bluuebunny/crossref_metadata_2025 huggingface dataset:
Cardiovascular and temperature changes in spinal cord injured rats at rest and during autonomic dysreflexia
Authors: Laird A. S. , Carrive P. , Waite P. M. E.
Published: September 2006

In patients with high spinal cord injuries autonomic dysfunction can be dangerous, leading to medical complications such as postural hypotension, autonomic dysreflexia and temperature disturbance. While animal models have been developed to study autonomic dysreflexia, associated temperature changes have not been documented. Our aim here was to use radiotelemetry and infrared thermography in rodents to record the development of cardiovascular and skin temperature changes following complete T4 transection. In adult male Wistar rats (n= 5), responses were assessed prior to spinal cord injury (intact) and for 6 weeks following injury. Statistical analysis by a repeated‐measure ANOVA revealed that following spinal cord injury (SCI), rats exhibited decreased mean arterial pressure (MAP, average decrease of 26 mmHg; P < 0.035) and elevated heart rate (HR, average increase of 65 bpm, P < 0.035) at rest. The basal core body temperature following SCI was also significantly lower than intact levels (−0.9°C; P < 0.0035). Associated with this decreased basal core temperature following SCI was an increased skin temperature of the mid‐tail and hindpaw (+5.6 and +4.0°C, respectively; P < 0.0003) consistent with decreased cutaneous vasoconstrictor tone. Autonomic dysreflexia, in response to a 1 min colorectal distension (25 mmHg), was fully developed by 4 weeks after spinal cord transection, producing increases in MAP greater than 25 mmHg (P < 0.0003). In contrast to the tachycardia seen in intact animals in response to colorectal distension, SCI animals exhibited bradycardia (P < 0.0023). During episodes of autonomic dysreflexia mid‐tail surface temperature decreased (approx. −1.7°C, P < 0.012), consistent with cutaneous vasoconstriction. This is the first study to compare cardiovascular dysfunction with temperature changes following spinal cord transection in rats.
Serotonin potentiates sympathetic responses evoked by spinal NMDA
Authors: Madden Christopher J. , Morrison Shaun F.
Published: September 2006

In urethane–chloralose anaesthetized, neuromuscularly blocked, ventilated rats, we examined the effects on sympathetic outflow to brown adipose tissue (BAT) of separate and simultaneous spinal microinjections of NMDA and serotonin. Microinjection of NMDA (12 pmol) into the right T4 spinal intermediolateral nucleus (IML) immediately increased ipsilateral brown adipose tissue (BAT) sympathetic nerve activity (SNA; peak: +546% of control), BAT thermogenesis (+0.8°C) and heart rate (+53 beats min−1), whereas microinjection of a lower dose of NMDA (1.2 pmol) did not change any of the recorded variables. Microinjection of 5‐hydroxytryptamine (5‐HT, 2 nmol) into the T4 IML increased BAT SNA (peak: +342% of control) at a long latency (mean onset: 23min). The long latency 5‐HT‐evoked increase in BAT SNA was prevented by microinjection of methysergide (600 pmol) into the T4 IML. The increases in BAT SNA evoked by T4 IML microinjections of NMDA (12 pmol) were significantly potentiated (two to three times larger than the response to NMDA alone) following T4 IML microinjections of 5‐HT (100 pmol to 2 nmol, but not 20 pmol). Also, microinjection of 5‐HT (200 pmol) converted the subthreshold dose of NMDA (1.2 pmol) into an effective dose for increasing BAT SNA and heart rate. The 5‐HT‐mediated potentiation of the increase in BAT SNA evoked by microinjection of NMDA into the T4 IML was reversed by microinjection of methysergide (600 pmol) into the T4 IML. These results demonstrate that BAT SNA and thermogenesis can be driven by activation of spinal excitatory amino acid or 5‐HT receptors and that concomitant activation of spinal NMDA and 5‐HT receptors can act synergistically to markedly increase BAT SNA and thermogenesis.
Involvement of intramuscular interstitial cells of Cajal in neuroeffector transmission in the gastrointestinal tract
Authors: Ward Sean M. , Sanders Kenton M.
Published: September 2006

Specialized cells known as interstitial cells of Cajal (ICC) are distributed in specific locations within the tunica muscularis of the gastrointestinal (GI) tract. ICC serve as electrical pacemakers, provide pathways for the active propagation of slow waves, are mediators of enteric motor neurotransmission and play a role in afferent neural signalling. Morphological studies have provided evidence that motor neurotransmission in the GI tract does not occur through poorly defined structures between nerves and smooth muscle, but rather via specialized synapses that exist between enteric nerve terminals and intramuscular ICC or ICC‐IM. ICC‐IM are coupled to smooth muscle cells via gap junctions and post‐junctional responses elicited in ICC‐IM are conducted to neighbouring smooth muscle cells. Electrophysiological studies from the stomachs and sphincters of wild‐type and mutant animals that lack ICC‐IM have provided functional evidence for the importance of ICC in cholinergic excitatory and nitrergic inhibitory motor neurotransmission. Intraperitoneal injection of animals with Kit neutralizing antibody or organ culture of gastrointestinal tissues in the presence of neutralizing antibody, which blocks the development and maintenance of ICC, has provided further evidence for the role of ICC in enteric motor transmission. ICC‐IM also generate an ongoing discharge of unitary potentials in the gastric fundus and antrum that contributes to the overall excitability of the stomach.
The influence of inspiratory muscle work history and specific inspiratory muscle training upon human limb muscle fatigue
Authors: McConnell Alison K. , Lomax Michelle
Published: September 2006

The purpose of this study was to assess the influence of the work history of the inspiratory muscles upon the fatigue characteristics of the plantar flexors (PF). We hypothesized that under conditions where the inspiratory muscle metaboreflex has been elicited, PF fatigue would be hastened due to peripheral vasoconstriction. Eight volunteers undertook seven test conditions, two of which followed 4 week of inspiratory muscle training (IMT). The inspiratory metaboreflex was induced by inspiring against a calibrated flow resistor. We measured torque and EMG during isometric PF exercise at 85% of maximal voluntary contraction (MVC) torque. Supramaximal twitches were superimposed upon MVC efforts at 1 min intervals (MVCTI); twitch interpolation assessed the level of central activation. PF was terminated (Tlim) when MVCTI was <50% of baseline MVC. PF Tlim was significantly shorter than control (9.93 ± 1.95 min) in the presence of a leg cuff inflated to 140 mmHg (4.89 ± 1.78 min; P= 0.006), as well as when PF was preceded immediately by fatiguing inspiratory muscle work (6.28 ± 2.24 min; P= 0.009). Resting the inspiratory muscles for 30 min restored the PF Tlim to control. After 4 weeks, IMT, inspiratory muscle work at the same absolute intensity did not influence PF Tlim, but Tlim was significantly shorter at the same relative intensity. The data are the first to provide evidence that the inspiratory muscle metaboreflex accelerates the rate of calf fatigue during PF, and that IMT attenuates this effect.
The glutamate transporter EAAT5 works as a presynaptic receptor in mouse rod bipolar cells
Authors: Wersinger Eric , Schwab Yannick , Sahel José‐Alain , Rendon Alvaro , Pow David V. , Picaud Serge , Roux Michel J.
Published: September 2006

Membrane neurotransmitter transporters control the concentration of their substrate in the synaptic clefts, through the thermodynamic coupling of uptake to the movement of Na+ and other ions. In addition, excitatory amino acid transporters (EAAT) have a Cl− conductance which is gated by the joint binding of Na+ and glutamate, but thermodynamically uncoupled to the flux of glutamate. This conductance is particularly large in the retina‐specific EAAT5 isoform. In the mouse retina, we located EAAT5 in both cone and rod photoreceptor terminals and in axon terminals of rod bipolar cells. In these later cells, application of glutamate on the axon terminal evoked a current that reversed at ECl, was insensitive to bicuculline, TPMPA, strychnine, dl‐AP5, CNQX and MCPG, but blocked by the glutamate transporter inhibitor dl‐tBOA. Furthermore, short depolarizations of the bipolar cells evoked a dl‐tBOA and Cd2+‐sensitive current whose amplitude was comparable to the glutamate‐evoked current. Its kinetics indicated that EAAT5 was located close to the glutamate release site. For 2 ms depolarizations evoking maximal responses, the EAAT5‐mediated current carried between 2 and 8 times more charge as an average inhibitory GABA or glycine postsynaptic current received spontaneously from amacrine cells, with 10 mm or 0.5 mm intracellular EGTA, respectively. In conditions for which reciprocal inhibition could be monitored, the charge carried by the EAAT5 current was 1.5 times larger than the one carried by the inhibitory postsynaptic currents received from amacrine cells. These results indicate that EAAT5 acts as a major inhibitory presynaptic receptor at mammalian rod bipolar cell axon terminals. This feedback mechanism could control glutamate release at the ribbon synapses of a non‐spiking neuron and increase the temporal contrast in the rod photoreceptor pathway.
Auditory mechanotransduction in the absence of functional myosin‐XVa
Authors: Stepanyan Ruben , Belyantseva Inna A. , Griffith Andrew J. , Friedman Thomas B. , Frolenkov Gregory I.
Published: September 2006

In hair cells of all vertebrates, a mechanosensory bundle is formed by stereocilia with precisely graded heights. Unconventional myosin‐XVa is critical for formation of this bundle because it transports whirlin and perhaps other molecular components responsible for programmed elongation of stereocilia to the stereocilia tips. A tip of a stereocilium is the site of stereocilia growth and one of the proposed sites of mechano‐electrical transduction. In adult shaker 2 mice, a mutation that disables the motor function of myosin‐XVa results in profound deafness and abnormally short stereocilia that lack stereocilia links, an indispensable component of mechanotransduction machinery. Therefore, it was assumed that myosin‐XVa is required for proper formation of the mechanotransduction apparatus. Here we show that in young postnatal shaker 2 mice, abnormally short stereocilia bundles of auditory hair cells have numerous stereocilia links and ‘wild type’ mechano‐electrical transduction. We compared the mechanotransduction current in auditory hair cells of young normal‐hearing littermates, myosin‐XVa‐deficient shaker 2 mice, and whirler mice that have similarly short stereocilia but intact myosin‐XVa at the stereocilia tips. This comparison revealed that the absence of functional myosin‐XVa does not disrupt adaptation of the mechanotransduction current during sustained bundle deflection. Thus, the hair cell mechanotransduction complex forms and functions independently from myosin‐XVa‐based hair bundle morphogenesis.
The frequency of human, manual adjustments in balancing an inverted pendulum is constrained by intrinsic physiological factors
Authors: Loram Ian D. , Gawthrop Peter J. , Lakie Martin
Published: September 2006

While standing naturally and when manually or pedally balancing an equivalent inverted pendulum, the load sways slowly (characteristic unidirectional duration ∼1 s) and the controller, calf muscles or hand, makes more frequent adjustments (characteristic unidirectional duration 400 ms). Here we test the hypothesis that these durations reflect load properties rather than some intrinsic property of the human neuromuscular system. Using a specialized set‐up mechanically analogous to real standing, subjects manually balanced inverted pendulums with different moments of inertia through a compliant spring representing the Achilles tendon. The spring bias was controlled by a sensitive joystick via a servo motor and accurate visual feedback was provided on an oscilloscope. As moment of inertia decreased, inverted pendulum sway size increased and it became difficult to sustain successful balance. The mean duration of unidirectional balance adjustments did not change. Moreover, the mean duration of unidirectional inverted pendulum sway reduced only slightly, remaining around 1 s. The simplest explanation is that balance was maintained by a process of manual adjustments intrinsically limited to a mean frequency of two to three unidirectional adjustments per second corresponding to intermittent control observed in manual tracking experiments. Consequently the inverted pendulum sway duration, mechanically related to the bias duration, reflects an intrinsic constraint of the neuromuscular control system. Given the similar durations of sway and muscle adjustments observed in real standing, we postulate that the characteristic duration of unidirectional standing sway reflects intrinsic intermittent control rather than the inertial properties of the body.
Effects of h1‐calponin ablation on the contractile properties of bladder versus vascular smooth muscle in mice lacking SM‐B myosin
Authors: Babu Gopal J. , Celia Gerard , Rhee Albert Y. , Yamamura Hisako , Takahashi Katsuhito , Brozovich Frank V. , Osol George , Periasamy Muthu
Published: September 2006

The functional significance of smooth muscle‐specific h1‐calponin up‐regulation in the smooth muscle contractility of SM‐B null mice was studied by generating double knockout mice lacking both h1‐calponin and SM‐B myosin. The double knockout mice appear healthy, reproduce well and do not show any smooth muscle pathology. Loss of h1‐calponin in the SM‐B null mice bladder resulted in increased maximal shortening velocity (Vmax) and steady‐state force generation. The force dilatation pressure, which was decreased in the SM‐B null mesenteric vessels, was restored to wild‐type levels in the double knockout vessels. In contrast, the half‐time to maximal constriction was significantly increased in the double knockout vessels similar to that of SM‐B null mice and indicating decreased shortening velocity in the double knockout vessels. Biochemical analyses showed that there is a significant reduction in smooth muscle α‐actin levels, whereas h‐caldesmon levels are increased in the double knockout bladder and mesenteric vessels, suggesting that these changes may also partly contribute to the altered contractile function. Taken together, our studies suggest that up‐regulation of h1‐calponin in the SM‐B null mice may be necessary to maintain a reduced level of cross‐bridge cycling over time in the absence of SM‐B myosin and play an important role in regulating the smooth muscle contraction.
Modulation of GABAergic inhibition in the rat superior colliculus by a presynaptic group II metabotropic glutamate receptor
Authors: Neale S. A. , Salt T. E.
Published: September 2006

Previous work has indicated that metabotropic glutamate receptors (mGluRs) modulate visual responses of superior colliculus (SC) neuronesin vivoin a variety of ways, in a manner that can be dependent upon visual stimulus properties. How this occurs remains unclear. In this study we aimed to determine how activation of mGluR2 and mGluR3 receptors (Group II) might modulate visual responses, by using field potential and whole‐cell patch clamp recording techniques in rat SC slice. Stimulation within the superficial layers of the SC, in the presence of ionotropic glutamate receptor antagonists, evoked IPSCs that were blocked by bicuculline indicating that they are mediated via GABAAreceptors. It is likely that these IPSCs were of heterogeneous origin as they showed substantial variation in paired‐pulse behaviour. Nevertheless, activation of Group II mGluRs with the group‐selective agonist LY354740 (300 nm, bath application) resulted in a reduction of these IPSCs (to 56% of control amplitude), and this was associated with a decrease in paired‐pulse depression. At the same concentration, LY354740 did not reduce the EPSC or field‐EPSP evoked by stimulation of the retinal input to the SC. The effects of LY354740 on IPSCs were not mimicked by the mGluR3‐selective agonistN‐acetyl‐aspartyl‐glutamate (NAAG, 200–500 μm). Stimulation of IPSCs with trains of impulses (10 at 20 Hz) in order to mimic natural activation patterns resulted in sequences of IPSCs that were reduced in amplitude towards the end of the stimulus train. Application of the Group II antagonist LY341495 (100 nm) under these conditions resulted in an increase in later IPSCs in a third of neurones tested. These findings indicate that mGluR2 (but not mGluR3) can selectively modulate GABAergic inhibition in SC, probably via a presynaptic mechanism. Furthermore, these receptors may be activated by synaptically released transmitter during patterns of activation similar to those seen during visual processing. Thus mGluR2 receptors could have a function in activity‐dependent modulation of inhibitory processing during visual responses.
Angiotensin II activates two cation conductances with distinct TRPC1 and TRPC6 channel properties in rabbit mesenteric artery myocytes
Authors: Saleh S. N. , Albert A. P. , Peppiatt C. M. , Large W. A.
Published: September 2006

Angiotensin II (Ang II) is a potent vasoconstrictor with an important role in controlling blood pressure; however, there is little information on cellular mechanisms underlying Ang II‐evoked vasoconstrictor responses. The aim of the present study is to investigate the effect of Ang II on cation conductances in freshly dispersed rabbit mesenteric artery myocytes at the single‐channel level using patch‐clamp techniques. In cell‐attached patches, bath application of low concentrations of Ang II (1 nm) activated cation channel currents (Icat1) with conductances states of about 15, 30 and 45 pS. At relatively high concentrations, Ang II (100 nm) inhibitedIcat1but evoked another cation channel (Icat2) with a conductance of approximately 2 pS. Ang II‐evokedIcat1andIcat2were inhibited by the AT1receptor antagonist losartan and the phospholipase C (PLC) inhibitor U73122. The diacylglycerol (DAG) lipase inhibitor RHC80267 initially inducedIcat1which was subsequently inhibited to revealIcat2. The DAG analogue 1‐oleoyl‐2‐acetyl‐sn‐glycerol (1 μm) activatedIcat1andIcat2but inositol 1,4,5‐trisphosphate did not evoke either conductance. The protein kinase C (PKC) inhibitor chelerythrine (3 μm) potentiated Ang II‐evokedIcat1and inhibitedIcat2whereas the PKC activator phorbol‐12,13‐dibutyrate (1 μm) reduced Ang II‐inducedIcat1but activatedIcat2. Moreover in cell‐attached patches pretreated with chelerythrine, application of 100 nmAng II activatedIcat1. These data indicate that PKC inhibitsIcat1but stimulatesIcat2. Agents that deplete intracellular Ca2+stores also activated cation channel currents with similar properties toIcat2. Bath application of anti‐TRPC6 and anti‐TRPC1 antibodies to inside‐out patches inhibitedIcat1andIcat2, respectively. Also flufenamic acid and zero external Ca2+concentration, respectively, potentiated and reduced Ang II‐evokedIcat1. Immunocytochemical studies showed TRPC6 and TRPC1 expression with TRPC6 preferentially distributed in the plasma membrane and TRPC1 expression located throughout the myocyte. These results indicate that Ang II activates two distinct cation conductances in mesenteric artery myocytes by stimulation of AT1receptors linked to PLC.Icat1is activated by DAG via a PKC‐independent mechanism whereasIcat2involves DAG acting via a PKC‐dependent pathway. Higher concentrations of Ang II inhibitIcat1by activating an inhibitory effect of PKC. It is proposed that TRPC6 and TRPC1 channel proteins are important components of Ang II‐inducedIcat1andIcat2, respectively.
Depolarization‐induced retrograde synaptic inhibition in the mouse cerebellar cortex is mediated by 2‐arachidonoylglycerol
Authors: Szabo Bela , Urbanski Michal J. , Bisogno Tiziana , Marzo Vincenzo Di , Mendiguren Aitziber , Baer Wolfram U. , Freiman Ilka
Published: September 2006

Endocannabinoids acting on CB1 cannabinoid receptors are involved in short‐ and long‐term depression of synaptic transmission. The aim of the present study was to determine which endocannabinoid, anandamide or 2‐arachidonoylglycerol (2‐AG), is involved in depolarization‐induced suppression of inhibition (DSI) in the cerebellar cortex, which is the most widely studied form of short‐term depression. Depolarization of Purkinje cells in the mouse cerebellum led to an increase in intracellular calcium concentration and to suppression of the inhibitory input to these neurons (i.e. DSI occurred). Orlistat and RHC80267, two blockers of sn‐1‐diacylglycerol lipase, the enzyme catalysing 2‐AG formation, abolished DSI by acting downstream of calcium influx. In contrast, DSI occurred also in the presence of a phospholipase C inhibitor. Intact operation of the calcium‐dependent messengers calmodulin and Ca2+–calmodulin‐dependent protein kinase II were necessary for DSI. DSI was potentiated by an inhibitor of the main 2‐AG‐degrading enzyme, monoacylglycerol lipase. Interference with the anandamide metabolizing enzyme, fatty acid amide hydrolase, did not modify DSI. Thus, three kinds of observations identified 2‐AG as the endocannabinoid involved in DSI in the mouse cerebellum: DSI was abolished by diacylglycerol lipase inhibitors; DSI was potentiated by a monoglyceride lipase inhibitor; and DSI was not changed by an inhibitor of fatty acid amide hydrolase. Further experiments indicated that 2‐AG is the endocannabinoid mediating short‐term retrograde signalling also at other synapses: orlistat abolished DSI in the rat cerebellum, DSI in the mouse substantia nigra pars reticulata and depolarization‐induced suppression of excitation in the mouse cerebellum.
Cell physiology of cAMP sensor Epac
Authors: Holz George G. , Kang Guoxin , Harbeck Mark , Roe Michael W. , Chepurny Oleg G.
Published: September 2006

Epac is an acronym for the exchange proteins activated directly by cyclic AMP, a family of cAMP‐regulated guanine nucleotide exchange factors (cAMPGEFs) that mediate protein kinase A (PKA)‐independent signal transduction properties of the second messenger cAMP. Two variants of Epac exist (Epac1 and Epac2), both of which couple cAMP production to the activation of Rap, a small molecular weight GTPase of the Ras family. By activating Rap in an Epac‐mediated manner, cAMP influences diverse cellular processes that include integrin‐mediated cell adhesion, vascular endothelial cell barrier formation, and cardiac myocyte gap junction formation. Recently, the identification of previously unrecognized physiological processes regulated by Epac has been made possible by the development of Epac‐selective cyclic AMP analogues (ESCAs). These cell‐permeant analogues of cAMP activate both Epac1 and Epac2, whereas they fail to activate PKA when used at low concentrations. ESCAs such as 8‐pCPT‐2′‐O‐Me‐cAMP and 8‐pMeOPT‐2′‐O‐Me‐cAMP are reported to alter Na+, K+, Ca2+ and Cl− channel function, intracellular [Ca2+], and Na+–H+ transporter activity in multiple cell types. Moreover, new studies examining the actions of ESCAs on neurons, pancreatic beta cells, pituitary cells and sperm demonstrate a major role for Epac in the stimulation of exocytosis by cAMP. This topical review provides an update concerning novel PKA‐independent features of cAMP signal transduction that are likely to be Epac‐mediated. Emphasized is the emerging role of Epac in the cAMP‐dependent regulation of ion channel function, intracellular Ca2+ signalling, ion transporter activity and exocytosis.
Source-to-sensation level ratio of transmitted biosonar pulses in an echolocating false killer whale
Authors: Supin Alexander Ya. , Nachtigall Paul E. , Breese Marlee
Published: September 2006

Transmitted biosonar pulses, and the brain auditory evoked potentials (AEPs) associated with those pulses, were synchronously recorded in a false killer whale Pseudorca crassidens trained to accept suction-cup EEG electrodes and to detect targets by echolocation. AEP amplitude was investigated as a function of the transmitted biosonar pulse source level. For that, a few thousand of the individual AEP records were sorted according to the spontaneously varied amplitude of synchronously recorded biosonar pulses. In each of the sorting bins (in 5-dB steps) AEP records were averaged to extract AEP from noise; AEP amplitude was plotted as a function of the biosonar pulse source level. For comparison, AEPs were recorded to external (in free field) sound pulses of a waveform and spectrum similar to those of the biosonar pulses; amplitude of these AEPs was plotted as a function of sound pressure level. A comparison of these two functions has shown that, depending on the presence or absence of a target, the sensitivity of the whale’s hearing to its own transmitted biosonar pulses was 30 to 45dB lower than might be expected in a free acoustic field.
Individual variation in the pup attraction call produced by female Australian fur seals during early lactation
Authors: Tripovich Joy S. , Rogers Tracey L. , Canfield Rhondda , Arnould John P. Y.
Published: September 2006

Otariid seals (fur seals and sea lions) are colonial breeders with large numbers of females giving birth on land during a synchronous breeding period. Once pups are born, females alternate between feeding their young ashore and foraging at sea. Upon return, both mother and pup must relocate each other and it is thought to be primarily facilitated by vocal recognition. Vocalizations of thirteen female Australian fur seals (Arctocephalus pusillus doriferus) were recorded during the breeding seasons of December 2000 and 2001, when pups are aged from newborns to one month. The pup attraction call was examined to determine whether females produce individually distinct calls which could be used by pups as a basis for vocal recognition. Potential for individual coding, discriminant function analysis (DFA), and classification and regression tree analysis were used to determine which call features were important in separating individuals. Using the results from all three analyses: F0, MIN F and DUR were considered important in separating individuals. In 76% of cases, the PAC was classified to the correct caller, using DFA, suggesting that there is sufficient stereotypy within individual calls, and sufficient variation between them, to enable vocal recognition by pups of this species.
Source levels and harmonic content of whistles in white-beaked dolphins (Lagenorhynchus albirostris)
Authors: Rasmussen M. H. , Lammers M. , Beedholm K. , Miller L. A.
Published: September 2006

Recordings of white-beaked dolphin whistles were made in Faxaflói Bay (Iceland) using a three-hydrophone towed linear array. Signals from the hydrophones were routed through an amplifier to a lunch box computer on board the boat and digitized using a sample rate of 125kHz per channel. Using this method more than 5000 whistles were recorded. All recordings were made in sea states 0–1 (Beaufort scale). Dolphins were located in a 2D horizontal plane by using the difference of arrival time to the three hydrophones, and source levels were estimated from these positions using two different methods (I and II). Forty-three whistles gave a reliable location for the vocalizing dolphin when using method II and of these 12 when using method I. Source level estimates on the center hydrophone were higher using method I [average source level 148(rms)±12dB,n=36] than for method II [average source level 139(rms)±12dB,n=36]. Using these rms values the maximum possible communication range for whistling dolphins given the local ambient noise conditions was then estimated. The maximum range was 10.5km for a dolphin whistle with the highest source level (167dB) and about 140m for a whistle with the lowest source level (118dB). Only two of the 43 whistles contained an unequal number of harmonics recorded at the three hydrophones judging from the spectrograms. Such signals could be used to calculate the directionality of whistles, but more recordings are necessary to describe the directionality of white-beaked dolphin whistles.
Background noise cancellation of manatee vocalizations using an adaptive line enhancer
Authors: Yan Zheng , Niezrecki Christopher , Cattafesta Louis N. , Beusse Diedrich O.
Published: September 2006

The West Indian manatee (Trichechus manatus latirostris) has become an endangered species partly because of an increase in the number of collisions with boats. A device to alert boaters of the presence of manatees is desired. Previous research has shown that background noise limits the manatee vocalization detection range (which is critical for practical implementation). By improving the signal-to-noise ratio of the measured manatee vocalization signal, it is possible to extend the detection range. The finite impulse response (FIR) structure of the adaptive line enhancer (ALE) can detect and track narrow-band signals buried in broadband noise. In this paper, a constrained infinite impulse response (IIR) ALE, called a feedback ALE (FALE), is implemented to reduce the background noise. In addition, a bandpass filter is used as a baseline for comparison. A library consisting of 100 manatee calls spanning ten different signal categories is used to evaluate the performance of the bandpass filter, FIR-ALE, and FALE. The results show that the FALE is capable of reducing background noise by about 6.0 and 21.4dB better than that of the FIR-ALE and bandpass filter, respectively, when the signal-to-noise ratio (SNR) of the original manatee call is −5dB.
Simulation of ultrasonic fields radiated by a circular source through a layer with nonparallel boundaries
Authors: Jasiūnienė Elena , Mažeika Liudas , Kažys Rymantas
Published: September 2006

Active elements of ultrasonic transducers are separated from the medium by thick protective layers, which may have nonparallel front and back surfaces. The objective of this work was to develop a simple method suitable for fast calculation of ultrasonic fields radiated through a layer with parallel or nonparallel boundaries and enabling one to take into account multiple reflections inside the layer. The main presumption of the proposed method is the following: after refraction at the boundary between two media, the ultrasonic field consists of plane and edge waves as before refraction. The proposed simulation method is based on transformation of a multi-layered medium into a virtual one without internal boundaries and equivalent to the actual medium from the point of a view of the times of flight of the direct plane and edge waves. The method enables simulation of radiated ultrasonic fields even after multiple reflections within the layer with parallel or nonparallel boundaries. The examples of simulated and experimentally measured ultrasonic fields of the transducer with a nonparallel front surface of protection layer, radiating into the water, are presented.
Orthogonal adaptation for active noise control
Authors: Yuan Jing
Published: September 2006

Many active noise control (ANC) systems apply the filtered-x least mean squares (FXLMS) algorithm for controller adaptation. The accuracy of path models is an important issue in these systems. Since parameter drifting in a noise field may cause model error between the secondary path and its prestored model in an ANC system, some ANC systems employ two adaptive processes for path modeling and controller adaptation respectively. In this paper, a new ANC system is proposed with adaptive path modeling and nonadaptive controller design. The proposed ANC system is noninvasive without persistent excitations. It avoids the slow convergence and inevitable estimation errors in controller adaptation. A rigorous analysis is presented to prove that the new ANC system will converge to an optimal one in the minimum H2 norm sense. Experimental results are presented to verify the performance of the proposed ANC system.
Application of spectral subtraction method on enhancement of electrolarynx speech
Authors: Liu Hanjun , Zhao Qin , Wan Mingxi , Wang Supin
Published: September 2006

Although electrolarynx (EL) serves as an important method of phonation for the laryngectomees, the resulting speech is of poor intelligibility due to the presence of a steady background noise caused by the instrument, even worse in the case of additive noise. This paper investigates the problem of EL speech enhancement by taking into account the frequency-domain masking properties of the human auditory system. One approach is incorporating an auditory masking threshold (AMT) for parametric adaptation in a subtractive-type enhancement process. The other is the supplementary AMT (SAMT) algorithm, which applies a cross-correlation spectral subtraction (CCSS) approach as a post-processing scheme to enhancing EL speech dealt with the AMT method. The performance of these two algorithms was evaluated as compared to the power spectral subtraction (PSS) algorithm. The best performance of EL speech enhancement was associated with the SAMT algorithm, followed by the AMT algorithm and the PSS algorithm. Acoustic and perceptual analyses indicated that the AMT and SAMT algorithms achieved the better performances of noise reduction and the enhanced EL speech was more pleasant to human listeners as compared to the PSS algorithm.
Auditory filter shapes of CBA/CaJ mice: Behavioral assessments
Authors: May Bradford J. , Kimar Sarah , Prosen Cynthia A.
Published: September 2006

Auditory filter shape and frequency tuning may be derived by measuring changes in pure tone thresholds as a function of the bandwidth of notched-noise maskers. When these psychophysical methods were applied to CBA/CaJ mice, the resulting filter shapes were well fit by roex(p,r) functions originally developed for human subjects. The equivalent rectangular bandwidths (ERBs) of the filter shapes ranged from 16 to 19% of test frequencies between 8 to 16kHz. These ERBs correspond well to the performance of humans at high frequencies and the limited number of mammalian species that have been characterized with notched-noise procedures. Frequency tuning was maintained throughout most of the adult lifespan and then showed a selective high-frequency loss at ages beyond 2 years. These results suggest that auditory filtering effects in adult CBA/CaJ mice are similar to normal processes in other mammalian species and provide an excellent model of human presbycusis when they begin to degrade in aging individuals.
Sonoelastographic imaging of interference patterns for estimation of shear velocity distribution in biomaterials
Authors: Wu Zhe , Hoyt Kenneth , Rubens Deborah J. , Parker Kevin J.
Published: September 2006

The authors have recently demonstrated the shear wave interference patterns created by two coherent vibration sources imaged with the vibration sonoelastography technique. If the two sources vibrate at slightly different frequencies ω and ω+Δω, respectively, the interference patterns move at an apparent velocity of (Δω∕2ω)*υshear, where υshear is the shear wave speed. We name the moving interference patterns “crawling waves.” In this paper, we extend the techniques to inspect biomaterials with nonuniform stiffness distributions. A relationship between the local crawling wave speed and the local shear wave velocity is derived. In addition, a modified technique is proposed whereby only one shear wave source propagates shear waves into the medium at the frequency ω. The ultrasound probe is externally vibrated at the frequency ω−Δω. The resulting field estimated by the ultrasound (US) scanner is proven to be an exact representation of the propagating shear wave field. The authors name the apparent wave motion “holography waves.” Real-time video sequences of both types of waves are acquired on various inhomogeneous elastic media. The distribution of the crawling/holographic wave speeds are estimated. The estimated wave speeds correlate with the stiffness distributions.
Theoretical detection ranges for acoustic based manatee avoidance technology
Authors: Phillips Richard , Niezrecki Christopher , Beusse Diedrich O.
Published: September 2006

The West Indian manatee (Trichechus manatus latirostris) has become endangered partly because of watercraft collisions in Florida’s coastal waterways. To reduce the number of collisions, warning systems based upon detecting manatee vocalizations have been proposed. One aspect of the feasibility of an acoustically based warning system relies upon the distance at which a manatee vocalization is detectable. Assuming a mixed spreading model, this paper presents a theoretical analysis of the system detection capabilities operating within various background and watercraft noise conditions. This study combines measured source levels of manatee vocalizations with the modeled acoustic properties of manatee habitats to develop a method for determining the detection range and hydrophone spacing requirements for acoustic based manatee avoidance technologies. In quiet environments (background noise ≈70dB) it was estimated that manatee vocalizations are detectable at approximately 250m, with a 6dB detection threshold. In louder environments (background noise ≈100dB) the detection range drops to 2.5m. In a habitat with 90dB of background noise, a passing boat with a maximum noise floor of 120dB would be the limiting factor when it is within approximately 100m of a hydrophone. The detection range was also found to be strongly dependent on the manatee vocalization source level.
The effect of superior-canal opening on middle-ear input admittance and air-conducted stapes velocity in chinchilla
Authors: Songer Jocelyn E. , Rosowski John J.
Published: September 2006

The recent discovery of superior semicircular canal (SC) dehiscence syndrome as a clinical entity affecting both the auditory and vestibular systems has led to the investigation of the impact of a SC opening on the mechanics of hearing. It is hypothesized that the hole in the SC acts as a “third window” in the inner ear which shunts sound-induced stapes volume velocity away from the cochlea through the opening in the SC. To test the hypothesis and to understand the third window mechanisms the middle-ear input admittance and sound-induced stapes velocity were measured in chinchilla before and after surgically introducing a SC opening and after patching the opening. The extent to which patching returned the system to the presurgical state is used as a control criterion. In eight chinchilla ears a statistically significant, reversible increase in low-frequency middle-ear input admittance magnitude occurred as a result of opening the SC. In six ears a statistically significant reversible increase in stapes velocity was observed. Both of these changes are consistent with the hole creating a shunt pathway that increases the cochlear input admittance.
Semirealistic models of the cochlea
Authors: Sieroka Norman , Dosch Hans Günter , Rupp André
Published: September 2006

The aim of this paper is the introduction and comparison of consistent albeit passive mechanical models for the whole cochlea. A widely used transmission line filterbank, which hydrodynamically speaking is a long wave approximation (L model), suffers from a well-known inconsistency: its main modeling assumption is not valid within the resonance region, where most of the overall excitation takes place. In the present paper two approaches to overcome this inconsistency are discussed. One model is the average pressure (AP) model by Duifhuis, the other is obtained by a combination of a long and a short wave approximation (LS model). Considerable differences between the L and the LS model are observed. All models are compared by inserting them into the full integral equation obtained from the hydrodynamic equations and the boundary conditions. Here the LS model fares better than the AP model for small damping, whereas the opposite is true for higher damping. As expected, the L model fails badly in the resonance region.
Simulated effects of cricothyroid and thyroarytenoid muscle activation on adult-male vocal fold vibration
Authors: Lowell Soren Y. , Story Brad H.
Published: September 2006

Adjustments to cricothyroid and thyroarytenoid muscle activation are critical to the control of fundamental frequency and aerodynamic aspects of vocal fold vibration in humans. The aerodynamic and physical effects of these muscles are not well understood and are difficult to study in vivo. Knowledge of the contributions of these two muscles is essential to understanding both normal and disordered voice physiology. In this study, a three-mass model for voice simulation in adult males was used to produce systematic changes to cricothyroid and thyroarytenoid muscle activation levels. Predicted effects on fundamental frequency, aerodynamic quantities, and physical quantities of vocal fold vibration were assessed. Certain combinations of these muscle activations resulted in aerodynamic and physical characteristics of vibration that might increase the mechanical stress placed on the vocal fold tissue.
Active control of drag noise from a small axial flow fan
Authors: Wang Jian , Huang Lixi
Published: September 2006

Noise sources in an axial flow fan can be divided into fluctuating axial thrust forces and circumferential drag forces. For the popular design of a seven-blade rotor driven by a motor supported by four struts, drag noise dominates. This study aims to suppress the drag noise globally by active control schemes. Drag noise features a rotating dipole and it has to be cancelled by a secondary source of the same nature. This is achieved experimentally by a pair of loudspeakers positioned at right angles to each other on the fan rotational plane. An adaptive LMS feedforward scheme is used to produce the control signal for one loudspeaker and the time derivative of this signal is used to drive the other loudspeaker. The antisounds radiated by the two loudspeakers have a fixed phase relation of 90° forming a rotating dipole. An open-loop control scheme is also implemented for the purpose of comparison and easier implementation in real-life applications. The results show that the globally integrated sound power is reduced by about 13dB for both closed- and open-loop schemes. A possible limiting factor for the cancellation performance is found to be the presence of higher order modes of drag noise.
Pure-tone auditory stream segregation and speech perception in noise in cochlear implant recipients
Authors: Hong Robert S. , Turner Christopher W.
Published: September 2006

This study examined the ability of cochlear implant users and normal-hearing subjects to perform auditory stream segregation of pure tones. An adaptive, rhythmic discrimination task was used to assess stream segregation as a function of frequency separation of the tones. The results for normal-hearing subjects were consistent with previously published observations (L.P.A.S van Noorden, Ph.D. dissertation, Eindhoven University of Technology, Eindhoven, The Netherlands 1975), suggesting that auditory stream segregation increases with increasing frequency separation. For cochlear implant users, there appeared to be a range of pure-tone streaming abilities, with some subjects demonstrating streaming comparable to that of normal-hearing individuals, and others possessing much poorer streaming abilities. The variability in pure-tone streaming of cochlear implant users was correlated with speech perception in both steady-state noise and multi-talker babble. Moderate, statistically significant correlations between streaming and both measures of speech perception in noise were observed, with better stream segregation associated with better understanding of speech in noise. These results suggest that auditory stream segregation is a contributing factor in the ability to understand speech in background noise. The inability of some cochlear implant users to perform stream segregation may therefore contribute to their difficulties in noise backgrounds.
Polymer acoustic matching layer for broadband ultrasonic applications
Authors: Tohmyoh Hironori
Published: September 2006

A polymer acoustic matching layer has been designed that can act as a frequency filter between water and a test sample, and a method for controlling the high-frequency components of broadband ultrasound by using the designed layer is described. Acoustic imaging of a silicon-bonding sample using a very-low-scale matching layer fabricated from poly(vinylidene chloride) is demonstrated, in which the air gaps between the layer and the sample are evacuated. The experimental results show that the layer, which was designed for signal amplification, works as a broadband filter, as predicted, as well as offering protection against water for dry acoustic imaging.
On the linewidth of the ultrasonic Larsen effect in a reverberant body
Authors: Weaver Richard L. , Lobkis Oleg I.
Published: September 2006

A simple ultrasonic feedback circuit is applied to a high-Q elastic body. At sufficient gain, an ultrasonic howl—or Larsen effect, ensues. It is a pure tone with an extraordinarily narrow spectrum. Theoretical estimates are constructed that predict linewidths proportional to the ratio between the spectral power density of the background noise and the intensity of the howl. In these experiments, this is of the order of nano-Hz and is unmeasurable. By augmenting the absorption and adding noise, the width is brought into a measurable regime, and the theory’s prediction of a wider line is confirmed. It is speculated and demonstrated that these narrow lines permit high precision measurements of tiny changes in structures.
Distortion product otoacoustic emission fine structure analysis of 50 normal-hearing humans
Authors: Reuter Karen , Hammershøi Dorte
Published: September 2006

When distortion product otoacoustic emissions (DPOAEs) are measured with a high-frequency resolution, the DPOAE shows quasi-periodic variations across frequency, called DPOAE fine structure. In this study the DPOAE fine structure is determined for 50 normal-hearing humans using fixed primary levels of L1∕L2=65∕45dB. An algorithm is developed, which characterizes the fine structure ripples in terms of three parameters: ripple spacing, ripple height, and ripple prevalence. The characteristic patterns of fine structure can be found in the DPOAE of all subjects, though the DPOAE fine structure characteristics are individual and vary from subject to subject. On average the ripple spacing decreases with increasing frequency from 18 oct at 1kHz to 332 oct at 5kHz. The ripple prevalence is two to three ripples per 13 oct, and ripple heights of up to 32dB could be detected. The 50 normal-hearing subjects were divided into two groups, the subjects of group A having slightly better hearing levels than subjects of group B. The subjects of group A have significantly higher DPOAE levels. The overall prevalence of fine structure ripples do not differ between the two groups, but are higher and narrower for subjects of group B than for group A.