Beneficial effects of regular exercise on sleep in old F344 rats

Neurobiology of Aging 27 (2006) 1859–1869

Beneficial effects of regular exercise on sleep in old F344 rats C.A. Blanco-Centurion, P.J. Shiromani ∗ West Roxbury Veterans Medical Center and Harvard Medical School, West Roxbury, MA 02132, USA Received 23 August 2005; received in revised form 11 October 2005; accepted 19 October 2005 Available online 23 November 2005

Abstract With aging there is a significant decline in the normal architecture of sleep and a reduction in the diurnal amplitude of core body temperature. Regular moderate exercise has been shown to have a positive impact in the elderly and here we investigate whether sleep–wake patterning can also be improved. Young (3 months) and old (22 months) F344 rats were exercised once a day for 50 min at night onset over an 8-week period. Thereafter, polysomnographic recordings were obtained immediately after exercise. To determine the lasting consequences of exercise, sleep was also recorded 2 days and 2 weeks after exercise had ended. Old rats that were exercised had a significant weight loss, were awake more during the last third of their active period, had less sleep fragmentation and the amplitude of the diurnal rhythm of core body temperature was significantly increased. Old exercised rats also had an overall increase in the amplitude of EEG power (0.5–16 Hz) during wake and theta EEG power during REM sleep. In young rats regular exercise increased EEG delta power (0.5–4 Hz) during NREM sleep. Our data indicate regular exercise in old rats improves sleep architecture, EEG power and diurnal rhythm of temperature. Published by Elsevier Inc. Keywords: Exercise; Sleep; Old rats; EEG power; Hypersomnolence; Sleep fragmentation; F344

1. Introduction The elderly show increased daytime sleepiness and fragmented night-time sleep [18,19,24,57,64,83,86]. The increase in sleep propensity, especially during late afternoon is present even in healthy elderly individuals [10,22]. In addition, the elderly have a significant decline in the amplitude of sleep-temperature rhythms, slow wave activity (SWA, also called delta activity, 0.5–4 Hz EEG) during non-rapid eye movement sleep (NREMS) [7,15,45,47] and in rapid eye movement sleep (REMS) [12,15,23,59]. The agerelated decline in sleep patterning is also evident in animals [50,61,66,75,77,84]. Little is known about the neurobiological mechanisms responsible for the decline of sleep patterning with age. Previously our laboratory determined that the decline in sleep with age was not due to a reduction in the number of sleep-active ∗ Corresponding author. Present address: Department of Neurology, Harvard Medical School & VA Medical Center, 1400 VFW Parkway Bld. 3 Rm. 2C-109, West Roxbury, MA 02132, USA. Tel.: +1 857 203 6162; fax: +1 857 203 5717. E-mail address: [email protected] (P.J. Shiromani).

0197-4580/$ – see front matter. Published by Elsevier Inc. doi:10.1016/j.neurobiolaging.2005.10.009

hypothalamic neurons [66] although a decline in adenosine A1 receptor sensitivity in the basal forebrain [48] together with a decline in hypocretin levels [13] might be contributing factors. Since the elderly population is expected to double in the next 10 years, interventions that can improve sleep quality are urgently needed. Pharmacotherapy is a possibility but there is a heavy risk of dependence and possible contraindications with the patient’s other medications [8]. A number of studies in humans have shown that exercise has a positive influence on health and well-being in young and the elderly [5,26,60]. Human data are supported by animal research demonstrating that exercise can increase the spontaneous activity of neurons [11], increase resistance to brain insult [69], preserve patterns of locomotor activity [67], restore adult brain microvasculature [6], enhance learning [78], increase neuronal survival [49] as well as promote adult neurogenesis [9,79]. Old mice (19 months) exercised for the first time show enhanced learning and neurogenesis in the hippocampus [80]. Sleep is also influenced by exercise. Healthy elderly individuals who perform regular aerobic exercise display sleep–wake patterns similar to young subjects, i.e. sleep less fragmented and higher amounts of slow wave activity during

1860

C.A. Blanco-Centurion, P.J. Shiromani / Neurobiology of Aging 27 (2006) 1859–1869

NREM sleep [14]. Most importantly, former sedentary seniors who engage in moderate intensity exercise improve their sleep and daytime performance as measured by either self-rated reports [4,32,35,74] or objective measures [4,51,72,82]. Regular exercise can also ease illnesses strongly linked to age-related sleep disorders such as mood disorders [63], obesity (combined with hypocaloric diet) [3], sleep apnea [52,55], osteoarthritis [16] and type 2 diabetes [25]. The effects of regular exercise on sleep–wake patterning in old rats are largely unknown, but it is likely that it is beneficial since old rats exposed to an enriched environment for 4–5 weeks, where physical activity is facilitated, display less sleep fragmentation and higher amounts of daytime sleep [76]. To better understand how exercise affects sleep–wake patterns with aging, it is important to have an animal model where this intervention can be experimentally tested. Hence in the present study we examined the effects of regular exercise on sleep–wake patterns in old and young F344 rats.

2. Methods 2.1. Animals Eighteen male F344 rats (Harlan-NIA) of two different ages, 3 months (young) and 22 months (old) at the time of shipping, were used. Animals were assigned to the following groups: young control (n = 4), young exercised (n = 4), old control (n = 4) and old exercised (n = 6). 2.2. Surgery Under deep anesthesia (ketamine [40 mg/kg, IM] + xylazine [5 mg/kg, IM] for induction; isofluorane for maintenance [1–2.5%, 2 L/min]) and using aseptic conditions animals were implanted with electrodes to record the electroencephalogram (EEG) and electromyogram (EMG). A transmitter (E-Mitter PDT-4000, MiniMitter, Bend, OR) to record core body temperature was inserted into the peritoneal cavity. The EEG electrodes consisted of four miniature screws (Plastics One Inc., Roanoke, VA). Two screws were placed on either side of the sagittal sinus over the frontal cortex (L ± 2, A + 3 referred to bregma) and the other two screws were placed on either side of the sagittal sinus but over the occipital cortex (L ± 2, A − 6 also referred to bregma). The EMG was recorded from two flexible multiwire electrodes inserted bilaterally into the nuchal muscles. EEG and EMG electrodes were then inserted into a six-pin plastic barrel and permanently fixed onto the skull surface with dental cement. 2.3. Housing conditions After surgery, the animals were housed singly and allowed 2 weeks to fully recover. In order to gauge the effects of exer-

cise training on body mass, rats were weighed once a week. Throughout the experiment rats had food (Harlan Teklad rodent diet LM-485, 7012) and water available ad libitum. Except during exercise periods, rats were always connected to a swivel with a lightweight recording cable (Plastic One Inc.), which allowed them to move freely in the cage. Throughout the experiment, the rats lived in a 12-h light:12-h dark cycle in an isolated room with controlled temperature (20–25 ◦ C; 200 lux during the day). 2.4. Exercise protocol Two weeks after surgery the rats were exercised for 50 min (total distance travelled = 100 m) in a slowly rotating wheel (2 m/min; Lafayette Instrument, Mod 80805). The slow speed was chosen because severe running has been reported to produce a deleterious effect on adult neurogenesis [58]. To further reduce stress the rats were allowed 5 min breaks during the exercise routine as follows: 20 min exercise, 5 min break, 20 min exercise, 5 min second break and lastly 10 min exercise. During breaks the wheel did not turn but rats remained in the wheel. The 50 min exercise regimen was done once each day (start of light-off period) for 5 days with Saturday and Sundays as days off, and it was continued for 8 consecutive weeks. Water was available ad libitum during the time rats were in the wheel. Age-matched control rats (both young and old) were not exercised but were kept awake as their experimental counterparts walked. Animals were kept awake by gently tapping their cages as soon as they showed behavioral and EEG signs of sleep. Thus, all rats were kept awake for 1 h at the start of the lights-off period, but one group was placed in the wheel and exercised while the other group was not. In this way, we controlled for the effects of sleep deprivation in both groups. 2.5. Sleep recording and analysis The EEG signal was recorded from two contralateral electrodes (frontal–occipital) and the EMG signal from the nuchal muscles. The EEG and EMG signals were recorded on a Grass Model 12 polygraph, filtered (EEG = 0.3–30 Hz, EMG = 0.3–1 KHz) digitized (sampling frequency = 128 Hz; National Instruments) and stored on the computer with the aid of a data acquisition software (ICELUS, Mark Opp, Univ. of Michigan, Ann Arbor). A technician (E. Winston) blind to the treatment scored the EEG and EMG data in 12 s epochs for wake, NREMS and REMS with the aid of a sleep-scoring program (ICELUS, M. Opp). Wake was identified by the presence of low amplitudehigh frequency EEG activity, high EMG integrated values coupled with low delta power relative to NREMS. NREMS was characterized by high amplitude-slow frequency EEG activity coupled to low EMG activity and high delta power compared to wake. REMS was identified by the presence of regular theta activity in the EEG, and a low to absent EMG signal relative to NREMS. A Fast

C.A. Blanco-Centurion, P.J. Shiromani / Neurobiology of Aging 27 (2006) 1859–1869

1861

Fourier Transformation (every 2 s) was performed on the EEG to determine power in the δ (0.5–4 Hz), θ (6–9 Hz) and α (12.0–16.0 Hz) frequency bands for each behavioral state. The following continuous blocks of 48 h sleep recordings were analyzed: immediately after the last day of the 8 week exercise period (end of exercise), 2 days after the end of exercise (2 days after exercise) and 2 weeks after exercise. Two-way ANOVA plus Tukey’s test, where appropriate, were used to analyze weights, sleep–wake parameters, EEG power and temperature at a significance threshold of P ≤ 0.05 (SigmaStat v.2.03). 2.6. Core temperature (CT) recordings and analysis CT was continuously recorded (except when rats were inside of the rotating wheels) every 6 min by a telemetry system (MiniMitter, Bend, OR). CT readouts from the last week of exercise or total sleep deprivation as well as readouts recorded 2 weeks later were used to perform the analysis of body temperature. In both conditions 5 consecutive days were taken (Monday–Friday). CT raw data were averaged every hour and plotted so as to visualize its diurnal variation. In order to analyze other body temperature parameters such as its diurnal amplitude, nighttime and daytime average, raw data for every rat was first smoothed 5% using the Lowell algorithm (DataFit v 8.0, Oakdale Engineering) and then smoothed data were inserted into a sine curve regression analysis (SigmaPlot v 5.0). The function chosen was f(y) = y0 + a sin(2πx/b + c). Overall the goodness of the curve fittings expressed as the R2 (coefficient of determination) was 0.90033 (±0.01122) and the P-values of the four equation’s parameters were <0.0001.

3. Results 3.1. Body weight Fig. 1 summarizes the change in body weight during the course of the experiment. As would be expected, the old rats weighed significantly more than the young rats at the start of the experiment (P < 0.001). The effects of exercise training on body mass were different depending on the age of the rats. Old exercised rats had a significant decline in body weight at the end of the first week of exercise compared to the old control rats, and this difference was still present by the end of the eighth week (P < 0.05). On the other hand, young exercised rats gained weight over the course of the experiment compared to young controls (F = 12.233, d.f. = 7, P < 0.001). After the last week of exercise, the weights of the old and young exercised rats were not significantly different (P = 0.252), but old controls weighed more than the other three groups (P = 0.002). Thus, the exercise regime tested in the present study decreased significantly the weight of the old rats.

Fig. 1. Effect of exercise on body weight. Rats were exercised at dark onset for 50 min once a day for at least 8 weeks and weighed at the end of each week. Controls were kept awake in their cages during the time when the experimental rats were exercised. Data represent means ± S.E.M. Young control n = 4, young exercised n = 4, old control n = 4, old exercised n = 6. Asterisks represent significance differences at P ≤ 0.05.

3.2. Sleep–wake patterns 3.2.1. Sleep fragmentation The architecture of the sleep–wake cycle in representative young and old rats is summarized in Fig. 2. Old control rats had significantly fragmented sleep patterns compared to young control rats (P < 0.05) (Table 1). The sleep fragmentation was identified by more frequent and shorter episodes of wake, NREMS and REMS throughout the day and night cycles (Table 1). Eight weeks of exercise improved the sleepfragmentation in old rats and this was identified by a 35% reduction in the total number of transitions among the behavioral states (P < 0.01). Especially at night old exercised rats, compared to old controls, had fewer and longer bouts of wake, NREMS and REMS, and their sleep pattern resembled that observed in young rats (see Fig. 2). The improved sleep patterning was still evident 2 weeks after the end of exercise (Table 1). During the daytime as well the total number of transitions was significantly reduced by exercise (−13%; P = 0.39). Two weeks after the end of exercise, old rats still showed significantly less and longer NREMS bouts during the daytime (Table 1). In summary, regular exercise training at night onset improved the sleep–wake architecture in old rats. 3.2.2. Sleep–wake states Exercised old rats were awake more at night (9.7% more wake time across the night cycle [P = 0.012 versus old control], especially during the last third of the night cycle [26.7% more time awake during late night, P = 0.029; Fig. 3]). These effects were still evident 2 weeks after the end of exercise (Figs. 3–5, bottom panels). Thus, 2 weeks after exercise

1862

C.A. Blanco-Centurion, P.J. Shiromani / Neurobiology of Aging 27 (2006) 1859–1869

Fig. 2. Effects of exercise on sleep patterns during the night cycle in young and old rats. Line plots represent the occurrence and duration of wake, NREMS and REMS in three representative rats immediately and 2 weeks after the end of exercise. The 12-h night period is broken in two halves (12–18 and 18–24 h). Time is represented along Y-axis (Zeitgeber 12 h = lights-off). The same rats were used to illustrate what occurred at both time points. Arrows indicate the timing when total sleep deprivation (TSD) or exercise was done (night onset). Note that the old control rats have a very fragmented sleep–wake pattern whereas the sleep pattern of the old exercised rats resembles that of the young control rat.

Table 1 Sleep–wake parameters in young and old F344 rats measured 2 weeks after end of exercise regime State

Total transitions

Wake

NREMS

No. bouts Time: night Young control Young exercised Old control Old exercised

28.4 30.0 41.8 28.3

± ± ± ±

1.8 3.0 5.5= 1.4**

Time: day Young control Young exercised Old control Old exercised

68.3 69.5 81.3 70.2

± ± ± ±

3.1 3.0 7.4 3.9

Duration

REMS

No. bouts

Duration

No. bouts

Duration

28.1 25.8 17.7 29.5

± ± ± ±

2.6 2.2 3.5= 3.2*

46.5 46.5 70.3 44.5

± ± ± ±

3.6 4.7 7.2= 3.1**

2.8 2.9 2.1 2.4

± ± ± ±

0.1 0.1 0.1= 0.3*

20.5 21.8 36.5 22.3

± ± ± ±

3.0 3.3 2.6= 1.3**

1.5 1.8 0.9 1.1

± ± ± ±

0.2 0.1 0.1= 0.1

136.6 133.5 208.8 127.3

± ± ± ±

12.3 13.0 18.8= 8.9**

4.8 4.4 3.9 5.3

± ± ± ±

1.0 0.6 0.4 0.8

120.5 119.3 139.3 115.6

± ± ± ±

7.5 4.0 7.5= 2.7**

3.3 3.3 2.5 3.2

± ± ± ±

0.1 0.1 0.2= 0.2**

46.5 55.8 72.0 61.4

± ± ± ±

3.0 4.6 9.1= 3.1

1.7 1.5 1.1 1.4

± ± ± ±

0.2 0.1 0.1= 0.1

350.5 373.0 396.5 343.2

± ± ± ±

16.14 5.05 19.53= 18.6*

Data represent means ± S.E.M. Young control n = 4, young exercised n = 4, old control n = 4, old exercised n = 6. Data were arranged by night (ZT12–23:59 h) or daytime (ZT0–11:59 h). Durations are expressed in minutes. Total number of transitions is the number of shifts among behavioral states (W ↔ NREMS ↔ REMS → W). * 0.05≤ P > 0.01 vs. old. = P ≤ 0.05 vs. young. ** P ≤ 0.01 vs. old.

C.A. Blanco-Centurion, P.J. Shiromani / Neurobiology of Aging 27 (2006) 1859–1869

1863

nificant differences in sleep–wake parameters (Figs. 3–5; Table 1). 3.3. EEG power spectra Overall, in the old rats there was a significant decline in EEG power during all behavioral states, a finding consistent with previous data (reviewed in ref. [66]). During wake old control rats showed significantly lower δ (0.5–4 Hz, −31.2%), θ (6–9 Hz, −43.6%) and α (12–16 Hz, −45.5%) EEG power compared to young control rats (Fig. 6). EEG delta power in NREMS was 14.2% (P < 0.001, Fig. 7) lower; while theta power during REMS was 46.2% (P < 0.05) below young control rats (Fig. 8). In old rats exercise increased significantly the EEG power during wake and REMS but it did not change the NREMS delta power. In old exercised rats, immediately after exercise, theta and alpha EEG power measured during waking were 65.7 and 59.9% higher with respect to old controls (P < 0.05) (Fig. 6, upper panel). Significantly higher values were still

Fig. 3. The effects of exercise on waking in young and old rats. Each data point represents the average of 4 consecutive hours. In the top panel, the first data point represents the average of 3 h since the rats were exercised (control rats were kept awake) during the first hour of the night cycle. Error bars (S.E.M.) are omitted for clarity. Crescent moon icons represent the night cycle (lights-off) whereas suns indicate the day cycle. * P ≤ 0.05 vs. control, ** P ≤ 0.01 vs. old exercise. Note that the old exercised rats were awake more during the last third of the night cycle, like the young rats.

ended, the percent NREMS and REMS during the last third of the night were 39.1 and 44.6% lower than those observed in old non-exercised rats. Consistent with our previous data [64] old non-exercised rats had blunted REMS diurnal rhythm, and exercise increased the amplitude of this rhythm (see Fig. 5). Young rats were also affected by the exercise. Immediately after exercise there was a significant increase in NREMS and REMS during the first third of the night (28.6%, P < 0.05 versus young control). However, by the middle third of the night this effect had disappeared (Fig. 2, upper panel). Two weeks after exercise this effect was not present either. In young exercised and non-exercised rats there were no sig-

Fig. 4. The effects of exercise on NREMS in young and old rats. As in Fig. 3, each data point represents the average of 4 consecutive hours. * P ≤ 0.05 vs. control, ** P ≤ 0.01 vs. old.

1864

C.A. Blanco-Centurion, P.J. Shiromani / Neurobiology of Aging 27 (2006) 1859–1869

Fig. 5. The effects of exercise on REMS in young and old rats.

evident 2 days after end of exercise (θ = +54.5%, α = 58.35%; P < 0.05, Fig. 6, middle panel). However, 2 weeks after end of exercise the EEG power had decreased so that there was no significant difference compared to old control rats (Fig. 6, lower panel). During REMS exercised old rats had 61.8% higher theta EEG power compared to old control rats (Fig. 8, set of bars on the left, P = 0.008). Two days after end of exercise theta power was still 55.9% above old control rats (Fig. 8, set of bars in the middle, P = 0.028). However, 2 weeks later the effect of exercise on REM sleep theta power was not observed (Fig. 8, set of bars on the right). Exercise did not change NREMS delta power in old rats (Fig. 7, panel A). However, in young rats significant effects of exercise were restricted to EEG delta power during NREMS (Fig. 7). Immediately after exercise NREMS EEG delta power increased significantly for several hours. Exercise also produced a significant higher peak of NREMS delta power when the lights turned on. Daytime values were consistently higher compared to the young control rats (Fig. 7, panel B). The increased NREMS delta power in young exercised rats was still

Fig. 6. Power spectral analysis of the EEG during the wake state in F344 young and old rats following regular exercise training. Fast Fourier Transformations were performed on artifact free EEG signal and generated absolute power values for three different frequency bands (δ = 0.5–4 Hz, θ = 6.0–9.0 Hz, α = 12.0–16.0 Hz). Data of absolute power represent averages obtained across 48 consecutive hours at every time point recorded (immediately, 2 days and 2 weeks after exercise). Error bars are not shown. * P < 0.05 and ** P < 0.01 vs. old control. • P < 0.05 vs. young control.

evident 2 weeks after the end of exercise (Fig. 7, panel C). 3.4. Core temperature (CT) In both age groups core body temperature was higher during the night than during the day (Fig. 9), which is consistent with the nocturnal activity in these animals. Old non-exercised rats had a decreased diurnal rhythm of core temperature, data that is consistent with previous studies [43]. In old rats, exercise increased the diurnal rhythm of CT (+0.19 ◦ C, P < 0.001) and old exercised rats showed lower

C.A. Blanco-Centurion, P.J. Shiromani / Neurobiology of Aging 27 (2006) 1859–1869

1865

Fig. 8. EEG theta power (6.0–9.0 Hz) during REMS in young and old rats following exercise training. Data represent means calculated over 48 consecutive hours of recording. Note that exercise restored REMS theta power in old rats. • P < 0.05 vs. young control, ** P < 0.05 vs. old control.

Fig. 7. EEG delta power (0.5–4.0 Hz, ␮V2 ) during NREMS in young and old F344 rats following regular exercise training. Panels (A) and (B) illustrate the delta power calculated immediately after exercise training had ended while panel (C) represents data obtained 2 weeks later. Data are averages ± S.E.M. calculated over 48 consecutive hours at every time point. Since at ZT 12 rats were exercising (A and B), these data are omitted. In (C), data at ZT 12 is omitted so that comparison with other data can be made. Filled and open bars at the bottom of every graph represent lights-off and lights-on conditions, respectively. * P < 0.05 vs. control. Note that exercise increases NREMS delta power in young but not in old rats.

core temperature during the day (−0.23 ◦ C, P < 0.05). These effects persisted for 2 weeks (P < 0.001, Table 2). Exercise also increased the amplitude of the day night rhythm of core temperature in young rats and this effect persisted 2 weeks after exercise ended (+0.09, P < 0.001 versus controls, Table 2). In summary, in both young and old rats exercise increased the amplitude of the temperature rhythm and decreased core temperature during the day.

4. Discussion The main findings of this study were that in old rats exercise increased waking at night, reduced sleep fragmentation,

the power of the EEG during waking was similar to young rats, and increased the amplitude of the diurnal rhythm of core temperature. The changes in sleep persisted for 2 weeks after the end of exercise, indicating the enduring effects of the exercise on CNS function. Control rats that were sleep deprived while experimental rats were exercising did not show changes in sleep. This indicates that it was not the 1-h waking per se that produced the sleep changes rather it was the effects of the exercise. The exercise was scheduled during the first hour of night to coincide with the start of the activity phase. In humans, this would be analogous to exercise in the morning. We hypothesized that exercise at the start of the activity period would increase waking. This hypothesis was confirmed. The exercised old rats had increased waking during the last third of the night. This might be due to increased levels of neuropeptides and neurotransmitters implicated in waking. In support of this hypothesis, there is strong evidence that physical activity increases the release of the wake-promoting neuropeptide hypocretin [41,85,87]. In old rats, there is a reduction in CSF levels of hypocretin, especially at the end of their active period [13]. We suggest that the exercise may have increased the activity of the hypocretin neurons and with it increased levels of arousal. Exercise also increases neurotransmitters implicated in waking. For instance, increased brain dopamine release occurs for at least 180 min after exercise [71]. Increased dopamine release induced by exercise could also explain decrease of sleepiness since strong dopamine stimulation with amphetamines enhances waking (reviewed by ref. [62]. Elderly Parkinson patients who walked daily for 1 week improved their motor performance [70]. Enhanced dopamine release in the brain after exercise has been reported using microdialysis as well (reviewed by ref. [44]). In rats, exercise significantly increases acetylcholine, noradrenaline and serotonin release in the parietal cortex [33]. Overall, the data suggests the activity of the basal forebrain cholinergic neurons, noradrenergic cells in the locus coeruleus and the serotoninergic neurons in

1866

C.A. Blanco-Centurion, P.J. Shiromani / Neurobiology of Aging 27 (2006) 1859–1869

Fig. 9. Effects of regular exercise on diurnal variations of core temperature (CT) in young and old F344 rats. Data represent hourly averages (±S.E.M.) over 5 consecutive days. CT data collected during the last week of the exercise regime were chosen to represent the condition of immediately after exercise (left panels). The ZT 12 time period is omitted because during this time rats were exercised (rats inside the wheels were out of range of the telemetry system). Closed bars represent lights-off whereas open bars indicate the lights-on. ZT, Zeitgeber time.

the dorsal raphe, all of which are the main input to cerebral cortex, might have increased in response to moderate exercise. Exercised old rats also had a significant increase in the amplitude of the diurnal rhythm of core body temperature compared to non-exercised old rats. With aging there is a decline in the amplitude of the temperature rhythm in rats [36,43] and humans (reviewed by ref. [81]. Our findings indicate that exercise can increase the amplitude of the diurnal rhythm of temperature. This is the first study to reveal changes in sleep after exercise in old rats, and can be compared with data in elderly humans. Naylor et al. [51] reported that a 2-week program featuring morning and evening physical–social activities increased daytime performance (memory-oriented tasks) and also stages 3 and 4 of NREM sleep in the first half of the night. Another report found that either morning or evening physical–social activities were effective in increasing daytime neuropsychological performance as well as self-rated sleep quality [4]. Tanaka et al. [72] found evening exercise combined with short naps after lunch decreased significantly daytime sleepiness and nighttime sleep fragmentation in a group of elderly Japanese. Li et al. [35] found that elderly

humans who practiced morning tai chi for 6 months reported significant reductions in daytime sleepiness and improved nighttime sleep quality. In the present study we found that the effects on sleep and EEG lasted for at least 2 weeks after the exercise had ended. Such enduring effects might result from changes in the activity of growth hormone (GH) and its main somatomedin, insulin-like growth factor 1 (IGF-1). In sedentary old rats continuous infusions of IGF-1 alone restores many agerelated changes in the brain such as declined capacity for hippocampal neurogenesis [2,37,73], deficits in learning and memory [40], reduced postsynaptic density [65], decreased brain microvasculature [38,68], decreased capacity to counteract injury [17] as well as reduced glucose utilization [39]. Blocking the exercise-induced release in IGF-1 also counteracts these effects. Elderly humans who have engaged in an exercise program for a long time have increased levels of IGF-1 compared to the elderly who are sedentary [1,27,56]. The intracerebroventricular infusion of IGF-1 in rats suppresses both NREMS and REMS [53]. It is suggested that the sleep suppression induced by IGF-1 is a result of an inhibition of GH [54].

37.53 37.12 37.95 0.67 0.15 0.19 0.19 0.082** ± ± ± ± 37.41 36.86 37.80 0.87 ± ± 0.07 ± 0.06• ± 0.016 37.54 37.11 37.97 0.68 ± ± 0.03** ± 0.04** ± 0.016** 37.43 36.93 37.94 0.80 0.04 0.03 0.04 0.009 ± ± ± ± 37.80 37.36 38.24 0.71 ± ± 0.04* ± 0.08 ± 0.008 37.53 37.09 37.97 0.68 37.73 ± 0.02 37.29 ± 0.03 38.18 ± 0.02 0.71 ± 0.014 24 h avg. Day avg. Night avg. Amplitude

Data are means ± S.E.M. calculated from curve-fitted raw data (see Section 2 for further details). Immediately after exercise curves were constructed using 5 consecutive days of CT samples measured during the last week of exercise training while another 5 days were pull out to make models representing what occurred 2 weeks after exercise regime finished. a Stage. b Group. * P < 0.05 vs. control. • P < 0.05 vs. young. ** P < 0.001 vs. control.

0.10 0.13* 0.09 0.066** ± ± ± ± 37.43 36.89 37.97 0.89 ± ± 0.05• ± 0.05• ± 0.013•

Exerciseb

0.05• Controlb Exerciseb Controlb

0.06• 0.03**

Exerciseb Controlb Exerciseb Controlb

0.06*

Immediately after exercisea Immediately after

Two weeks after exercisea Young

Age

Table 2 Age-related effects of regular exercise on core temperature main parameters

exercisea

Old

Two weeks after exercisea

C.A. Blanco-Centurion, P.J. Shiromani / Neurobiology of Aging 27 (2006) 1859–1869

1867

Increasing levels of IGF-1 in the brain following exercise could also explain changes in the EEG power spectra. In the present study, old exercised rats had significant increases in the EEG power (0.5–16 Hz) during waking as well as during REMS (6–9 Hz). Because EEG power is gauging the potency of multiple cortical-subcortical neuronal networks along different firing frequencies, increased EEG power may reflect higher neuronal synchrony. Both IGF-1 and exercise enhance neuronal activity directly and indirectly by increasing blood flow to these cells (brain angiogenesis) [30,38]. In the present study, the sleep of young exercised rats was also affected compared to their unexercised controls. In young exercised rats, the main effect was a significant increase in delta power (slow wave activity) during NREMS throughout the 24 h cycle. This effect was still evident 2 weeks after exercise ended. Also a short-lived increase in NREMS and REMS following exercise was observed in these rats. These findings are consistent with other report showing increase of NREMS, REMS and delta power during NREMS in young Wistar rats undergoing light or moderate acute exercise (36 and 180 m) for 45 min [20]. Young Sprague–Dawley rats also showed increase of the delta band during NREMS after 4 h of acute low or moderate walking activity [46]. It is proposed that heat load associated with exercise promotes increase of slow wave activity during sleep [28,29]. The old rats that were exercised lost approximately 5% of their weight in the first week and by the end of the experiment weighed significantly less compared to the old unexercised rats. Young rats increased weight over the 8-week course of the experiment and this may be due to maturation. The reduction in weight in our study is comparable to another study where the F344 rats were exercised for 3 months and lost 4% weight compared to unexercised rats [42]. In their study exercise increased lean body mass which offset the loss of fat mass. In humans, cross-sectional as well as longitudinal studies clearly show that remaining physically active throughout late life prevents the age-related gain of body weight [21,31], especially in fat mass [34]. Elderly humans who are physically active weigh less and have more lean mass than sedentary age-matched [27,34]. Thus, the body mass of both old rats and humans respond alike to regular exercise. In summary, the present study indicates that moderate regular exercise as a behavioral intervention can improve both the sleep architecture and core temperature physiology disrupted by age. This is relevant given that the elderly population is increasing.

Acknowledgements We thank Jill Winston and Elizabeth Winston for providing excellent technical assistance. This study was funded by the Veterans Affairs Research Service and the following NIH grants: AG 09975, AG 15853, MH 55772 and NS 30140.

1868

C.A. Blanco-Centurion, P.J. Shiromani / Neurobiology of Aging 27 (2006) 1859–1869

References [1] Ambrosio MR, Valentini A, Trasforini G, Minuto F, Ghigo E, Cella S, et al. Function of the GH/IGF-1 axis in healthy middle-aged male runners. Neuroendocrinology 1996;63(6):498–503. [2] Anderson MF, Aberg MA, Nilsson M, Eriksson PS. Insulin-like growth factor-I and neurogenesis in the adult mammalian brain. Brain Res Dev Brain Res 2002;134(1–2):115–22. [3] Ballor DL, Poehlman ET. Exercise-training enhances fat-free mass preservation during diet-induced weight loss: a meta-analytical finding. Int J Obes Relat Metab Disord 1994;18(1):35–40. [4] Benloucif S, Orbeta L, Ortiz R, Janssen I, Finkel SI, Bleiberg J, et al. Morning or evening activity improves neuropsychological performance and subjective sleep quality in older adults. Sleep 2004;27(8):1542–51. [5] Berkman LF, Seeman TE, Albert M, Blazer D, Kahn R, Mohs R, et al. High, usual and impaired functioning in community-dwelling older men and women: findings from the MacArthur Foundation Research Network on Successful Aging. J Clin Epidemiol 1993;46(10):1129–40. [6] Black JE, Isaacs KR, Anderson BJ, Alcantara AA, Greenough WT. Learning causes synaptogenesis, whereas motor activity causes angiogenesis, in cerebellar cortex of adult rats. Proc Natl Acad Sci USA 1990;87(14):5568–72. [7] Bliwise DL. Sleep in normal aging and dementia. Sleep 1993;16(1):40–81. [8] Bonnet MH, Balkin TJ, Dinges DF, Roehrs T, Rogers NL, Wesensten NJ. The use of stimulants to modify performance during sleep loss: a review by the sleep deprivation and stimulant task force of the American academy of sleep medicine. Sleep 2005;28(9):1163–87. [9] Brown J, Cooper-Kuhn CM, Kempermann G, van Praag H, Winkler J, Gage FH, et al. Enriched environment and physical activity stimulate hippocampal but not olfactory bulb neurogenesis. Eur J Neurosci 2003;17(10):2042–6. [10] Buysse DJ, Monk TH, Reynolds III CF, Mesiano D, Houck PR, Kupfer DJ. Patterns of sleep episodes in young and elderly adults during a 36-hour constant routine. Sleep 1993;16(7):632–7. [11] Carro E, Nunez A, Busiguina S, Torres-Aleman I. Circulating insulinlike growth factor I mediates effects of exercise on the brain. J Neurosci 2000;20(8):2926–33. [12] Darchia N, Campbell IG, Feinberg I. Rapid eye movement density is reduced in the normal elderly. Sleep 2003;26(8):973–7. [13] Desarnaud F, Murillo-Rodriguez E, Lin L, Xu M, Gerashchenko D, Shiromani SN, et al. The diurnal rhythm of hypocretin in young and old F344 rats. Sleep 2004;27(5):851–6. [14] Edinger JD, Morey MC, Sullivan RJ, Higginbotham MB, Marsh GR, Dailey DS, et al. Aerobic fitness, acute exercise and sleep in older men. Sleep 1993;16(4):351–9. [15] Ehlers CL, Kupfer DJ. Slow-wave sleep: do young adult men and women age differently? J Sleep Res 1997;6(3):211–5. [16] Felson DT, Lawrence RC, Hochberg MC, McAlindon T, Dieppe PA, Minor MA, et al. Osteoarthritis: new insights. Part 2: Treatment approaches. Ann Intern Med 2000;133(9):726–37. [17] Fernandez AM, Gonzalez de la Vega AG, Planas B, Torres-Aleman I. Neuroprotective actions of peripherally administered insulin-like growth factor I in the injured olivo-cerebellar pathway. Eur J Neurosci 1999;11(6):2019–30. [18] Foley D, Ancoli-Israel S, Britz P, Walsh J. Sleep disturbances and chronic disease in older adults: results of the 2003 National Sleep Foundation Sleep in America Survey. J Psychosom Res 2004;56(5): 497–502. [19] Foley DJ, Monjan AA, Brown SL, Simonsick EM, Wallace RB, Blazer DG. Sleep complaints among elderly persons: an epidemiologic study of three communities. Sleep 1995;18(6):425–32. [20] Gambelunghe C, Rossi R, Mariucci G, Tantucci M, Ambrosini MV. Effects of light physical exercise on sleep regulation in rats. Med Sci Sports Exerc 2001;33(1):57–60. [21] Haapanen N, Miilunpalo S, Pasanen M, Oja P, Vuori I. Association between leisure time physical activity and 10-year body mass change

[22]

[23]

[24]

[25] [26]

[27]

[28]

[29] [30] [31]

[32]

[33]

[34]

[35]

[36] [37]

[38]

[39]

[40]

[41]

[42] [43]

among working-aged men and women. Int J Obes Relat Metab Disord 1997;21(4):288–96. Haimov I, Lavie P. Circadian characteristics of sleep propensity function in healthy elderly: a comparison with young adults. Sleep 1997;20(4):294–300. Hayashi Y, Endo S. Comparison of sleep characteristics of subjects in their 70’s with those in their 80’s. Folia Psychiatr Neurol Jpn 1982;36(1):23–32. Hays JC, Blazer DG, Foley DJ. Risk of napping: excessive daytime sleepiness and mortality in an older community population. J Am Geriatr Soc 1996;44(6):693–8. Henriksen EJ. Invited review: effects of acute exercise and exercise training on insulin resistance. J Appl Physiol 2002;93(2):788–96. Hill RD, Storandt M, Malley M. The impact of long-term exercise training on psychological function in older adults. J Gerontol 1993;48(1):12–7. Horber FF, Kohler SA, Lippuner K, Jaeger P. Effect of regular physical training on age-associated alteration of body composition in men. Eur J Clin Invest 1996;26(4):279–85. Horne JA, Moore VJ. Sleep EEG effects of exercise with and without additional body cooling. Electroencephalogr Clin Neurophysiol 1985;60(1):33–8. Horne JA, Staff LH. Exercise and sleep: body-heating effects. Sleep 1983;6(1):36–46. Ide K, Secher NH. Cerebral blood flow and metabolism during exercise. Prog Neurobiol 2000;61(4):397–414. Kahn HS, Tatham LM, Rodriguez C, Calle EE, Thun MJ, Heath Jr CW. Stable behaviors associated with adults’ 10-year change in body mass index and likelihood of gain at the waist. Am J Public Health 1997;87(5):747–54. King AC, Oman RF, Brassington GS, Bliwise DL, Haskell WL. Moderate-intensity exercise and self-rated quality of sleep in older adults. A randomized controlled trial. JAMA 1997;277(1):32–7. Kurosawa M, Okada K, Sato A, Uchida S. Extracellular release of acetylcholine, noradrenaline and serotonin increases in the cerebral cortex during walking in conscious rats. Neurosci Lett 1993;161(1):73–6. Kyle UG, Morabia A, Schutz Y, Pichard C. Sedentarism affects body fat mass index and fat-free mass index in adults aged 18 to 98 years. Nutrition 2004;20(3):255–60. Li F, Fisher KJ, Harmer P, Irbe D, Tearse RG, Weimer C. Tai chi and self-rated quality of sleep and daytime sleepiness in older adults: a randomized controlled trial. J Am Geriatr Soc 2004;52(6):892– 900. Li H, Satinoff E. Changes in circadian rhythms of body temperature and sleep in old rats. Am J Physiol 1995;269(1 Pt 2):R208–14. Lichtenwalner RJ, Forbes ME, Bennett SA, Lynch CD, Sonntag WE, Riddle DR. Intracerebroventricular infusion of insulin-like growth factor-I ameliorates the age-related decline in hippocampal neurogenesis. Neuroscience 2001;107(4):603–13. Lopez-Lopez C, LeRoith D, Torres-Aleman I. Insulin-like growth factor I is required for vessel remodeling in the adult brain. Proc Natl Acad Sci USA 2004;101(26):9833–8. Lynch CD, Lyons D, Khan A, Bennett SA, Sonntag WE. Insulin-like growth factor-1 selectively increases glucose utilization in brains of aged animals. Endocrinology 2001;142(1):506–9. Markowska AL, Mooney M, Sonntag WE. Insulin-like growth factor-1 ameliorates age-related behavioral deficits. Neuroscience 1998;87(3):559–69. Martins PJ, D’Almeida V, Pedrazzoli M, Lin L, Mignot E, Tufik S. Increased hypocretin-1 (orexin-a) levels in cerebrospinal fluid of rats after short-term forced activity. Regul Pept 2004;117(3):155–8. Mazzeo RS, Horvath SM. Effects of training on weight, food intake, and body composition in aging rats. Am J Clin Nutr 1986;44(6):732–8. McDonald RB, Hoban-Higgins TM, Ruhe RC, Fuller CA, Horwitz BA. Alterations in endogenous circadian rhythm of core temperature in senescent Fischer 344 rats. Am J Physiol 1999;276(3 Pt 2): R824–30.

C.A. Blanco-Centurion, P.J. Shiromani / Neurobiology of Aging 27 (2006) 1859–1869 [44] Meeusen R, Piacentini MF, De Meirleir K. Brain microdialysis in exercise research. Sports Med 2001;31(14):965–83. [45] Miles LE, Dement WC. Sleep and aging. Sleep 1980;3(2):1–220. [46] Mistlberger R, Bergmann B, Rechtschaffen A. Period-amplitude analysis of rat electroencephalogram: effects of sleep deprivation and exercise. Sleep 1987;10(6):508–22. [47] Mourtazaev MS, Kemp B, Zwinderman AH, Kamphuisen HA. Age and gender affect different characteristics of slow waves in the sleep EEG. Sleep 1995;18(7):557–64. [48] Murillo-Rodriguez E, Blanco-Centurion C, Gerashchenko D, SalinPascual RJ, Shiromani PJ. The diurnal rhythm of adenosine levels in the basal forebrain of young and old rats. Neuroscience 2004;123(2):361–70. [49] Narath E, Skalicky M, Viidik A. Voluntary and forced exercise influence the survival and body composition of ageing male rats differently. Exp Gerontol 2001;36(10):1699–711. [50] Naylor E, Buxton OM, Bergmann BM, Easton A, Zee PC, Turek FW. Effects of aging on sleep in the golden hamster. Sleep 1998;21(7):687–93. [51] Naylor E, Penev PD, Orbeta L, Janssen I, Ortiz R, Colecchia EF, et al. Daily social and physical activity increases slow-wave sleep and daytime neuropsychological performance in the elderly. Sleep 2000;23(1):87–95. [52] Norman JF, Von Essen SG, Fuchs RH, McElligott M. Exercise training effect on obstructive sleep apnea syndrome. Sleep Res Online 2000;3(3):121–9. [53] Obal Jr F, Kapas L, Bodosi B, Krueger JM. Changes in sleep in response to intracerebral injection of insulin-like growth factor-1 (IFG-1) in the rat. Sleep Res Online 1998;1(2):87–91. [54] Obal Jr F, Kapas L, Gardi J, Taishi P, Bodosi B, Krueger JM. Insulin-like growth factor-1 (IGF-1)-induced inhibition of growth hormone secretion is associated with sleep suppression. Brain Res 1999;818(2):267–74. [55] Peppard PE, Young T. Exercise and sleep-disordered breathing: an association independent of body habitus. Sleep 2004;27(3):480–4. [56] Poehlman ET, Rosen CJ, Copeland KC. The influence of endurance training on insulin-like growth factor-1 in older individuals. Metabolism 1994;43(11):1401–5. [57] Prinz PN. Sleep and sleep disorders in older adults. J Clin Neurophysiol 1995;12(2):139–46. [58] Ra SM, Kim H, Jang MH, Shin MC, Lee TH, Lim BV, et al. Treadmill running and swimming increase cell proliferation in the hippocampal dentate gyrus of rats. Neurosci Lett 2002;333(2):123–6. [59] Reynolds III CF, Kupfer DJ, Taska LS, Hoch CC, Sewitch DE, Spiker DG. Sleep of healthy seniors: a revisit. Sleep 1985;8(1):20–9. [60] Rogers RL, Meyer JS, Mortel KF. After reaching retirement age physical activity sustains cerebral perfusion and cognition. J Am Geriatr Soc 1990;38(2):123–8. [61] Rosenberg RS, Zepelin H, Rechtschaffen A. Sleep in young and old rats. J Gerontol 1979;34(4):525–32. [62] Rye DB. The two faces of eve: dopamine’s modulation of wakefulness and sleep. Neurology 2004;63(8 Suppl. 3):S2–7. [63] Salmon P. Effects of physical exercise on anxiety, depression, and sensitivity to stress: a unifying theory. Clin Psychol Rev 2001;21(1):33–61. [64] Schmitt FA, Phillips BA, Cook YR, Berry DT, Wekstein DR. Self report on sleep symptoms in older adults: correlates of daytime sleepiness and health. Sleep 1996;19(1):59–64. [65] Shi L, Linville MC, Tucker EW, Sonntag WE, Brunso-Bechtold JK. Differential effects of aging and insulin-like growth factor-1 on synapses in CA1 of rat hippocampus. Cereb Cortex 2004. [66] Shiromani PJ, Lu J, Wagner D, Thakkar J, Greco MA, Basheer R, et al. Compensatory sleep response to 12 h wakefulness in young and old rats. Am J Physiol Regul Integr Comp Physiol 2000;278(1): R125–33.

1869

[67] Skalicky M, Bubna-Littitz H, Viidik A. Influence of physical exercise on aging rats. I. Life-long exercise preserves patterns of spontaneous activity. Mech Ageing Dev 1996;87(2):127–39. [68] Sonntag WE, Lynch CD, Cooney PT, Hutchins PM. Decreases in cerebral microvasculature with age are associated with the decline in growth hormone and insulin-like growth factor 1. Endocrinology 1997;138(8):3515–20. [69] Stummer W, Weber K, Tranmer B, Baethmann A, Kempski O. Reduced mortality and brain damage after locomotor activity in gerbil forebrain ischemia. Stroke 1994;25(9):1862–9. [70] Sunvisson H, Lokk J, Ericson K, Winblad B, Ekman SL. Changes in motor performance in persons with Parkinson’s disease after exercise in a mountain area. J Neurosci Nurs 1997;29(4):255–60. [71] Sutoo D, Akiyama K. Regulation of brain function by exercise. Neurobiol Dis 2003;13(1):1–14. [72] Tanaka H, Taira K, Arakawa M, Urasaki C, Yamamoto Y, Okuma H, et al. Short naps and exercise improve sleep quality and mental health in the elderly. Psychiatry Clin Neurosci 2002;56(3):233–4. [73] Trejo JL, Carro E, Torres-Aleman I. Circulating insulin-like growth factor I mediates exercise-induced increases in the number of new neurons in the adult hippocampus. J Neurosci 2001;21(5):1628–34. [74] Tworoger SS, Yasui Y, Vitiello MV, Schwartz RS, Ulrich CM, Aiello EJ, et al. Effects of a yearlong moderate-intensity exercise and a stretching intervention on sleep quality in postmenopausal women. Sleep 2003;26(7):830–6. [75] van Gool WA, Mirmiran M. Age-related changes in the sleep pattern of male adult rats. Brain Res 1983;279(12–):394–8. [76] van Gool WA, Mirmiran M. Effects of aging and housing in an enriched environment on sleep–wake patterns in rats. Sleep 1986;9(2):335–47. [77] van Gool WA, Witting W, Mirmiran M. Age-related changes in circadian sleep–wakefulness rhythms in male rats isolated from time cues. Brain Res 1987;413(2):384–7. [78] van Praag H, Christie BR, Sejnowski TJ, Gage FH. Running enhances neurogenesis, learning, and long-term potentiation in mice. Proc Natl Acad Sci USA 1999;96(23):13427–31. [79] van Praag H, Kempermann G, Gage FH. Running increases cell proliferation and neurogenesis in the adult mouse dentate gyrus. Nat Neurosci 1999;2(3):266–70. [80] van Praag H, Shubert T, Zhao C, Gage FH. Exercise enhances learning and hippocampal neurogenesis in aged mice. J Neurosci 2005;25(38):8680–5. [81] van Someren EJ. More than a marker: interaction between the circadian regulation of temperature and sleep, age-related changes, and treatment possibilities. Chronobiol Int 2000;17(3):313–54. [82] van Someren EJ, Lijzenga C, Mirmiran M, Swaab DF. Long-term fitness training improves the circadian rest-activity rhythm in healthy elderly males. J Biol Rhythms 1997;12(2):146–56. [83] Whitney CW, Enright PL, Newman AB, Bonekat W, Foley D, Quan SF. Correlates of daytime sleepiness in 4578 elderly persons: the Cardiovascular Health Study. Sleep 1998;21(1):27–36. [84] Witting W, Mirmiran M, Bos NP, Swaab DF. The effect of old age on the free-running period of circadian rhythms in rat. Chronobiol Int 1994;11(2):103–12. [85] Wu MF, John J, Maidment N, Lam HA, Siegel JM. Hypocretin release in normal and narcoleptic dogs after food and sleep deprivation, eating, and movement. Am J Physiol Regul Integr Comp Physiol 2002;283(5):R1079–86. [86] Yoon IY, Kripke DF, Youngstedt SD, Elliott JA. Actigraphy suggests age-related differences in napping and nocturnal sleep. J Sleep Res 2003;12(2):87–93. [87] Yoshida Y, Fujiki N, Nakajima T, Ripley B, Matsumura H, Yoneda H, et al. Fluctuation of extracellular hypocretin-1 (orexin A) levels in the rat in relation to the light–dark cycle and sleep–wake activities. Eur J Neurosci 2001;14(7):1075–81.