Nuchal Muscle Activity Research Articles

Effect of pulsatile oxytocin administration to the pregnant ewe in the last third of gestation on fetal ACTH and cortisol response to acute hypoxemia.

The aim of this study was to examine the effect of increased myometrial contractility throughout the last third of pregnancy on the ovine fetal response to short-term hypoxemia. Oxytocin (600 microU/kg/minute, n = 5) or saline (n = 7) was infused for 5 minutes every 20 minutes into the maternal jugular vein starting at 95-99 days of gestation and continuing throughout the last third of gestation. Fetuses were subjected to a hypoxemic challenge (1 hour) at 131 days of gestation while fetal plasma ACTH and cortisol levels and nuchal muscle electromyogram activity were monitored. The fetal plasma ACTH concentration before and during the hypoxemic challenge was similar in the control and oxytocin groups. The fetal plasma cortisol concentration in the oxytocin group was significantly lower before and during the hypoxemia than in the controls. During hypoxemia, fetal nuchal muscle activity was significantly reduced only in the control group. Increased myometrial contracture frequency throughout the last third of pregnancy alters both the neuroendocrine and behavioral responses of fetal sheep to short-term hypoxemia.

GABAergic and glutamatergic effects on behaviour in fetal sheep.

1. Studies were carried out in unanaesthetized fetal sheep at 125-135 days gestation to investigate neurotransmitters involved in behavioural state. 2. Catheters and electrodes were chronically placed to record tracheal and arterial pressure, electrocortical activity (ECoG), nuchal muscle activity and to instill drugs into the cerebrospinal fluid (CSF) of the fourth ventricle. 3. Administration of the N-methyl-D-aspartate receptor antagonists DL-2-amino-5-phosphopentanoic acid (AP5) or (+)-5-methyl-10,11-dihydro-5H-dibenzol[a,d]cyclohepten-5,10- iminemoleate (MK-801) increased the incidence of fetal behaviour characterized by low voltage ECoG, nuchal muscle activity and an increase in mean arterial blood pressure from 4.1 +/- 6 to 60.6 +/- 6.2% (mean +/- S.E.M.) (AP5; P = 0.003) and from 7.6 +/- 3.6 to 50.8 +/- 7.0% (MK-801; P = 0.004; values are expressed as the percentage of each 60 min period in which the state was present). 4. The incidence of fetal breathing during periods of low voltage (LV)-ECoG and nuchal muscle activity was 83.1 +/- 5.6%. The incidence of fetal breathing during LV-ECoG associated with nuchal muscle atonia was 63.1 +/- 5.0% before AP5 or MK-801 and 64.4 +/- 9.8% after instillation of these drugs. The amplitude of fetal breaths increased from 4.0 +/- 0.3 mmHg in low voltage ECoG periods to 6.7 +/- 0.8 mmHg (P = 0.006) during periods of low voltage with nuchal muscle activity. There was no significant change in breath timing during these periods.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of repeated administration of cocaine to the fetal sheep in the last days of pregnancy

There are no reports on the direct effects of repeated cocaine administration to the fetus in late pregnancy. The aim of our study was therefore to examine the effects of repeated fetal exposure to cocaine on fetal development. Ten fetal sheep were instrumented at 123 +/- 1 days' gestation. Five fetuses received a single daily intravenous injection of cocaine (2 mg/kg) commencing at 130 to 131 days of gestation until delivery at 132 to 144 days of gestation; those fetuses were compared with fetuses that did not receive cocaine (n = 5). Basal fetal arterial blood gas values, blood pressure, heart rate, and nuchal and diaphragmatic activities did not change in the days preceding labor. Fetal arterial PO2 fell after cocaine administration, but this was significant only on the first day. Cocaine induced consistent significant alterations in fetal pH and PCO2, blood pressure, and heart rate. During labor cocaine stimulated diaphragmatic and nuchal muscle activity when compared with the other days. There was no increase in diaphragmatic and nuchal muscle activity in the controls. Our studies indicate that in fetal sheep the cardiovascular and blood gas response to cocaine in late pregnancy is not altered by repeated exposure to cocaine and that cocaine stimulates fetal breathing during labor.

Effects of sustained hypoxemia on the sheep fetus at midgestation: Endocrine, cardiovascular, and biophysical responses

The purpose of our study was to examine the effects of induced hypoxia on endocrine, cardiovascular, and biophysical measurements of the ovine fetus at 0.6 (83 to 93 days) of gestation and to compare the fetal responses at this earlier gestation with those reported near term. Fourteen fetal sheep were studied (9 in the hypoxia group and 5 in the control group) at 0.6 of gestation during a 24-hour control period, 8 hours of either sustained hypoxemia or room air, and a 40-hour recovery period. Induced fetal hypoxemia resulted in a progressive lactic metabolic acidosis; however, all fetuses had recovered within 24 hours. The fetal endocrine response was variable with norepinephrine, the only measured hormone showing a significant hypoxia-related increase (p less than 0.05). Fetal heart rate and mean arterial blood pressure showed little hypoxia-induced change, although fetal heart rate was significantly increased over the first 2 hours (p less than 0.05). The percent time fetal breathing movements, electroocular activity, and nuchal muscle activity likewise showed little hypoxia-induced change. The cardiovascular and biophysical response of the preterm fetus to induced hypoxemia is thus much less pronounced than that of the older gestational-aged fetus; this difference may impact on survival and the success of antenatal assessment protocols.

Behavioral changes in fetal sheep caused by vibroacoustic stimulation: The effects of cochlear ablation

We measured the effects of 2 minutes of vibroacoustic stimulation on the activity of unanesthetized fetal sheep in utero. We were unable to detect any changes in activity after stimulation with a model 5C electrolarynx. With more powerful stimulation using a mechanical oscillator, fetal electrocortical activity desynchronized. Fetal breathing and eye movements changed with electrocortical activity and there was an increase in nuchal muscle activity. Stimulation caused a small decrease in fetal heart rate. Responses to stimulation were not seen in four of the five fetuses with bilateral cochlear ablation. These results indicate that in fetal sheep the auditory apparatus is necessary for the detection of vibroacoustic stimuli. The difference in responsiveness of the sheep and human fetus appears to be because of a difference in central processing after detection of the stimulus.

迷路性，自己受容性直立姿勢制御の検討 フィードバックモデルを用いた分析

To clarify the role of vestibular and proprioceptive reflexes in the regulation of the upright standing posture, we analysed with feedback models sways of the head and of the body's center of gravity (BCG) and the activity of the nuchal and soleus muscles.Seven healthy adults were asked to stand upright with eyes closed and feet together on a stabilometer. The forward-backward sways of the head and BCG and the activity of the nuchal and soleus muscles were recorded polygraphically. The head sway and the nuchal muscle activity (head-nuchal muscle system) were analysed with a 2-dimensional feedback model to study vestibulo-spinal postural regulation. The sway of BCG and the soleus muscle activity (BCG-soleus muscle system) were analysed with a 2-dimensional feedback model to study proprio-spinal postural regulation.1. The determinants of the noise correlation matrix in the head-nuchal muscle system and in the BCG-soleus muscle system were close to 1, indicating good feedback.2. The order. of the autoregressive process, i. e. the length of the past sway forming the present sway, was greater in the head-nuchal muscle system than in the BCG-soleus muscle system.3. The power spectrum showed a higher power in the frequency range in the BCG sway than in the head sway. The correlogram showed that the correlation ratio decreased more rapidly to the base line in the BCG sway than in the head sway. These results indicate that regulation of the standing posture by proprioceptive reflexes is more minute than that by labyrinthine reflexes.4. The impulse responses calculated with the head sway as output and the nuchal muscle activity as input were divergent in 4 subjects. The impulse responses calculated with the head sway as input and the nuchal muscle activity as output were convergent in all 7. On the other hand, the impulse responses calculated with the BCG sway as output and the soleus muscle activity as input and with the BCG sway as input and the soleus muscle activity as output were convergent in all 7. These results suggest that the BCG-soleus muscle system provides greater stability than the head-nuchal muscle system.

Nuchal muscle activity at different levels of hypoxemia in fetal sheep

The effects of hypoxemia on nuchal muscle activity, a parameter of gross body movements, were studied during 12 experiments in five chronically instrumented fetal lambs. Hypoxemia was accomplished by tracheal infusion of nitrogen and did not result in significant changes in fetal arterial pH and PCO2. Fetal arterial blood gases and pH were continuously measured with an extracorporeal flow-through cuvette. Nuchal muscle activity was measured by electromyography and was expressed as the percentage of time spent moving. A decrease in fetal arterial oxygen saturation to three fourths of the initial value for 2 hours was not associated with significant changes in nuchal muscle activity. When fetal arterial oxygen saturation was further reduced for 2 hours to one half, fetal nuchal muscle activity fell significantly from 34.6% +/- 10.5% during normoxemia to 20.9% +/- 13.9% during hypoxemia. However, the most pronounced changes in fetal nuchal muscle activity occurred in the first 15 minutes after the changes in arterial oxygen saturation. A considerable transient increase in nuchal muscle activity was observed during the first 15 minutes after recovery from hypoxemia. During hypoxemia there was a relative predominance of short-lasting (less than 3 minute) movements.

直立検査とその基礎 直立制御機構の解析

This paper deals with our analysis and examination of the standing posture.1. Romberg, Mann, and one-leg tests were useful not only to demonstrate the degree of equilibrium disturbance but also to differentiate labyrinthine equilibrium disturbance from cerebellar ataxia.2. Stabilometry with computer analysis of the sway of the body's center of gravity was useful to record sway in the standing posture and to demonstrate peculiarities of equilibrium disturbances due to disorders of the labyrinth, cerebellum, basal ganglia, and cervical spinal cord.3. Analysis with a feedback model of interactions between sway of the head and the nuchal muscle activity (labyrinthine righting system) and between sway of the body's center of gravity and activity of the soleus muscle (proprioceptive righting system) was useful to demonstrate characteristics of the labyrinthine and proprioceptive controls which act to maintain the standing posture.4. Evoked electromyograms induced by the stimulation of the labyrinth appeared in the muscles of the gluteal and femoral regions and the legs. These muscle activities were varied with changes in head postition indicating that vestibulospinal reflexes are modulated by input from the neck proprioceptors.All kinds examinations related to standing posture are nesessary to clarify the mechanism of control of standing posture and to examine static equilibrium in clinical practice.

Effects of chronic hyperglycemia on electrocortical activity states in unanesthetized fetal lambs

Electrocortical activity (ECoG), tracheal pressure and nuchal muscle activity were recorded in utero in 8 chronically hyperglycemic and 10 control unanesthetized fetal lambs to investigate the effects of chronic hyperglycemia on fetal electrocortical activity states. The chronically hyperglycemic state, induced by alloxan administered to the ewes, existed for at least 40 days prior to the experiments. The mean duration of episodes of high voltage (HV) ECoG was significantly increased in the hyperglycemic group (mean ± SD: 21.8 ± 9.2 min) compared with the control group (14.8 ± 3.3 min), but the incidence of low voltage (LV) ECoG was not different between the groups. ECoG power spectra were not different between the groups. During LV ECoG, the proportions of time with neck movements were significantly less in the hyperglycemic than in the control group. No difference in percentages of time with long neck muscle activity was seen during the HV state in both groups. The incidence of breathing movements was equal in both groups, during HV as well as LV ECoG. No differences in breathing interval were observed.

Variations in nuchal muscle tonus following paradoxical sleep deprivation in the rabbit

Although tonic inhibition of nuchal or facial musculature is considered an intrinsic component of paradoxical sleep (PS) in mammals, this inhibition is either absent or greatly attenuated in the rabbit. To further explore the characteristics of this phenomenon in this species, variations in quantified nuchal muscle activity were examined before, during and following 24 h of PS deprivation. It was postulated that if the substrate for PS-associated tonic electromyogram (EMG) inhibition is present, this procedure—which is known to affect both tonic and phasic components of PS—might enhance such inhibition. For these investigations chronically implanted rabbits (electroencephalographic, eye movement and nuchal muscle placements) were recorded continuously for 5 consecutive days (two day baseline, one day deprivation, two day recovery). Muscle activity was quantified by resetting integration techniques and comparisons made of activity levels before, during and after PS episodes across conditions. The deprivation procedure significantly reduced the amount of PS relative to baseline values, and a significant PS increase (rebound) occurred during postdeprivation recordings. Across-condition EMG-related effects included the corroboration of previous reports of an absence of nuchal atonia during PS, a significant diurnal variation in EMG activity—with greater activity occurring during the dark portion of the light-dark cycle, and enhanced activity immediately following PS episodes relative to either pre-PS or PS levels. Deprivation-related changes in quantified EMG activity included a pre-PS decrease during both the last 12 h of deprivation and the initial 12 h of recovery sleep, and an enhancement of EMG activity during PS. The results are interpreted as indicating a deprivation-related enhancement of excitatory influences on nuchal muscle tonus during PS which is modulated by diurnal variations in levels of muscle activity. The findings suggest that the occurrence and maintenance of extended PS episodes undisturbed by excessive or unusual motor behavior are not dependent on the presence of tonic EMG inhibition as reflected in nuchal muscle recordings.

Changes in breathing, electrocortical and muscle activity in unanaesthetized fetal lambs with age.

Electrocortical and electro-ocular activity, breathing movements and nuchal muscle activity were recorded continuously in the unanaesthetized lamb in utero (95-135 days). Electrocortical activity was recorded simultaneously from various sites. The bi-parietal electrocorticogram gave the clearest differentiation between high- and low-voltage activity. The onset of cortical differentiation from 110 days gestation was attributed to the superimposition of high-voltage electrocortical activity at 3-10 Hz on existing low-voltage activity. Three distinct patterns in the relationships between electrocortical activity, ocular activity breathing movements and nuchal muscle activity were observed at 95-106, 107-114 and 120-135 days. Isocapnic hypoxia caused a diminution in fetal breathing from 95-135 days gestation, quantitatively greater near term. After cortical differentiation, hypoxia caused the appearance of high-voltage activity within 4 min, if low-voltage electrocortical activity was present initially. The relationship, changing with age, between electrocortical activity, breathing movements, ocular and nuchal muscle activity is discussed.

EEG and behavioral effects of gamma-hydroxybutyrate in the rabbit

The effects of gamma-hydroxybutyrate (GHB) upon sleep wakefulness patterns and quantified nuchal muscle activity were examined in the rabbit in a dose-response paradigm (25–1,000 mg/kg). Relative to control (saline) values, there was no facilitation of sleep onset or epileptogenic activity at any of the dosages studied. However, at the higher GHB concentrations, slow wave sleep and tonic muscle activity were enhanced and a high amplitude, slow activity was superimposed on background EEG patterns. The highest concentration of GHB (1,000 mg/kg) was associated with depression of motor activity. An enhancement of paradoxical sleep observed at lower GHB levels in other species occured in attenuated form in the rabbit. The results indicate dose-related effects on both sleep and motor activation in the rabbit, but the absence of seizure activity for the concentrations of GHB studied.