Spectral analysis of the electroencephalogram in the developing rat

Adolescent sleep patterns in humans and laboratory animals

This article is part of a Special Issue "Puberty and Adolescence". One of the defining characteristics of adolescence in humans is a large shift in the timing and structure of sleep. Some of these changes are easily observable at the behavioral level, such as a shift in sleep patterns from a relatively morning to a relatively evening chronotype. However, there are equally large changes in the underlying architecture of sleep, including a >60% decrease in slow brain wave activity, which may reflect cortical pruning. In this review we examine the developmental forces driving adolescent sleep patterns using a cross-species comparison. We find that behavioral and physiological sleep parameters change during adolescence in non-human mammalian species, ranging from primates to rodents, in a manner that is often hormone-dependent. However, the overt appearance of these changes is species-specific, with polyphasic sleepers, such as rodents, showing a phase-advance in sleep timing and consolidation of daily sleep/wake rhythms. Using the classic two-process model of sleep regulation, we demonstrate via a series of simulations that many of the species-specific characteristics of adolescent sleep patterns can be explained by a universal decrease in the build-up and dissipation of sleep pressure. Moreover, and counterintuitively, we find that these changes do not necessitate a large decrease in overall sleep need, fitting the adolescent sleep literature. We compare these results to our previous review detailing evidence for adolescent changes in the regulation of sleep by the circadian timekeeping system (Hagenauer and Lee, 2012), and suggest that both processes may be responsible for adolescent sleep patterns.

Functional in vivo assessment of retinal artery microirregularities in glaucoma

PURPOSE

We investigated whether retinal branch arteries in healthy subjects, and non-treated and treated primary open-angle glaucoma (POAG) patients show irregular local patterns during dynamic reaction to acute increases of different magnitudes in intraocular pressure (IOP).

METHODS

Nine POAG patients and nine age-matched normal volunteers were examined with the retinal vessel analyser (RVA) using a suprasystolic IOP increase (Study 1). Fourteen POAG patients and 13 age-matched controls were examined using a moderate IOP increase for 100 seconds (Study 2). Longitudinal arterial profiles were obtained for the chosen time intervals. The high-frequency waviness (HFW) of these profiles was analysed quantitatively.

RESULTS

No significant changes in HFW were found in controls in different phases of the arterial reaction. Significant increases in HFW from baseline to dilation (Study 1, P < 0.03) and from dilation to constriction (Study 2, P < 0.05) were found in POAG patients. High-frequency waviness was higher in POAG patients than in controls during dilation (P < 0.05) in both studies.

CONCLUSIONS

Our results indicate a local vessel wall difference in glaucoma patients compared with age-matched controls. Increasing HFW might worsen hydraulic resistance of the vessel segment to blood flow. Significant increase of arterial microirregularities in the POAG retina during vascular dilation might be an indication for vascular endothelial alterations in glaucoma, leading to impaired perfusion in response to IOP increase.

Hippocampal theta in the newborn rat is revealed under conditions that promote REM sleep

Hippocampal theta activity, a high-amplitude, slow (4-12 Hz) oscillation that occurs in a variety of behavioral contexts, is thought to emerge in infant rats only after 1 week of age. However, we report here that unanesthetized 2- and 4-d-old rats with electrodes implanted in the CA1 field of the hippocampus and tested in thermoneutral conditions exhibit theta activity. Moreover, this infant theta is characterized by the same neuronal bursting pattern and power spectrum that characterize theta in adults. Simultaneous measures of behavior and neck muscle tone indicated that bouts of theta occurred predominantly during periods of muscle atonia (with or without concurrent myoclonic twitching), indicative of REM sleep. In contrast, sharp waves were accompanied by startles (i.e., simultaneous and vigorous movement of all four limbs). These findings underscore the need for comprehensive in vivo investigations of the pharmacology, neural substrates, and behavioral correlates of hippocampal field activity in neonates.

Development of spatial firing in the hippocampus of young rats

The hippocampal formation participates in learning and memory, particularly that of a spatial nature. In adult rats, individual CA1 pyramidal neurons only fire when the animal visits specific locations in an environment, the "place field" of the neuron. Other structures (postsubiculum, thalamus, cingulum) contain neurons that code for the animal's instantaneous head direction. Previous work has shown that the rat hippocampal formation undergoes anatomical and neurophysiological maturation during the first 2 months of life and that rats <40 days of age are impaired in spatial navigation tasks. Here we show that the locational firing of CA1 pyramidal neurons is both less specific and less stable in animals aged <50 days. However, preliminary results indicate that head directional firing recorded around day 30 is essentially identical to that seen in adult animals. Therefore, the development of reliable, spatially specific place cell activity parallels the developmental time course of spatial navigational ability, but head directional firing appears before full maturation of the hippocampus.

EEG as a measure of developmental changes in the chicken brain

Scalp-applied recording electrodes were used to monitor changes in basal EEG patterns in chickens during posthatch development. Frequency spectra produced by Fast Fourier Transform show a biphasic morphology in all chickens with one peak at about 6 Hz and another at 26 Hz. Changes in the lower frequency band show progressive development and provide a possible index of brain development. Both amplitude and dominant frequency of the spectra decrease between Weeks 3 and 8 posthatch, reaching adult levels between Weeks 5 and 7. These results suggest that modifications of basal EEG reflect the widespread functional changes in neuronal circuits occurring in chicken during the "synapse maturation" period between 3 and 8 weeks' posthatch.

Effects of temperature on sleep in the developing rat

In altricial species, such as humans and rats, much of the development of autonomic systems occurs postnatally. Consequently, vulnerabilities exist early in postnatal development when immature autonomic functions are challenged by external factors such as variations in ambient temperature (Ta). Ta profoundly influences sleep/wake state structure in adult animals and humans, and exposure to excessive warmth has been implicated as a risk factor in sudden infant death syndrome. To better understand the relationship between temperature and sleep during development, we investigated the effect of Ta variation on sleep/wake state structure and sleep intensity in developing rats. In this experiment, sleep intensity was measured by the intensity of slow-wave activity during slow-wave sleep. Neonatal Long-Evans hooded rat pups were surgically prepared for chronic sleep/wake state and brain temperature (Tbr) recording. Two-hour recordings of sleep/wake state and Tbr were obtained from rats on postnatal day 12 (P12), P14, P16, P18, and P20 at a Ta of either 28.0-30.0, 33.0-35.0, or 38.0-40.0 degrees C. Ta significantly influenced sleep/wake state structure but had little, if any, effect on sleep intensity in developing rats.

Postnatal development of EEG patterns, catecholamine contents and myelination, and effect of hyperthyroidism in Suncus brain

The postnatal development of the central nervous system (CNS) in house musk shrew in the early stage of maturation was studied. The electroencephalogram (EEG) and visual evoked potential (VEP) in association with catecholamine contents and myelin basic protein (MBP) immunoreactivity were carried out from the 1st to the 20th day of postnatal age. Different EEG patterns which were specific to behavioral states (awake and drowsy) were first recorded on the 5th day, and the total power which was obtained by power spectrum analysis increased after this stage. The latencies of all peaks in VEP markedly shortened between the 5th and the 7th day. Noradrenalin (NA) content of the brain showed a slight increase after the 3rd day, and reached maximum levels on the 7th day, which was delayed a few days compared to dopamine (DA). In hyperthyroidism, the peak latency of VEP was shortened and biosynthesis of NA in cerebral cortex and DA in hippocampus was accelerated. The most obvious change in MBP-immunoreactivity of the telencephalon occurred from the 7th to the 10th day. These morphological changes in the brain advanced at the identical time-course to those in the electrophysiological development and increment of DA and NA contents.

The effects of REM sleep-inhibiting drugs in neonatal rats: evidence for a distinction between neonatal active sleep and REM sleep

Neonatal active sleep (AS) has been considered to be homologous and continuous with rapid-eye-movement (REM) sleep in adult animals. We have recently proposed an alternative view that AS is an undifferentiated sleep state distinct from REM sleep. To test these opposing views on the relationship of AS and REM sleep, neonatal rats (P11, P14 and P20) were systemically injected with compounds that inhibit REM sleep in adults. Zimelidine (ZMI) and desipramine (DMI) are monoamine uptake inhibitors which increase synaptic concentrations of serotonin and norepinephrine, respectively. Serotonin and norepinephrine inhibit brainstem cholinergic neurons important in REM sleep generation. Atropine (ATR) is a muscarinic receptor antagonist that blocks the post-synaptic effects of cholinergic projections. Only DMI (5 mg/kg) suppressed AS at P11. ZMI (6 mg/kg) and ATR (6 mg/kg) did not suppress AS until P14. These data suggest that serotonergic and cholinergic regulation of AS are absent before P14. The fact that AS in P11 rats is not affected by cholinergic antagonists supports the hypothesis that AS and REM sleep represent different sleep states.

Expression, control, and probable functional significance of the neuronal theta-rhythm

The data on theta-modulation of neuronal activity in the hippocampus and related structures, obtained by the author and her colleagues have been reviewed. Analysis of extracellularly recorded neuronal activity in alert rabbits, intact and after various brain lesions, in slices and transplants of the hippocampus and septum allow one to make the following conclusions. Integrity of the medial septal area (MS-DB) and its efferent connections are indispensable for theta-modulation of neuronal activity and EEG of the hippocampus. The expression of hippocampal theta depends on the proportion of the MS-DB cells involved in the rhythmic process, and its frequency in the whole theta-range, is determined by the corresponding frequencies of theta-burst in the MS-DB. The neurons of the MS-DB have the properties of endogenous rhythmic burst and regular single spike oscillators. Input signals ascending to the MS-DB from the pontomesencephalic reticular formation increase both the frequency of the MS-DB theta-bursts and the proportion of neurons involved in theta-activity; serotonergic midbrain raphe nuclei have the opposite effect on the MS-DB rhythmic activity and hippocampal EEG theta. Increase of endogenous acetylcholine (by physostigmine) also increases the proportion of the MS-DB neurons discharging in theta-bursts (both in intact and basally-undercut septum), but does not influence the theta-frequency. The primary effect of the MS-DB on hippocampal neurons (pyramidal and non-pyramidal) consists in GABAergic reset inhibition. Reset inhibition, after which theta-modulation follows in constant phase relation, is triggered also by sensory stimuli. About two-thirds of the hippocampal pyramidal neurons are tonically inhibited by sensory stimuli which evoke EEG theta, while others are excited, or do not change their activity. Anticholinergic drugs restrict the population of rhythmic neurons but do not completely suppress theta-bursts in the MS-DB and hippocampus. Under their action, EEG theta can be evoked (presumably through GABAergic MS-DB influences) by strong reticular or sensory stimuli with corresponding high frequency. However information processing in this condition is defective: expression of reset is increased, responses to electrical stimulation of the perforant path and to sensory stimuli are often augmented, habituation to sensory stimuli is absent and tonic responses are curtailed. On a background of continuous theta induced by increase of endogenous acetylcholine, reset is absent or reduced, responsiveness of the hippocampal neurons to electrical and sensory stimulation is strongly reduced.(ABSTRACT TRUNCATED AT 400 WORDS)

Spectral analysis of the electroencephalogram in neonatal rats chronically treated with the NMDA antagonist MK-801

In order to study the involvement of NMDA-receptor activation in brain development, rat pups were chronically treated with the non-competitive NMDA antagonist MK-801 during the neonatal period. We recorded the cortical EEG at various vigilance states throughout the treatment period. Spectral analysis of the EEG showed reduced power in the delta (delta) frequency range (1.5-4 Hz) during quiet sleep and less power in the theta (theta) range (4-7 Hz) during REM-sleep in MK-801 animals than in controls. No significant differences were found for the total time spent in each of the different vigilance states. We conclude that chronic MK-801 treatment probably causes a developmental retardation in state-related brain activities.

MIF-1 can accelerate neuromotor, EEG and behavioral development in mice

Newborn mice were injected SC daily with 1 mg/kg of MIF-1 or saline during the first 19 days of life. The progress of each pup was monitored for physical (body weight, eye and ear opening), neurobehavioral (reflexes) and neurophysiological (EEG) development until the weaning stage. In early adulthood (40 days of age) mice were tested on a maze learning task. Results indicate that MIF-1 can accelerate neurologic (days 3-9), somatic (days 10-14) and electroencephalographic (days 16-19) parameters, and that the effects of treatment last into the early adult stage with increased learning abilities in an appetitive task.