Training Rats to Voluntarily Dive Underwater: Investigations of the Mammalian Diving Response

Underwater submergence produces autonomic changes that are observed in virtually all diving animals. This reflexly-induced response consists of apnea, a parasympathetically-induced bradycardia and a sympathetically-induced alteration of vascular resistance that maintains blood flow to the heart, brain and exercising muscles. While many of the metabolic and cardiorespiratory aspects of the diving response have been studied in marine animals, investigations of the central integrative aspects of this brainstem reflex have been relatively lacking. Because the physiology and neuroanatomy of the rat are well characterized, the rat can be used to help ascertain the central pathways of the mammalian diving response. Detailed instructions are provided on how to train rats to swim and voluntarily dive underwater through a 5 m long Plexiglas maze. Considerations regarding tank design and procedure room requirements are also given. The behavioral training is conducted in such a way as to reduce the stressfulness that could otherwise be associated with forced underwater submergence, thus minimizing activation of central stress pathways. The training procedures are not technically difficult, but they can be time-consuming. Since behavioral training of animals can only provide a model to be used with other experimental techniques, examples of how voluntarily diving rats have been used in conjunction with other physiological and neuroanatomical research techniques, and how the basic training procedures may need to be modified to accommodate these techniques, are also provided. These experiments show that voluntarily diving rats exhibit the same cardiorespiratory changes typically seen in other diving animals. The ease with which rats can be trained to voluntarily dive underwater, and the already available data from rats collected in other neurophysiological studies, makes voluntarily diving rats a good behavioral model to be used in studies investigating the central aspects of the mammalian diving response.     

Insights into Young of the Year White Shark, Carcharodon carcharias, Behavior in the Southern California Bight

A young of the year female white shark, Carcharodon carcharias, was tagged with a pop-up satellite archival tag off Southern California in early June of 2000. The tag was recovered after 28 days, and records of temperature, depth and light intensity were extracted. Depth and temperature records indicate a number of interesting behaviors, including a strong diurnal pattern. At night the shark remained in the top 50 m, often making shallow repetitive vertical excursions. Most dives below the mixed layer were observed during the day, 91% of which occurred from 05:00 to 21:00 h, with depths extending to 240 m. Many of the dives exhibited secondary vertical movements that were consistent with the shark swimming at the bottom (at depths from 9 to 165 m) where it was most likely foraging. The white shark experienced dramatic and rapid changes in temperature, and demonstrated a considerable tolerance for cold waters. Temperatures ranged from 9°C to 22°C, and although 89% of the total time was spent in waters 16–22°C, on some days the small shark spent as much as 32% of the time in 12°C waters. The deep dives into cold waters separate the white sharks from mako sharks, which share the California Bight nursery ground but appear to remain primarily in the mixed layer and thermocline. Movement information (derived from light-based geolocation, bottom depths and sea surface temperatures) indicated that the white shark spent the 28 days in the Southern California Bight, possibly moving as far south as San Diego, California. While the abundance and diversity of prey, warm water and separation from adults make this region an ideal nursery ground, the potential for interaction with the local fisheries should be examined.     

DIVING BEHAVIOR AND PERFORMANCE OF HARBOR PORPOISES, PHOCOENA PHOCOENA, IN FUNKA BAY, HOKKAIDO, JAPAN

In order to monitor the diving behavior of free-ranging cetaceans, microdataloggers, with pre-programmed release mechanisms, were attached to the dorsal fins of two female harbor porpoises ( Phocoena phocoena ) in Funka Bay, Hokkaido, Japan, in 1994. The two loggers were successfully recovered and a total of 141 h of diving data (depth and water temperature in 4,671 dives) was obtained. Both porpoises dived almost continuously, rarely exhibiting long-term rest at the surface. Maximum dive depths were 98.6 m and 70.8 m, respectively, with more than 70% of diving time at 20 m or less. Most shallow dives were V-shaped with no bottom time. The V-shaped dives were significantly shallower in dive depth and shorter in dive duration than U-shaped dives. Descent rate was not constant during a dive. The deeper the dive depths, the faster the mean descent and initial descent rates. This suggests that porpoises have anticipated the depth to which they will dive before initiating the dive itself.     

Scuba diving enhances endogenous antioxidant defenses in lymphocytes and neutrophils

The aim was to study the effects of a scuba diving session on the lymphocyte antioxidant system, NO synthesis, the capability to produce reactive oxygen species and the antioxidant response in neutrophils. For that purpose seven male divers performed an immersion at a depth of 40 m for 25 min. The same parameters were measured after an hyperbaric oxygen (HBO) treatment at resting conditions in a hyperbaric chamber. Lymphocyte H₂O₂ production rose after diving and after HBO treatment. Glutathione peroxidase (GPx) and catalase activities increased after diving in lymphocytes, while after HBO exposure only increased GPx activity. Lymphocyte HO-1 mRNA expression increased after diving and after HBO exposure, while iNOS levels and nitrite levels significantly increased after diving. The hyperoxia associated to scuba diving leads to a condition of oxidative stress with increased lymphocyte H₂O₂ production, HO-1 expression, NO synthesis and antioxidant enzyme adaptations in order to avoid oxidative damage.     

Bone microstructure of Vegavis iaai (Aves,Anseriformes) from the Upper Cretaceous of Vega Island,Antarctic Peninsula

Vegavis iaai is a neornithine bird coming from the Late Cretaceous Sandwich Bluff Member of the López de Bertodano Formation (Maastrichtian), Antarctic Peninsula. Vegavis constitutes the only unquestionable Cretaceous neornithine bird, and is known by the holotype and specimen MACN-PV 19.748. The goal of this paper is to present a detailed osteohistological analysis of V. iaai. Vegavis shows a highly vascularized fibrolamellar matrix lacking lines of arrested growths, features widespread among modern birds. This is consistent with previous hypotheses indicating that modern birds were dominant at high latitudes. This is probably related to high-metabolic rates shared by modern birds, whereas archaic taxa as Enantiornithes are absent or form a minority part of High-Latitude bird assemblages. Vegavis was a diver, characterised by a certain degree of limb osteosclerosis, with an increase of bone inner compactness, and inhibition of secondary remodelling, with no effect on the external dimensions of the bone, a combination of characters related to diving lifestyle. Based on Relative Bone Thickness it is possible to infer that Vegavis was a foot-propelled diving bird, similar to some extant anseriforms. Occurrence of osteosclerotic limb bones in Vegavis and Polarornis may constitute a derived shared feature, sustaining the hypothesis that both taxa are phylogenetically related.     

SEASONAL MOVEMENTS AND DIVE PATTERNS OF JUVENILE BAIKAL SEALS, PHOCA SIBIRICA

The Baikal seal ( Phoca sibirica ) is confined to Lake Baikal in southern Siberia. The breeding distribution of seals in winter, when the lake is frozen over, is fairly well known, whereas their movements and foraging behaviors have been relatively unstudied. With satellite-linked radio transmitters, we documented the movements and dive patterns of four juvenile Baikal seals from autumn through spring. The seals moved extensively in the lake, each covering minimal distances of 400–1,600 km between September and early May. They spent little time hauled out from September through May and, apparently, dived continuously. Dives were mostly to depths of lo-50 m, though a few exceeded 300 m. Most lasted between 2 and 6 mm, within theoretical aerobic dive limits, although a few exceeded 40 min. The exceptionally long dives occurred while the seals were in areas of extensive ice cover, suggesting that they were, perhaps, under ice-pilotage in search of breathing holes rather than foraging dives. Otherwise, the dive performances of these Baikal seals were, relative to body mass, similar to those of other well-studied phocids. Movements and dive patterns of seals appeared to be primarily associated with seasonal and die1 movements of their primary prey, golomyanka and sculpins, and secondarily correlated with patterns of ice formation and thaw.     

Foraging behaviour of Magellanic Penguins during the early chick‐rearing period at Isla de los Estados,Argentina

Studies of the at‐sea distribution and trophic ecology of penguins are essential to understand their role in the broader marine food web. Magellanic Penguins Spheniscus magellanicus have a wide distribution and their foraging behaviour varies across breeding sites and between sexes, among others. In this study, we characterized the at‐sea areas, the diving strategies and the relative trophic level of Magellanic Penguins breeding at Isla de los Estados, Argentina, during the early chick‐rearing period. In addition, we quantified the interannual, sexual and individual variability in those parameters during three breeding seasons (2011–2013) using devices recording position and dive depth, and obtained blood samples for stable isotope analysis. During the early chick‐rearing period, Magellanic Penguins showed small differences between the sexes in their foraging behaviour and large overlap in the at‐sea areas used, suggesting no intraspecific variation between sexes. Although there was interannual variability in the foraging behaviour and the trophic level of the penguins, most of the studied nests managed successfully to raise both chicks during the first stage of the breeding cycle (guard stage). The foraging ecology of Magellanic Penguins from this colony was comparable with results of past studies at other breeding colonies. This study contributes to the identification of important at‐sea areas for Magellanic Penguins at the southern edge of their distribution and also to the identification of possible threats in the study area such as interaction with fisheries.     

Self‐admission in psychiatry: The ethics

Self‐admission to inpatient treatment is a novel approach that aims to increase agency and autonomy for patients with severe psychiatric illness and a history of high utilization of inpatient care. By focusing on brief, preventive hospital admissions in times of increased risk of relapse, self‐admission seeks to reduce the need for prolonged episodes of inpatient treatment. Participants are generally satisfied with the model, which is not surprising given that self‐admission programs allocate a scarce resource—hospital beds—to a select group. However, the patients targeted by these programs are not necessarily those in most need of hospital admission, which may compromise the commonly accepted ‘principle of need’ in allocation of public healthcare resources. In light of the current lack of consistent evidence of the usefulness and cost‐effectiveness of the model, several aspects need to be further studied in order to guide any large‐scale implementation of self‐admission in psychiatry.     

Oral administration of cholecystokinin receptor antagonists increase feed intake in rainbow trout

Individual immature rainbow trout consumed 1–2% body weight per day, but significantly more ( P < 0·001) when fed by hand than by demand feeder. When treated with CCK antagonists (L 364, 718; 100 μg kg⁻¹ on day 12 or SR 27, 897; 50 μg kg⁻¹ on day 16), the fish ate significantly more than their mean daily intake on the other days of the experiment. This increase in feed intake was affected by the feeding technique: hand-fed fish increased by 70–80% their feed intake while in demand-fed fish the increase was significantly less (50–60%). However, the increase in feed intake observed on days 12 and 16 was identical for both drugs used.