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PubMed1986

Projection of pulmonary rapidly adapting receptors to the medulla of the cat: an antidromic mapping study.

The activity of pulmonary rapidly adapting receptor (r.a.r.) neurones was recorded extracellularly in the nodose ganglion of the decerebrate cat. The receptors were identified by their rapid adaptation to 'ramp and hold' hyperinflations of the lung. The antidromic mapping technique was used to determine the sites of projection and branching patterns within the nucleus of the tractus solitarius (n.t.s.) of eleven r.a.r.s. The medulla was explored with a stimulating electrode to activate the r.a.r.s. antidromically. In each penetration, depth-threshold measurements were made for each antidromic response characterized by a distinct latency. Using the anatomical sites of the minimum threshold points, the locations of central branches of individual r.a.r.s. were determined. The main axons of all of them coursed within the tractus solitarius (t.s.) at levels from 2 mm rostral to 0.5 mm caudal to the obex. The axonal conduction velocities within the t.s. were 6.2-9.7 m/s, where the peripheral conduction velocities were 11.2-20.4 m/s (28 degrees C). Different latencies of response evoked in a single penetration were considered to indicate branching. The densest branching was found in the ipsilateral commissural subnucleus of the n.t.s. at levels 0.3-1.3 mm caudal to the obex and, to a lesser degree, in the contralateral commissural subnucleus. All r.a.r.s. sent a few branches to the medial n.t.s. rostral to the obex. Four r.a.r.s. ramified in the ventrolateral n.t.s. where inspiratory cells are located. Depth-threshold graphs were interpolated by best fitting parabolic equations: Ith = Ad2 + Bd + C; where Ith is the threshold current, d the corresponding depth of stimulation, and A, B and C are coefficients. Coefficient A is a measure of steepness of the parabola. The A coefficients were inversely related to the conduction velocity (v) of the stimulated branch. An analysis of the data from the present study (v = 5.0-9.7 m/s) combined with data from the literature (v = 2.2-85 m/s) led to a simple relationship between the A coefficient and the conduction velocity of the stimulated fibre: A = 6500/v, where A is expressed in microA/mm2 and v is expressed in m/s. Within the range 3-35 m/s, the formula is useful in predicting the effective current spread when the conduction velocity is known, or to estimate the conduction velocity from the shape of a depth-threshold curve. Two slowly adapting pulmonary stretch receptors (p.s.r.s) were studied.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1986

A role of pulmonary rapidly adapting receptors in control of breathing.

We analysed the breathing pattern of anaesthetised rabbits during unloaded breathing when breathing was accelerated by inspired CO2 and when they breathed against positive or negative pressures before and during block of pulmonary stretch receptors by SO2, and after bilateral vagotomy. Before block moderate steps of inflation or deflation (0.5 kPa) produced relatively larger changes in duration of expiration than in duration of inspiration, indicating the relative sensitivities of the two phases. With stretch receptors, blocked inflation or deflation shortened expiration, demonstrating the influence of rapidly adapting receptors on that phase of breathing. If pulmonary stretch receptors were the major determinants of the duration of inspiration, we would have expected inspiratory duration in the stretch receptor blocked and vagotomised states to be almost identical. They were not, inspiratory duration being less in the blocked than in the vagotomised state. Possibly vagal afferent activity other than that of stretch receptors shortens inspiratory duration. However, we have found that rapidly adapting receptor activity (and any unmyelinated fibre activity provoked by rapid inflation or deflation of the lungs) never directly shortened inspiration. We therefore propose a mechanism whereby rapidly adapting receptors may indirectly affect duration of inspiration.

Adaptation, Physiological↗
PubMed1997

Neural coding mechanisms in tactile pattern recognition: the relative contributions of slowly and rapidly adapting mechanoreceptors to perceived roughness.

Tactile pattern recognition depends on form and texture perception. A principal dimension of texture perception is roughness, the neural coding of which was the focus of this study. Previous studies have shown that perceived roughness is not based on neural activity in the Pacinian or cutaneous slowly adapting type II (SAII) neural responses or on mean impulse rate or temporal patterning in the cutaneous slowly adapting type I (SAI) or rapidly adapting (RA) discharge evoked by a textured surface. However, those studies found very high correlations between roughness scaling by humans and measures of spatial variation in SAI and RA firing rates. The present study used textured surfaces composed of dots of varying height (280-620 micron) and diameter (0.25-2.5 mm) in psychophysical and neurophysiological experiments. RA responses were affected least by the range of dot diameters and heights that produced the widest variation in perceived roughness, and these responses could not account for the psychophysical data. In contrast, spatial variation in SAI impulse rate was correlated closely with perceived roughness over the whole stimulus range, and a single measure of SAI spatial variation accounts for the psychophysical data in this (0.974 correlation) and two previous studies. Analyses based on the possibility that perceived roughness depends on both afferent types suggest that if the RA response plays a role in roughness perception, it is one of mild inhibition. These data reinforce the hypothesis that SAI afferents are mainly responsible for information about form and texture whereas RA afferents are mainly responsible for information about flutter, slip, and motion across the skin surface.

Adaptation, Physiological↗
PubMed1991

Mechanisms of cigarette smoke-induced stimulation of rapidly adapting receptors in canine lungs.

The stimulation of rapidly adapting receptors (RARs) in the lungs evoked by cigarette smoke consists of an initial and either a type I or a type II delayed response (Kou and Lee, J. Appl. Physiol. 68: 1203, 1990). In the type I response, receptor activity increased during expirations and exhibited a prominent cardiac modulation, whereas in the type II response, receptor discharge reached its peak during inspiration at peak transpulmonary pressure. To investigate the mechanisms of this stimulation, we recorded the vagal afferent activity arising from 39 RARs and delivered a single breath (120 ml) of cigarette smoke in 15 anesthetized, open-chest and artificially ventilated dogs. Studies were repeated after a pretreatment with aerosolized hexamethonium (3-8 breaths, 10%), aerosolized isoproterenol (12-15 breaths, 2%), or after the cardiac impact on the lung had been minimized by elevating the apex of the heart. The initial response of RARs was totally abolished by hexamethonium but was not affected by isoproterenol. The increase of total lung resistance induced by cigarette smoke and the concomitant type II delayed response of RARs were both abolished by isoproterenol. The type I delayed response of RARs was eliminated or largely attenuated after the apex of the heart had been elevated. Based upon these results, we conclude that a direct effect of nicotine on these receptors may be responsible for the immediate stimulation while the systemic effects of absorbed nicotine may play a part in evoking the delayed stimulation.

Adaptation, Physiological↗
PubMed1984

Effect of prostaglandin F2 alpha on pulmonary rapidly-adapting-receptors in the guinea pig.

Pulmonary rapidly-adapting-receptors ( RARs ) are sensory nerve endings whose afferent fibers can be recorded in the vagus nerve. RARs may play a role in reflex bronchoconstriction as seen in anaphylaxis. They can be stimulated by chemical mediators of anaphylaxis, such as prostaglandin F2 alpha (PGF2 alpha). PGF2 alpha aerosol was administered to saline and bovine serum albumin (BSA)-treated guinea pigs while recording the activity of RARs . PGF2 alpha (250 micrograms/ml) given for 7-13 minutes increased both tracheal pressure and nerve activity over that produced by saline exposure in untreated guinea pigs. PGF2 alpha administered for three minutes (5-100 micrograms/ml) increased RAR nerve activity in a dose-related manner in the first five minutes of the experiment only in the BSA treated guinea pigs. Since changes in tracheal pressure did not show a significant dose-response relationship, the RARs responding to PGF2 alpha seemed to be stimulated by a direct mechanism. No correlation was shown between tracheal pressure and RAR nerve activity during PGF2 alpha treatment. Whereas, a significant correlation was found between tracheal pressure and RAR nerve activity during histamine aerosol treatment (r = 0.985). Histamine aerosol (1 to 1000 micrograms/ml, 3 min.) increased intratracheal pressure for 3 out of 4 doses. RAR nerve activity increased significantly only at the highest dose. Therefore, a possible direct effect of PGF2 alpha upon RARs exists while the effect of histamine seems dependent upon changes in airway pressure in the guinea pig.

Aerosols↗
PubMedDate not supplied

Modeling population responses of rapidly-adapting mechanoreceptive fibers.

The population response of rapidly-adapting (RA) fibers is one component of the physiological substrate of the sense of touch. Herein, we describe a computational scheme based on the population-response model by K.O. Johnson (J. Neurophysiol. 37: 48-72, 1974) which we extended by permitting the capability to include the spatial distributions of receptors in the glabrous skin linked to RA fibers. The hypothetical cases simulated were rectangular, uniformly random and proximo-distally Gaussian distributions. Each spatial organization produced qualitatively distinct population-response profiles that also varied due to stimulus parameters. The effects of stimulus amplitude, average innervation density and contactor-probe location were studied by considering various response measures: number of active fibers, summated firing rate and the average firing rate of a subset of the modeled population. The outcome of the measures were statistically compared among simulated anatomical distributions. The response is the same for rectangular and uniformly random distributions, both of which have a homogeneous innervation density. However, the Gaussian distribution produced statistically different responses when the measure was not averaged over the subset population which represented the receptive field of a higher-order neuron. These results indicate that, as well as stimulus parameters, the anatomical organization is a significant determinant of the population response. Therefore, reconstructing population activity for testing psychophysical hypotheses must presently be done with care until the organization of the receptors within the skin has been clarified.

Action Potentials↗
PubMed2003

Frequency responses of cat rapidly adapting mechanoreceptive fibers.

The frequency responses of 11 rapidly adapting (RA) fibers in cat were studied by representing the average firing rate as a function of sinusoidal stimulus amplitude and stimulus frequency. Specifically, rate-intensity functions at different stimulation frequencies were fitted by four-parameter (a0, a1, a2, a3), piece-wise linear functions using nonlinear regression (n = 59; R2 > 0.877). Rate-intensity functions at intermediate frequencies were found by linear interpolation. The result of this analysis is rate-amplitude-frequency functions plotted as two-dimensional surfaces. The surfaces consist of five regions separated and sufficiently defined by four space curves. At 14 different frequencies, the statistical distribution of each rate-intensity-function parameter could be approximated by a particular lognormal distribution (n = 56; R2 > 0.796). The Kolmogorov-Smirnov test fails to reject this hypothesis for each combination of frequency and parameter (56 tests; p > 0.39). Therefore, at a given frequency, the variation of the parameters can be represented by lognormal distributions with specific means and standard deviations. Responses of six RA fibers, which are different from the data-set used for modeling, were compared with the stochastic model at different frequencies. The parameters of those fibers were tested against the null hypotheses that they were sampled from the particular parameter distributions dictated by the model. The Kolmogorov-Smirnov test fails to reject all the hypotheses at the alpha = 0.05 level (44 tests). At the alpha = 0.10 level, only a few test parameters were found to be departing from the model (a0 and a1 at 5 Hz; a2 at 20 Hz; a2 and a3 at 50 Hz). The remaining test parameters could be accurately described by the model. Having confirmed the validity of the model, the logarithmic means and the logarithmic standard deviations of the lognormally distributed rate-intensity-function parameters were estimated in the frequency range of 4-200 Hz. The rate-amplitude-frequency surfaces sampled from the established stochastic model completely characterize the rate responses of RA fibers to sinusoidal stimuli and are superior to tuning curves which require selecting criterion responses. The current rate-response model is promising for future computational work, especially on population modeling.

Action Potentials↗
PubMed1994

Visco-elastic properties of the rapidly adapting stretch receptor muscle of the crayfish.

The visco-elastic properties of the receptor muscle associated with the rapidly adapting stretch receptor organ of crayfish (Pacifastacus Leniusculus) were studied by recording the tension responses to various length changes. Steady-state length changes resulted in a non-linear tension development in the receptor muscle. The tension increased slowly for small extensions and more rapidly when extension increased. Muscle tension responses to ramp-and-hold extension were characterized by a transient peak followed by a gradual non-exponentional decline in tension. At the onset of the ramp the tension increased rapidly, similar to what has been observed in the muscle of the slowly adapting receptor (SM). The steeper rise in tension during the first part of the ramp indicating higher initial stiffness, resulted in a 'hump' when large extensions (> 15%) were applied. The results show that the rapidly adapting receptor muscle has a more pronounced dynamic component; the ratio between the amplitude of the peak and the steady state response was larger in the rapidly than in the slowly adapting receptor muscle. Accordingly, different values for the elements of a visco-elastic model of the muscle had to be set for the two types of receptors. The different properties of the rapidly and slowly adapting receptor muscles are in line with the differences in the overall adaptive behaviour of the organ and give further support to the idea that mechanical factors contribute to the adaptive properties.

Animals↗
PubMed2000

The effect of dopamine on the rapidly adapting receptors in the dog lung.

The effect of an infusion of dopamine (50 microg/kg per min) on both resting and histamine-stimulated discharge of rapidly adapting receptors has been studied in the dog lung. In dogs pretreated with propranolol and phentolamine (1 mg/kg) dopamine inhibited the ability of histamine to stimulate the rapidly adapting receptors. This inhibition was attenuated by sulpiride, a selective D(2)antagonist, (0.5 mg/kg i.v.). Dopamine did not affect the increases in R(L)or the falls in C(dyn)produced by histamine. It is suggested that dopamine may play a role in the control of lung function by reducing the ability of sensory nerves to produce harmful reflex activity.

Adrenergic beta-Agonists↗
PubMed1998

Action of moguisteine on the activity of tracheobronchial rapidly adapting receptors in the dog.

We have studied the effects of moguisteine, a new non-narcotic, peripherally acting antitussive compound, on tracheobronchial rapidly adapting irritant receptors (RARs). Experiments were carried out on dogs anaesthetized with a mixture of urethane and alpha-chloralose, paralysed with gallamine, vagotomized and artificially ventilated. Single unit action potentials identified as originating from tracheobronchial RARs were recorded from the peripheral cut end of the right vagus nerve. The activity of these receptors was recorded together with oesophageal pressure and arterial blood pressure. Fourteen RARs were challenged with moguisteine (200 microg x kg[-1] i.v.) in 0.4% dimethylsulphoxide (DMSO) or 0.4% DMSO alone (vehicle). Receptor activity was recorded before (control) and at 2, 5, 10, 15, 20, 30 and 45 min after administration of the challenging compounds. When the results at intervals of 2, 5, 10, 15 and 20 min were averaged for each dog, it was found that moguisteine decreased the mean activity of the 14 receptors to 75% of the control value (p<0.05); the greatest inhibition occurred 10-20 min after moguisteine administration. DMSO did not significantly affect the activity of these endings. Oesophageal pressure, arterial blood pressure and cardiac frequency were not altered during the experimental procedures. The overall results indicate the presence of an inhibitory effect of moguisteine on rapidly adapting irritant receptors that could account for the antitussigenic effect of this compound.

Adaptation, Physiological↗
PubMed2006

The rapidly adapting receptors in mammalian airways and their responses to changes in extravascular fluid volume.

In this short review, we shall focus on some recent findings on the physiological stimulus for the rapidly adapting receptors (RAR) of the airways. They are readily activated by a sustained inflation of the lungs and they are usually identified by their rapid adaptation to this stimulus. They are also activated by both tactile stimuli and irritant gases applied to the epithelium of the airways. The investigations reviewed here suggest that these receptors are activated by changes in extravascular fluid volume. The principal factors governing fluid flux from the microcirculation are identified in the Starling equation. These are the hydrostatic pressure, plasma oncotic pressure and capillary permeability. Findings from recent studies suggest that all these factors increase the activity of RAR. In addition, these receptors are also activated by obstruction of lymph drainage from the lung. Evidence is presented to show that manipulation of Starling forces also increases the extravascular fluid volume of the airways in areas where the RAR are located. On the basis of these findings, it is suggested that, along with mechanosensitivity to stimuli such as stretch, inflation and deflation, another physiological stimulus to the RAR is a change in extravascular fluid volume in the regions of the airways where these receptors are located.

Adaptation, Physiological↗
PubMed1989

Excitation of both slowly and rapidly adapting pulmonary stretch receptors attenuates tachypnea induced by ammonia.

To elucidate the mechanism of attenuating the ammonia-induced tachypnea, the present study examined the discharge patterns and rates of slowly adapting pulmonary stretch receptors (SARs) and rapidly adapting pulmonary stretch receptors (RARs) in relation to the change in respiration produced by ammonia inhalation in anesthetized, spontaneously breathing rabbits. Extracellular action potentials of these two receptors were recorded at the peripheral cut-end of the left vagus nerve. A prolongation of expiration following ammonia inhalation occurred during the discharge of receptors increased continuously, particularly when the level of the discharge rate during expiration reached to approximately 20-fold, and under such circumstances the respiratory response was regularly associated with gasps. On the other hand, RARs increased their activity during only inspiration; this increased activity correlated with augmentation of inspiration. Furthermore, the prolongating effect of expiration due to ammonia inhalation was not observed after surgical denervation of the remaining right vagus nerve. These results suggest that vigorous stimulation of the SAR activity induced by ammonia inhalation can elicit a prolongation of expiration possibly resulting from augmentation of the Hering-Breuer inflation reflex and that augmentation of the increased RAR activity after ammonia inhalation counteracts the Hering-Breuer inflation reflex to shorten inspiration. Therefore, it is conceivable that strong stimulation of the SAR activity after ammonia inhalation counteracts the ammonia-induced tachypnea.

Action Potentials↗
PubMed1989

Effects of 5-hydroxytryptamine on rapidly adapting pulmonary stretch receptor activity in the rabbit.

In anesthetized rabbits, intravenous administration of 5-hydroxytryptamine (5-HT, 10, 20, 40 and 80 micrograms/kg) led to an increase of rapidly adapting pulmonary stretch receptor activity. The magnitude of the increase was dose-dependent. The excitatory responses to any doses of 5-HT were not inhibited by prior treatment with isoprenaline (100-150 micrograms). The results indicate that the stimulation of rapidly adapting pulmonary stretch receptors by 5-HT is not caused by contraction of the airway smooth muscle.

Animals↗
PubMed1987

Analysis of gated membrane currents and mechanisms of firing control in the rapidly adapting lobster stretch receptor neurone.

1. The gated membrane currents (a tetrodotoxin-sensitive Na+ current and a tetraethylammonium- and 4-aminopyridine-sensitive K+ current) of the rapidly adapting stretch receptor neurone of lobster were investigated with respect to their kinetic properties using electrophysiological, pharmacological, and mathematical techniques. 2. The currents were found to be controlled by slow inactivations as well as by fast Hodgkin-Huxley (1952) gating processes. They could be described by kinetic expressions which differed from those inferred for the slowly adapting receptor (Gestrelius & Grampp, 1983a; Gestrelius, Grampp & Sjölin, 1983) only with respect to some of the parameter values. 3. With these expressions, and additional equations for the cell's pump and leak current components (Edman, Gestrelius & Grampp, 1986), a mathematical receptor model was formulated which accurately predicts the impulse activity of the living preparation in different functional circumstances and which, therefore, was adopted as an appropriate theory of firing regulation. 4. From a model analysis it appeared (a) that the 'rapid' adaptation of the receptor's impulse activity is mainly an effect of slow Na+ current inactivation starting a regenerative process of accommodation which, basically, is due to a small ratio of subthreshold Na+ to K+ currents; (b) that, because of the transmembrane Na+ influx being limited by accommodation, impulse firing is only little affected by a Na+-dependent pump current activation; and (c) that the phenomenon of increased firing frequency initially during prolonged stimulation ('negative adaptation') is an effect of the slow K+ current inactivation being faster than the slow Na+ current inactivation at comparable degrees of membrane polarization. 5. From further model studies it also appeared that, during depolarizations between successive action potentials evoked by constant stimulation, the membrane behaves like a high-resistance constant-current generator feeding into a short-circuiting capacitor. In consequence, the cell's stimulus sensitivity (change in firing frequency with stimulation strength) is, at functionally relevant stimulation intensities, mainly determined by the membrane capacitance and by the amplitude of the interspike membrane depolarization while, at higher stimulation intensities and firing frequencies, it becomes more and more a function of the spike duration itself.

Action Potentials↗
PubMed1991

Intracellular measurements from a rapidly adapting sensory neuron.

1. The femoral tactile spine of the cockroach contains a single sensory neuron with its cell body in the lumen of the spine. Step movements of the spine produce rapidly adapting bursts of action potentials that decay to 0 in 1 s. Previous work has shown that a large part of this adaptation occurs during action potential encoding. 2. Intracellular recordings from the tactile spine neuron were obtained by lowering a microelectrode through the spine lumen and penetrating the cell body. Injection of Lucifer yellow followed by fluorescence microscopy confirmed the morphology of the soma, with a diameter of 30 microns, and showed an axon of 9 microns leaving the spine and proceeding proximally along the femur. 3. Membrane-potential records were digitized and examined at high resolution during bursts of action potentials produced by depolarizing current pulses. No significant changes in action potential shape were detected during adaptation. However, the rate of depolarization between action potentials slowed dramatically during the burst. This slowing could be reduced and the burst substantially prolonged by chloramine-T (CT), an agent that reduces sodium channel inactivation in several preparations. 4. A 100 Hz sinusoidal current was superimposed on depolarizing current pulses to test for changes in membrane conductance during a burst of action potentials. No such changes were detected, indicating that rapid adaptation is not due to changes in membrane permeability.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1996

Rapid adaptation of myocardial calcium homeostasis to short episodes of ischemia in isolated rat hearts.

Short episodes of ischemia and reperfusion (ischemic preconditioning) have been shown to attenuate the detrimental rise in intracellular free Ca2+ ([Ca2+]i) caused by subsequent sustained ischemia. The purpose of this study was to investigate the detailed time course of [Ca2+]i during such short episodes of ischemia and reperfusion. [Ca2+]i was measured at a high time resolution by surface fluorometry and indo-1 in isolated perfused rat hearts during three episodes of 5 minutes of ischemia followed by 5 minutes of reperfusion. We found that the rise in systolic [Ca2+]i was significantly smaller during the second (191% +/- 67%) and third (194% +/- 75%) episodes of ischemia than during the first episode (289% +/- 75%, P < 0.05 vs both subsequent episodes). This attenuated rise in systolic [Ca2+]i was preserved during perfusion with low extracellular Na+ (105.5 mmol/L [Na+]o). During short episodes of ischemia and reperfusion, [Ca2+]i rises less during the second and third ischemic episode than during the first episode. Thus one transient ischemic stimulus led to a rapid adaptation of [Ca2+]i homeostasis to subsequent ischemic conditions. Such a rapid adaptation might be an important mechanism of the ischemic preconditioning phenomenon in protecting against ischemic injury.

Adaptation, Physiological↗
PubMed2001

Central anatomy of individual rapidly adapting low-threshold mechanoreceptors innervating the "hairy" skin of newborn mice: early maturation of hair follicle afferents.

Adult skin sensory neurons exhibit characteristic projection patterns in the dorsal horn of the spinal gray matter that are tightly correlated with modality. However, little is known about how these patterns come about during the ontogeny of the distinct subclasses of skin sensory neurons. To this end, we have developed an intact ex vivo somatosensory system preparation in neonatal mice, allowing single, physiologically identified cutaneous afferents to be iontophoretically injected with Neurobiotin for subsequent histological analyses. The present report, centered on rapidly adapting mechanoreceptors, represents the first study of the central projections of identified skin sensory neurons in neonatal animals. Cutaneous afferents exhibiting rapidly adapting responses to sustained natural stimuli were encountered as early as recordings were made. Well-stained representatives of coarse (tylotrich and guard) and fine-diameter (down) hair follicle afferents, along with a putative Pacinian corpuscle afferent, were recovered from 2-7-day-old neonates. All were characterized by narrow, uninflected somal action potentials and generally low mechanical thresholds, and many could be activated via deflection of recently erupted hairs. The central collaterals of hair follicle afferents formed recurrent, flame-shaped arbors that were essentially miniaturized replicas of their adult counterparts, with identical laminar terminations. The terminal arbors of down hair afferents, previously undescribed in rodents, were distinct and consistently occupied a more superficial position than tylotrich and guard hair afferents. Nevertheless, the former extended no higher than the middle of the incipient substantia gelatinosa, leaving a clear gap more dorsally. In all major respects, therefore, hair follicle afferents display the same laminar specificity in neonates as they do in adults. The widely held misperception that their collaterals extend exuberant projections into pain-specific regions of the dorsal horn during early postnatal life is shown to have multiple, deep-rooted underpinnings.

Animals↗
PubMed2003

Rapid adaptation of the 2f1-f2 DPOAE in humans: binaural and contralateral stimulation effects.

The present data were collected in humans to characterize the effects of monaural and binaural stimulation and contralateral noise on the 2f1-f2 distortion-product otoacoustic emission (DPOAE) adaptation response. DPOAE levels (f2/f1=1.21, L1=70 dB SPL, L2=65 dB SPL) were measured in both ears for a range of f2 frequencies (1.2 to 10.0 kHz). The f2 frequency producing the largest amplitude DPOAE was used for further testing employing three different stimulus conditions: the primary tones were presented to only one ear for 4 s; the two tones were presented simultaneously in both ears; and, contralateral broadband noise (60 dB SPL) was presented for 5 s, beginning 4 s after the onset of the monaural primaries in the test ear. Acoustic reflex thresholds were measured to verify that the middle-ear muscles played no systematic role in the measured DPOAE reductions. Estimates of monaural rapid adaptation levels and time constants agreed well with previous human findings. The magnitude of the rapid adaptation under binaural stimulation, as compared with monaural primaries, was 25% greater on average, though adaptation time constants were comparable. With added contralateral noise, the average DPOAE suppression was 1.1 dB (0.3-2.7 dB). The magnitude of the monaural adaptation and the effects of binaural and contralateral stimulation, however, were smaller than those measured previously in experimental animals, though the time constants were in good agreement.

Acoustic Stimulation↗