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Biomedical subjects

D Megirian

Publications and source records attributed to D Megirian.

At least 37 records · Page 2Linked to original sources
PubMed1984

Sleep-waking pattern and body temperature in hypoxia at selected ambient temperatures.

We studied the effect of mild hypoxia (15% O2) and low ambient temperature (Ta = 15 degrees C) on the rat's sleep-waking pattern (SWP) and maximum-minimum core temperature (max-min Tb). Mild hypoxia at neutral Ta (29 degrees C) disrupted the SWP in the same way as low Ta during normoxia: both affected the pattern of frequency of state changes (P less than 0.01), not the pattern of epoch durations. Mild hypoxia and low Ta together caused a degree of disruption of the SWP which was the sum of each alone, i.e., additive. Although both mild hypoxia and low Ta significantly depressed max-min Tb, low Ta exerted a greater effect than mild hypoxia. Together they further depressed max-min Tb in an additive way. We conclude that mild hypoxia disrupts the rat's SWP independent of central thermoregulatory mechanisms at neutral Ta, that the effects of mild hypoxia and low Ta on the SWP are additive at the stimulus levels used, and that Ta, not inspired O2, determines Tb.

Animals↗
PubMed1983

Sleep-waking patterns of intact and carotid sinus nerve-transected rats during hypoxic-CO2 breathing.

Two groups, each consisting of six male rats, breathed 21% O2-4% CO2 or 10% O2-4% CO2, respectively, before and after carotid sinus nerve (CSN) transection. Polygraphic recording techniques served to monitor sleep and wakefulness. The effects of these gas mixtures on the sleep-waking pattern (SWP) were studied. The SWPs of the intact and CSN-transected rats breathing 21% O2-4% CO2 were no different from rats breathing air. While breathing 10% O2-4% CO2, the greatest alteration in the rat's SWP, compared with breathing 10% O2 devoid of CO2, was in the pattern of frequency of change of states, an effect unchanged by CSN transection. We conclude that CO2 added to air did not affect the rat's SWP. However, a hypoxic-CO2 gas mixture radically altered all parameters of the SWP, an effect which was centrally mediated.

Animals↗
PubMed1983

The effects of hypoxia and CO2 on the sleep-waking pattern of the potoroo (Potorous tridactylus apicalis).

Four male potoroos (Potorous tridactylus apicalis) breathed 21% and 7% O2 with and without the addition of 5% CO2. The effects of these gas mixtures on the potoroo's sleeping-waking pattern (SWP) were studied. The SWP while breathing 21% O2/5% CO2 was unchanged when compared with that of breathing ambient air (21% O2). While breathing 7% O2, the SWP was severely disrupted: total sleep time (TST) and slow wave sleep (SWS) increased markedly. Brain temperature fell substantially. Paradoxical sleep (PS) was almost abolished and wakefulness (W) decreased. The addition of 5% CO2 to the O2 deficient gas mixture, i.e., 7% O2/5% CO2, restored the SWP to that obtained while breathing ambient air. It is concluded that CO2 neutralizes the disruptive effect which hypoxia has on the potoroo's SWP. It is hypothesized that this constitutes a homeostatic mechanism for stabilizing the SWP and is carried over from pouch life.

Animals↗
PubMed1982

Sleep-wake patterns of intact and carotid sinus nerve sectioned rats during hypoxia.

Six male rats breathed 21 an 10% O2 before and after carotid sinus nerve (CSN) section. Polygraphic recording techniques were used to monitor sleep and wakefulness. The effects that these gas mixtures had on the rats' sleep-wake pattern (SWP) were studied. The SWP of CSN sectioned rats breathing 21% O2 was unchanged compared with that of intact rats. While breathing 10% O2, the intact rats' SWP was altered dramatically. Paradoxical sleep (PS) was absent on the first day's exposure to hypoxia. After CSN section, the SWP approximated that of rats in normoxic conditions. The amount of PS increased considerably. It is concluded that the peripheral chemoreceptor reflex pathway contributes, in part, to disruption of the SWP under hypoxic conditions, but not under normoxic conditions. Mechanisms underlying changes in states of consciousness due to hypoxia are discussed.

Animals↗
PubMed1981

Effects of decortication and carotid sinus nerve section on ventilation of the rat.

The effect on ventilation of exposure to hypoxic, hypercapnic and hypoxic/hypercapnic gas mixtures was studied before and after functional decortication of intact rats and rats in which the carotid chemoreceptors had been disconnected. Unanaesthetized rats responded to both hypoxia and hypercapnia with an increase in minute ventilation (V) through increases in both frequency (f) and tidal volume (VT). Decortication led to a greater V response to CO2. This was through an effect on f, rather than VT. Carotid sinus nerve section (CSNS) caused a lessening in the V response to gas mixtures, f and VT being equally affected. Decortication, following CSNS, increased the V response but this time through increased VT rather than f. This effect on VT was not specific to any particular gas mixture. It is concluded that the carotid body chemoreceptors, together with the bulbopontine rate controller, influence the response to CO2. It is further suggested that this integration takes place in the reticular formation and is normally under some degree of inhibition from the cerebral cortex.

Animals↗
PubMed1980

An electrophysiological analysis of sleep and respiration of rats breathing different gas mixtures: diaphragmatic muscle function.

The effects of breathing 21% O2, 21% O2 + 5% CO2, 10% O2 + 4% CO2 and 10% O2 on the sleep-waking rhythm, respiratory rate, diaphragmatic EMG, inspiratory (Ti) and expiratory (Te) times were studied in rats. They carried chronically implanted electrodes to permit polygraphic recordings of the ECoG, EOG and dorsal neck and integrated diaphragmatic EMG activity. Average respiratory rates, independent of state of consciousness varied depending on the gas mixture breathed. Sleep-waking times, expressed as percentages, were determined as a function of the gas mixture breathed. Oxygen deficiency caused PS deprivation which was partially alleviated by the addition of 4% CO2. Diaphragmatic EMG activity decreased during PS when rats breathed gas mixtures rich in CO2 but increased when they breathed 10% O2. In general, at a given frequency of breathing, Ti was shorter during PS than during SWS except when rats breathed 10% O2. It is concluded that: (1) regardless of the state of consciousness hypoxia is a more potent stimulus of respiratory rate than hypercapnia, (2) diaphragmatic effort is reduced when rats breathe CO2 enriched gas mixtures but is increased by hypoxia due to changes in upper airway resistance, and (3) low O2 content of an inspired gas disrupts the inspiratory and expiratory off-switch mechanisms, this disruption being prevented by the addition of CO2.

Animals↗
PubMed1980

Respiratory EMG activity of the posterior cricoarytenoid, cricothyroid and diaphragm muscles during sleep.

The respiratory activity (EMGs) of the posterior cricoarytenoid (PCA), cricothyroid (CT) and diaphragm (D) were examined during slow wave sleep (SWS) and paradoxical sleep (PS).-Chronically implanted, free-to-move adult rats were used. In SWS, CT exhibited inspiratory or expiratory or inspiratory and expiratory bursts in each respiratory cycle. The latter was common during CO2 (4%) breathing. PCA manifested phasic inspiratory discharges along with tonic expiratory activity. The latter was augmented by breathing CO2. At onset of PS, inspiratory PCA and CT activity declined. In those PS epochs of irregular D activity, PCA and CT further declined during eye movements. In other PS epochs, D arrest coincided with co-activation of PCA and CT, occasionally CT activation alone. CO2 breathing did not affect the above described during PS. In PS, loss of PCA and CT's inspiratory activity during rhythmic D activity may contribute to obstructive apnea; PCA and CT co-activation with D arrest characterizes central type apnea.

Animals↗
PubMed1978

Rhythmical activity of the rat's tongue in sleep and wakefulness.

Nine chronically implanted rats were used to study rhythmical activity of suprahyoidal muscles controlling tongue motility. This muscle group exhibited a fixed, regular rhythm of 5--8 c/sec during PS, not during SWS, resembling that observed when the awake rat drank, ate or groomed. In PS the tongue rhythm occurred less frequently than did eye movements and phasic nasolabial muscle activity; when it did, it was associated with such eye movements 80% of the time and 20% of the time before or after an episode of eye movements. A respiratory-related suprahyoidal EMG was observed in one rat to precede the onset of the diaphragm's EMG. Mechanisms for entraining phasic activity of extraocular, nasolabial and suprahyoidal muscles in PS are discussed.

Animals↗
PubMed1975

Corticobulbar fibres in the North American opossum (Didelphis marsupialis virginiana) with notes on the Tasmanian brust-tailed possum (Trichosurus vulpecula) and other marsupials.

Corticobulbar projections have been studied in the American opossum by both degeneration and autoradiographic methods and, for the most part, the results confirm our earlier observations (Martin & West, 1967; Martin, 1968). However, we have obtained evidence for certain connexions not previously described and have delineated the origin(s) of several connexions more precisely by paying particular attention to the degeneration present at thalamic levels in all cases and by the use of autoradiography. When our results are collated and correlated with new somatosensory cortical maps arrived at by microelectrode techniques (Pubols et al. 1975), it is obvious that corticolbulbar connexions in the North American opossum are remarkably similar to those in the monkey and differ mainly in quantity, relative origins and distribution and in the fact that some of them arise from spatially co-extensive motor-sensory areas (Lende, 1963a, b). In the light of our findings on the American opossum we have examined a large collection of brush-tailed possum material (as well as some from the potoroo and Tasmanian native cat) and have been able to extend our previous findings (Martin et al. 1971; Martin & Megirian, 1972) to a more precise evaluation of the origin of projections from the limb, face motor-sensory cortex. Differences between these representatives of the marsupial radiation, as well as features which are common to all, are described.

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