High Voltage ECoG Research Articles

Pulmonary feedback and gestational age-dependent regulation of fetal breathing movements

Prenatal lung development requires fetal breathing movements (FBM). To investigate the dependence of FBM on feedback originating from the lung, we hypothesized that pneumonectomy stimulates FBM. Time-dated fetal sheep underwent bilateral pneumonectomy, unilateral pneumonectomy, or sham surgery at 125-130 days gestation. The incidence of FBM decreased in sham-operated fetuses at 142 days versus 130 days (p = 0.013), but was unchanged across all gestational ages in bilaterally pneumonectomized fetuses (p > or = 0.52). In unilaterally pneumonectomized fetuses, the incidence of FBM remained unchanged until 139 days and was higher than that of the bilaterally pneumonectomized fetuses at 130-136 days gestation (p < or = 0.03). The amplitude of integrated diaphragmatic electromyographic activity (integralEMG(di)) and total respiratory output (frequency of breathing x integralEMG(di)) were lower in pneumonectomized fetuses versus sham-operated fetuses at later gestational ages (p < 0.05). These decreases in integralEMG(di) and total respiratory output were most pronounced at 142 days in bilaterally pneumonectomized fetuses versus sham-operated fetuses (p = 0.006 and 0.016, respectively). Low-voltage electrocortical activity (ECoG) increased, and high-voltage ECoG decreased, in unilaterally pneumonectomized fetuses compared with sham-operated fetuses (p = 0.04). In conclusion, we provide new evidence that feedback from the fetal lung modulates the incidence and various components of phrenic nerve output, suggesting a positive feedback mechanism between FBM and lung development.

Effects of fetal behavioral states on renal sympathetic nerve activity and arterial pressure of unanesthetized fetal sheep.

Fetal behavior, renal sympathetic nerve activity (RSNA), mean arterial pressure (MAP), and heart rate (HR) were studied 1-3 days after surgery in seven fetal sheep (aged 127-136 days). Five behavioral states were defined from chart recordings of electrocortical (electrocorticographic; ECoG) activity and eye, limb, and breathing movements. Most records were of high-voltage ECoG (HV) or low-voltage (LV) ECoG with breathing (LVB); 6.7 +/- 1.7% were LV ECoG with no breathing (LV0). RSNA was lower in LV0 (P < 0.001) and greater in LVB than in HV (P < 0.05). MAP was lower in both LV states than in HV and when the fetuses went from LV to HV (P < 0.001 to P < 0.03). HR was highest in HV (P < 0.001). In HV and LVB and when the fetus went from LV to HV, MAP and HR were inversely related (P = 0.012-0.003). In LVB and from LV to HV there were direct relationships between MAP and RSNA (P = 0.0014, P = 0.08), and when the fetus went from LV to HV there was also an inverse relationship between HR and RSNA (P = 0.02). Thus fetal RSNA, MAP, and HR are affected by behavioral state as is fetal cardiovascular control. The increase in RSNA during fetal breathing showed that there was an altered level of fetal RSNA associated with fetal breathing activity.

Fetal behavioural state changes following maternal fluoxetine infusion in sheep

Clinical depression is diagnosed in 5–15% of women during pregnancy, increasing the risk of negative outcomes. Fluoxetine (FX), a selective serotonin reuptake inhibitor, is prescribed during pregnancy. In adults, FX alters sleep patterns with single doses decreasing total sleep time and rapid eye movement sleep. The effects of FX on sleep in the fetus are unknown. However, 5-hydroxytryptophan, the precursor of serotonin, has been reported to prolong high-voltage (HV) electrocortical (ECoG) activity and increase the incidence of fetal breathing movements (FBM) in the sheep fetus. We hypothesize that FX exposure will decrease the incidence of LV ECoG in the fetus. Twenty-one pregnant sheep were surgically prepared for chronic study of blood gases, ECoG activity, eye movements and FBM. After 3 days of recovery, ewes received a 70-mg bolus i.v. infusion of FX or sterile water followed by continuous infusion at a rate of 0.036 mg/min for 8 days. The incidence of low-voltage (LV) ECoG decreased from 54±4% on the preinfusion day to 45±5% on infusion day 1 in the FX group and remained decreased throughout the infusion period. In addition, the incidence of both eye movements and FBM was decreased on infusion day 1 compared to preinfusion day in the FX group. HV ECoG increased from 39±3% on preinfusion day to 68±14% on FX infusion day 1 and remained elevated throughout the infusion period. These data show that maternal FX administration alters fetal behavioural state.

Effect of pregnane steroids on electrocortical activity and somatosensory evoked potentials in fetal sheep

The effect of infusing the neuroactive steroids pregnanolone and iso-pregnanolone on somatosensory evoked potentials (SEP) and electrocortical (ECoG) activity was studied in unanaesthetised fetal sheep, 130–135 days gestation. Intravenous infusion of pregnanolone (6 mg/kg per h) significantly increased the proportion of high voltage ECoG (56.1±4.8% vs. control 43.5±3.2%, P<0.05), and decreased low voltage ECoG (43.9±4.8% vs. control 56.6±3.2%, P<0.05). Pregnanolone treatment decreased the amplitude of the N25 peak of the SEP (89.9±2.8% of control, P<0.05) evoked following stimulation of the skin of the upper lip. In contrast, iso-pregnanolone treatment had no effect on ECoG activities, or on the amplitude and latency of peaks in the SEP. We conclude that 3 α-hydroxy pregnane steroids are active at GABA A receptors in fetal sheep and can modulate sleep/wake activity before birth.

Urine production rate and renal blood flow in the near-term ovine fetus are not related to high and low voltage electrocortical activity.

Studies in both the human and ovine near-term fetus have identified the clustering of physiologic and behavioral parameters into states. In a recent study in the human fetus a considerable decrease was found in fetal urine production during non-rapid eye movement (non-REM) compared with REM sleep. Whether this decrease was caused by decreased renal blood flow or changes in urine concentration is not known. This prompted us to investigate the relation between fetal urine production rate and electrocortical activity in the near-term ovine fetus. We hypothesized that in the ovine fetus urine production and renal blood flow during REM [comparable to low voltage electrocortical activity (LV ECoG)] would be lower than during non-REM [(high voltage (HV) ECoG)]. In eight fetal sheep between 123 and 127 d of gestation (term 147 d), ECoG, renal blood flow, urine flow, and urine osmolality were measured continuously for 6 h on 2 consecutive days. Data were analyzed into HV ECoG and LV ECoG whereafter urine flow, urine osmolality, and renal blood flow data were averaged per state. We found no significant differences in urine flow, urine osmolality, or renal blood flow between the two behavioral states in the ovine fetus. Because these data are in sharp contrast to those found in the human fetus, we conclude that the observed dissimilarities in renal responses between the human and sheep fetus add to the already known differences in behavioral states between the two species.

The effects of `sleep promoting agents' on behavioural state in the ovine fetus

Fetal behavioural states, with similarities to adult sleep states, exist in both the human and ovine fetus near term. The purpose of the present study was to determine the effects of intracerebral administration of pharmacologic agents, known to affect sleep states in the adult, on fetal behavioural states and physiologic correlates using the chronically catheterized ovine fetus near term. Each drug was infused into either the cisterna magna or lateral ventricle for 90 min in one of two doses. Carbachol (1.35×10 −5 and 4.25×10 −6 M) led to an increase in low-voltage ECOG, eye movement and FBM activities, while scopolamine (4.68×10 −4 and 1.56×10 −4 M) led to a decrease in low-voltage ECOG and eye movement activity with an increase in high-voltage ECOG activity. l-5-Hydroxytryptophan (5-HTP) (2.04×10 −3 and 6.81×10 −4 M) infusion led to an increase in FBM, while VIP (3.00×10 −7 and 1.00×10 −7 M) infusion had no effect on fetal behavioural state parameters. Study results indicate that fetal behavioural states can be altered pharmacologically and in a manner similar to that seen in the adult but with notable differences that may relate to species, developmental or dose–response issues.

Flow and velocity waveform indices in the ovine fetal abdominal aorta with changes in behavioural state.

The purpose of this study was to determine the extent to which flow and velocity waveform indices are comparable as measured from the ovine fetal abdominal aorta and reflect downstream vascular resistance with changes in electrocortical activity. Nine chronically catheterized fetal sheep were studied near term with continuous measurement of electrocortical activity, perfusion pressure, and fetal heart rate. A cuffed Doppler crystal and a Transonic flow probe on the descending abdominal aorta were used for the simultaneous measurement of velocity waveforms and flow waveforms, with the Resistance Index (RI), calculated for each. Mean blood flow was also obtained from the Transonic flow probe. Whereas the change in cardiovascular parameters between the low- and high-voltage electrocortical activity (ECOG) states was small, with little relationship to the change in RI measurements, across all animals there was an inverse correlation between the RI measurements and fetal heart rate, perfusion pressure and aortic blood flow during both low- and high-voltage ECOG states. The RI as measured from the velocity waveforms showed only a modest correlation to those measured from the flow waveforms. It is concluded that over the range of circulatory change generated with spontaneous change in behavioural state, the RI as measured in the abdominal aorta of the ovine fetus is primarily determined by pulsatile cardiovascular variables rather than lower body vascular resistance.

Regional brain blood flow in the ovine fetus during transition to the low-voltage electrocortical state

Sequential changes in cerebral blood flow and regional distribution were studied in nine chronically catheterized fetal sheep during the transition to the low-voltage ECOG (REM) state to determine the time course for blood flow change within the brain and whether executive centres for REM state generation might thus be identified. Blood flows were measured during the first, second and third minutes after the transition to the low-voltage ECOG state and during the third minute of the subsequent high-voltage ECOG (NREM) state using the radioactive labelled microsphere technique. Blood flow to the brain was increased during the low-voltage REM state when compared to that of the high-voltage NREM state, with the increase evident when measured during the first minute after the state transition and with no sequential change thereafter. Regional blood flow increases during the low-voltage state were greatest to those areas variously associated with the generation of REM state activity, but were again remarkably stable through the first 3 minutes after the state transition. This rapid increase in blood flow within the brain and the regional hierarchy for such, supports the participation of multiple anatomical areas which are highly integrated and act in concert to give rise to what is known as the REM state.

A cholinergic mechanism involved in fetal breathing during the high voltage ECoG state

The effects of muscarininc cholinergic neurotransmission on fetal breathing was determined by administration of carbachol or carbachol plus a muscarinic receptor antagonist into the cerebrospinal fluid of the fourth ventricle in unanesthetized fetal sheep. In the hour following the instillation of carbachol (1.0 μg), the incidence of fetal breathing in high voltage electrocortical state (ECoG) increased to 63 ± 11.7 (SEM) percent compared to 1.2 ± 0.9 after instillation of vehicle (Ringer solution). The cholinergic agonist increased breath amplitude from 4.5 ± 0.4 to 10.6 ± 1.4 mmHg. These effects were eliminated when the M 1 receptor antagonist pirenzipine (50–100 μg) was administered with carbachol but not by antagonists which are relatively selective for M 2 or M 3 receptors. When administered alone, muscarinic receptor antagonists did not effect the incidence or amplitude of fetal breathing in low voltage. These data indicate that the apnea which occurs during high voltage in the sheep fetus involves an inhibition of acetylcholine acting at M 1 muscarinic receptor bearing neurons.

Effects of intracisternal monoamines on breathing movements in fetal sheep.

The effects of intracisternal administration of tyramine on fetal breathing movements (FBM), electrocortical (ECoG) and nuchal muscle activities, and cerebrospinal fluid (CSF) monoamine concentrations have been studied in unanesthetized fetal sheep (124-140 days gestation) in utero. In 18 trials (8 fetuses) infusion of 50 or 100 micrograms/kg tyramine increased the incidence of FBM from 32.2 +/- 2.0 to 79.4 +/- 4.7%/h (P < 0.05) and increased mean breath amplitude from 6.4 +/- 0.4 to 11.8 +/- 1.6 mmHg (P < 0.05). FBM incidence during high-voltage ECoG activity increased from 3.3 +/- 0.6 to 22.5 +/- 3.6%/h (P < 0.05). Tyramine infusion (100 micrograms/kg) significantly increased (P < 0.05) the CSF concentrations of dopamine from 129.5 +/- 26.2 to 10,222.4 +/- 1,103.6 pg/ml, of norepinephrine from 74.7 +/- 11.0 to 2,238.6 +/- 143.5 pg/ml, and of serotonin from 1,824.5 +/- 340.7 to 3,888.7 +/- 1,335.2 pg/ml. Intracisternal injection of dopamine or norepinephrine (10-20 micrograms) caused the rapid onset of large-amplitude FBM, which often continued throughout high-voltage ECoG activity. In contrast, serotonin (20-40 micrograms) caused cessation of FBM and change of the ECoG from low- to high-voltage activity. These results indicate that neuronal release of catecholamines in the CNS has excitatory effects on FBM.

Intra-nigral infusion of Cu-free superoxide dismutase prevents paraquat-induced behavioural stimulation and ECoG epileptogenic discharges in rats

In adult rats, with cannulae chronically implanted by a stereotactie instrument into the substantia nigra (pars compacta), the electrocortical (ECoG) and behavioural effects elicited by intranigral infusion of paraquat and the prevention of these effects by prior administration into the same site of different types of superoxide dismutase, were studied. Paraquat (50 μg) produced an intense pattern of behavioural stimulation, contralateral circling and repetitive discharges of high voltage ECoG spikes. The effects of paraquat were abolished in all of the animals pretreated into the same site with copper-free superoxide dismutase. Pretreatment with native Cu, Zn-superoxide dismutase prolonged significantly the latency of onset but did not prevent the behavioural stimulation and ECoG spikes evoked by paraquat. On the contrary, pretreatment with albumin or saline did not confer any protection against the neurotoxicological changes induced by paraquat. In conclusion, the present experiments showed that motor, ECoG and lethal effects of paraquat were completely prevented by Cu-free Superoxide dismutase, suggesting that the central effects of this herbicide are in some way related to the release in the brain of copper and/or other transition metal ions.

FETAL BEHAVIOR IN SHEEP MEASURED THROUGH A DOUBLE WALL PLEXIGLASS WINDOW

The inability to see the fetus makes the assessment of fetal behavior impossible. To circumvent this problem we implanted a plexiglass window on the left flank of the ewe. Fetuses were instrumented for measurements of sleep, respiration and swallowing. Thirty-four fetal sheep were studied on 112 occasions. Six fetuses were delivered through the window at term and postnatal behavior was compared to intra-uterine behavior. Fetuses were observed for 1214 hours and videotaped for 312 hours. During resting conditions and during administration of agents known to stimulate fetal breathing; CO2, indomethacin, 5-HTP, pilocarpine and naloxone. During resting conditions the fetus alternated between periods of quiet sleep (high voltage ECoG) and active sleep (low voltage ECoG). In quiet sleep, movements were absent except for periodic generalized tonic discharges. Eye and breathing movements were absent. Sucking, licking and swallowing were also absent. In active sleep, movements were increased with powerful breathing activity. Sucking, licking and swallowing were present. The effect of CO2, indomethacin, 5-HTP, pilocarpine and naloxone was to increase or induce breathing without major change in state. Fetal wakefulness defined by open eyes and purposeful movements of the head were never seen in utero but were clearly observed after delivery. We conclude that fetal wakefulness as defined postnatally is not seen in utero and appears only after birth.(Videotape will be shown)

Central chemical regulation of breathing movements in fetal lambs

In 12 chronically prepared fetal lambs between 126 and 136 days of gestation, 17 ventriculocisternal perfusions (123 μl/min) were performed. The concentration of bicarbonate ([HCO 3 −1]) in the mock cerebrospinal fluid (CSF) perfusate was altered to manipulate the [HCO 3 −1] in the cerebral ventricles. These perfusions did not systematically alter fetal arterial P CO 2 , P O 2 , pH, heart rate or mean blood pressure. Fetal breathing movements (FBM) were noted as rhythmic negative intrathoracic pressures with reference to amniotic fluid pressure. The incidence of FBM was determined and expressed as the percent of the 3 h observation period during which breathing movements were present. Perfusions with mock CSF having an approximately normal [HCO 3 −1], resulted in cisternal [HCO 3 −1] of 23.9 ± 0.8 (SEM) meq/L and an incidence of fetal breathing movements (FBM) of 22.1 ± 10.0%. Perfusions with an elevated [HCO 3 −1] in the mock CSF increased the cisternal [HCO 3 −1] to 30.7 ± 0.4 meq/L and lowered the incidence of FBM to 0.6 ± 0.2%. Perfusions with a lowered [HCO 3 −1] mock CSF decreased the cisternal [HCO 3 −1] to 17.3 ± 0.8 meq/L and increased the incidence of FBM to 45.7 ± 6.8%. These perfusions did not alter the relative incidence of low voltage (LV) versus high voltage (HV) electrocortical (ECOG) state. In 4 animals, low [HCO 3 −1] perfusions induced FBM in the normally apneic HV ECOG state. We conclude that in the near-term fetal lamb, central chemoreceptors can modulate the incidence of rhythmic respiratory efforts, that tonic afferent stimuli arising from these receptors are critical for the generation of spontaneous FBMs and that central acidosis is capable of evoking FBMs in the normally apneic HV ECOG state.