Evelyn Satinoff

Maximal REM Sleep Time Defines a Narrower Thermoneutral Zone Than Does Minimal Metabolic Rate

Abstract Sleep states and oxygen consumption were simultaneously measured in rats at environmental temperatures of 23, 25, 27, 29, 31, and 33°C. Rapid eye movement (REM) sleep was more sensitive to environmental temperature than was metabolic rate. Oxygen consumption was minimal and constant between 25 and 31°C, whereas REM sleep time varied significantly over this range, with a peak at 29°C. Thus, maximal REM sleep time defines a more precise thermoneutral zone than does minimal metabolic rate. Furthermore, REM sleep time at 29°C was more than double the amount seen at 23°C, which is a standard laboratory temperature. Thus, varying the thermal environment is a simple noninvasive way to manipulate REM sleep time, and could be used to assess the effects of differing amounts of REM sleep on waking behaviors.

Ambient Temperature-Dependence of Sleep Disturbances Produced by Basal Forebrain Damage in Rats,

Amounts of sleep and waking were determined in rats at ambient temperatures (Tas) of 20, 25, and 30 degrees C, before and after basal forebrain lesions. Rats were hyposomniac at all Tas for 1-2 days postlesion. After that, sleep was highly Ta-dependent. Rats were typically hyperthermic after complete ablation of the medial preoptic area (MPOA), and the Ta at which maximal amounts of rapid-eye movement sleep (REMS) occurred frequently shifted from 30 to 25 degrees C. During the first postlesion month, amounts of slow-wave sleep (SWS), REMS, total sleep time ( TST ), and the proportion of time spent in REMS to TST (REMS/ TST ) all improved significantly at the Tas at which the most REMS occurred (high REMS temperatures). In contrast, at the Tas at which the least REMS occurred, these variables were as depressed one month after MPOA damage as they were at 5 days postlesion. REMS/ TST recovered most rapidly, returning to prelesion levels at high REMS temperatures within the first postlesion week. REMS bout durations were severely shortened after forebrain damage, and this was the only sleep disturbance not attenuated at high REMS temperatures. After smaller basal forebrain lesions, initial deficits were less severe and normal amounts of sleep returned earlier. However, as was the case for large lesions, sleep deficits were most severe and persistent at low REMS temperatures.

Interactions between body temperature and wheel running over the estrous cycle in rats

Female rats were housed in Wahmann wheels under a 12:12 light-dark (LD) photoperiod for 36 days and then were switched to LD 10:14 for 36-64 days. Running was 95-100% nocturnal. Overall amounts of running were higher in LD 12:12, but changes over the estrous cycle were similar. On the night of proestrus running increased by 64% in LD 12:12 and 123% in LD 10:14 (p less than 0.0001) compared to the first night of diestrus. Nighttime Tbs were correlated with running levels. In LD 12:12 Tb on proestrus was higher by 0.3 +/- 0.0 degrees C (p less than 0.0001); in LD 10:14 it was higher by 0.2 +/- 0.0 degrees C (p less than 0.001) compared to diestrus-1. During L, Tb was lowest on proestrus and highest on estrus. Half of the rats exhibited a consistent phase advance of at least 30 min in both Tb and activity on proestrus. The advanced Tb acrophase was correlated with both the activity acrophase (r = .91; p less than 0.0001) and the amount of running (r = .60; p less than 0.01). The wheels of 6 rats were then locked at night in LD 10:14. There were no significant Tb changes from diestrus-1 across the cycle. However, Tb acrophase was delayed a mean of 76 +/- 16 min (p less than 0.01) in these rats. Also, the Tb acrophase across all days of the estrous cycle was delayed by 94 +/- 18 min (p less than 0.001) compared to when the wheels were open.(ABSTRACT TRUNCATED AT 250 WORDS)

Suprachiasmatic Nuclear Lesions Eliminate Circadian Rhythms of Drinking and Activity, but Not of Body Temperature, in Male Rats

Male Long-Evans rats were maintained in lightproof cabinets while drinking, ac tivity, and telemetered body temperature (Tb) data were collected. After suprachiasmatic nuclear (SCN) lesions, the rats were exposed to a 12:12 light-dark cycle, a 6-hr delay in the lighting cycle, and constant dark. Lesions that abolished the drinking and activity rhythms did not eliminate the Tb rhythm. However, the amplitude, phase, and free-running period of the Tb rhythm were altered. Lesions that only partially damaged the SCN had similar, though lesser, effects. In some cases, Tb rhythms remained normal, activity rhythms were only temporarily disrupted, and drinking rhythms were eliminated in the same animals. These results support the conclusion that Tb can remain rhythmic after lesions that permanently or temporarily disrupt other circadian rhythms. Of the three rhythms, it appears that drinking rhythms are most easily and Tb rhythms least easily disrupted by SCN lesions.

Phentolamine and thermoregulation in rats.

Phentolamine (PHEN), a nonselective alpha-adrenoceptor antagonist, causes a dose and ambient temperature (Ta)-dependent fall in body temperature (Tb) when injected intraperitoneally. In this paper, we investigated whether this was caused by integrated behavioral and autonomic thermoregulatory responses and whether it was due to a central action of the drug. Male rats were trained to press a bar for warm air in the cold or cold air in the heat. Rats were tested in both conditions near their Tb peaks and troughs after injections of saline or PHEN (5 and 10 mg/kg, IP). Tb fell significantly within the first 30 min post-PHEN, and after that, in the cold, the rats worked to increase Ta. In the heat they did not change Ta. To determine what was responsible for the Tb fall, we measured heat loss and heat production after saline or PHEN (10 mg/kg; IP) at Ta 2, 20, and 30 degrees C. Decreases in Tb at 2 and 20 degrees C were caused by increased heat loss during the first 15-30 min post-PHEN. At 2 degrees C, heat production increased after the drop in Tb. We conclude that the main reason the rats do not start to work immediately to prevent their core temperature from falling is that skin temperature is high, due to peripheral vasodilation, and that skin temperature is the major stimulus for regulating preferred Ta. We believe these effects are mediated by peripheral mechanisms because intracerebro-ventricular injections of PHEN did not cause a fall in Tb.

Development of the circadian rhythm of body temperature in rats

Seven male and seven female rat pups, all from separate litters of 10 pups each, had biotelemetry thermistors implanted into their peritoneal cavities when they were 10-15 days old. Body temperatures (Tb) were recorded by an Apple computer every 10 minutes until the rats were 60-75 days old so that the development of the circadian temperature rhythm (CTR) could be studied. The data were compared with eight parameters taken from adult CTRs. All rats were maintained on a 12 hr light/12 hr dark photoperiod. The results indicate that the CTR begins to develop after thermoregulatory mechanisms mature to produce an adult like daily range of TbS around day 24. From days 25 to 45, there was a steady increase in the percentage of TbS greater than the daily mean occurring in the dark. This process organized Tb into the characteristic sinusoidal waveform of the adult. Proper phasing of the trough and peak relative to the light/dark cycle took place between days 30-36. By day 42, 90% of TbS higher than the daily mean were occurring in the dark, while those lower than the mean were in the light. This is the typical adult pattern. The waveforms appearance continued to develop until day 50.

Diurnal rhythms of body temperature, drinking and activity over reproductive cycles

These studies describe diurnal rhythm changes in female rats during gestation and lactation. In Experiment I, we measured the diurnal temperature rhythm (DTR) of 20 females through gestation, lactation and the post-lactational period and found that rhythm amplitude decreased during gestation and increased during lactation. Phase changes were also common features of the DTR during these states. In Experiment II, we measured drinking rhythms in 12 females during lactation and post-lactation and found phase and amplitude changes that were similar to the DTR changes seen in Experiment I. In Experiment III, we correlated the behavior of lactating females with their DTR and found that there was a consistent internal organization between behavior and Tb regardless of the degree of change in the DTR during the postpartum period. Females showing large phase changes in their DTR patterns were distinguishable from those showing smaller phase changes, however, on the basis of the absolute temporal organization of their behavior during lactation. All phase and amplitude changes disappeared immediately after pups were removed from the cage.

Acute thermoregulatory effects of unilateral electrolytic lesions of the medial and lateral preoptic area in rats

Unilateral anodal lesions of the medial or lateral preoptic area (POA) in unanesthetized rats had opposite thermoregulatory effects immediately after the lesion were made. Lesions of the medial POA evoked hyperthermias and accompanying cold defense responses, including vasoconstriction of the tail, increased oxygen consumption, shivering, and heat conservation postures. The hyperthermias had latencies of 0-30 minutes and reached maximum values within 120 minutes postlesion. They were independent of ambient temperature and dissociable from the hyperactivity often seen after such lesions. Damage to the lateroventral POA elicited acute falls in body temperature, as well as vasodilation of the tail, decreased oxygen consumption, inhibition of shivering in cool environments, and prone body extension. Unilateral cathodal lesions throughout the POA yielded only hyperthermia. These results suggest a possible anatomical segregation of heat and cold defense functions within the anterior basal forebrain.

Brief skin temperature changes towards thermoneutrality trigger REM sleep in rats

Abstract When rats were in slow-wave sleep (SWS) at an environmental temperature (23°C) below their thermoneutral zone (27–31°C), brief skin warming by either radiant heating, or forced air convection resulted in REM sleep on 79–80% of the trials. During control nonwarmed SWS bouts, the animals went into REM sleep on only 22–24% of the trials. When the environmental temperature was above thermoneutrality, 34°C, lowering skin temperature by convective cooling resulted in REM sleep entry 68% of the time, compared to 21% for noncooled, control trials. Skin warming and cooling at 29°C decreased the percent occurrence of REM sleep to 22% and 9% respectively, for at this thermoneutral temperature 46% of the control SWS bouts ended in REM sleep. Thus, peripheral temperature changes towards thermoneutrality trigger REM sleep in mildly thermally stressed rats.

Body temperature rhythms, cold tolerance, and fever in young and old rats of both genders

The circadian rhythm of body temperature (CTR) of male and female rats living at 23 degrees C, as well as their body temperature response to a yeast injection or to a 2-h exposure to 0 degree C, was investigated by telemetry. Young rats had a clear CTR with a mean nocturnal peak of 38.0 +/- 0.1 degree C and diurnal trough of 36.2 +/- 0.1 degree C. Older rats, starting at about 18 months of age, tended to have poor (that is, lower amplitude) rhythms. Mean daily body temperature was 37.1 +/- 0.2 degree C at all ages. After exposure to the cold, the body temperature of young rats, old rats with a strong CTR, and old rats with a poor CTR changed in the ranges of -0.3 to +1.5 degree C, -3.1 to +0.7 degree C, and -5.2 to +0.4 degree C, respectively. This indicates that old animals, especially but not exclusively those with poor CTRs, are less resistant to cold stress. On the other hand, the capacity to develop a fever in response to a yeast injection was equivalent in the three groups of animals, although females had a smaller response than males. It is concluded that the process of aging does not have a generalized debilitating effect on temperature regulation in rats. Rather, aging seems to affect individual components of the thermoregulatory system differentially.