Selective effects of neuronal-synaptobrevin mutations on transmitter release evoked by sustained versus transient Ca2+ increases and by cAMP. (1/98)

Synaptobrevin is a key constituent of the synaptic vesicle membrane. The neuronal-synaptobrevin (n-syb) gene in Drosophila is essential for nerve-evoked synaptic currents, but miniature excitatory synaptic currents (mESCs) remain even in the complete absence of this gene. To further characterize the defect in these mutants, we have examined conditions that stimulate secretion. Despite the inability of an action potential to trigger fusion, high K+ saline could increase the frequency of mESCs 4- to 17-fold in a Ca2+-dependent manner, and the rate of fusion approached 25% of that seen in wild-type synapses under the same conditions. Similarly, the mESC frequency in n-syb null mutants could be increased by a Ca2+ ionophore, A23187, and by black widow spider venom. Thus, the ability of the vesicles to fuse in response to sustained increases in cytosolic Ca2+ persisted in the absence of this protein. Tetanic stimulation could also increase the frequency of mESCs, particularly toward the end of a train and after the train of stimuli. In contrast, these mutants did not respond to an elevation of cAMP induced by an activator of adenylyl cyclase, forskolin, or a membrane-permeable analog of cAMP, dibutyryl cAMP, which in wild-type synapses causes a marked increase in the mESC frequency even in the absence of external Ca2+. These results are discussed in the context of models that invoke a special role for n-syb in coupling fusion to the transient, local changes in Ca2+ and an as yet unidentified target of cAMP.  (+info)

Fetal peripheral bronchial fluid flow during breathing movement in normal pregnancies: a preliminary study. (2/98)

OBJECTIVE: To determine the fluid flow velocity waveforms in the fetal peripheral bronchus during fetal breathing movement by means of pulsed Doppler ultrasonography. DESIGN: A preliminary cross-sectional study. SUBJECTS: Twenty-eight normal pregnant women between 32 and 38 weeks of gestation. METHODS: Velocity waveforms from fetal peripheral respiratory fluid flow were acquired from the segmental bronchus (B6 or B8) which runs along the segmental artery (A6 or A8). The maximum velocity of the intrabronchial fluid flow and duration of inspiratory and expiratory phases were quantified. RESULTS: The flow velocity signal from the fluid in the fetal segmental bronchus of 17 of the 28 fetuses was detected. We observed two types of fetal breathing movement. CONCLUSION: During fetal breathing movement, the fluid in the fetal respiratory tract moves in the fetal segmental bronchus. This movement can be detected by pulsed Doppler velocimetry aided by power Doppler ultrasonography.  (+info)

A new photogrammetric method to measure fetal breathing movements. (3/98)

OBJECTIVE: In most recent studies, fetal respiratory movements have been measured with real-time and Doppler echography. We describe an alternative approach using photogrammetry that provides more objective measurements. METHODS: Respiratory movements were studied in 28 women with uncomplicated pregnancies of 30-38 weeks' gestation. Fetal echographic images were recorded on videotape and digitized to obtain coordinates of the reference point (midpoint on the anterior abdominal wall of the fetus between the xiphoid process and the insertion of the umbilical vessels) and generate graphic representations of fetal movements in the anterior abdomen. RESULTS: The mean duration of a complete respiratory cycle was 1.194 s, the mean distance representing the extent of movement was 2.92 mm, the mean inspiratory velocity was 5.52 mm/s and the mean expiratory velocity was 5.06 mm/s. CONCLUSIONS: Photogrammetric analysis of images obtained with real-time echography provided accurate measurements of fetal breathing movements.  (+info)

The adenosine A(1)-receptor antagonist 8-CPT reverses ethanol-induced inhibition of fetal breathing movements. (4/98)

Administration of either ethanol or adenosine inhibits fetal breathing movements (FBM), eye movements, and low-voltage electrocortical activity (LV ECoG). The concentration of adenosine in ovine fetal cerebral extracellular fluid increases during ethanol-induced inhibition of FBM. The purpose of this study was to determine the effect of a selective adenosine A(1)-receptor antagonist, 8-cyclopentyltheophylline (8-CPT) on the incidence of FBM during ethanol exposure. After a 2-h control period, seven pregnant ewes received a 1-h intravenous infusion of ethanol (1 g/kg maternal body wt), followed 1 h later by a 2-h fetal intravenous infusion of either 8-CPT (3.78 +/- 0.08 microg. kg(-1). min(-1)) or vehicle. Ethanol reduced the incidence of FBM from 44.0 +/- 10.4 to 2.7 +/- 1.3% (P < 0.05) and 51.2 +/- 7.6 to 11.9 +/- 5.0% (P < 0.05) in fetuses destined to receive 8-CPT or vehicle, respectively. In the vehicle group, FBM remained suppressed for 7 h. In contrast, during the first hour of 8-CPT infusion, FBM returned to baseline (31 +/- 11%) and was not different from control throughout the rest of the experiment. Ethanol also decreased the incidence of both low-voltage electrocortical activity and eye movements, but there were no differences in the incidences of these behavioral parameters between the 8-CPT and vehicle groups throughout the experiment. These data are consistent with the hypothesis that adenosine, acting via A(1) receptors, may play a role in the mechanism of ethanol-induced inhibition of FBM.  (+info)

Adaptation of laser-Doppler flowmetry to measure cerebral blood flow in the fetal sheep. (5/98)

The purpose of this study was to devise a means to use laser-Doppler flowmetry to measure cerebral perfusion before birth. The method has not been used previously, largely because of intrauterine movement artifacts. To minimize movement artifacts, a probe holder was molded from epoxy putty to the contour of the fetal skull. A curved 18-gauge needle was embedded in the holder. At surgery, the holder, probe, and skull were fixed together with tissue glue. Residual signals were recorded after fetal death and after maternal death 1 h later. These averaged <5% of baseline flow signals, indicating minimal movement artifact. To test the usefulness of the method, cerebral flow responses were measured during moderate fetal hypoxia induced by giving the ewes approximately 10% oxygen in nitrogen to breathe. As fetal arterial PO(2) decreased from 21.1 +/- 0.5 to 10.7 +/- 0.4 Torr during a 30-min period, cerebral perfusion increased progressively to 56 +/- 8% above baseline. Perfusion then returned to baseline levels during a 30-min recovery period. These responses are quantitatively similar to those spot observations that have been recorded earlier using labeled microspheres. We conclude that cerebral perfusion can be successfully measured by using laser-Doppler flowmetry with the unanesthetized, chronically prepared fetal sheep as an experimental model. With this method, relative changes of perfusion from a small volume of the ovine fetal brain can be measured on a continuous basis, and movement artifacts can be reduced to 5% of measured flow values.  (+info)

Effects of morphine and naloxone on fetal heart rate and movement in the pig. (6/98)

To test the hypothesis that an increasing opioid tonus is involved in decreases in fetal heart rate (FHR) and movement (FM) during late gestation, we studied the effects of intravenous bolus injections of morphine (1 mg) and naloxone (1 mg) on FHR and FM in the fetal pig. Twenty-one fetuses (1 per sow) were catheterized at 90-104 days of gestation (median 100 days). Recordings of FHR (electrocardiograph or Doppler-derived signals) and FM (ultrasonography) were made from 15 min before to 45 min after treatment. Morphine administration significantly decreased FHR, but it increased FHR variation and forelimb movements (LM). LM were clustered, and this stereotyped behavior has never before been observed in any mammalian fetus. Naloxone administration increased gross body movements and FHR without significant changes in FHR variation. It is concluded that FHR and motility are under opioidergic control in the pig fetus. Both morphine and naloxone induce hypermotility, suggesting that naloxone does not act as a pure opioid antagonist in the fetal pig.  (+info)

Ultrasound measurements of fetal breathing movements in the rat. (7/98)

The goal of this study was to determine when fetal breathing movements (FBMs) commence in the rat and to characterize age-dependent changes of FBMs in utero. These data provide a frame of reference for parallel in vitro studies of the cellular, synaptic, and network properties of the perinatal rat respiratory system. Ultrasound recordings were made from unanesthetized Sprague-Dawley rats from embryonic (E) day 15 (E15) to E20. Furthermore, the effects of respiratory stimulants (doxapram and aminophylline) and hypoxia on FBMs were studied. Single FBMs, occurring at a very low frequency (approximately 8 FBMs/h), commenced at E16. The incidence of single FBMs increased to approximately 80 FBMs/h by E20. Episodes of clustered rhythmic FBMs were first observed at E18 (approximately 40 FBMs/h). The incidence of episodic clustered FBMs increased to approximately 300 FMBs/h by E20, with the duration of each episode ranging from approximately 40 to 180 s. Doxapram, presumably acting to stimulate carotid body receptors, did not increase FBMs until E20, when the incidence of episodic clustered FBMs increased twofold. Aminophylline, a central-acting stimulant, caused an increase in episodic clustered FBMs after E17, reaching significance at E20 (3-fold increase). Exposing the dam to 10% O(2) caused a rapid, marked suppression of FBMs (5-fold decrease) that was readily reversed on exposure to room air.  (+info)

Fetal stimulation by pulsed diagnostic ultrasound. (8/98)

OBJECTIVE: To show that pulsed ultrasound from a clinical ultrasonic imaging system can stimulate the fetus. Stimulation is defined mainly as increased fetal gross body movements in response to excitation. METHODS: Fetuses of a group of 9 volunteer women (mean gestational age, 33.37 weeks; range, 25-40 weeks) were evaluated for body movement under 3 different conditions: (1) control, with no ultrasound exposure; (2) ultrasound in continuous wave Doppler mode; and (3) pulsed ultrasound in pulsed Doppler and B modes. A conventional external fetal monitor, with negligible ultrasonic output, was used to monitor fetal gross body motions. After an initial rest period of 3 minutes with 1 or no fetal motion, fetuses were monitored for an additional 3 minutes under the exposure criterion defined for each condition. Resulting fetal motions under the 3 conditions were compared using the Wilcoxon signed rank test. RESULTS: The test showed that fetuses moved significantly more frequently under condition 3 (mean +/- SD, 3.43 +/- 1.93 movements per minute) than under condition 1 (0.40 +/- 7.33 movements per minute) or condition 2 (0.63 +/- 7.67 movements per minute); P = .004 and .016, respectively. Fetal movements under conditions 1 and 2 did not differ significantly. CONCLUSION: Diagnostic ultrasound may stimulate fetal body motion.  (+info)