Sleep in amphibians and reptiles: a review and a preliminary analysis of evolutionary patterns.
This work considers comparative behavioral, somatoautonomic, and neurophysiological characteristics of three forms of passive defensive behavior included in the amphibian wakefulness-sleep cycle and their dynamics in the ascending vertebrate series. Considered in parallel is sleep formation in early postnatal ontogenesis of mature-and immature-born mammals-from undifferentiated sleep to the mature sleep divided into two phases as well as of stress-reaction. Comparative phylo-and ontogenetic analysis of several aspects of stress-reactions, sleep, and immobility phenomenon of the catalepsy type allows concluding that the immobility state of the catalepsy type in amphibians and reptiles can be considered the preadaptive behavior type that underlies the homoiothermal stress-reaction. It is the genetically programmed to the poikilothermal state characterized by a relatively high animal alertness, a freezing of the animal in the immobile, but active posture, with a possibility of a fast exit into the wakefulness state, which, alongside with other somatoautonomic and neurophysiological characteristics, which determines the entire subsequent complex of evolutionary morphofunctional changes of neuroregulatory and hormonal changes in the homoiothermal organism. In poikilothermal animals, this in many aspects unspecific behavioral adaptive reaction is realized at the corresponding hormonal and neurological levels of development of the organism and promotes fast mobilization and stabilization of constancy of the internal medium. At the higher evolutionary ladder levels, on the background of maturation of most neurotransmitter systems of brain and the hypothalamo-pituitary-adrenal system, the leading role in the stress-reaction regulation begins to be played predominantly by hormones, and only in the phase of the stress-reaction alertness, there are observed elements of activation of extrapyramidal systems of regulation of locomotor activity, which is manifested as the cataleptic freezing reaction. Thus, stress as the general adaptational syndrome reflects evolutionary regularities of development of specific functions supporting the total homeostasis. A scheme of evolutionary development of the wakefulness-sleep cycle in the vertebrate subtype is presented; according to it, the immobility state of the catalepsy type, on one hand, is considered as a part of wakefulness providing mainly specific elements of the stress-reaction, while, on the other hand,—as a certain step of the process of inhibition in CNS for subsequent involvement of the sleep-regulatory systems of compensation and maintenance of recovery reactions.