Ontogeny of ultradian and nocturnal activity rhythms in the isolated albino rat

Acute Sleep Deprivation Reduces Oscillatory Network Inhibition in the Young Rat Basolateral Amygdala

The amygdala is concerned with the emotional memory consolidation, and is known as a stress-vulnerable region of the brain. Slow network oscillation is considered to play roles in memory consolidation during sleep. We investigated the relationship between the sleep and oscillation in the basolateral nucleus (BL) of the amygdala, in which burst firing is preferentially observed during sleep and the slow inhibitory oscillation is recorded from projection neuron. We examined whether sleep deprivation (SD) alters the properties of the network inhibition by whole-cell recordings from BL projection neurons and interneurons of the slice preparation of the juvenile rats. The level of the oscillatory network inhibition, measured as summed power of the spectral density between 0.1 and 3 Hz of the synaptic currents in the projection neurons, was significantly attenuated by acute (3 h) SD in older (P20-24) but not in younger (P15-19) animals. This reduction was mainly derived from the reduced peak amplitude of periodic IPSC bursts. In inhibitory interneurons in BL, spontaneous firings were reduced in older SD rats. The spike threshold of interneurons was increased and the power of the periodic excitatory transmission was reduced in the SD rats. Moreover, a reduction in input resistance in projection neurons was observed in SD rats without significant difference in the excitability which was measured by the spike number induced by depolarizing currents. These results suggest that SD stress affects the network oscillatory property accompanied by changes of individual neuronal excitability and synaptic communications.

Behaviors in the Home Cage Reveal Toxicity: Recent Findings and Proposals for the Future

Nervous system impairment is prominent among signs of chemical toxicity in humans and animals, yet evaluation of behavioral and neurologic responses is seldom included in premarket screening. The sensitivity and validity of automatically recorded rodent locomotor activity, whether inside or outside of the home cage, justifies its inclusion in first-tier testing. Home cage behaviors are studied in the toxicologic laboratory using quantitative techniques from behavioral neuroscience. A practical, noninvasive, automated system was developed and validated at New York University, in accord with Federal guidelines for testing neurotoxicity. Effects of neurotoxicants on motor activity, eating, drinking, and the daily cycle of rest-activity indicate sensitivity to a variety of chemicals as well as new avenues to the understanding of mechanisms of toxicity. The rat's pattern of nocturnal activity is particularly sensitive to neurotoxicants and thus deserves additional attention. The coefficient of variability of various end points did not correlate with sensitivity to toxicants. This underscores the need for behavioral data to supplement theoretical considerations in test selection. The system's advantages are economy, high data capacity, humaneness, accessible and well-known end points, widely available equipment, automation, and the potential for direct comparisons of several different animal species.

Circadian pattern of simulated flight performance of pilots is derived from ultradian components

Studies suggest some physiologic, cognitive, and behavioral 24h rhythms are generated by cyclic components that are shorter in period than circadian. The aim of this study was (1) to examine the hypothesis that 24h human performance rhythms arise from the integration of high-frequency endogenous components and (2) to quantify the contribution of each higher frequency component to the phenotype of the rhythm. We monitored the performance of 9 experienced pilots by employing an array of cognitive-based tests conducted in a flight simulator so that, over the 6-day experiment, data were obtained for each 2h interval of the 24h. The activity-rest schedule of the subjects, no matter the exact clock time schedule of sleep and activity, always consisted of 14h activity (when they carried out regular professional duties) and 10h rest, with at least 8h of sleep. The simulated combat scenarios consisted of simple and complex tasks associated with target interception, aircraft maneuvering, and target shooting and downing. The results yielded two indices: the number of prominent periodicities in the time series and the relative magnitude of the amplitude of each relative to the construction of the composite 24h waveform. Three cyclic components (8h, 12h, and 24h) composed the observed 24h performance pattern. The dominant period and acrophase (peak time) of the compound output rhythm were determined by the interplay between the amplitudes of the various individual ultradian components. Task complexity (workload) increases the expression of the ultradian entities in the 24h pattern. We constructed a model composed of the multiple ultradian components; the composite output defined a "time span" (of 2h-4h duration) as opposed to an exact "time point" of high and low performance, endowing elevated functional capability.

Daily variation of CNS gene expression in nocturnal vs. diurnal rodents and in the developing rat brain

Expression of c-fos has been shown to vary throughout the brain over the course of the 24-h day. The magnitude of these changes appear to be similar in a light:dark (LD) cycle or in constant dark (DD). To further examine whether the diurnal and circadian changes in c-fos and other immediate-early gene (IEG) expression in brain are related to waking behaviors such as locomotor activity, we conducted three experiments using Northern analysis. First, we compared IEG expression in nocturnal vs. diurnally active species. Second, we investigated IEG expression in a hibernating species during its active and inactive phases. Third, we examined the development of IEG expression in the young post-natal rat. As a comparison to results obtained in extra-SCN brain regions, we also examined IEG and vasopressin expression in the SCN itself across the circadian cycle. Animals maintained under a 12:12-h LD cycle were sacrificed in the morning (10:00-11:00 h, ZT2-ZT3) or night (22:00-23:00 h, ZT14-ZT15) or at the corresponding circadian times (CT) when kept in DD. Rats sacrificed in the morning always showed lower c-fos expression than at night in all brain areas examined while the reverse pattern was seen in squirrels under both LD and DD conditions, suggesting a direct correlation between c-fos message and activity. The cerebellum displayed the greatest magnitude change between morning and night (often reaching 10-fold). Among other IEGs examined, the expression of NGFI-A and junB are similar to c-fos, but of lesser magnitude, whereas c-jun appears to be invariant in the rat but is increased during the active phase in squirrels. During the hibernation season, squirrels have lower levels of c-fos consistent with their low levels of activity even during their euthermic interbout periods. c-fos expression in the cerebellum and rest of brain of 1-week-old rats sacrificed at ZT3 and ZT15 showed low levels at both timepoints whereas 2- and 3-week-old animals had higher levels at night as do adults. Among other IEGs, junB and NGFI-A again were similar to c-fos while c-jun and junD were more constant. Our observations support the idea of a diurnal rhythm of IEG expression in the CNS that is related to waking behaviors. Among IEGs, c-fos exhibits the greatest daily variation in expression.

Biological clocks: mechanisms and developments

Almost all organisms ranging from unicellular protists to mammals were found to show biological rhythms. Many workers have performed various kinds of experiment to understand the mechanism as well as to find the origin of the clock responsible for these rhythms. However, there is no doubt about the existence of a biologically controlled clock in almost all organisms; yet its origin and mechanism still remain a mystery. Many theories have been put forward to explain the mechanism of these biological clocks and it seems that the cell membrane may play a key role. The existence of a very high electric field of the order of 10(5) V cm-1 across the cell membrane may have some role in the mechanism of the biological clock. Of all the factors which have the effects on biological rhythms, light and temperature are found to be the most common. Also, the study of these biological clocks can help to solve the sleeping problems of international travellers and shift workers as well as to improve diagnosis, cure and prevention from diseases.

Continuous recording of locomotor activity in groups of rats: postweaning maturation

A method was developed for continuous recording of locomotor activity in ten groups of rats housed in standard plastic cages under controlled lighting conditions. An inexpensive pressure transducer detected movements in the cage, and a light resistor monitored the lighting. The output voltages from the sensors were digitized, integrated for 5 s, and stored for off-line analysis. The data from separate cages were averaged for the detection of statistical differences between the experimental groups. The method was applied to study maturational changes after weaning. Wistar rats were recorded from 21 to 62 days of age under 12/12 h light/dark cycle. The cumulative activity distributions of the pups of 4 and 5 weeks of age differed significantly from those of 7-9 weeks, or older. Differences between the rats aged 8 or 9 weeks and the older adults were less consistent, but still detectable. The cumulative activity distributions of the males and females did not differ significantly from each other.

Ultradian, circahoral and circadian structures in endothermic vertebrates and humans

1. For more than 30 years many studies have been carried out concerning rhythms with periods approaching 24 hr (circadian rhythms). 2. The latter have been demonstrated as resulting from environmental 24 hr synchronizers (zeitgebers), but they usually persist in the absence of a 24 hr synchronization, which proves their endogenous nature. 3. Biological rhythms with periods less than 20 hr (ultradian rhythms) and particularly those approaching 1 hr (circahoral rhythms) have been determined: for motility, rest-activity, sleep phases, endocrine secretions and other physiological functions. 4. These ultradian and circahoral rhythms have been found in rodents, birds, monkeys and humans. 5. Existing at all stages of ontogeny, they have been proved to be endogenous and species and strain specific. 6. As these ultradian rhythms can be influenced by environmental factors and sometimes by circadian rhythms they are not truly periodic, so therefore cannot be computed by the usual processes of mathematical time analysis.

Effects of selective monoaminergic reuptake blockade on activity rhythms in developing rats

Developing rats display prominent ultradian rhythms of locomotor activity when separated from the litter. A pharmacological analysis was undertaken to provide preliminary data on the role of monoaminergic neurotransmitter systems in the modulation or manifestation of this fundamental biological rhythm. Twenty-four hour activity profiles were monitored in 15-day-old rats, tested in darkness, after intraperitoneal treatment with desipramine (DMI), zimelidine (ZMI), or GBR-13069 (GBR), selective uptake inhibitors of norepinephrine, serotonin, and dopamine, respectively. Time series data were analyzed by low-resolution variance spectral analysis. DMI significantly diminished ultradian (greater than 1 cycle per day; cpd) rhythmicity, and enhanced the circadian rhythm. Equimolar doses of ZMI had little effect on the ultradian band (7-15 cpd), but slightly reduced the circadian peak. The effects of acute GBR administration were complex, as this agent produced prominent effects on basal activity. In a second study these agents were administered continuously over a 5-day period, using subcutaneously implanted Alzet osmotic minipumps, to avoid the confounding effects of acute administration. Continuously-infused DMI virtually eliminated characteristic ultradian rhythms in the 9-15 cpd bandwidth. ZIM diminished ultradian oscillations only in the 14-15 cpd range, and GBR-12909 had little effect on ultradian rhythms throughout the usually prominent 7-16 cpd domain. All three reuptake inhibitors increased the prominence of slow ultradian rhythms with frequencies of 3-4 cpd. Continuous reuptake blockade had no significant effects on circadian amplitude or phase, as determined by cosinor analysis.(ABSTRACT TRUNCATED AT 250 WORDS)

Amphetamine accelerates and attenuates ultradian activity rhythms in preweanling rats

Developing rats, studied in environmental isolation, display prominent fluctuations in locomotor activity with a periodicity of about 1-3 hr. This ultradian rhythmic pattern is most marked at 2 weeks of age, and appears to be endogenously mediated. (+)Amphetamine (1 mg/kg) was administered to 2 week old rat pups, and their locomotor activity levels were recorded continuously and stored in 5 min intervals using a sensitive computer-interfaced vibrational activity monitor. Activity was recorded for 12 hr after treatment and resulting time-series data were analyzed by harmonic spectral techniques. During the first 6 hr of testing, amphetamine induced a prominent low frequency perturbation in baseline activity levels corresponding to the expected period of acute drug action. During this time, normally prominent ultradian activity rhythms in the range of 8-12 cycles per day (cpd) were diminished in amplitude, even following low frequency smoothing to remove the changes in baseline. Correspondingly, there was also an increase in ultradian rhythm amplitude in amphetamine-treated pups at higher frequencies (32-40 cpd). During the final 6 hr of testing there was a marked suppression of typical ultradian rhythms in amphetamine-treated pups but not in controls. These results suggest that amphetamine treatment both accelerates and attenuates ultradian activity rhythms in developing rats during the acute period of drug action, and produces a prominent diminution in these rhythms during subsequent rebound and recovery periods.

Effects of feeding and light cycles on activity rhythms of maternally isolated rat pups

Motor activity of infant rat pups was measured continuously between days 3 and 18 of postnatal age. Mother-reared rats on a 12:12 LD cycle exhibited significant rhythmic activity in the circadian range as early as day 5 of postnatal age. Some of the pups reared in isolation from maternal and sibling contact and kept on 12:12 LD cycles, feeding cycles, or combinations of feeding, temperature, and LD cycles also showed rhythmic activity but it was less persistent and of a lower amplitude than the rhythms of the mother-reared group. In the isolated rat pups nocturnal partitioning of activity was strengthened in the presence of both a light-dark cycle and a feeding cycle but only when the feeding resembled more natural nursing rhythms. In animals kept on constant light and a feeding cycle, activity occurred slightly more often during the 12-hr interval of decreased food intake. The addition of a temperature cycle--cooler nocturnal temperature--decreased the proportions of nocturnal motor activity. These results indicate that feeding and light-dark cycles may contribute to the synchronization of activity rhythms during the early postnatal period.

Sleep-wake behavior of newborn rats recorded with movement sensitive method

The aim of this study was to determine criteria for classification of sleep-wake behavior in newborn rats by recording total body and respiratory movements with a static charge sensitive bed (SCSB). Initially, the sleep-wake behavior was simultaneously observed visually and recorded by the SCSB mattress, from the fourth to the twenty-second postnatal days. Thus, the criteria for scoring the SCSB recordings were obtained by comparison of the behavioral scorings with the SCSB tracings. To further validate this movement sensitive method for neonatal sleep studies in rats, deep neck muscle electrograms were studied at the age range of 8-13 days, and electroencephalograms as well as electromyograms from the age of 12-17 days, simultaneously with the SCSB recordings. Finally, the sleep-wake behavior of other rat pups was recorded only with the SCSB from the fourth to the twenty-second postnatal days. These latter recordings were afterwards scored by using the criteria defined in the first part of this study. The results thus obtained indicate that the SCSB method is sensitive and reliable in recording and classifying the sleep-wake behavior of newborn rats.

Altered locomotor activity in neuropsychiatric patients

Movement was monitored continuously for 24-48 hours in representative neuropsychiatric patients, using a wrist-worn portable piezoelectric activity monitor with solid-state memory. Striking differences were observed in both circadian and more rapid (ultradian) rhythms between these patients and normal controls of a similar age. We found a loss of circadian rhythm following stroke, and a marked 4-hour activity rhythm in patients with dementia and brain tumor. These results may provide insights into the neural substrate of activity rhythms and may lead to better care of neuropsychiatric patients.