Evidências comportamentais de um estado análogo ao sono REM em polvos

Abstract

Sleep is a behavior that occurs in several taxa of the animal kingdom, suggesting that sleep emerged primarily in the evolutionary chain of metazoans. Despite being a widely studied behavior in vertebrates, mainly mammals and birds, it is known that some invertebrates also present this quiescence state. Octopus is one of the invertebrates in which this behavior is expressed in a complex way, with electrophysiological records showing that brain activity increases when the animal is resting. However, these data were observed only in 4 Octopus vulgaris, due to technical challenges of conducting electrophysiological records in the aquatic environment that make this type of experiment difficult. However, sleep studies can be performed using the behavioral criteria used to identify this state in vertebrates. Thus, this work aimed to investigate, classify and describe in detail the quiescence states observed in Octopus insularis and Octopus cf. vulgaris through comprehensive behavioral quantification using video recordings. In addition, to assess potential differences in the arousal threshold of each state, O. insularis were exposed to visual and vibratory stimuli during each identified sleep-wake state. The results showed that O. insularis and O. cf. vulgaris have conspicuous behavioral variations during quiescence. Some of them have been cited in the literature, such as presenting half-andhalf body pattern (QHH) and narrow or completely closed eye pupil (QCP). But other changes in the quiescent state have not been described yet: The change in body pattern to dark color (observed only in O. cf. vulgaris); one eye movement (QOEM) (observed in both species); and a REM-like sleep of vertebrates (QEMBPC) (observed only in O. insularis). In this last, occurs movement of both eyes while the animal changes the skin color and texture, accompanied by contractions of the body similar to muscular spasms and random movement of the suckers. The test to evaluate the arousal threshold of each state showed significant difference between the states, with the highest latency observed in the QEMBPC state, followed by the QPC, QHH and, finally, the alert, with the lowest arousal threshold. These results suggest the existence of different sleep states in the octopus, which makes the quiescence of this animal even more similar with the vertebrates sleep. For example, the "QCP" state appears to be analogous to slow wave sleep, while QEMBPC appears to be analogous to REM sleep. In addition, the QOEM state may be an evidence of uni-hemispheric sleep, which is an adaptation commonly observed in marine mammals and birds. Thus, this work suggests investigating whether, in addition to the behavioral similarities observed, the sleep of these cephalopods also have the same physiological functions that it performs in vertebrates. This will be possible with the improvement of techniques for conducting electrophysiology in the aquatic environment or without the use of wires, as well as by investigating immediate early genes that may be associated with the sleep of these animals.