Biomedical subjects

M Mirmiran

Publications and source records attributed to M Mirmiran.

At least 55 records · Page 3Linked to original sources

PubMed1993

Symposium: Normal and abnormal REM sleep regulation: The importance of REM sleep for brain maturation.

A number of studies, some done by us, are reviewed concerning the function of foetal/neonatal REM sleep. The hypothesis is put forward that REM sleep in early life serves as an indicator for: (1) the degree of brain maturation, and (2) the promotion of further brain development. This hypothesis, although not exclusive, differs from: the original theory of Roffwarg et al. (1966) that REM sleep serves as "wakefulness" during the period in which wakefulness is limited; and also from the theory of Crick and Mitchson (1983-the "unlearning" hypothesis of REM sleep). As the functions of sleep in general, and REM sleep in particular, are still unclear, we hope this review will suggest new possibilities for future research.

Journal Article↗

PubMed1992

Hippocampal neuronal responsiveness to NMDA agonists and antagonists in the adult rat neonatally treated with MK-801.

Long-lasting effects of neonatal interference with N-methyl-D-aspartate (NMDA) receptors were investigated by measuring responses to micro-iontophoretically applied NMDA agonists/antagonist in hippocampal neurons of the adult rat. Rat pups were chronically treated with MK-801 from postnatal day 8 through 19 and tested at postnatal day 70-100. CA1 cell responses to glutamate were not affected by the neonatal treatment. However, a stronger suppression of the NMDA evoked response by the NMDA site antagonist amino-5-phosphonovalerate (APV) was measured, suggesting a long-lasting configurational change of the NMDA receptor. The NMDA evoked responses were equally strong suppressed by MK-801 in both groups, suggesting that channel sites were not affected by this treatment.

2-Amino-5-phosphonovalerate↗

PubMed1992

Circadian rhythms and the suprachiasmatic nucleus in perinatal development, aging and Alzheimer's disease.

Circadian rhythms are already present in the fetus. At a certain stage of pre-natal hypothalamic development (around 30 weeks of gestation) the fetus becomes responsive to maternal circadian signals. Moreover, recent studies showed that the fetal biological clock is able to generate circadian rhythms, as exemplified by the rhythms of body temperature and heart rate of pre-term babies in the absence of maternal or environmental entrainment factors. Pre-term babies that are deprived of maternal entrainment and kept under constant environmental conditions (e.g., continuous light) in the neonatal intensive care unit run the risk of developing a biological clock dysfunctioning. However, the fact should be acknowledged that at least in mice the development of the circadian pacemaker (i.e., SCN) does not depend on environmental influences (Davis and Menaker, 1981), although other data suggest that severe disruption of the maternal circadian rhythm indeed abolishes the circadian rhythm of the fetal SCN (Shibata and Moore, 1988). During aging and in particular in AD circadian rhythms are disturbed. These disturbances include phase advance and reduced period and amplitude, as well as an increased intradaily variability and a decreased interdaily stability of the rhythm. Among the factors underlying these changes the loss of SCN neurons seems to play a central role. Other contributory factors may be reduced amount of light, degenerative changes in the visual system and the level of activity and decreased melatonin.

Aging↗

PubMed1992

Perinatal development of human circadian rhythms: role of the foetal biological clock.

The development of circadian rhythms and the neuronal mechanisms underlying their generation (particularly the suprachiasmatic nucleus of the hypothalamus) were reviewed. Based on perinatal animal studies and data from human foetuses and/or preterm infants it was concluded that human circadian rhythms are present as early as at 30 weeks of gestation. The significance of the mother and/or the environment regarding the entrainment of the "endogenous" foetal biological clock was emphasized.

Circadian Rhythm↗

PubMed1991

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.

Animals↗

PubMed1991

Effects of behavioural state on visual processing in neonates.

Assessment of visual capacity in full-term neonates as a function of behavioural state was investigated with the luminance flash visual evoked potential (VEP). Infant state (quiet sleep, active sleep, quiet wakefulness, active wakefulness) was determined by behavioural observation and polygraphic recording of EEG, eye movements, electrocardiogram, electromyogram and respiration. VEPs were recorded across the sleep/waking cycle only under carefully defined state conditions. The results indicate that state dramatically effects the amplitude, latency and waveform of the transient luminance flash VEP with the most significant differences between sleep and wakefulness. The results further suggest that controlled state recording reduces intra and intersubject VEP variability.

Apgar Score↗

PubMed1991

Physiological effects of kangaroo care in very small preterm infants.

Kangaroo care for preterm infants has great benefits for the parents and for the parent-infant bonding process. A clinical observational study was conducted in which several physiological variables were collected, including among others transcutaneous oxygen pressure, heart rate, respiratory rate, occurrence of apneic attacks, breathing pattern (studied with power spectrum analysis), behavioral states and rectal temperature, during kangaroo care in small preterm infants. Kangaroo-care did not significantly affect any of these physiological variables comparing the period of 1 h before, 1 h during and 1 h after kangaroo care. We conclude that kangaroo care is a safe method, even for very small nonstabilized preterm infants.

Blood Gas Monitoring, Transcutaneous↗

PubMed1990

Neonatal clonidine treatment results in long-lasting changes in noradrenaline sensitivity and kindling epileptogenesis.

In the present experiment we tested the hypothesis that early interference with noradrenaline transmission can have permanent consequences for brain function in adulthood. Neonatal depletion of noradrenaline by daily subcutaneous injections of clonidine results in supersensitivity to noradrenaline in adult hippocampal CA1 cells as shown in our previous microiontophoretic study. These findings were confirmed and extended here with dose-response curves. Furthermore, we tested whether this form of neonatal interference with noradrenaline also permanently affects long-lasting plasticity as revealed in kindling epileptogenesis in adulthood. The initiation of the epileptic activity after the kindling stimulation was significantly delayed in the clonidine-treated group, and all measured parameters of seizure expression tended to be retarded in comparison with saline-treated control rats. This indicates that noradrenaline supersensitivity induced by neonatal clonidine treatment retards kindling development in adulthood.

Animals↗

PubMed1990

Alterations in the circadian rest-activity rhythm in aging and Alzheimer's disease.

The suprachiasmatic nucleus, considered to be the endogenous circadian clock in the mammalian brain, shows morphological changes with aging, which become even more pronounced in Alzheimer's disease (AD). In order to assess possible functional implications of these alterations, circadian rest-activity rhythms of 6 young and 13 old volunteers and of 12 AD patients were studied with a recently developed ambulatory rest-activity monitor (RA24). Young and old volunteers showed no differences in their rest-activity rhythm in any of the variables studied. Comparison of old controls versus AD patients revealed that (1) rest-activity rhythm was markedly disturbed in many of the AD patients and tended to be correlated with the severity of the dementia; (2) disturbances were most pronounced in subjects using sedating drugs; (3) disturbances in the latter group did not result from medication as no differences were found in the rest-activity patterns before and after administration of sedating drugs; (4) negative findings reported in the literature concerning circadian disturbances in AD may well have resulted from selection criteria that excluded the group of patients with the most severely affected rest-activity rhythm; and (5) rest-activity monitors offer a practical and fruitful approach for the study of circadian rhythms in humans.

Adult↗

PubMed1990

Circadian rhythms in spontaneous neuronal discharges of the cultured suprachiasmatic nucleus.

The suprachiasmatic nucleus (SCN) is believed to play a major role in the generation and control of circadian rhythms in mammals. In order to obtain further evidence concerning this, single and multiple neuronal discharges were continuously recorded over a period of several days in neonatal rat SCN explants. These organotypic explants, which had been cultured for several weeks in a chemically defined medium, showed alternating high and low levels of spontaneous neuronal discharges with a periodicity around 24 h. Such explants can serve as a useful model to study the neuronal mechanisms underlying the generation of mammalian circadian rhythms.

Action Potentials↗

PubMed1990

Role of noradrenaline in behavioral changes after defeat in male and female rats.

We have tested the effect of noradrenaline depletion by clonidine in agonistic behavior of intact male and gonadectomized testosterone-treated female rats. Animals were subjected to the 'resident-intruder' paradigm: in 4 consecutive daily confrontations residents defeated intruders. Clonidine-treated intruder males showed higher levels of aggression than did their saline-injected controls. In contrast, in females, in which defeat was also followed by reduction of aggression, no effect of clonidine treatment was found.

Aggression↗

PubMed1990

Quantitative analysis of eye movements during REM-sleep in developing rats.

Development of eye movements in REM-sleep was studied in rats during the second and third week of postnatal life. An increased frequency of eye movements was found after eye opening, which was due only to changes in burst activity. Since pups reared in constant darkness showed an increase in eye movement activity similar to that of those exposed to diurnal light-dark alterations, the change seems to be part of an endogenous developmental timetable rather than due to an increase of visual stimulation by eye opening.

Animals↗

PubMed1990

Circadian rhythms in preterm infants: a preliminary study.

A method has been developed for long-term continuous recordings of several physiological variables in humans, including body movements, core temperature, heart rate and respiratory rate. This method enabled us to study circadian rhythms of body temperature and rest-activity in preterm infants. In 5 out of 9 infants (recorded at 28-34 weeks conceptional age) circadian rhythms were found in body temperature. We conclude that circadian rhythmicity is present during the early neonatal period in certain physiological variables (body temperature) but not in others (rest-activity).

Circadian Rhythm↗

PubMed1990

Cortical neuron sensitivity to neurotransmitters following neonatal noradrenaline depletion.

In order to test the functional significance of rapid eye movement (REM)-sleep and noradrenergic activity for cerebral cortex maturation, rat pups were daily injected with clonidine from 8 to 21 days of life. Previous studies have shown that this treatment reduces the amount of time spent in REM-sleep and the level of noradrenaline turnover in the brain. For long-term consequences of such treatment in adulthood, cortical neuron responses to micro-iontophoretically applied neurotransmitters were studied. No significant differences were found in the single cell responses to glutamate, GABA or noradrenaline in the cerebral cortex of clonidine treated rats as compared with age matched controls. However, the magnitude of GABAergic depression of glutamate induced neuronal responses was greater in the clonidine than in the control group.

Animals↗

PubMed1990

Spontaneous neuronal firing patterns in the occipital cortex of developing rats.

Spontaneous action potentials have been recorded in the cerebral cortex of developing rats under chloral hydrate anaesthesia. These "spike-trains" were subjected to a multivariate analysis of parameters describing different aspects of temporal patterning within each train. Three parameters which reflected clustering of action potentials in, respectively, the range of: (i) milliseconds (the modal interval, derived from the interval histograms); (ii) seconds (the mean "burst period", i.e. the time elapsing between the onset of successive clusters of relatively short intervals); and (iii) minutes (the coefficient of variation for the number of spikes in consecutive 2 min time bins) showed distinctive developmental patterns.

Action Potentials↗

PubMed1990

Lasting effects of early noradrenergic receptor occupation on brain noradrenaline turnover and on beta-receptors.

Neuroactive substances reaching the developing brain can affect the formation of the functionality of nervous circuitry. To explain this so-called functional neuroteratology it has been proposed that neurotransmission has persistently been altered. Pharmacological interference with the developing central noradrenergic system in the rat by means of drugs like clonidine, yohimbine and propranolol, indeed revealed lasting changes in the turnover of noradrenaline in several brain areas, but no changes were found in beta-receptor density. It is assumed that either alpha-receptor density is affected or that signal transduction is altered, since electrophysiologically a persistent supersensitivity was found for the noradrenaline-evoked depression of glutamate-evoked firing in e.g. CA1 pyramidal cells of the hippocampus. Elucidation of the underlying neurochemical mechanisms of such lasting effects of perinatal exposure to noradrenergic drugs aims at establishing the role of noradrenaline in development, but also to provide physicians with the possibility to better assess the advantages and disadvantages of drugs to be prescribed during reproduction and, hence, to make the best choice of treatment.

Animals↗

PubMed1989

Serotonergic denervation does not reduce brain uptake of n-isopropyl-p-[123I]iodoamphetamine in vivo.

The relation between brain uptake of radiolabeled n-isopropyl-p-iodoamphetamine [( 123I]IMP) and serotonin re-uptake sites was studied in vivo by lesioning serotonergic nerve endings. The reduction of brain serotonin demonstrated the effectiveness of the procedure. Accumulation of radioactivity/g brain tissue was higher in the lesioned than in the sham-operated rats. This was explained by the loss of body weight of the lesioned animals, allowing an increased distribution to the brain. These results demonstrate that the in vivo distribution and binding of [123I]IMP in the brain is not limited to the specific serotonin re-uptake sites on nerve endings.

Amphetamines↗

PubMed1988

Decrease of rapid-eye-movement sleep in the light by intraventricular application of a VIP-antagonist in the rat.

Vasoactive intestinal polypeptide (VIP) has been shown to increase the amount of time spent in rapid-eye-movement (REM) sleep both in cats and in rats. In the present study we examined the effect of a newly available competitive VIP-antagonist ([4Cl-D-Phe6-Leu17]-VIP) on sleep-wake patterns in male rats during both the light and the dark phase of 24 h. Continuous intracerebroventricular application of this VIP-antagonist reduced by 44% the amount of time spent in REM sleep during the light period. It is concluded that VIP may play a role in the generation and maintenance of REM sleep.

Animals↗