Volume 118, Issue 5, November 2005
Index of content:
- BIOACOUSTICS 
High intensity focused ultrasound-induced gene activation in sublethally injured tumor cells in vitro118(2005); http://dx.doi.org/10.1121/1.2041247View Description Hide Description
Cultured human cervical cancer (HeLa) and rat mammary carcinoma (R3230Ac) cells were transfected with vectors encoding green fluorescent protein (GFP) under the control of hsp70B promoter. Aliquots of transfected cells were placed in thin-wall polymerase chain reaction tubes and exposed to high intensity focused ultrasound (HIFU) at a peak negative pressure . By adjusting the duty cycle of the HIFU transducer, the cell suspensions were heated to a peak temperature from in . Exposure dependent cell viability and gene activation were evaluated. For a HIFU exposure, cell viability dropped from 95% at to 13% at . Concomitantly, gene activation in sublethally injured tumorcells increased from 4% at to 41% at . A similar trend was observed at peak temperature as the exposure time increased from . Further increase of exposure duration to led to significantly reduced cell viability and lower overall gene activation in exposed cells. Altogether, maximum HIFU-induced gene activation was achieved at in . Under these experimental conditions, HIFU-induced gene activation was found to be produced primarily by thermal rather than mechanical stresses.
Off-axis effects on the multipulse structure of sperm whale usual clicks with implications for sound production118(2005); http://dx.doi.org/10.1121/1.2082707View Description Hide Description
Sperm whales (Physeter macrocephalus) produce multipulsed clicks with their hypertrophied nasal complex. The currently accepted view of the sound generation process is based on the click structure measured directly in front of, or behind, the whale where regular interpulse intervals (IPIs) are found between successive pulses in the click. Most sperm whales, however, are recorded with the whale in an unknown orientation with respect to the hydrophone where the multipulse structure and the IPI do not conform to a regular pulse pattern. By combining far-field recordings of usual clicks with acoustic and orientation information measured by a tag on the clicking whale, we analyzed clicks from known aspects to the whale. We show that a geometric model based on the bent horn theory for sound production can explain the varying off-axis multipulse structure. Some of the sound energy that is reflected off the frontal sac radiates directly into the water creating an intermediate pulse p1/2 seen in off-axis recordings. The powerful p1 sonar pulse exits the front of the junk as predicted by the bent-horn model, showing that the junk of the sperm whale nasal complex is both anatomically and functionally homologous to the melon of smaller toothed whales.
118(2005); http://dx.doi.org/10.1121/1.2046747View Description Hide Description
During a recent cetacean survey of the U.S. waters surrounding the Hawaiian Islands, the probable source of the mysterious “boing” sound of the North Pacific Ocean was identified as a minke whale, Balaenoptera acutorostrata. Examination of boing vocalizations from three research surveys confirms previous work that identified two distinct boing vocalization types in the North Pacific. The eastern boing has a pulse repetition rate of and a duration of and was found only east of . The central boing has a pulse repetition rate of and a duration of approximately and was found only west of . Central boing vocalizations produced by a single source indicate that variation in repetition rate and duration of the calls of the individual were not significantly different than the variation among individuals of the same boing type. Despite a slight latitudinal overlap in the vocalizations, pulse repetition rates of the eastern and central boings were distinct.
Target representation of naturalistic echolocation sequences in single unit responses from the inferior colliculus of big brown bats118(2005); http://dx.doi.org/10.1121/1.2041227View Description Hide Description
Echolocating big brown bats (Eptesicus fuscus) emit trains of frequency-modulated(FM)biosonar signals whose duration, repetition rate, and sweep structure change systematically during interception of prey. When stimulated with a sequence of 54 FM pulse-echo pairs that mimic sounds received during search, approach, and terminal stages of pursuit, single neurons in the bat’s inferior colliculus (IC) register the occurrence of a pulse or echo with an average of spike/sound. Individual IC neurons typically respond to only a segment of the search or approach stage of pursuit, with fewer neurons persisting to respond in the terminal stage. Composite peristimulus-time-histogram plots of responses assembled across the whole recorded population of IC neurons depict the delay of echoes and, hence, the existence and distance of the simulated biosonar target, entirely as on-response latencies distributed across time. Correlated changes in pulse duration, repetition rate, and pulse or echo amplitude do modulate the strength of responses (probability of the single spike actually occurring for each sound), but registration of the target itself remains confined exclusively to the latencies of single spikes across cells. Modeling of echo processing in FMbiosonar should emphasize spike-time algorithms to explain the content of biosonar images.