Effects of sleep deprivation in neonatal rats.

This investigation represents the first systematic study of sleep homeostasis in developing mammals that spans the preweaning and postweaning periods. Neonatal rats from 12 to 24 days of postnatal life (P12-P24) were anesthetized with Metofane (methoxyflurane) and implanted with miniaturized electroencephalographic (EEG) and electromyographic electrodes. After 48 h of recovery, neonatal rats were sleep deprived for 3 h by either gentle handling or forced locomotion. We find that 3-h sleep deprivation produces dramatically different compensatory responses at different stages of postnatal development. In striking contrast to adult rats, sleep deprivation does not increase slow-wave sleep EEG delta (0.5-4.0 Hz) activity in rats younger than P24. However, P12-P20 rats do show evidence of sleep regulation because they show compensatory increases in sleep time and sleep continuity during recovery. In P12 rats, approximately 90% of total slow wave sleep time lost during the sleep-deprivation period was recovered during subsequent sleep. A similar recovery of active sleep time was observed in P20-P24 rats. These findings suggest not only that sleep is regulated in neonatal rats but that the accumulation and/or discharge of sleep need changes dramatically between the third and fourth postnatal weeks.

Effects of temperature on sleep in the developing rat.

In altricial species, such as humans and rats, much of the development of autonomic systems occurs postnatally. Consequently, vulnerabilities exist early in postnatal development when immature autonomic functions are challenged by external factors such as variations in ambient temperature (Ta). Ta profoundly influences sleep/wake state structure in adult animals and humans, and exposure to excessive warmth has been implicated as a risk factor in sudden infant death syndrome. To better understand the relationship between temperature and sleep during development, we investigated the effect of Ta variation on sleep/wake state structure and sleep intensity in developing rats. In this experiment, sleep intensity was measured by the intensity of slow-wave activity during slow-wave sleep. Neonatal Long-Evans hooded rat pups were surgically prepared for chronic sleep/wake state and brain temperature (Tbr) recording. Two-hour recordings of sleep/wake state and Tbr were obtained from rats on postnatal day 12 (P12), P14, P16, P18, and P20 at a Ta of either 28.0-30.0, 33.0-35.0, or 38.0-40.0 degrees C. Ta significantly influenced sleep/wake state structure but had little, if any, effect on sleep intensity in developing rats.

[Keratometric characteristics and astigmatism of globes from eye bank]. / Caractéristiques kératométriques et de l'astigmatisme des globes d'une banque d'yeux.

We measured by means of keratometry the dioptric power of the main meridians of 142 globes (79 subjects) obtained from an eye bank. The mean dioptric power was 43.56 (standard deviation [SD] 1.97) dioptres. Eyes from female subjects had a significantly higher mean power than those from male subjects (p < 0.05). The keratometric readings were used to quantify corneal astigmatism. The mean degree of astigmatism was 1.03 (SD 0.95) dioptres. There was no significant difference in the amount of astigmatism between age groups, between eyes from female and male subjects, and between left and right eyes. However, subjects with astigmatism in one eye were likely to have it in the fellow eye (p < 0.001). A predominance of "against-the-rule" astigmatism was noted.