This study investigated the effects on rainbow trout (Oncorhynchus mykiss) of exposure to high-intensity, low-frequency sonar using an element of the standard Surveillance Towed Array Sensor System Low Frequency Active (LFA) sonar source array. Effects of the LFA sonar on hearing were tested using auditory brainstem responses. Effects were also examined on inner ear morphology using scanning electron microscopy and on nonauditory tissues using general pathology and histopathology. Animals were exposed to a maximum received rms sound pressure level of 193 dB re 1 microPa(2) for 324 or 648 s, an exposure that is far in excess of any exposure a fish would normally encounter in the wild. The most significant effect was a 20-dB auditory threshold shift at 400 Hz. However, the results varied with different groups of trout, suggesting developmental and/or genetic impacts on how sound exposure affects hearing. There was no fish mortality during or after exposure. Sensory tissue of the inner ears did not show morphological damage even several days post-sound exposure. Similarly, gross- and histopathology observations demonstrated no effects on nonauditory tissues.

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Visible light activates a large guanosine cyclic 3',5'-phosphate (cGMP)- and phosphodiesterase (PDE)-dependent infrared light-scattering change in suspensions of photoreceptor disk membranes. Reconstitution experiments show that this signal requires bleached rhodopsin, G protein (three polypeptide subunits of Mr 39 000, 37 000, and 6000 which comprise the GTPase), phosphodiesterase, cGMP, and GTP. The lowest light intensity which elicits the light-scattering signal bleaches 0.002% rhodopsin. cGMP and GTP hydrolysis occurs more slowly than the initial phase of the scattering signal, and the kinetics of nucleotide hydrolysis do not correlate with any phase of the signal. Hydrolysis-resistant analogues of cGMP and GTP support the initial decreasing phase of the signal. Thus, the signal apparently depends upon nucleotide binding rather than hydrolysis. Microscopic observations made under the same conditions as light-scattering experiments show that vesicle-vesicle aggregation and disaggregation occur. The data suggest that light and nucleotide activations of the cyclic nucleotide cascade enzymes are responsible for the vesicle aggregation process and nucleotide hydrolysis for vesicle disaggregation. The vesicle aggregation-disaggregation phenomenon appears likely to be the physical basis of the cGMP- and PDE-dependent changes in infrared transmission.

Abstract. Geophones mounted on floating ice sheets can potentially provide data for a robust method to monitor mechanical properties of the ice. The technique relies on the measurement and inversion of low-frequency elastic waves propagating in the ice. To test this hypothesis, several geophone systems were deployed on the Arctic ice as part of the Office of Naval Research Sea Ice Mechanics Initiative (SIMI), including a winter-over system of 20 triaxial geophones at the fall 1993 SIMI camp. An inversion technique is discussed here through references to the literature and by analysis of geophone data, specifically those data collected on "clean" first-year ice off Resolute Bay, Canada, and on highly irregular multiyear ice found at the fall SIMI camp. For undeformed first-year ice, the inversion technique gave an estimate of ice properties that agreed well with known values, although extensive work remains to determine the effects of anisotropy and inhomogeneity. The geophone data for the nonuniform ice at the SIMI camp were very complex and difficult to analyze. The inversion yielded only trends in what can, at best, be termed effective ice thickness and bending rigidity; it is uncertain how these relate to actual ice properties. The SIMI geophone system demonstrated the feasibility of performing autonomous measurements of the characteristics of propagating waves in the Arctic ice; with continued study, it seems evident that such systems can be used in clean first-year ice to monitor ice properties. However, extensive research is required to make this technique useful in multiyear or complex first-year ice. IntroductionModels for prediction of Arctic ice cover and global climate require long-term measurements of ice properties. These will be used as input data to drive models and as ground truth for remote sensing. The unmanned autonomous systems that will be required to make these measurements must be inexpensive and easy to deploy. Existing systems that meet these requirements make only point measurements. Examples are ice stress sensors, temperature sensors, and small, upward looking sonar systems used to measure ice thickness. Such point measurements can yield properties significantly different from those averaged over even a small area, especially in multiyear ice. Important properties such as ice modulus, porosity, and salinity have yet to be measured autonomously; such measurements are currently made by taking ice core samples, a labor intensive and costly procedure.The objective of the work reported here was to explore a proposed method to autonomously determine averaged mechanical properties of Arctic ice. The technique was the inversion of the equations of motion for low-frequency elastic waves in the ice, in order to calculate mechanical properties of the ice from measured characteristics of the traveling waves, such as wave speed. This inversion was similar to that typically performed for seismic signals in land-based geologic studies. The characteristics of the waves that propagate in the ice depen...

Five GTP binding proteins in rat cerebral cortex synaptic membranes were identified by photoaffinity labelling with [3H] or [32P](P3-azido-anilido)-P1-5' GTP (AAGTP). When AAGTP-treated membranes were incubated with colchicine or vinblastine and subsequently washed, a single AAGTP-labelled protein of 42 kD was released into the supernatant. About 30% of the total labelled 42-kD protein was released into supernatants from membranes pretreated with colchicine or vinblastine compared with 15% released from control membranes. The amount of adenylate cyclase regulatory subunit (G unit) remaining in these membranes was assessed with reconstitution studies after inactivating the adenylate cyclase catalytic moiety with N-ethylmaleimide (NEM). Forty to fifty percent of functional G units were lost from membranes treated with colchicine prior to washing. This 40-50% loss of functional G unit after colchicine treatment corresponds to the previously observed 42% loss of NaF and guanylyl-5'-imidodiphosphate [Gpp(NH)p]-activated adenylate cyclase. Release of the AAGTP-labelled 42-kD protein from colchicine-treated synaptic membranes is double that from lumicolchicine-treated membranes. This colchicine-mediated release of 42-kD protein correlates with a doubling of functional G unit released from synaptic membranes after colchicine treatment. These findings suggest multiple populations of the G unit within the synaptic plasma membrane, some of which may interact with cytoskeletal components.