An instrumental method for long-term continuous REM sleep deprivation of neonatal rats

STUDY OBJECTIVES

The present study describes a new method for instrumental REM sleep deprivation (RSD) of neonatal rats.

DESIGN

In the new method, an experimental neonatal rat and a yoked control neonatal rat were singly housed in a small plexiglass chamber which was divided into two separate units by a vertical wall. The floor of the housing chamber was attached to the platform of a standard laboratory test tube shaker. EEG and EMG electrodes were implanted by the soft head plug method which permitted continuous, long-term polysomnography. EEG and EMG signals were sent to a computer that was programmed to turn on the shaker for 5 seconds whenever the experimental rat entered REM sleep.

SETTING

NA PATIENTS: NA INTERVENTIONS: NA RESULTS: The shaking of the chamber usually terminated REM sleep by entry to slow-wave sleep or wake. Amount of RSD depended on the shaker's oscillation speed. At higher speed the method reduced REM sleep by more than 80%.

CONCLUSIONS

Thus, the new instrumental method of RSD can be used to study developmental functions of neonatal REM sleep. In particular, the instrumental method can test the hypothesis that in rats neonatal RSD produces the adult depressogenic effect of neonatally administered clomipramine.

Modeling daily and subdaily cycles in rat sleep data

We developed a statistical model for rat sleep-wake behavior over the 24-hour day; this model could be used for animals exposed to shorter cycles of light and dark conditions. Rat behavior was classified either as "wake" or "sleep," as determined by analysis of electrophysiological data. The proposed model consists of three parts: the first two explain cyclic effects relating to the lighting conditions, whereas the last part reflects any acyclic effect. Hypothesis tests were conducted on the magnitude of the parts. The model also accounts for correlated errors.

Sleep deprivation in the rat: XX. Differences in wake and sleep temperatures during recovery

We examined the relationship between wake and sleep peritoneal temperature (T(ip)) during recovery from short-term (five rats, 5 days of deprivation) and long-term (nine rats, 14-21 days) total sleep deprivation (TSD). Mammalian body temperature normally declines in the passage from wakefulness to sleep. Recovery from TSD featured reductions of the typical wake-sleep T(ip) differences. Previous studies from our laboratory have shown that chronic TSD in the rat produces a progressive rise in energy production and an initial rise in wake T(ip), followed by a later fall in T(ip) to below baseline that becomes more acute as death becomes imminent. During recovery from both short-term TSD (wherein pre-recovery wake T(ip) was still above baseline) and long-term TSD (wherein pre-recovery wake T(ip) had fallen to below baseline), wake T(ip) and energy production quickly returned towards baseline. On the first recovery day, both short- and long-term TSD rats showed mean non-rapid eye movement (NREM) and paradoxical sleep (PS) T(ip) values that were slightly, although not significantly, above mean wake T(ip). In short-term TSD rats, wake-NREM and wake-PS T(ip) differences were reduced from baseline significantly (p < 0.0025) on the first recovery day and nonsignificantly on the remaining three recovery days. In long-term TSD rats, wake-NREM and wake-PS T(ip) differences were significantly (p < 0.001) reduced from baseline on the first four recovery day block. On the last four recovery day block, wake-sleep T(ip) differences tended to return toward baseline. Hypothalamic wake-sleep temperature differences in long-term TSD rats showed similar reductions during recovery. The reduction of wake-sleep temperature differences in recovery does not support either energy reduction or cooling functions for sleep.

Sleep deprivation in the rat: XIV. Comparison of waking hypothalamic and peritoneal temperatures

Earlier studies of rats subjected to total sleep deprivation (TSD) by the disk-over-water method had shown an initial increase in waking peritoneal temperature (T(ip)) followed by an even greater decrease as deprivation proceeded. In the present study, hypothalamic temperature (T(hy)), as well as T(ip), were recorded continuously. As in the earlier studies, TSD rats showed an increase in energy expenditure and an initial increase followed by a decrease in T(ip). Waking T(hy) showed a more prolonged initial rise and a smaller late decline than waking T(ip) Assuming that, as the literature suggests, T(hy) is held closer to temperature setpoint (TSET) than is T(ip), the present results suggest an elevated waking TSET during deprivation. T(ip) became progressively lower than T(hy) over the course of deprivation, indicating a decreased ability to maintain the whole body near TSET. This decreased ability could result from insufficient thermogenesis or excessive heat loss. Because thermogenesis rose progressively throughout deprivation, heat loss must have increased even more than heat production. Thus, the results are consistent with other data which indicate that TSD in the rat produces two opposing effects on waking temperature, an elevation of setpoint and excessive heat loss, which together increase the demand for energy expenditure.

Sleep deprivation in the rat: XII. Effect on ambient temperature choice

Previous studies of total sleep deprivation in the rat by the disk-over-water method had shown an initial rise in body temperature (Tb), a later decline to below baseline levels, and a progressive rise in energy expenditure (EE). To evaluate the role of changes in temperature setpoint in these results, the ambient temperature choices (Tc) of six totally sleep-deprived (TSD) rats and their yoked control (TSC) rats were determined by the position in a thermally graded alley at which they chose to fall asleep. (Rats were removed from the alley and returned to the deprivation apparatus 1 min after sleep onset). Sleep deprivation was continued until TSD rats were near death. Tb and EE results were like those of the earlier studies. Tc rose progressively from 26.8 degrees C during baseline to 49.9 degrees C near the end of the deprivation period in TSD rats, whereas TSC rats showed only modest, nonsignificant increases. The attempt by TSD rats to get warmer, in spite of an elevated Tb, indicates a raised setpoint for behavioral thermoregulation and suggests that the increase in EE was also, at least in part, an attempt to reach an elevated setpoint. The progressively raised Tc also indicates that the late decline in Tb was a decline below setpoint rather than a response to a lower setpoint. Because EE increased, Tb decline must have resulted from excessive heat loss. Thus, TSD in the rat produced two thermoregulatory deficits-increased setpoint and excessive heat loss.(ABSTRACT TRUNCATED AT 250 WORDS)

Sleep deprivation in the rat: II. Methodology

Methods common to several studies in this series are described. A key feature is a sleep deprivation apparatus in which an experimental and a yoked control rat are housed on opposite sides of a divided disk suspended over shallow water. When the experimental rat enters a "forbidden" sleep stage, the disk is automatically rotated, forcing the experimental rat to walk to avoid being carried into the water. The control rat receives the same physical stimulation but can sleep ad lib when the disk is stationary.