Prenatal Development of Sleep-Wake Patterns in Sheep

Abstract

Chronic intrauterine monitoring of electrocortical activity, eye movements, and electromyographic activity of the nuchal muscles has permitted the use of established polygraphic criteria to study the ontogenetic development of organized sleep-wake patterns in the fetal lamb in utero. Sixty-five polygraphic recordings obtained from 21 fetal lambs ranging from 112 to 144 days of gestation (term = 145 days) were analyzed. The results show that the transition from disorganized to organized behavioral state patterns occurs at approximately 115-120 days (0.8 term). The physiologic characteristics of the arousal, quiet sleep (QS), and REM sleep (REMS) states are qualitatively similar to those in the adult. There is initially a high proportion of REMS (greater than 50%), with only 11% time spent in arousal. The direct transition from arousal to REMS without a QS period is frequently seen in the fetus at all ages. Quantitative changes in the distribution of behavioral states continue throughout gestation. There is a significant decrease in the incidence of REMS, with a small increase in arousal and QS. The duration of QS and REMS episodes increases with age until a steady level is achieved by 130 days. There is also an increase in the frequency of occurrence of arousal periods, with no change in episode duration.

Sleep and Development in Genetically Tractable Model Organisms

“…In utero sleep is prominently exhibited by all mammalian prenatals that have been carefully observed (Ruckebusch 1972;Drucker-Colín et al 1979;Awoust and Levi 1984;Szeto and Hinman 1985). Human fetal sleep begins early in the third trimester of pregnancy.…”

Spectral Edge Frequency as a Simple Quantitative Measure of the Maturation of Electrocortical Activity

“…Electrocortical activity can be detected in prenatal life and has been shown to undergo maturational changes throughout late gestation. These developmental changes include the progression from an immature waveform pattern of variable frequencies to the typical HVSA and LVFA patterns described by a number of investigators (1 -6); changes in the relative incidence of these two predominant patterns (2, 6); as well as maturational changes in the waveform characteristics of the two predominant patterns (5,6).…”

Arterial Oxygen Tension Threshold Range for the Onset of Arousal and Breathing in Fetal Sheep

“…These discrepancies in fetal behavioral state might have been because of the different criteria used to define fetal arousal as well as different techniques to induce continuous breathing. Most investigators have used the electrographic criteria to define the fetal sleep states (6,7), whereas Rigatto (34) observed the fetus through a Plexiglas window implanted in the ewe's left flank. However, no studies comparing the electrographic and visual observation have been reported in a chronically prepared fetal sheep.…”

“…Breathing stopped at a Pao2 of 38.5 +: 9.5 torr (5.1 f 1.3 kPa) but could be restarted by increasing the Pao2. In response to an increase in fetal Pao, (4)(5)(6)(7)(8), amplitude of breathing and total respiratory output significantly increased from the control values. Further increases in Pao2 or Hb O2 saturation did not significantly affect the respiratory output.…”

“…Fetal arousal was defined by the simultaneous presence of LVECoG, nuchal tone, and eye movements (6,7).…”