Rong-Yu Liu

Age-associated difference in circadian sleep-wake and rest-activity rhythms

Using actigraphic monitoring of wrist activity, we investigated the sleep and rest-activity patterns of 65 young, middle-aged, old and the oldest subjects in their natural environmental conditions. To assess the effects of age and gender on sleep and circadian rhythms in activity, multivariate analyses were performed. Age significantly affected circadian sleep and rest-activity rhythms. In the old and oldest groups, the actigraphic estimates of actual sleep time and sleep efficiency decreased significantly. The estimates of sleep latency, the number of nighttime awakening, sleep fragmentation and daytime naps significantly increased in the old and oldest groups. Concerning the circadian patterning of rest and activity, the interdaily stability (IS) was similar in the four age groups, while the old and oldest subjects showed significant increases in intradaily variability (IV) and nighttime activity and a decrease in amplitude (AMP). The present study demonstrated weakened and fragmented circadian sleep and rest-activity rhythms during aging. However, no gender-related difference was found.

Early neuropathological Alzheimer's changes in aged individuals are accompanied by decreased cerebrospinal fluid melatonin levels

Abstract: Neuropathology is the most reliable criterion for diagnosing Alzheimers disease (AD). A well‐established system for staging the spread of neuropathological changes in AD is available. The clinical use of a biomarker that reflects the neuropathological change occurring in brain tissue has not yet been established. Melatonin is a product that plays not only a major role in the regulation of the circadian rhythms but may also exert neuroprotective effects in AD. Melatonin levels were determined in ventricular postmortem cerebrospinal fluid (CSF) of 121 subjects. Braak staging and a modified Braak staging for cortex (MBSC) were used to evaluate the severity of AD neuropathology. The present study revealed that not only the Braak stages of AD, but also the MBSC were negatively correlated with CSF melatonin levels. By using MBSC, we now demonstrate for the first time that CSF melatonin levels were significantly decreased in the aged individuals with early neuropathological changes in the temporal cortex, where the AD process starts. Those individuals that did not have any neurofibrillary tangle (NFT) or neuritic plaque (NP) in the temporal cortex, had much higher melatonin levels (287u2003±u200368 and 280u2003±u200364u2003pg/mL, respectively) than those individuals that had a few NFTs and NPs (82u2003±u20034 and 39u2003±u20038u2003pg/mL, respectively) in the temporal cortex. These results suggest that the decrease in CSF melatonin levels may be an early event in the development of AD possibly occurring even before the clinical symptoms.

Pineal clock gene oscillation is disturbed in Alzheimer’s disease, due to functional disconnection from the “master clock”

The suprachiasmatic nucleus (SCN) is the “master clock” of the mammalian brain. It coordinates the peripheral clocks in the body, including the pineal clock that receives SCN input via a multisynaptic noradrenergic pathway. Rhythmic pineal melatonin production is disrupted in Alzheimers disease (AD). Here we show that the clock genes hBmal1, hCry1, and hPer1 were rhythmically expressed in the pineal of controls (Braak 0). Moreover, hPer1 and hβ1‐adrenergic receptor (hβ1‐ADR) mRNA were positively correlated and showed a similar daily pattern. In contrast, in both preclinical (Braak I‐II) and clinical AD patients (Braak V‐VI), the rhythmic expression of clock genes was lost as well as the correlation between hPer1 and hβ1‐ADR mRNA. Intriguingly, hCry1 mRNA was increased in clinical AD. These changes are probably due to a disruption of the SCN control, as they were mirrored in the rat pineal deprived of SCN control. Indeed, a functional disruption of the SCN was observed from the earliest AD stages onward, as shown by decreased vasopressin mRNA, a clock‐controlled major output of the SCN. Thus, a functional disconnection between the SCN and the pineal from the earliest AD stage onward could account for the pineal clock gene changes and underlie the circadian rhythm disturbances in AD.—Wu, Y‐H., Fischer, D. F., Kalsbeek, A., Garidou‐Boof, M‐L., van der Vliet, J., van Heijningen, C., Liu, R‐Y., Zhou, J‐N., Swaab, D. F. Pineal clock gene oscillation is disturbed in Alzheimers disease, due to functional disconnection from the “master clock.” FASEB J. 20, E1171–E1180 (2006)

Alterations in the circadian rhythm of salivary melatonin begin during middle-age

Abstract: To investigate whether free melatonin may be better suited to reveal age‐related changes, we studied the circadian rhythm alterations in saliva melatonin levels during aging. Special attention was paid to the question as to how the free melatonin rhythms change in aging and when such changes take place. A total of 52 healthy volunteers participated in the study consisting of young, middle‐aged, old and the oldest groups. In each subject, a total of 12 time‐point salivary melatonin samples was taken over 24 hr. Of the 52 data sets, 51 exhibited significant circadian rhythm over 24 hr by using the base cosine function analysis to fit the data. A clear circadian rhythm of salivary melatonin was present in all age groups. The decline in nocturnal peak levels (amplitude) in salivary melatonin was found in old and the oldest subjects. Both the old and the oldest subjects showed an increased daytime (baseline) melatonin levels. The off‐set melatonin levels were more than two times higher in the oldest group than that in the other groups indicating a delayed phase of salivary melatonin. Most strikingly, we found that a step‐wise decrease in the circadian rhythms of saliva melatonin occurred early in life, around 40 yr of ages. The middle‐aged subjects had only 60% of the amplitude of the young subjects. In addition, the middle‐aged subjects showed the longest peak levels duration and the lowest daytime melatonin levels. The present study showed that the alterations in the circadian rhythms of salivary melatonin begin during middle‐age. Our results showed that salivary melatonin measurement is a reliable, sensitive and easy method to monitor changes in the circadian rhythms of melatonin during the course of aging.

Diurnal rhythms of free estradiol and cortisol during the normal menstrual cycle in women with major depression

To investigate whether depression is accompanied by changes in diurnal rhythms of free estradiol and cortisol in different phases of the menstrual cycle, we measured these two hormone levels in saliva samples collected every 2 h for 24 h from 15 healthy normally cycling women and 12 age-matched normally cycling women suffering from major depression taking antidepressants. The assessments were repeated four times over one menstrual cycle: during menstruation and in the late follicular/peri-ovulating, early to mid-luteal and late luteal phases, respectively. Quantification with a nonlinear periodic regression model revealed distinct diurnal rhythms in free estradiol and free cortisol in all subjects. For the diurnal cortisol rhythm, significant differences were found in the peak-width and ultradian amplitude among different menstrual phases, both in controls and depressed patients, while no significant differences were found between the two groups. The diurnal estradiol rhythm, on the other hand, was quite consistent among different menstrual phases within both groups, while the depressed patients had overall larger amplitudes than controls, which is negatively correlated with disease duration. Significant positive correlations between the two hormone rhythms were found for 24-h mean level (mesor), peak, and trough in late luteal phase, and for ultradian harmonics in early to mid-luteal phase in controls, but only for ultradian harmonics in late follicular/peri-ovulating phase and for acrophase in the menstruation phase in depressed patients. A sub-analysis was also performed in patients who received Fluoxetine (n = 7). The findings implicate a close correlation between the hypothalamic-pituitary-adrenal axis and the hypothalamic-pituitary-gonadal axis, both of which may be involved in depression.

Age-related learning and memory impairments in adult-onset hypothyroidism in Kunming mice.

The memory impairment induced by adult-onset hypothyroidism is a common symptom. However, the exact onset time that will influence on memory function is still an issue of debate. The purpose of this study is to determine the onset effect of hypothyroidism on the memory during adulthood. Three age groups of Kunming (KM) mice were used, including 2, 8, and 15-month-old mice. Adult-onset hypothyroidism was made by adding PTU to drinking water and hypothyroid states were documented by the measurement of serum thyroid hormones level. A battery of tasks, i.e. novel-object recognition, olfactory discrimination, Morris water maze, was used to test mices memory. The results showed that adult-onset hypothyroidism induced the impairment of odor and spatial memory consolidation whereas it did not affect visual memory encoding or consolidated spatial memory retention. Age at onset of hypothyroidism was an important factor for the memory impairment induced by hypothyroidism. The 2-month-old hypothyroid mice had significantly impaired abilities in both the olfactory discrimination and the spatial cognitive tasks relative to the 2-month-old controls. The 8-month-old hypothyroid mice had only impaired ability in the spatial cognitive task relative to the same age controls. The 15-month-old hypothyroid mice retained these cognitive abilities relative to the same age controls. These results suggested that adult-onset hypothyroidism could induce an age- and task-dependent impairment of memory in female KM mice.

Age-related spatial cognitive impairment is correlated with increase of synaptotagmin 1 in dorsal hippocampus in SAMP8 mice

The age-related decline of learning and memory is a common phenomenon in humans and animals, even though the underlying mechanism is not yet known. In the present study, we propose that synaptotagmin 1 (Syt 1) might be a synaptic protein involved in the loss of learning and memory with aging. To test this hypothesis, the age-related spatial cognitive ability of 36 P8 mice (15 mice aged 4 months, 11 mice aged 8 months and 10 mice aged 13 months) was measured in a Morris water maze. After the behavioral test, both the protein and mRNA levels of Syt 1 were determined in the dorsal hippocampus by means of immunocytochemistry and reverse transcriptase polymerase chain reaction (RT-PCR), respectively. In the Morris water maze, the latency of the 4-month mice to find the submerged platform was significantly shorter than that of the older mice, while there were no significant differences between the 8- and 13-month-old mice in this respect. Compared to the 4-month-old mice, the Syt 1 protein in the 13-month-old mice was significantly increased in almost all layers of each subfield of the hippocampus. The average level of Syt 1 mRNA in the dorsal hippocampus of the P8 mice had not changed with aging. The latency of the 13-month-old P8 mice tested in the Morris water maze was positively correlated with the Syt 1 immunoreactivity in four circuit-specific regions in the dorsal hippocampus. Interestingly, the latency in the Morris water maze was also positively correlated with the level of Syt 1 mRNA in the dorsal hippocampus in individual aged P8 mouse. These results suggest that increased Syt 1 in the dorsal hippocampus in aged mice might be responsible for the age-related impairment of learning and memory.

Glucocorticoids suppress vasopressin gene expression in human suprachiasmatic nucleus.

Sleep impairment is one of the major side effects of glucocorticoid therapy. The mechanism responsible for this circadian disorder is unknown, but alterations in the suprachiasmatic nucleus (SCN), the biological clock of the human brain, are presumed to play a major role. In the present study, the amount of vasopressin mRNA (AVP mRNA) expression in the SCN was investigated in 10 glucocorticoid-exposed patients and 10 glucocorticoid free, age- and clock time of death-matched controls. The total amount of AVP mRNA, expressed as masked silver grains in the SCN, was two times lower in glucocorticoid-exposed patients (n = 10; 5115 +/- 1314 microm(2)) than that in controls (n = 10; 11,021 +/- 1408 microm(2)) (P = 0.006). There was also a 53% decrease in the total number of profiles in the SCN that expressed AVP mRNA in glucocorticoid-exposed patients (16,759 +/- 3110) compared with those in controls (31,490 +/- 3816) (P = 0.01). In conclusion, glucocorticoids have an inhibitory effect on AVP mRNA expression in the human SCN, which may be the biological basis of the circadian rhythm disturbances during glucocorticoid therapy.

Age-related changes in anxiety are task-specific in the senescence-accelerated prone mouse 8

In the senescence-accelerated prone mouse 8 (SAMP8), an excellent model of brain aging, aged individuals have impairments in learning and memory. One study has indicated that the anxiety is also reduced in those mice. However, increased anxiety with aging has been observed in other models, such as C57BL mice and rats. Altered emotion is linked to impairments in learning and memory. Thus, we were interested in further characterizing the pattern of age-related changes in anxiety in this strain. In the present study, a battery of tasks (i.e., elevated plus maze, open field, black-white alley, food neophobia and hole-board) was used to determine the age-related alterations in anxiety in the SAMP8 mice. Three age groups (2, 6, and 10 months of age) of SAMP8 mice and their control SAMR1 (senescence-accelerated resistant mouse 1) mice were used. The results showed that the effect of age was significant only in the elevated plus maze and black-white alley tasks. The SAMP8 showed a tendency toward increased anxiety with age as measured by the time spent on the open arms of elevated plus maze. When the sexes were separated for analysis, the increased anxiety was significant in the old (10-month-old) male SAMP8. In the black-white alley task, however, anxiety levels in the old male SAMP8 mice were lower than those of the middle-aged (6-month-old) mice, but similar to those in the young (2-month-old) mice. These results suggested that the age-related anxiety levels of SAMP8 mice are sex- and task-specific.

Effect of aging on species-typical behaviors in senescence-accelerated mouse

The species-typical behaviors have been extensively studied, especially in the rodents. But little is known about whether the aging impacts on these species-typical behaviors. In the present study, the species-typical behaviors, including burrowing, hoarding and nesting, were assessed in the accelerated senescence-prone mouse 8 (SAMP8, P8) and the control strain senescence-resistant mouse 1 (SAMR1, R1). Total 147 SAM mice including 74 P8 mice and 73 R1 mice were grouped according to the age, 3, 7 and 11 months, respectively. In the hoarding test, an age-related increase was observed in the both P8 and R1 mice, whereas in the burrowing task, the age-related increment only took place in the P8 mice. The nesting ability in the P8 mice at different ages was inferior to that in the age-matched R1 mice, and the 3-month P8 mice showed the poorest nesting ability. The principal component analysis revealed that the burrowing, hoarding and nesting tests detected the different aspects of species-typical behaviors respectively for all mice combined. Our findings indicated that all tasks of hoarding, burrowing and nesting could detect the aging effect in the P8 mice, whereas, only the hoarding test could detect the aging effect in the R1 mice. These different species-typical behaviors were dissociable.