[Sleep in cetaceans].

Over the course of evolution, cetaceans have adapted to sleep in conditions that can be considered extreme for warm-blooded and air breathing animals. Studies of sleep in cetaceans have led to the discovery of an unusual type of sleep called unihemispheric slow wave sleep. The ability of cetaceans to sleep during swimming and to close only one eye at a time are two other features of their sleep, directly related to its unihemispheric nature. Paradoxical sleep in the form it is recorded in all terrestrial mammals is absent in cetaceans. The pattern of sleep in cetaceans allows them to 1) monitor the environment for predators and conspecifics to maintain group coherence, 2) surface regularly for breathing and 3) maintain effective thermoregulation.

[Rest and activity states in the Commerson's dolphin (Cephalorhynchus commersonii)].

The unihemispheric slow-wave sleep, the ability to sleep during swimming with one open eye and the absence of paradoxical sleep in the form of it is observed in all terrestrial mammals are unique features of sleep in cetaceans. Visual observations supplement electrophysiological studies and allow obtaining novel data about sleep of cetaceans. In the present study we examined behavior of 3 adult Commerson's dolphins Cephalorhynchus commersonii which were housed in the oceanarium Sea-World (San Diego, USA). The behavior of the dolphins can be subdivided into 5 swimming types: 1) active swimming marked by variable speed and irregular trajectory of movement (on average for 3 dolphins 35.1 +/- 2.7% of the 24-h period) was scored as active wakefulness; 2) circular swimming was divided into slow and fast swimming and occupied, on average, 44.4 +/- 3.8 and 9.7 +/- 0.8% of the 24-h period, respectively; while in circular swimming, dolphins swam from 1 to 6 circles on one respiration pause; 3) quiet chaotic swimming (3.9 +/- 1.2%) that occurred at the bottom and was not accompanied by signs of activity; 4) floating, and 5) slow swimming at the surface (4.1 +/- 0.5 and 2.8 +/- 0.4%), respectively; the latter two swimming types were accompanied by frequent respiration (hyperventilation). We suggest that sleep in Commerson's dolphins occurred predominantly during the circular and quiet swimming. From time to time the dolphins slowed down their speeds and even stopped for several seconds. Such episodes appeared to be the deepest sleep episodes. In all dolphins muscle jerks as well erections in the male were observed. Jerks and erections occurred during the circular and quiet chaotic swimming. Similar to other studied small cetaceans, Commerson's dolphins are in a state of almost uninterrupted swimming during 24 h per day and they sleep during swimming. Some muscle jerks that we observed in the dolphins in this study might have been episodes of paradoxical sleep.

[Sleep and wakefulness in Greenland seal pups]. / Son i bodrstvovanie u shchenkov grenladskogo tiulenia.

ECoG of both hemispheres, EOG, neck EMG and EKG were recorded in 2 white (age 10 days) and 2 gray pups (age 1 month) of harp seal. The active wakefulness occupied 23.4 +/- 3.8% of total recording time, the relaxed wakefulness--32.6 +/- 3.6%, drowsiness--4.8 +/- 1.1%, slow wave sleep--31.5 +/- 3.0%, paradoxical sleep--7.7 +/- 0.8%. The sleep cycle averaged 18.2 +/- 1.4 min. Interhemispheric asymmetry of the ECoG was not seen in all 4 pups. The respiration was fast and regular in the relaxed wakefulness, then long respiration pauses were alternated with episodes of hyperventilation during slow wave sleep and there was rare and irregular respiration in the paradoxical sleep. The heart rate was lowest during the paradoxical sleep. It is suggested that this pattern of sleep, allowing seals to delay their breathing during sleep for a long time may be considered as an adaptation to existence in freezing seas.

[Features of sleep in the water by the northern fur seal Callorhinus ursinus]. / Osobennosti sna v vode u severnykh morskikh kotikov.

The peculiarities of sleep in water and on land were investigated in four adult Northern fur seals (Callorhinus ursinus) of both sexes. The electrocorticogram of both hemispheres, the neck electromyogram, the electrooculogram and electrocardiogram were recorded with implanted electrodes. The interhemispheric asymmetry of EEG during slow wave sleep was observed in all the animals sleeping in water and on land. The relative amount of interhemispheric slow wave asymmetry was higher during the sleep in water comparing to that on land. The fur seals maintain their special sleep posture on the water surface by moving only one of their front flippers. The asymmetric EEG in fur seals sleeping in the water may be attributed to the asymmetric motor activity of their flippers.

[Sleep and wakefulness in Callorhinus ursinus]. / Son i bodrstvovanie u severnykh morskikh kotikov.

Sleep and wakefulness of northern fur seals were studied on three subadult bulls carrying the implanted electrodes for recording the electrocorticogram of the two hemispheres, the neck electromiogram, the electrooculogram and the electrocardiogram. The active wakefulness accounted for 32.0 +/- 5.3% of total recording time, the relaxed wakefulness -31.7 +/- 3.1%, the slow wave sleep -30.5 +/- 5.1% and the paradoxical sleep -5.8 +/- 0.9%. The sleep cycle averaged 22,6 +/- 1.2 minutes. Interhemispheric asymmetry of the ECoG slow waves was pronounced in all three animals. Different forms of the asymmetry occupied 15.0 +/- 0.7% of total recording time. Such interhemispheric asymmetry was found in pinnipeds for the first time, in this respect the northern fur seals differ from the Caspean seals but resemble the dolphins.

[The effects of electric stimulation of the visual cortex of the cat in a behavior model of placing reaction]. / Effekty élektricheskogo razdrazheniia zritel'noi kory mozga koshki na povedencheskoi modeli postanovki lapy na oporu.

In 5 alert cats, the dependence of latency and probability of placing reaction on the parameters of electrical stimulation of visual cortex (the pulse duration and frequency in a series, number of pulses in a series) was studied. The values of current parameters were analogous to those that aroused human phosphens. The results revealed the conformity of the dependence of phosphens and cat's motor reaction on the current parameters. An addition of sound or electrocutaneous stimuli to the current stimulation decreases the threshold of the motor reaction and increases its probability. It is particularly obvious in case of weak and middle intensity currents when the probability of correct reactions to the current is insignificant.