Age-related changes in the sleep pattern of male adult rats

A large scale, high resolution, automated system for rat sleep staging. II. Validation and application

An automated rat sleep staging system was used to describe sleep-waking behaviour in a large number of rats. The computer scorings were validated by visual analysis of a limited set of data by two human raters and the agreement varied between 82 and 100% for homogeneous segments of the different sleep-waking stages. The automated system proved to be very consistent in view of the small variation in placebo values over 110 experiments. The data show that classification of rat sleep waking behaviour into 6 different stages is both advisable and feasible. The experiments further show that rat age (over a range from 0.5 to 2 years) does not greatly affect rat sleep-waking behaviour.

Individual differences in aging: behavioral and neurobiological correlates

The goal of this experiment was to determine the correlations among different behavioral and neurobiological measures in aged rats. Aged Sprague-Dawley rats were given a battery of cognitive and sensorimotor tests, followed by electrophysiological assessment of sleep and biochemical measurements of various neurotransmitter systems. The behavioral tests included the following: Activity level in an open field; short-term and long-term memory of a spatial environment as assessed by habituation: spatial navigation, discrimination reversal, and cue learning in the Morris water pool; spatial memory in a T-maze motivated by escape from water; spatial memory and reversal on the Barnes circular platform task; passive avoidance; motor skills. Sleep was assessed by electrographic cortical records. The following neurotransmitter markers were examined: Choline acetyltransferase; the density of nicotinic, benzodiazepine and glutamine receptors in the cortex and caudate nucleus; endogenous levels of norepinephrine, dopamine, and serotonin in the cortex and hippocampus. The duration of bouts of paradoxical sleep was strongly correlated with several cognitive measures and selected serotonergic markers. This finding suggests that changes in sleep patterns and brain biochemistry contribute directly to deficits in learning and memory, or that the same neurobiological defect contributes to age-related impairments in sleep and in learning and memory.

Sleep and memory relationships in intact old and amnestic young rats

Age-related changes in sleep are observed in many species, including rats and humans. Old rats often exhibit less total and paradoxical sleep, shorter sleep bouts and more random sleep-wake periods across 24 hours, than young rats. This paper evaluates recent evidence that deterioration of selected sleep parameters, usually involving levels of paradoxical sleep or durations of sleep bouts, may be related to deterioration of memory in old rats. Similar findings are reviewed with respect to young animals with different forms of experimentally-induced amnesia. Furthermore, a drug that enhances memory in rats and old humans, glucose, also enhances paradoxical sleep in old rats. These data suggest the utility of sleep measures as neurobiological markers of memory dysfunction in old rats.

Vasoactive intestinal polypeptide neuron changes in the senile rat suprachiasmatic nucleus

The suprachiasmatic nucleus (SCN) is thought to be the main neuronal oscillator underlying circadian rhythmicity of different biological phenomena such as sleep-wakefulness and body temperature. Although numerous studies in old rats showed that circadian organization is clearly disturbed in senescence, no decrease in total SCN cell number has been observed. However, in an earlier study we found a significant decrease of approximately 30% in the number of immunocytochemically-stained vasopressin (VP) neurons in the SCN of the old rat. The aim of the present study was to examine whether another group of SCN neurons, i.e., the vasoactive intestinal polypeptide (VIP) cells, shows age-related changes parallel with disturbances found in sleep/wake parameters. Immunocytochemical staining with antiVIP followed by morphometric analysis revealed a 36% decrease in the number of immunoreactive VIP neurons in the SCN of old rats as compared to young ones. The average size of the remaining VIP cells increased in aged rats. The rapid-eye-movement (REM)-sleep time was negatively correlated with the immunoreactive VIP cell number in the old animals. VP and VIP alterations in the SCN may constitute an anatomical substrate for the circadian disturbances observed in senescence.

Effect of running wheel availability on circadian patterns of sleep and wakefulness in mice

Sleep/wake expression in mice varies predictably with circadian phase. Such circadian rhythms are known to depend on intact suprachiasmatic nuclei (SCN) in the hypothalamus, but the mechanism by which SCN activity modulates sleep/wake expression is unknown. This paper examines the possibility that circadian patterns of sleep/wake derive partly from circadian timing of waking behaviors that are incompatible with sleep, such as locomotor activity. Voluntary locomotor activity was restricted in five mice adapted to a running wheel by locking the wheel in place. Continuous electrographic monitoring of sleep and wakefulness over multiple circadian cycles revealed: (1) during the active phase, shorter wake bouts and more frequent bouts of sleep, resulting in greater sleep/wake fragmentation and more time spent asleep; (2) during the rest phase, a small compensatory reduction in NREM sleep; (3) reduced amplitude of circadian sleep/wake rhythms and a greater amount of sleep overall. Thus, voluntary locomotor activity has an important influence on sleep/wake expression in mice, and the normal circadian pattern of sleep/wake depends on circadian timing of activity. Previous reports of damped circadian sleep/wake rhythms in rodents may therefore be explained by coincident diminutions in locomotor activity associated with age or health status. Our results also support analogous findings in human subjects, and we propose that elderly humans may benefit from therapies that augment daytime activity.

Effect of housing in an enriched environment on the size of the cerebral cortex in young and old rats

To assess whether or not environmental changes may continue to affect measures relating to cortical size, the size of the cerebral cortex of young adult (7 to 8 months) and old (32 to 33 months) "standard" and "enriched" rats were compared. Enriched rats were housed in large cages during 10 weeks and had access to many different objects; age-matched controls remained in standard laboratory cages. Effects on the cerebral cortex were small; a significant increase in cortical thickness at one, albeit different, site in both age groups was observed. Significant correlations were not present between environmentally induced changes in sleep parameters (recorded in the same rats prior to the present experiment) and the small change in cortical size. The results do, however, support the hypothesis that a certain amount of plasticity of the cerebral cortex is preserved in old age.

Effects of melatonin and 5-methoxytryptamine on sleep-wake patterns in the male rat

Melatonin and 5-methoxytryptamine were administered continuously over a period of 1-3 months to adult male rats by means of subcutaneously implanted silastic capsules containing one or the other of these pineal hormones. Polygraphic recordings during several weeks following hormonal application showed an increase in the amount of time spent in both quiet and rapid eye movement sleep, during the light as well as the dark period; however, diurnal sleep-wake rhythmicity was not affected by either treatment. We conclude that pineal hormones have sleep-promoting effects, but that their correlation with the light-dark cycle does not imply that they are causal factors in generating diurnal rhythms of sleep and wakefulness.

Changes with aging in the vasopressin and oxytocin innervation of the rat brain

The effect of aging on the vasopressin (AVP) and oxytocin (OXT) innervation of the brain was studied by means of immunocytochemistry, comparing the major innervated areas in 5-month-old and 34-month-old male Brown-Norway rats. A marked decrease of AVP fiber density was found in the old rats as compared with the young animals in the vertical limb of the diagonal band, the basal nucleus of Meynert, the lateral habenular nucleus, the medial amygdaloid nucleus, the substantia nigra, the ventral hippocampus, the central gray, the locus coeruleus and in the ambiguus nucleus. The AVP innervation of the lateral septum and the dorsomedial hypothalamic nucleus was moderately, although not significantly reduced. No age difference in AVP innervation was found in the paraventricular thalamic nucleus or in the nucleus of the solitary tract. OXT fiber density did not differ between young and old animals in the locus coeruleus, the nucleus of the solitary tract and the ambiguus nucleus. Thus, the aging process appears to affect AVP cells in a differential, rather than in a general way. Changes were found to be more pronounced in those areas where the AVP innervation is dependent upon circulating androgens.

The suprachiasmatic nucleus of the human brain in relation to sex, age and senile dementia

The suprachiasmatic nucleus (SCN) is considered to be the endogenous clock of the brain, essential for the ovulation cycle and the temporal organization of sleep-wake patterns, among other things. Immunocytochemical staining with anti-vasopressin as a marker permitted a morphometric study of this nucleus in the human brain, which revealed that the shape of the SCN is sexually dimorphic. The shape of the SCN was elongated in women and more spherical in men. In both sexes a decrease in SCN volume and cell number was observed in senescence (80-100 years). The latter change was especially pronounced in patients with senile dementia of the Alzheimer type (SDAT). This suggests the presence of a structural defect in the SCN which underlies the general disturbance of biological rhythms in senescence and SDAT.