Circadian rhythm of serotonin binding in rat brain--II. Influence of sleep deprivation and imipramine

Sleep deprivation (SD) modified the circadian rhythm of specific high affinity serotonin (5-HT) binding to rat brain membranes. In control rats a 24-hr rhythm was evident with a trough at 1000-1200 and a nadir at 0000. During the last 26 hr of a 49 hr SD period, trough and peak values were delayed by 4-6 hr. The 24-hr mean binding was significantly (P less than 0.001) different from that of controls. If sleep deprivation was followed by recovery sleep (RS), the normal rhythm of 5-HT binding was obtained already within 1 hr after SD. The effects of SD and RS were ascertained by plasma ACTH and corticosterone assay. No significant change in the hormone rhythms were observed through the mean plasma level of ACTH and corticosterone were enhanced to about 180 and 150%, respectively. Chronic treatment with the antidepressant imipramine resulted in a decrease of the 24-hr mean 5-HT binding by about 50% and a 2-hr delay of peak and trough values. Imipramine treatment decreased the peak value of 5-HT concentration at 1000 to about 65% and appears to abolish the rhythm of 5-HT concentration.     

Circadian Rhythm of Serotonin Binding in Rat Brain—II. Influence of Sleep Deprivation and Imipramine

Sleep deprivation (SD) modified the circadian rhythm of specific high affinity serotonin (5-HT) binding to rat brain membranes. In control rats a 24-hr rhythm was evident with a trough at 1000-1200 and a nadir at 0000. During the last 26 hr of a 49 hr SD period, trough and peak values were delayed by 4-6 hr. The 24-hr mean binding was significantly (P < 0.001) different from that of controls. If sleep deprivation was followed by recovery sleep (RS), the normal rhythm of 5-HT binding was obtained already within 1 hr after SD. The effects of SD and RS were ascertained by plasma ACTH and corticosterone assay. No significant change in the hormone rhythms were observed though the mean plasma level of ACTH and corticosterone were enhanced to about 180 and 150%, respectively. Chronic treatment with the antidepressant imipramine resulted in a decrease of the 24-hr mean 5-HT binding by about 50% and a 2-hr delay of peak and trough values. Imipramine treatment decreased the peak valueof 5-HT concentration at 1000 to about 65% and appears to abolish the rhythm of 5-HT concentration.     

Memory for semantically related and unrelated declarative information: the benefit of sleep, the cost of wake

Numerous studies have examined sleep's influence on a range of hippocampus-dependent declarative memory tasks, from text learning to spatial navigation. In this study, we examined the impact of sleep, wake, and time-of-day influences on the processing of declarative information with strong semantic links (semantically related word pairs) and information requiring the formation of novel associations (unrelated word pairs). Participants encoded a set of related or unrelated word pairs at either 9 am or 9 pm, and were then tested after an interval of 30 min, 12 hr, or 24 hr. The time of day at which subjects were trained had no effect on training performance or initial memory of either word pair type. At 12 hr retest, memory overall was superior following a night of sleep compared to a day of wakefulness. However, this performance difference was a result of a pronounced deterioration in memory for unrelated word pairs across wake; there was no sleep-wake difference for related word pairs. At 24 hr retest, with all subjects having received both a full night of sleep and a full day of wakefulness, we found that memory was superior when sleep occurred shortly after learning rather than following a full day of wakefulness. Lastly, we present evidence that the rate of deterioration across wakefulness was significantly diminished when a night of sleep preceded the wake period compared to when no sleep preceded wake, suggesting that sleep served to stabilize the memories against the deleterious effects of subsequent wakefulness. Overall, our results demonstrate that 1) the impact of 12 hr of waking interference on memory retention is strongly determined by word-pair type, 2) sleep is most beneficial to memory 24 hr later if it occurs shortly after learning, and 3) sleep does in fact stabilize declarative memories, diminishing the negative impact of subsequent wakefulness.     

Diurnal Variations of Beta-Endorphin at Rest and After Moderate Intensity Exercise

To determine the effect of time of day on circulating beta-endorphin concentrations 14 men exercised at 75% of their maximal capacity at 0600, 1200, 1800 and 2400 hr. Each trial was separated by 3-5 days and preceded by a normal sleep cycle except for the 0600 hr trials which was preceded by 6 hr sleep. Resting physiological data indicated normal diurnal variations in heart rate, core temperature and oxygen uptake, being lowest during the 0600 hr trials and highest during the 1800 hr trials. Resting plasma beta-endorphin concentrations averaged 11.9 +/- 8.4 pmol/l during the 0600 hr trials, significantly greater than the 2400 hr trials (6.4 +/- 3.6 pmol/l; P less than 0.05). No other significant differences existed at rest. Post exercise beta-endorphin concentrations were elevated and found to be inversely related to time of day with the 0600 hr trials having the highest mean (25.7 +/- 14.7) and the 2400 hr trials the lowest (14.7 +/- 8.3). These data suggest that the plasma beta-endorphin concentrations at rest and after exercise are affected by the time of day. The results also suggest that the changes in beta-endorphin associated with exercise are not major contributors to cardiorespiratory control or changes in psychological effect associated with exercise.     

Daily profiles of aldosterone levels during normal, high and low sodium intake in patients with essential hypertension.

The episodic secretion of aldosterone depends on the dietary sodium intake, alterations in posture and follows ACTH circadian rhythm. Aldosterone daily profiles have been studied in 23 supine essential hypertensive patients on normal sodium intake. Secretory pulses at a frequency of two to five pulses per 12 hr have occurred, independent of PRA levels. Among 13 patients with normal PRA two lost pulsatility when sodium was loaded (10 g/24 hr) and the same happened with two others on sodium restricted diet (2 g/24 hr). These results suggest a profound effect of dietary sodium intake on the pulsatile pattern of aldosterone secretion, particularly in normal PRA essential hypertension.     

The internal circadian clock increases hunger and appetite in the evening independent of food intake and other behaviors

Objective:

Despite the extended overnight fast, paradoxically, people are typically not ravenous in the morning and breakfast is typically the smallest meal of the day. We assessed whether this paradox could be explained by an endogenous circadian influence on appetite with a morning trough, while controlling for sleep/wake and fasting/feeding effects.

Design and Methods:

Twelve healthy non‐obese adults (six males; age, 20‐42 years) were studied throughout a 13‐day laboratory protocol that balanced all behaviors, including eucaloric meals and sleep periods, evenly across the endogenous circadian cycle. Participants rated their appetite and food preferences by visual analog scales.

Results:

There was a large endogenous circadian rhythm in hunger, with the trough in the biological morning (8 AM) and peak in the biological evening (8 PM; peak‐to‐trough amplitude = 17%; P = 0.004). Similarly‐phased significant endogenous circadian rhythms were present in appetites for sweet, salty and starchy foods, fruits, meats/poultry, food overall, and for estimates of how much food participants could eat (amplitudes 14‐25%; all P < 0.05).

Conclusions:

In people who sleep at night, the intrinsic circadian evening peak in appetite may promote larger meals before the fasting period necessitated by sleep, whereas the circadian morning trough would theoretically facilitate the extended overnight fast. Furthermore, the circadian decline in hunger across the night would theoretically counteract the fasting‐induced hunger increase that could otherwise disrupt sleep.     

To sleep, to strive, or both: how best to optimize memory

While numerous studies have shown that a night of sleep profits memory relative to wake, we still have little understanding about what factors mediate this effect of sleep. A clear understanding of the dynamics of this effect of sleep beyond the initial night of sleep is also lacking. Here, we examined the effect of extrinsic rewards on sleep-dependent declarative memory processing across 12 and 24 hr training-retest intervals. Subjects were either paid based on their performance at retest ($1 for each correct answer), or received a flat fee for participation. After a 12 hr interval we observed pronounced benefits of both sleep and reward on memory. Over an extended 24 hr interval we found 1) that an initial night of sleep partially protects memories from subsequent deterioration during wake, and 2) that sleep blocks further deterioration, and may even have a restorative effect on memory, when it follows a full day of wake. Interestingly, the benefit imparted to rewarded (relative to unrewarded) stimuli was equal for sleep and wake subjects, suggesting that the sleeping brain may not differentially process rewarded information, relative to wake. However, looking at the overall impact of sleep relative to reward in this protocol, it was apparent that sleep both imparted a stronger mnemonic boost than reward, and provided a benefit to memory regardless of whether it occurred in the first or the second 12 hrs following task training.     

Polyphasic Wake/Sleep Episodes in the Fire Ant, Solenopsis Invicta

Sleep is a well-studied biological process in vertebrates, particularly birds and mammals. Less is know about sleep in solitary and social invertebrates, particularly the ants. This paper reports a study of light/dark periods on worker activity as well as sleep location, posture and the wake/sleep cycles of fire ant workers and queens located in an artificial nest chamber. Workers slept in one of three locations: on the ceiling, against the chamber wall or in the center of the chamber floor. Workers on the ceiling or against the chamber wall slept for longer periods than those at the center of the chamber floor where most grooming and feeding activity occurred. When sleeping, queens huddled together. Their close contact generated synchronized wake/sleep cycles with each other. Sleep posture was distinctly different than wake posture. During deep sleep, queens and workers folded their antennae and were non-responsive to contact by other ants. Another indicator of deep sleep was rapid antennal movement (RAM sleep). Sleep episodes were polyphasic. Queens averaged ~92 sleep episodes per day, each episode lasting ~6 min, for a total of ~9.4 h of sleep per day. Workers averaged ~253 sleep episodes lasting 1.1 min each for a total of ~4.8 h of sleep per day. Activity episodes were unaffected by light/dark periods. Workers were hypervigilant with an average of 80% of the labor force completing grooming, feeding or excavation tasks at any given time. These findings reinforce the parental exploitation hypothesis—sterile workers are a caste of disposable, short-lived helpers whose vigilance and hyperactivty increases the queen’s fitness by buffering her and her fertile offspring from environmental stresses.     

Induction of antibacterial activity in the haemolymph of the silkworm, Bombyx mori, by injection of formalin-treated Escherichia coli K-12 in the anterior and posterior body part of the ligated larvae.

1. Induction of antibacterial activity was investigated in the ligated fifth instar larvae of the silkworm, Bombyx mori, by injection of formalin-treated Escherichia coli K-12 into the haemocoel in the anterior and in the posterior body part, followed by activity determination by inhibition zone assay of the haemolymph at 12 and 24 hr after immunization. 2. At 12 hr after immunization, high antibacterial activity, approximately 6.8-7.5 mm in the anterior body part and 4.5-6.4 mm in the posterior body part in diameter of a clear zone (2.0 mm for no activity) was detectable in day 3 larvae. This result was in good contrast to expression of lectin gene in the ligated flesh fly, Sarcophaga peregrena (Shiraishi and Natori, 1988, FEBS Lett. 232, 163-166), in which only the anterior part of insect responded to stimulus of injury. 3. Antibacterial activity at 24 hr after immunization in days 3 or 4 ligated larvae was lower than that at 12 hr; 4.0-4.5 mm of activity was observed in the anterior body part, and no activity was observed in day 3 ligated larvae in the posterior body part. 4. Acid polyacrylamide gel electrophoresis of the haemolymph of immunized insects followed by overlay assay showed that the size of antibacterial activity bands were similar between the haemolymph from 12 hr and from 24 hr, and between the anterior and the posterior body part. This result was contradictory to the observation of activity by inhibition zone assay. The activity bands were associated with peptides that were similar to cecropin-like peptides A and B in the silkworm.(ABSTRACT TRUNCATED AT 250 WORDS)     

Circadian Rhythm of Prohormone Atrial Natriuretic Peptides 1-30, 31-67 and 99-126 in Man

Two peptides consisting of amino acids 1-30 and 31-67 of the N-terminal end of the prohormone of the atrial natriuretic factor (pro ANF), vasodilate aortas in vitro, lower blood pressure in vivo, and have natriuretic properties similar to the atrial natriuretic factor (ANF, amino acids 99-126 of the prohormone). It has been recently discovered that pro ANF 1-30 and pro ANF 31-67 as well as ANF circulate in man. To determine if these three peptide hormones have a circadian variation in their circulating plasma concentrations, eight housestaff volunteers were studied on a day when they were in the hospital for 24 hr. These 5 men and 3 women, ages 25 to 39 had blood samples taken at 0800, 1200, 1600, 2000, 0000, 0400 and 0800 on the following day. One-half of these house officers were up all night while the other half went to sleep from midnight to 0800 and had their 0400 plasma samples drawn while in a supine position. The peak level for all three peptide hormones was at 0400 for both supine and upright subjects. It was concluded that there are circadian rhythms in normal, active people of these three peptide hormones, whose peak levels are at 0400 irrespective of posture.