5, 1, 2, 4, 8kHz tone pip as acoustic stimuli. Electrocochleographical audiograms consisted of 0.5μV level of CM and AP responses were obtained. The AP wave form was also investigated, and an aural reflex was tested. Temporal summating effect of conditioned tone, which reduced CM amplitude evoked by 0.5kHz tone pip (test tone), by the aural reflex, was observed. Cases of brain stem lesion revealed an abnormal pattern of temporal summating envelope.We reviewed 11 cases of deafness caused by head trauma, and dissociation of CM and AP responses observed on the electrocochleographical audiograms, abnormal AP wave form and abnormal pattern of the temporal summating envelope by the aural reflex, and the auditory lesion of these cases were discussed.The results were as follows:1) Labyrinthine damage... 4 cases2) First auditory neuron disorder... 4 cases3) Brain stem lesion... 3 cases

Pollen Grains Indicating Culture in Peat, Mud and Till

The peat profile is seen to provide a more sharply defined picture of the response of both AP and NAP absolute and relative values to human interference, e.g. slash and burn cultivation, draining and early arable farming, than does the lake sediment profile. Although local factors in both the lake and peatland environments give rise to major differences between the profiles in terms of the NAP species present, the true culture indicators constitute similar proportions of total NAP in both cases when sampled at equal distances from the cultivation site. The generally small proportion of NAP present, however, requires counting to a total of 1 000 AP per sample at least. Human interference results in more pronounced changes in AP and NAP in the case of the mineral soil profile, which reflects the effect of slash and burn cultivation on the vegetation, the local nature of this pollen being indicated by the absence of such features in the corresponding horizons of the lake sediment and peat profiles.

Aspirin Intolerance, Asthma, Prostaglandins, and Cromolyn Sodium

Asthma associated with ingestion of aspirin (acetylsalicylic acid) has been recognized for more than 70 years. 1 Gilbert GB Unusual idiosyncrasy to aspirin. JAMA. 1911; 56: 1262 Crossref Scopus (31) Google Scholar , 2 Gilbert GB Hirschberg: Mittheilung uber einen Fall von Nebenwirkung des Aspirin. Dtsch Med Wochenschr. 1928; 75: 1588 Google Scholar , 3 Cooke RA Allergy in drug idiosyncrasy. JAMA. 1919; 73: 759 Crossref Scopus (36) Google Scholar The most distinctive features of this peculiar subset of asthmatic patients are nasal polyps, hyperplasia of the mucous membranes of the sinuses, and the ability of ingested aspirin to precipitate an asthmatic crisis. Other, less constant but important features have been described. 4 Samter M Beers RF Intolerance to aspirin. Ann Intern Med. 1968; 68: 975-983 Crossref PubMed Scopus (720) Google Scholar , 5 Smith AP Response of aspirin-allergic patients to challenge by some analgesics in common use. Br Med J. 1971; 2: 494496 Google Scholar , 6 Von Maur K Adkinson F Van Metre TE et al. Aspirin intolerance in a family. J Allergy Clin Immunol. 1974; 54: 380-395 Abstract Full Text PDF Scopus (27) Google Scholar , 7 Lockey RF Rucknagel DL Vanselow NA Familial occurence of asthma, nasal polyps, and aspirin intolerance. Ann Intern Med. 1973; 78: 57-63 Crossref PubMed Scopus (80) Google Scholar In many of these patients, the asthmatic attacks become more frequent and severe, in spite of the absence of any apparent continuing exposure to aspirin or similar drugs. When such patients become dependent on therapy with steroids, as they often do, the orally administered steroids generally prove reasonably effective in controlling their chronic symptoms. This contrasts with the inability of these same steroids to prevent the acute asthmatic attacks evoked by ingestion of aspirin, 4 Samter M Beers RF Intolerance to aspirin. Ann Intern Med. 1968; 68: 975-983 Crossref PubMed Scopus (720) Google Scholar and it suggests some difference between the pathogenesis of the chronic and the acute forms of airway obstruction in these patients.

Electrocochleographic Study in Cases of Posterior Cranial Fossa Tumor

Electrocochleography was performed on six patients with posterior cranial Fossa tumors which consist of three cases of acoustic neurinoma of grade II-III, a case of glioblastoma multiforme originating from cerebello-superior pons, a case of astrocytoma of grade III originating from medulla oblongata-inferior pons, and a case of meningioma originating from Meckel's cavity. Recording was made with the use of the transtympanic needle technique. AP input-output functions with acoustic neurinoma were very similar to those obtained in patients with sensorineural hearing loss showing the phenomenon of recruitment. In AP responses recorded from the patients with cerebello-superior pontine tumor and Meckel's cavity tumor, a loss of the positive portion of the potentials (P1) was characteristic. This phenomenon may be due to the compression on the auditory nerve by the growing tumor. The polarity of SP in all cases showed negative deflection without abnormal increment. CM responeses recorded from the patients were the same as in a normal subject. In the cases presented, although the abnormal changes in input-output functions as well as the changes in the wave form patterns of AP responses revealed a lesion of the portions corresponding to the sensory and/or to the neural structure, the presence of a well-developed CM may be explained by the fact that the hair cells remain unaffected. Therefore, it is thought that simultaneous recording of CM and AP gives great promise as a means of differential diagnosis between neural and cochlear pathology.

Whole-Nerve Action Potentials as an Index of Severity of Cochlear Injury in Chinchilla

The N1 peak voltage of the AP response to a wide-band click is proving to be a sensitive index to injuries following exposures to noise. Over a wide range of injury, changes in magnitude and sensitivity of N1 responses correctly rank ears with respect to amount of loss of hair cells. With loss of 100–300 hair cells, the voltages are one to two standard deviations below normal means at all levels of the input-output function. The voltages are down two to three standard deviations with 300–800 missing cells. With greater losses the input-output functions are also shifted to a lower sensitivity. A small response can still be elicited 70 dB above normal visual detection levels when an estimated 6800 out of 9100 (75%) hair cells are missing. Differential masking of the N1 responses with selected bands of noise provides additional information concerning the locations of the injuries.

TTS Accompanied by Sustained Reduction of AP Amplitudes in Noise-Exposed Guinea Pigs

Guinea pigs were fitted with permanent recording macroelectrodes having tips located in the auditory-nerve-cochlear-nucleus region. After recording detection levels and input-output functions for clicks or pure-tone bursts under waking conditions using computer-averaging techniques, the animals were exposed to 115 dB SPL of broad-band noise for 1 h. Postnoise measurements were made within the hour following exposure and for at least four weeks thereafter. VDLs shifted for clicks and midfrequency tonal stimuli, although corresponding suprathreshold AP responses showed sustained reduction of peak-to-peak amplitudes. The altered form of the AP input-output functions is characteristic of nerve fiber depopulation conditions and suggests that damage occurred to the ear in spite of the fact that VDLs returned to prenoise levels.

Cochlear Microphonic and Action Potential Thresholds during Acute Salicylism

Guinea pigs were prepared with indwelling rigid depth electrodes located in the auditory nerve or flexible electrodes placed on the round window membrane. Absolute thresholds (VDL) were traced by the experimenter over 3-min periods by controlling stimulus intensity with a motor driven recording attenuator so that electrophysiological responses displayed on an oscilloscope were kept just detectable from the baseline. Threshold traces were obtained from restrained, waking animals under control conditions and at 2, 4, and 24 h following single injections of 300 mg/kg of sodium salicylate solution. Stimuli were continuous or pulsed trains of 1, 100, 250, or 1000 clicks/sec. Cochlear microphonic threshold traces showed little or no shift, while action potential thresholds were elevated 5–9 dB 2–4 h after injection. No differences between pulsed- and steady-stimulus conditions were demonstrable during salicylism for either CM or AP responses. Envelopes of traces (width in decibels showed no systematic differences between types of response or experimental conditions.

Auditory Function in Atherosclerotic Rabbits

Atherosclerosis was induced in a population of rabbits by feeding a high-cholesterol diet for a period of six months. A control group from the same colony was maintanied on an identical diet without the cholesterol. Observations of auditory function were made on five diet animals and four control animals by means of acute round window electrode implants. The action potential response to a standard acoustic click and microphonic sensitivity response curves for gradated 1-sec tone bursts at frequencies from 125 Hz to 15 kHz were recorded from all animals. The AP responses for the diet animals are consistently lower than for the control animals by 10–20 dB. On the other hand, the microphonic responses indicate no obvious differences between the two groups except at 2 kHz, where the diet animals appear to be in the order of 20 dB more sensitive than the controls. The significance of this latter finding, however, is open to question. [This research supported in part by Public Health Service grants.]

Biochemical effects in rats from irritating air contaminants

The effect of inhalation of acrolein vapors on the activity of several enzymes of male rat tissues was investigated. Elevated hepatic alkaline phosphatase activity occurred following continous 40-hour exposure to acrolein at concentration as low as 2.1 ppm. Exposure to higher concentrations for shorter periods of time also increased liver AP activity, but the effect was not constant with a constant Ct. Inhalation of ozone, nitrogen dioxide, formaldehyde, and sulfur dioxide also increased liver AP activity. It appears that the hepatic AP response is a nonspecific effect and may be a symptom of the alarm-reaction to stress.

Factor Analysis of Cochlear Injuries and Changes in Electrophysiological Potentials Following Acoustic Trauma in the Guinea Pig

The changes in “threshold” and maximum responses for cochlear microphonic potentials and whole-nerve action potentials were measured following acoustic trauma with 500-cps tones. The cochlear-microphonic responses were measured locally in the first turn of the cochlea for 500-, 2000-, and 8000-cps test tones and locally in the third turn for a 500 cps test tone. The whole-nerve action potentials were measured in response to 500- and 5000-cps tone pips. Injury to the organ of Corti in the first and third turns was rated after examination of histological sections of the temporal bones. The physiological measurements, the injury ratings, and the sound pressures and durations of the traumatic exposures were examined together for correlations and analyzed for common factors. The results served primarily to confirm previous conclusions. For durations of exposure from 5 to 80 min, equal total acoustic energy in the exposure produced equal changes in the electrophysiological responses. The ratings of anatomical injury in the cochlea departed significantly from this relation and tended to depend more strongly on sound pressure than on duration of exposure. The “threshold” shifts for CM responses from the first turn were the same for the three test frequencies, but loss of maximum potential was significantly different for the three test frequencies. The factor analysis grouped the whole-nerve AP responses to 500-cps tone pips with the CM responses from the first turn instead of with the CM responses from the third turn.