S. Dennison - Profile on Academia.edu (original) (raw)
Papers by S. Dennison
Frontiers in physiology, 2013
A yearling California sea lion (Zalophus californianus) was admitted into rehabilitation with sig... more A yearling California sea lion (Zalophus californianus) was admitted into rehabilitation with signs of cerebellar pathology. Diagnostic imaging that included radiography and magnetic resonance imaging (MRI) demonstrated space-occupying lesions predominantly in the cerebellum that were filled partially by CSF-like fluid and partially by gas, and cerebral lesions that were fluid filled. Over a maximum period of 4 months, the brain lesions reduced in size and the gas resorbed and was replaced by CSF-like fluid. In humans, the cerebellum is known to be essential for automating practiced movement patterns (e.g., learning to touch-type), also known as procedural learning or the consolidation of "motor memory." To test the animal in this study for motor memory deficits, an alternation task in a two-choice maze was utilized. The sea lion performed poorly similar to another case of pneumocerebellum previously reported, and contrary to data acquired from a group of sea lions with sp...
Diseases of Aquatic Organisms, 2020
Pulmonary function testing was performed in 3 bottlenose dolphins Tursiops truncatus (1 female an... more Pulmonary function testing was performed in 3 bottlenose dolphins Tursiops truncatus (1 female and 2 males) under managed care during a 2 yr period to assess whether these data provide diagnostic information about respiratory health. Pulmonary radiographs and standard clinical testing were used to evaluate the pulmonary health of each dolphin. The female dolphin (F1) had evidence of chronic pulmonary fibrosis, and 1 male (M2) developed pneumonia during the study. Pulmonary function data were collected from maximal respiratory efforts in water and from spontaneous breaths while beached. From these data, the flow-volume relationship, the flow measured between 25 and 75% of the expired vital capacity (mid forced expiratory flow, FEF25%-75%), and the percent of the vital capacity (VC) at the peak expiratory flow (%VCPEF), were evaluated and compared with the diagnostic assessment. For maximal respiratory manoeuvres in water, there were no differences in FEF25%-75% or %VCPEF, and the flo...
The Journal of Experimental Biology, 2019
We measured respiratory flow (V̇), breathing frequency (fR), tidal volume (VT), breath durations,... more We measured respiratory flow (V̇), breathing frequency (fR), tidal volume (VT), breath durations, and end-expired O2 content in bottlenose dolphins (Tursiops truncatus) before and after static surface breath-holds ranging from 34 to 292 s. There was considerable variation in the end-expired O2, tidal volume VT, and fR following a breath-hold. The analysis suggests that the dolphins attempt to minimize recovery following a dive by altering VT, and fR to rapidly restore the O2 stores. For the first breath following a surface breath-hold, the end-expired O2 decreased with dive duration, while VT, and fR increased. Throughout the recovery, end-expired O2 increased while the respiratory effort (VT, fR) decreased. We propose that the dolphins alter respiratory effort following a breath-hold according to the reduction in end-expired O2 levels, allowing almost complete recovery after 1.2 min.
Bilaterally symmetrical lesions of the caudate nucleus in a northern fur seal pup (Callorhinus ursinus)
Veterinary Record Case Reports, 2015
ABSTRACT A northern fur seal (Callorhinus ursinus) pup was stranded and brought to The Marine Mam... more ABSTRACT A northern fur seal (Callorhinus ursinus) pup was stranded and brought to The Marine Mammal Center (TMMC) in Sausalito, California, USA, for rehabilitation. Upon admission, the animal was lethargic, underweight and ataxic. Clinical diagnostics, including complete blood cell count (CBC), serum chemistry, protozoal antibody titres, radiographs and cisterna magna ultrasonography, were completed and considered within normal limits. MRI of the brain revealed bilaterally symmetrical focal lesions of the rostrolateral caudate nucleus. Treatment for thiamine deficiency and immune-mediated disease was initiated, but the pup did not improve. The pup was euthanased and postmortem examination revealed no gross lesions. Histopathology revealed bilateral regions of oedema, and areas of early malacia, within the caudate nucleus. Although the aetiology is not identified, the distribution of the lesions suggests a toxic insult or could be related to a developmental neurodegenerative disease. This case also gives an insight into the potential role of the caudate nucleus in fur seals.
Diseases of aquatic organisms, Jan 16, 2014
An adult female long-beaked common dolphin Delphinus capensis live-stranded in La Jolla, Californ... more An adult female long-beaked common dolphin Delphinus capensis live-stranded in La Jolla, California, USA, on July 30, 2012 and subsequently died on the beach. Computed tomography and magnetic resonance imaging revealed gas bubble accumulation in the vasculature, organ parenchyma, mandibular fat pads, and subdermal sheath as well as a gas-filled cavity within the liver, mild caudal abdominal effusion, and fluid in the uterus. Gross examination confirmed these findings and also identified mild ulcerations on the palate, ventral skin, and flukes, uterine necrosis, and multifocal parenchymal cavitations in the brain. Histological review demonstrated necrosis and round clear spaces interpreted as gas bubbles with associated bacterial rods within the brain, liver, spleen, and lymph nodes. Anaerobic cultures of the lung, spleen, liver, bone marrow, and abdominal fluid yielded Clostridium perfringens, which was further identified as type A via a multiplex PCR assay. The gas composition of s...
RESEARCH ARTICLES-Evidence of injury caused by gas bubbles in a live marine mammal: Barotrauma in a California sea lion Zalophus californianus
Frontiers in Physiology, 2012
Recent dogma suggested that marine mammals are not at risk of decompression sickness due to a num... more Recent dogma suggested that marine mammals are not at risk of decompression sickness due to a number of evolutionary adaptations. Several proposed adaptations exist. Lung compression and alveolar collapse that terminate gas-exchange before a depth is reached where supersaturation is significant and bradycardia with peripheral vasoconstriction affecting the distribution, and dynamics of blood and tissue nitrogen levels. Published accounts of gas and fat emboli and dysbaric osteonecrosis in marine mammals and theoretical modeling have challenged this view-point, suggesting that decompression-like symptoms may occur under certain circumstances, contrary to common belief. Diagnostic imaging modalities are invaluable tools for the non-invasive examination of animals for evidence of gas and have been used to demonstrate the presence of incidental decompression-related renal gas accumulations in some stranded cetaceans. Diagnostic imaging has also contributed to the recognition of clinically significant gas accumulations in live and dead cetaceans and pinnipeds. Understanding the appropriate application and limitations of the available imaging modalities is important for accurate interpretation of results. The presence of gas may be asymptomatic and must be interpreted cautiously alongside all other available data including clinical examination, clinical laboratory testing, gas analysis, necropsy examination, and histology results.
Journal of Experimental Biology, 2011
SUMMARYLung compression of vertebrates as they dive poses anatomical and physiological challenges... more SUMMARYLung compression of vertebrates as they dive poses anatomical and physiological challenges. There has been little direct observation of this. A harbor and a gray seal, a common dolphin and a harbor porpoise were each imaged post mortem under pressure using a radiolucent, fiberglass, water-filled pressure vessel rated to a depth equivalent of 170 m. The vessel was scanned using computed tomography (CT), and supported by a rail and counterweighted carriage magnetically linked to the CT table movement. As pressure increased, total buoyancy of the animals decreased and lung tissue CT attenuation increased, consistent with compression of air within the lower respiratory tract. Three-dimensional reconstructions of the external surface of the porpoise chest showed a marked contraction of the chest wall. Estimation of the volumes of different body compartments in the head and chest showed static values for all compartments except the lung, which showed a pressure-related compression....
A Longman's beaked whale ( Indopacetus pacificus ) strands in Maui, Hawaii, with first case of morbillivirus in the central Pacific
Marine Mammal Science, 2012
Journal of Zoo and Wildlife Medicine, 2013
A loggerhead sea turtle (Caretta caretta) was suspected of ingesting rubber suction cups during r... more A loggerhead sea turtle (Caretta caretta) was suspected of ingesting rubber suction cups during rehabilitation following a cold-stun event. Survey radiographs were inconclusive. Computed tomography (CT) was performed to determine whether the objects had been ingested after traditional radiographs failed to resolve the material. The items were identified, and a partial obstruction was diagnosed. The case was managed with medical therapy using white petrolatum and light mineral oil administered to the turtle in fish for 3 wk. The CT exam was repeated 2 wk into the therapy. A persistent partial obstruction was identified; however, progression of the foreign objects through the intestinal tract was evident and continued medical mangement was deemed appropriate. The foreign bodies were passed with feces 26 days after ingestion.
Hiatal Hernia in a Harbor Seal (Phoca Vitulina) Pup
Journal of Zoo and Wildlife Medicine, 2012
Proceedings. Biological sciences / The Royal Society, Jan 22, 2012
Decompression sickness (DCS; 'the bends') is a disease associated with gas uptake at pr... more Decompression sickness (DCS; 'the bends') is a disease associated with gas uptake at pressure. The basic pathology and cause are relatively well known to human divers. Breath-hold diving marine mammals were thought to be relatively immune to DCS owing to multiple anatomical, physiological and behavioural adaptations that reduce nitrogen gas (N(2)) loading during dives. However, recent observations have shown that gas bubbles may form and tissue injury may occur in marine mammals under certain circumstances. Gas kinetic models based on measured time-depth profiles further suggest the potential occurrence of high blood and tissue N(2) tensions. We review evidence for gas-bubble incidence in marine mammal tissues and discuss the theory behind gas loading and bubble formation. We suggest that diving mammals vary their physiological responses according to multiple stressors, and that the perspective on marine mammal diving physiology should change from simply minimizing N(2) lo...
Proceedings. Biological sciences / The Royal Society, 2008
Harmful algal blooms are increasing worldwide, including those of Pseudo-nitzschia spp. producing... more Harmful algal blooms are increasing worldwide, including those of Pseudo-nitzschia spp. producing domoic acid off the California coast. This neurotoxin was first shown to cause mortality of marine mammals in 1998. A decade of monitoring California sea lion (Zalophus californianus) health since then has indicated that changes in the symptomatology and epidemiology of domoic acid toxicosis in this species are associated with the increase in toxigenic blooms. Two separate clinical syndromes now exist: acute domoic acid toxicosis as has been previously documented, and a second novel neurological syndrome characterized by epilepsy described here associated with chronic consequences of previous sub-lethal exposure to the toxin. This study indicates that domoic acid causes chronic damage to California sea lions and that these health effects are increasing.
Diseases of Aquatic Organisms, 2011
Diseases of Aquatic Organisms, 2010
Our goal in this study was to compare magnetic resonance images and volumes of brain structures o... more Our goal in this study was to compare magnetic resonance images and volumes of brain structures obtained alive versus postmortem of California sea lions Zalophus californianus exhibiting clinical signs of domoic acid (DA) toxicosis and those exhibiting normal behavior. Proton density-(PD) and T2-weighted images of postmortem-intact brains, up to 48 h after death, provided similar quality to images acquired from live sea lions. Volumes of gray matter (GM) and white matter (WM) of the cerebral hemispheres were similar to volumes calculated from images acquired when the sea lions were alive. However, cerebrospinal fluid (CSF) volumes decreased due to leakage. Hippocampal volumes from postmortem-intact images were useful for diagnosing unilateral and bilateral atrophy, consequences of DA toxicosis. These volumes were similar to the volumes in the live sea lion studies, up to 48 h postmortem. Imaging formalin-fixed brains provided some information on brain structure; however, images of the hippocampus and surrounding structures were of poorer quality compared to the images acquired alive and postmortem-intact. Despite these issues, volumes of cerebral GM and WM, as well as the hippocampus, were similar to volumes calculated from images of live sea lions and sufficient to diagnose hippocampal atrophy. Thus, postmortem MRI scanning (either intact or formalin-fixed) with volumetric analysis can be used to investigate the acute, chronic and possible developmental effects of DA on the brain of California sea lions.
Diseases of Aquatic Organisms, 2011
A yearling male California sea lion Zalophus californianus with hypermetric ataxia and bilateral ... more A yearling male California sea lion Zalophus californianus with hypermetric ataxia and bilateral negative menace reflexes was brought to The Marine Mammal Center, Sausalito, California, USA, in late 2009 for medical assessment and treatment. The clinical signs were due to multiple gas bubbles within the cerebellum. These lesions were intraparenchymal, multifocal to coalescing, spherical to ovoid, and varied from 0.5 to 2.4 cm diameter. The gas composed 21.3% of the total cerebellum volume. Three rib fractures were also noted during diagnostic evaluation and were presumed to be associated with the gas bubbles in the brain. The progression of clinical signs and lesion appearance were monitored with magnetic resonance imaging, cognitive function testing and computed tomography. Gas filled voids in the cerebellum were filled with fluid on follow up images. Clinical signs resolved and the sea lion was released with a satellite tag attached. Post release the animal travelled approximately 75 km north and 80 km south of the release site and the tag recorded dives of over 150 m depth. The animal re-stranded 25 d following release and died of a subacute bronchopneumonia and pleuritis. This is the first instance of clinical injury due to gas bubble formation described in a living pinniped and the first sea lion with quantifiable cerebellar damage to take part in spatial learning and memory testing.
The Anatomical Record: Advances in Integrative Anatomy and Evolutionary Biology, 2009
The California sea lion (Zalophus californianus) has been a focal point for sensory, communicatio... more The California sea lion (Zalophus californianus) has been a focal point for sensory, communication, cognition, and neurological disease studies in marine mammals. However, as a scientific community, we lack a noninvasive approach to investigate the anatomy and size of brain structures in this species and other free-ranging, live marine mammals. In this article, we provide the first anatomically labeled, magnetic resonance imagingbased atlas derived from a live marine mammal, the California sea lion. The brain of the California seal lion contained more secondary gyri and sulci than the brains of terrestrial carnivores. The olfactory bulb was present but small. The hippocampus of the California sea lion was found mostly in the ventral position with very little extension dorsally, quite unlike the canids and the mustelids, in which the hippocampus is present in the ventral position but extends dorsally above the thalamus. In contrast to the canids and the mustelids, the pineal gland of the California sea lion was strikingly large. In addition, we report three-dimensional reconstructions and volumes of cerebrospinal fluid, cerebral ventricles, total white matter (WM), total gray matter (GM), cerebral hemispheres (WM and GM), cerebellum and brainstem combined (WM and GM), and hippocampal structures all derived from magnetic resonance images. These measurements are the first to be determined for any pinniped species. In California sea lions, this approach can be used not only to relate cognitive and sensory capabilities to brain size but also to investigate the neurological effects of exposure to neurotoxins such as domoic acid.
Pneumocerebellum in a Live Yearling Zalophus californianus: The Bends in a Sea Lion?
Nature Precedings
Marine mammals possess exquisite biochemical, anatomical, physiological, and behavioral adaptatio... more Marine mammals possess exquisite biochemical, anatomical, physiological, and behavioral adaptations to life in the oceans, including mechanisms to prevent barotrauma during repetitive diving ^1,2^. However, recent evidence suggests that pinnipeds and cetaceans are not entirely resistant to decompression sickness (DCS), although this conclusion is controversial. Hypothetical causes of disruption to marine mammal defenses against barotraumas include behavioral responses to acoustic exposure and insonification of bubbles in supersaturated tissues, both of which may be associated with SONAR exposure ^3-5^. Gas bubbles and emboli in dead whales associated with naval exercises indicate DCS resulted in mortality, but gas bubbles have also been observed in tissues of dead cetaceans and pinnipeds dying from other causes, suggesting bubbles can form post mortem in supersaturated tissues. To date, reported cases of presumed barotrauma in marine mammals have been based upon post mortem findings...
Proceedings of the Royal Society B: Biological Sciences, 2012
Bubbles in supersaturated tissues and blood occur in beaked whales stranded near sonar exercises,... more Bubbles in supersaturated tissues and blood occur in beaked whales stranded near sonar exercises, and post-mortem in dolphins bycaught at depth and then hauled to the surface. To evaluate live dolphins for bubbles, liver, kidneys, eyes and blubber-muscle interface of live-stranded and capture-release dolphins were scanned with B-mode ultrasound. Gas was identified in kidneys of 21 of 22 live-stranded dolphins and in the hepatic portal vasculature of 2 of 22. Nine then died or were euthanized and bubble presence corroborated by computer tomography and necropsy, 13 were released of which all but two did not re-strand. Bubbles were not detected in 20 live wild dolphins examined during health assessments in shallow water. Off-gassing of supersaturated blood and tissues was the most probable origin for the gas bubbles. In contrast to marine mammals repeatedly diving in the wild, stranded animals are unable to recompress by diving, and thus may retain bubbles. Since the majority of beached dolphins released did not re-strand it also suggests that minor bubble formation is tolerated and will not lead to clinically significant decompression sickness.
Proceedings. Biological sciences / The Royal Society, 2008
Harmful algal blooms are increasing worldwide, including those of Pseudo-nitzschia spp. producing... more Harmful algal blooms are increasing worldwide, including those of Pseudo-nitzschia spp. producing domoic acid off the California coast. This neurotoxin was first shown to cause mortality of marine mammals in 1998. A decade of monitoring California sea lion (Zalophus californianus) health since then has indicated that changes in the symptomatology and epidemiology of domoic acid toxicosis in this species are associated with the increase in toxigenic blooms. Two separate clinical syndromes now exist: acute domoic acid toxicosis as has been previously documented, and a second novel neurological syndrome characterized by epilepsy described here associated with chronic consequences of previous sub-lethal exposure to the toxin. This study indicates that domoic acid causes chronic damage to California sea lions and that these health effects are increasing.
Frontiers in physiology, 2013
A yearling California sea lion (Zalophus californianus) was admitted into rehabilitation with sig... more A yearling California sea lion (Zalophus californianus) was admitted into rehabilitation with signs of cerebellar pathology. Diagnostic imaging that included radiography and magnetic resonance imaging (MRI) demonstrated space-occupying lesions predominantly in the cerebellum that were filled partially by CSF-like fluid and partially by gas, and cerebral lesions that were fluid filled. Over a maximum period of 4 months, the brain lesions reduced in size and the gas resorbed and was replaced by CSF-like fluid. In humans, the cerebellum is known to be essential for automating practiced movement patterns (e.g., learning to touch-type), also known as procedural learning or the consolidation of "motor memory." To test the animal in this study for motor memory deficits, an alternation task in a two-choice maze was utilized. The sea lion performed poorly similar to another case of pneumocerebellum previously reported, and contrary to data acquired from a group of sea lions with sp...
Diseases of Aquatic Organisms, 2020
Pulmonary function testing was performed in 3 bottlenose dolphins Tursiops truncatus (1 female an... more Pulmonary function testing was performed in 3 bottlenose dolphins Tursiops truncatus (1 female and 2 males) under managed care during a 2 yr period to assess whether these data provide diagnostic information about respiratory health. Pulmonary radiographs and standard clinical testing were used to evaluate the pulmonary health of each dolphin. The female dolphin (F1) had evidence of chronic pulmonary fibrosis, and 1 male (M2) developed pneumonia during the study. Pulmonary function data were collected from maximal respiratory efforts in water and from spontaneous breaths while beached. From these data, the flow-volume relationship, the flow measured between 25 and 75% of the expired vital capacity (mid forced expiratory flow, FEF25%-75%), and the percent of the vital capacity (VC) at the peak expiratory flow (%VCPEF), were evaluated and compared with the diagnostic assessment. For maximal respiratory manoeuvres in water, there were no differences in FEF25%-75% or %VCPEF, and the flo...
The Journal of Experimental Biology, 2019
We measured respiratory flow (V̇), breathing frequency (fR), tidal volume (VT), breath durations,... more We measured respiratory flow (V̇), breathing frequency (fR), tidal volume (VT), breath durations, and end-expired O2 content in bottlenose dolphins (Tursiops truncatus) before and after static surface breath-holds ranging from 34 to 292 s. There was considerable variation in the end-expired O2, tidal volume VT, and fR following a breath-hold. The analysis suggests that the dolphins attempt to minimize recovery following a dive by altering VT, and fR to rapidly restore the O2 stores. For the first breath following a surface breath-hold, the end-expired O2 decreased with dive duration, while VT, and fR increased. Throughout the recovery, end-expired O2 increased while the respiratory effort (VT, fR) decreased. We propose that the dolphins alter respiratory effort following a breath-hold according to the reduction in end-expired O2 levels, allowing almost complete recovery after 1.2 min.
Bilaterally symmetrical lesions of the caudate nucleus in a northern fur seal pup (Callorhinus ursinus)
Veterinary Record Case Reports, 2015
ABSTRACT A northern fur seal (Callorhinus ursinus) pup was stranded and brought to The Marine Mam... more ABSTRACT A northern fur seal (Callorhinus ursinus) pup was stranded and brought to The Marine Mammal Center (TMMC) in Sausalito, California, USA, for rehabilitation. Upon admission, the animal was lethargic, underweight and ataxic. Clinical diagnostics, including complete blood cell count (CBC), serum chemistry, protozoal antibody titres, radiographs and cisterna magna ultrasonography, were completed and considered within normal limits. MRI of the brain revealed bilaterally symmetrical focal lesions of the rostrolateral caudate nucleus. Treatment for thiamine deficiency and immune-mediated disease was initiated, but the pup did not improve. The pup was euthanased and postmortem examination revealed no gross lesions. Histopathology revealed bilateral regions of oedema, and areas of early malacia, within the caudate nucleus. Although the aetiology is not identified, the distribution of the lesions suggests a toxic insult or could be related to a developmental neurodegenerative disease. This case also gives an insight into the potential role of the caudate nucleus in fur seals.
Diseases of aquatic organisms, Jan 16, 2014
An adult female long-beaked common dolphin Delphinus capensis live-stranded in La Jolla, Californ... more An adult female long-beaked common dolphin Delphinus capensis live-stranded in La Jolla, California, USA, on July 30, 2012 and subsequently died on the beach. Computed tomography and magnetic resonance imaging revealed gas bubble accumulation in the vasculature, organ parenchyma, mandibular fat pads, and subdermal sheath as well as a gas-filled cavity within the liver, mild caudal abdominal effusion, and fluid in the uterus. Gross examination confirmed these findings and also identified mild ulcerations on the palate, ventral skin, and flukes, uterine necrosis, and multifocal parenchymal cavitations in the brain. Histological review demonstrated necrosis and round clear spaces interpreted as gas bubbles with associated bacterial rods within the brain, liver, spleen, and lymph nodes. Anaerobic cultures of the lung, spleen, liver, bone marrow, and abdominal fluid yielded Clostridium perfringens, which was further identified as type A via a multiplex PCR assay. The gas composition of s...
RESEARCH ARTICLES-Evidence of injury caused by gas bubbles in a live marine mammal: Barotrauma in a California sea lion Zalophus californianus
Frontiers in Physiology, 2012
Recent dogma suggested that marine mammals are not at risk of decompression sickness due to a num... more Recent dogma suggested that marine mammals are not at risk of decompression sickness due to a number of evolutionary adaptations. Several proposed adaptations exist. Lung compression and alveolar collapse that terminate gas-exchange before a depth is reached where supersaturation is significant and bradycardia with peripheral vasoconstriction affecting the distribution, and dynamics of blood and tissue nitrogen levels. Published accounts of gas and fat emboli and dysbaric osteonecrosis in marine mammals and theoretical modeling have challenged this view-point, suggesting that decompression-like symptoms may occur under certain circumstances, contrary to common belief. Diagnostic imaging modalities are invaluable tools for the non-invasive examination of animals for evidence of gas and have been used to demonstrate the presence of incidental decompression-related renal gas accumulations in some stranded cetaceans. Diagnostic imaging has also contributed to the recognition of clinically significant gas accumulations in live and dead cetaceans and pinnipeds. Understanding the appropriate application and limitations of the available imaging modalities is important for accurate interpretation of results. The presence of gas may be asymptomatic and must be interpreted cautiously alongside all other available data including clinical examination, clinical laboratory testing, gas analysis, necropsy examination, and histology results.
Journal of Experimental Biology, 2011
SUMMARYLung compression of vertebrates as they dive poses anatomical and physiological challenges... more SUMMARYLung compression of vertebrates as they dive poses anatomical and physiological challenges. There has been little direct observation of this. A harbor and a gray seal, a common dolphin and a harbor porpoise were each imaged post mortem under pressure using a radiolucent, fiberglass, water-filled pressure vessel rated to a depth equivalent of 170 m. The vessel was scanned using computed tomography (CT), and supported by a rail and counterweighted carriage magnetically linked to the CT table movement. As pressure increased, total buoyancy of the animals decreased and lung tissue CT attenuation increased, consistent with compression of air within the lower respiratory tract. Three-dimensional reconstructions of the external surface of the porpoise chest showed a marked contraction of the chest wall. Estimation of the volumes of different body compartments in the head and chest showed static values for all compartments except the lung, which showed a pressure-related compression....
A Longman's beaked whale ( Indopacetus pacificus ) strands in Maui, Hawaii, with first case of morbillivirus in the central Pacific
Marine Mammal Science, 2012
Journal of Zoo and Wildlife Medicine, 2013
A loggerhead sea turtle (Caretta caretta) was suspected of ingesting rubber suction cups during r... more A loggerhead sea turtle (Caretta caretta) was suspected of ingesting rubber suction cups during rehabilitation following a cold-stun event. Survey radiographs were inconclusive. Computed tomography (CT) was performed to determine whether the objects had been ingested after traditional radiographs failed to resolve the material. The items were identified, and a partial obstruction was diagnosed. The case was managed with medical therapy using white petrolatum and light mineral oil administered to the turtle in fish for 3 wk. The CT exam was repeated 2 wk into the therapy. A persistent partial obstruction was identified; however, progression of the foreign objects through the intestinal tract was evident and continued medical mangement was deemed appropriate. The foreign bodies were passed with feces 26 days after ingestion.
Hiatal Hernia in a Harbor Seal (Phoca Vitulina) Pup
Journal of Zoo and Wildlife Medicine, 2012
Proceedings. Biological sciences / The Royal Society, Jan 22, 2012
Decompression sickness (DCS; 'the bends') is a disease associated with gas uptake at pr... more Decompression sickness (DCS; 'the bends') is a disease associated with gas uptake at pressure. The basic pathology and cause are relatively well known to human divers. Breath-hold diving marine mammals were thought to be relatively immune to DCS owing to multiple anatomical, physiological and behavioural adaptations that reduce nitrogen gas (N(2)) loading during dives. However, recent observations have shown that gas bubbles may form and tissue injury may occur in marine mammals under certain circumstances. Gas kinetic models based on measured time-depth profiles further suggest the potential occurrence of high blood and tissue N(2) tensions. We review evidence for gas-bubble incidence in marine mammal tissues and discuss the theory behind gas loading and bubble formation. We suggest that diving mammals vary their physiological responses according to multiple stressors, and that the perspective on marine mammal diving physiology should change from simply minimizing N(2) lo...
Proceedings. Biological sciences / The Royal Society, 2008
Harmful algal blooms are increasing worldwide, including those of Pseudo-nitzschia spp. producing... more Harmful algal blooms are increasing worldwide, including those of Pseudo-nitzschia spp. producing domoic acid off the California coast. This neurotoxin was first shown to cause mortality of marine mammals in 1998. A decade of monitoring California sea lion (Zalophus californianus) health since then has indicated that changes in the symptomatology and epidemiology of domoic acid toxicosis in this species are associated with the increase in toxigenic blooms. Two separate clinical syndromes now exist: acute domoic acid toxicosis as has been previously documented, and a second novel neurological syndrome characterized by epilepsy described here associated with chronic consequences of previous sub-lethal exposure to the toxin. This study indicates that domoic acid causes chronic damage to California sea lions and that these health effects are increasing.
Diseases of Aquatic Organisms, 2011
Diseases of Aquatic Organisms, 2010
Our goal in this study was to compare magnetic resonance images and volumes of brain structures o... more Our goal in this study was to compare magnetic resonance images and volumes of brain structures obtained alive versus postmortem of California sea lions Zalophus californianus exhibiting clinical signs of domoic acid (DA) toxicosis and those exhibiting normal behavior. Proton density-(PD) and T2-weighted images of postmortem-intact brains, up to 48 h after death, provided similar quality to images acquired from live sea lions. Volumes of gray matter (GM) and white matter (WM) of the cerebral hemispheres were similar to volumes calculated from images acquired when the sea lions were alive. However, cerebrospinal fluid (CSF) volumes decreased due to leakage. Hippocampal volumes from postmortem-intact images were useful for diagnosing unilateral and bilateral atrophy, consequences of DA toxicosis. These volumes were similar to the volumes in the live sea lion studies, up to 48 h postmortem. Imaging formalin-fixed brains provided some information on brain structure; however, images of the hippocampus and surrounding structures were of poorer quality compared to the images acquired alive and postmortem-intact. Despite these issues, volumes of cerebral GM and WM, as well as the hippocampus, were similar to volumes calculated from images of live sea lions and sufficient to diagnose hippocampal atrophy. Thus, postmortem MRI scanning (either intact or formalin-fixed) with volumetric analysis can be used to investigate the acute, chronic and possible developmental effects of DA on the brain of California sea lions.
Diseases of Aquatic Organisms, 2011
A yearling male California sea lion Zalophus californianus with hypermetric ataxia and bilateral ... more A yearling male California sea lion Zalophus californianus with hypermetric ataxia and bilateral negative menace reflexes was brought to The Marine Mammal Center, Sausalito, California, USA, in late 2009 for medical assessment and treatment. The clinical signs were due to multiple gas bubbles within the cerebellum. These lesions were intraparenchymal, multifocal to coalescing, spherical to ovoid, and varied from 0.5 to 2.4 cm diameter. The gas composed 21.3% of the total cerebellum volume. Three rib fractures were also noted during diagnostic evaluation and were presumed to be associated with the gas bubbles in the brain. The progression of clinical signs and lesion appearance were monitored with magnetic resonance imaging, cognitive function testing and computed tomography. Gas filled voids in the cerebellum were filled with fluid on follow up images. Clinical signs resolved and the sea lion was released with a satellite tag attached. Post release the animal travelled approximately 75 km north and 80 km south of the release site and the tag recorded dives of over 150 m depth. The animal re-stranded 25 d following release and died of a subacute bronchopneumonia and pleuritis. This is the first instance of clinical injury due to gas bubble formation described in a living pinniped and the first sea lion with quantifiable cerebellar damage to take part in spatial learning and memory testing.
The Anatomical Record: Advances in Integrative Anatomy and Evolutionary Biology, 2009
The California sea lion (Zalophus californianus) has been a focal point for sensory, communicatio... more The California sea lion (Zalophus californianus) has been a focal point for sensory, communication, cognition, and neurological disease studies in marine mammals. However, as a scientific community, we lack a noninvasive approach to investigate the anatomy and size of brain structures in this species and other free-ranging, live marine mammals. In this article, we provide the first anatomically labeled, magnetic resonance imagingbased atlas derived from a live marine mammal, the California sea lion. The brain of the California seal lion contained more secondary gyri and sulci than the brains of terrestrial carnivores. The olfactory bulb was present but small. The hippocampus of the California sea lion was found mostly in the ventral position with very little extension dorsally, quite unlike the canids and the mustelids, in which the hippocampus is present in the ventral position but extends dorsally above the thalamus. In contrast to the canids and the mustelids, the pineal gland of the California sea lion was strikingly large. In addition, we report three-dimensional reconstructions and volumes of cerebrospinal fluid, cerebral ventricles, total white matter (WM), total gray matter (GM), cerebral hemispheres (WM and GM), cerebellum and brainstem combined (WM and GM), and hippocampal structures all derived from magnetic resonance images. These measurements are the first to be determined for any pinniped species. In California sea lions, this approach can be used not only to relate cognitive and sensory capabilities to brain size but also to investigate the neurological effects of exposure to neurotoxins such as domoic acid.
Pneumocerebellum in a Live Yearling Zalophus californianus: The Bends in a Sea Lion?
Nature Precedings
Marine mammals possess exquisite biochemical, anatomical, physiological, and behavioral adaptatio... more Marine mammals possess exquisite biochemical, anatomical, physiological, and behavioral adaptations to life in the oceans, including mechanisms to prevent barotrauma during repetitive diving ^1,2^. However, recent evidence suggests that pinnipeds and cetaceans are not entirely resistant to decompression sickness (DCS), although this conclusion is controversial. Hypothetical causes of disruption to marine mammal defenses against barotraumas include behavioral responses to acoustic exposure and insonification of bubbles in supersaturated tissues, both of which may be associated with SONAR exposure ^3-5^. Gas bubbles and emboli in dead whales associated with naval exercises indicate DCS resulted in mortality, but gas bubbles have also been observed in tissues of dead cetaceans and pinnipeds dying from other causes, suggesting bubbles can form post mortem in supersaturated tissues. To date, reported cases of presumed barotrauma in marine mammals have been based upon post mortem findings...
Proceedings of the Royal Society B: Biological Sciences, 2012
Bubbles in supersaturated tissues and blood occur in beaked whales stranded near sonar exercises,... more Bubbles in supersaturated tissues and blood occur in beaked whales stranded near sonar exercises, and post-mortem in dolphins bycaught at depth and then hauled to the surface. To evaluate live dolphins for bubbles, liver, kidneys, eyes and blubber-muscle interface of live-stranded and capture-release dolphins were scanned with B-mode ultrasound. Gas was identified in kidneys of 21 of 22 live-stranded dolphins and in the hepatic portal vasculature of 2 of 22. Nine then died or were euthanized and bubble presence corroborated by computer tomography and necropsy, 13 were released of which all but two did not re-strand. Bubbles were not detected in 20 live wild dolphins examined during health assessments in shallow water. Off-gassing of supersaturated blood and tissues was the most probable origin for the gas bubbles. In contrast to marine mammals repeatedly diving in the wild, stranded animals are unable to recompress by diving, and thus may retain bubbles. Since the majority of beached dolphins released did not re-strand it also suggests that minor bubble formation is tolerated and will not lead to clinically significant decompression sickness.
Proceedings. Biological sciences / The Royal Society, 2008
Harmful algal blooms are increasing worldwide, including those of Pseudo-nitzschia spp. producing... more Harmful algal blooms are increasing worldwide, including those of Pseudo-nitzschia spp. producing domoic acid off the California coast. This neurotoxin was first shown to cause mortality of marine mammals in 1998. A decade of monitoring California sea lion (Zalophus californianus) health since then has indicated that changes in the symptomatology and epidemiology of domoic acid toxicosis in this species are associated with the increase in toxigenic blooms. Two separate clinical syndromes now exist: acute domoic acid toxicosis as has been previously documented, and a second novel neurological syndrome characterized by epilepsy described here associated with chronic consequences of previous sub-lethal exposure to the toxin. This study indicates that domoic acid causes chronic damage to California sea lions and that these health effects are increasing.