Expression of functional neurotransmitter receptors in an uninnervated tissue: avian amnion

Changes in umbilical arterial blood flow by an intraamniotic distilled water infusion

OBJECTIVES

The purpose is to investigate how umbilical arterial blood flow changes by an intraamniotic distilled water infusion and to determine whether the changes in umbilical circulation have any relationship with fetal cardiovascular status and osmolality in amniotic fluid and fetal plasma.

METHODS

Eleven chronically catheterized pregnant sheep were used in this study. After a 1-hour control period, 1.5 L of warmed sterile distilled water was injected over 10 minutes into the amniotic cavity. Fetal heart rate and carotid arterial pressure, blood flow of the umbilical and fetal carotid arteries were continuously measured. Fetal arterial blood sampled twice during the control period and then at 30, 60, 90, 120, 180, 240, 300, and 360 minutes after the start of the infusion, was analyzed for blood gases, pH, plasma electrolytes, and osmolality.

RESULTS

Data obtained from seven sheep with normoxemic fetuses were studied statistically. Umbilical arterial blood flow decreased significantly from 229.5 +/- 3.83 mL/min in the control to 167.4 +/- 11.1 mL/min at 30 minutes after water infusion (P < .001). Umbilical arterial vascular resistance increased rapidly and reached its peak at approximately 60 minutes after infusion and then showed a gradual recovery to the control level (P < .001). Amniotic fluid osmolality had a high degree of correlation with umbilical arterial blood flow and vascular resistance, while fetal arterial blood pressure and heart rate had only little correlation with umbilical blood flow.

CONCLUSION

A distilled water infusion into the amniotic cavity in near-term pregnant sheep led to an acute drop in umbilical arterial blood flow. The changes in umbilical flow were closely correlated with those in amniotic fluid osmolality. Hemolysis in the capillary networks in the fetal membranes seems to be one of the main causes of umbilical vasoconstriction. It is speculated that the fetal membranes, including capillary networks, intramembranous pathway, and amnion epithelial cells, sense the changes in amniotic fluid osmolality, which leads to a fetal adaptation to the hypotonic environment.

Rhythmic contractions in chick amnio-yolk sac and snake amnion during embryogenesis

The rhythmic movements of fetal membranes in chick and reptile embryos were studied to explore the developmental role of the extra-embryonic motor activity. In the snakes Lamprophis fuliginosus and Elaphe radiata, rhythmic contractions of amnion inside the developing egg were recorded from the 11th incubation day until pre-hatching stages (ca. day 60-72). The duration of these contractions averaged 2.02+/-0.27 min. The frequency ranged from 2 to 6 per 10 min and averaged 4.61+/-0.57 per 10 min. A tendency of frequency to increase toward the end of embryogenesis was observed. Lowering the temperature from 28 to 20 degrees C significantly decreased the frequency of amnion contractions to 2.85+/-0.91 per 10 min. The isolated snake amnion retained its capacity for spontaneous contraction. Noradrenaline inhibited, acetylcholine stimulated and serotonin did not affect the rhythmic activity of the isolated snake amnion. Similar effects were found when these agents were applied into the snake amniotic cavity. In the chick, yolk sac rhythmic contractions were recorded from the fifth until the 12th incubation days. The duration of these contractions ranged from 15 to 60 s, their frequency averaged 11.8+/-3.18 per 10 min and depended on temperature. The low temperature threshold was approximately 30 degrees C. After surgical removal of the amnion and embryo, the yolk sac continued contracting inside the egg. The yolk sac rhythmic contractions likely participate in the space movement of the embryo inside the egg during embryogenesis.

Differential phosphodiesterase activity contributes to restrictive endothelial barrier function during angiogenesis

Angiogenic endothelial hyperpermeability is abruptly diminished between days 4.5 and 5.0 of the 18-day lifespan of the chick chorioallantoic membrane. Here, we evaluated phosphodiesterase (PDE) activity during the differentiation of barrier function. At day 4.5, rolipram-mediated inhibition of cAMP-specific PDE IV reduced FITC-dextran extravasation. Moreover, inhibition of PDE III by HL 725, but not PDE I by 8-IBMX, decreased the temporal angiogenic endothelial hyperpermeability. Reduced FITC-dextran was also observed at day 4.5 after application of KT 5823, a selective inhibitor of cGMP-specific protein kinase G (PKG), LY 83583, an inhibitor of soluble guanylate cyclase, or LNMMA, an inhibitor of nitric oxide synthase. At day 5.0, Rp-cAMPS-mediated inhibition of cAMP-specific protein kinase A (PKA) diminished barrier function and interstitial accumulation of FITC-dextran was increased. In all cases, the mean widths of interendothelial separation remained uniform. Together, the results support the concept that differentiation of restrictive angiogenic endothelial barrier function in vivo includes inactivation of PDE III and PDE IV with consequent up-regulation of cAMP/PKA signaling and down-regulation of the cGMP/PKG pathway.

Role of motility in embryonic development I: Embryo movements and amnion contractions in the chick and the influence of illumination

This study provides a quantitative analysis of the active movements of the chick embryo and of the contractions of the amnion over the entire developmental period of 21 days. Four types of embryo movements are distinguished. The motor activity of the embryo shows two characteristic peaks, with maximum contraction frequencies on the 12th and on the 16th day. In contrast, the amnion activity is higher at earlier stages and decreases as the body activity increases. The amnion activity is largely independent of the body activity. Illumination has a strong influence on embryo movements. It is shown that increases of light intensity affect the patterns of activity of both the embryo and the amnion. While the effect of light on the embryo can be interpreted as being transmitted via the optic system, the mechanism of the amniotic response is unclear. The results suggest that the amnion itself may be sensitive to light. J. Exp. Zool. (Mol. Dev. Evol.) 291:186-194, 2001.

Light irradiation increases embryotoxicity of photodynamic therapy sensitizers (5-aminolevulinic acid and protoporphyrin IX) in chick embryos

Photodynamic therapy (PDT) of malignant processes is based on the ability of a photosensitizer to first, accumulate in malignant (immature) tissue and second, to be destroyed following light irradiation. Because of the similarity between malignant and embryonic immature tissues, we investigated the deleterious effect of the PDT procedure on day 4 chick embryos in ovo. We compared experimentally the photodynamic effect (light-toxic) and the side effect (dark-toxic) of the clinically attractive photosensitizers 5-aminolevulinic acid (ALA) and protoporphyrin IX (PP IX). The dark and light embryotoxicity (i.e. lethality plus teratogenicity) was determined after intra-amniotic injection of one of a range of dose of each compound. Under dark conditions, PP IX exhibited embryotoxicity at a dose of 10 microg/embryo; however ALA did not exhibit embryotoxicity even at the highest dose (300 microg/embryo). Light irradiation of embryos following injection induced strong embryotoxic effects of both substances even at dark-ineffective doses.

Extraembryonic motor activity during the embryogenesis of higher vertebrates

Extraembryonic rhythmic motor activity in higher vertebrates, along with the intrinsic motor activity of the embryo, is important for the normal development of the embryo. This can have different natures in different classes of amniotes (i.e., motor activities of the amnion, yolk sac, and uterus), but these have similar functional importance. This activity changes reproducibly during the process of embryogenesis, providing the optimum conditions for normal embryo development. During embryogenesis, a system for controlling extraembryonic rhythmic motor activity is also formed. There is a trend for the regulation of this activity to become more complex in mammals as compared with birds. Reptiles have received little study from this point of view. In addition to regular changes in extraembryonic rhythmic motor activity during embryogenesis which depend on the developmental stage of the embryo, motor activity can also change in response to changes in a number of environmental factors (for example, temperature and the gas composition of the air). This demonstrates the possible involvement of embryo-associated extraembryonic motor activity in adapting the embryo to changing environmental conditions and maintaining homeostasis for the development of the embryo itself.

Simultaneous measures of contraction and intracellular calcium in single, cultured smooth muscle cells

Simple methods are presented for quantitating contraction and intracellular calcium simultaneously in single, cultured smooth muscle cells. These methods are the first to demonstrate that reliable velocities of cell shortening can be measured in cultured smooth muscle cells and that cells in vitro exhibit shortening velocities comparable to those measured in the fastest phasic muscles in situ. Temporal relationships between changes in intracellular calcium and shortening within single cells were determined with a resolution of 100 ms and were consistent with measures in more "classical" preparations. Intracellular calcium rose quickly and transiently 10-fold above the basal level of 80-90 nM in response to the muscarinic agonist, carbachol. Shortening of the cells occurred 200 ms after intracellular calcium began to rise. The sensitivity and reliability of these methods allowed the effects of different stimuli to be easily resolved. The present report demonstrates that genuine contractility need not be ignored in cultured smooth muscle cells and that the temporal relations between shortening and intracellular calcium mobilization can be quantitatively assessed in controlled in vitro environments.

Modulation of angiogenic endothelial permselectivity by the cAMP pathway

The chorioallantoic membrane (CAM) of the chick embryo provides an accessible model of normal angiogenesis in vivo. Previously, we reported a rapid reduction in CAM microvascular permeability to macromolecules between Days 4.5 and 5.0 of the normal 21-day gestation (V. Rizzo et al., 1995, Microvasc. Res. 49, 49-63). Here, we tested the hypothesis that activation of the cAMP signaling pathway at Day 4.5 would acutely increase permselectivity prior to normal differentiation of CAM endothelial barrier properties at Day 5.0. Changes in interstitial optical intensities due to extravasation of a graded series of FITC-dextrans (20, 40, and 70 kDa) were evaluated by computer-assisted image analysis, and endothelial ultrastructure was monitored by transmission electron microscopy. The cAMP analogue 8-bromo-cAMP (10(-4) and 10(-3) M) and forskolin (10(-5) and 10(-4) M), an adenylyl cyclase activator, acutely decreased permeability of the graded FITC-dextran series in a dose-dependent fashion. In addition, the nonspecific phosphodiesterase inhibitor IBMX (10(-4) M) served to increase basal restriction of the 20- and 40-kDa tracers. Further, Rp-cAMPS (10(-4) M), a cAMP antagonist for cAMP-dependent protein kinase, abolished the effects of both 8-bromo-cAMP (10(-3) M) and forskolin (10(-4) M) on FITC-Dextran 40 restriction. In all cases, ultrastructural presentation of both the endothelial cell junctions and the vesicles remained unchanged. The present results are consistent with the concept that exogenous cAMP activation decreased permeability of the angiogenic CAM endothelium at Day 4.5 without concomitant ultrastructural changes in the transendothelial macromolecular exchange pathways. Whether endogenous activity of cAMP contributes to normal differentiation of CAM endothelial barrier properties between Days 4.5 and 5.0 remains to be tested.

The presence of cortisol receptors in the human amnion

Cytosol extracts of human amnion tissue contained high affinity binding of cortisol (Ka=2.48+/-1.06 x 10(9) M(-1); n = 30) and low capacity binding of cortisol (Nmax=279+/-15.5 fmol mg(-1) protein). Kinetic studies of cortisol binding resulted in a similar value of Ka to that obtained by Scatchard analysis. Nuclear extracts of amnion tissue contained high affinity binding of cortisol (Ka=5.8+/-1.91 x 10(7) M[-1]) and low binding capacity (Nmax=91.4+/-21.4 fmol mg(-1) protein). Ka values were an order of magnitude higher in cytosol than in blood serum when amnion and blood were obtained from the same individuals. Differences in competitive ligand binding, especially dexamethasone, were observed between the amnion receptor and transcortin in serum. Gel permeation chromatography gave only one peak at 320 kDa for amnion receptor and only one peak at 48 kDa for transcortin from serum. When amnion tissue was incubated with or without cortisol, cytosol receptor activity was significantly lower in cortisol treated tissue than in control. The nuclear extracted receptor activity was significantly higher in cortisol treated tissue than control. The Ka values from cortisol treated tissue were significantly lower from control. Together the data support the presence of a specific cortisol receptor in the human amnion that is different from transcortin.

Superfluous neurotransmitters?

In recent years, studies have suggested that the complexity of eukaryotic gene regulation, with its recurring and interacting motifs of cis and trans-acting regulatory elements, might result in superfluous gene expression. This conclusion is supported by a variety of experimental results that suggest that non-adaptive gene expression might be common. However, with few exceptions, the practical ramifications of unnecessary gene expression for cell biologists have not been addressed directly; this is particularly true for peptidergic neurophysiology, a field that might be plagued more than most with the consequences of this phenomenon. In this article, Chauncey W. Bowers discusses the superfluous expression of neuropeptides in the nervous system in the context of gene regulation extrapolated from studies in Drosophila.

Extracellular matrix regulates smooth muscle responses to substance P

Little is known about the extracellular factors that determine a cell's responsiveness to neurotransmitters. This is a particularly important issue for pharmacologically diverse cell types such as neurons and smooth muscle. This report demonstrates that the contractile responses of amniotic smooth muscle to a specific neuropeptide, substance P, is controlled by a molecule(s) intimately associated with the extracellular basement membrane. This molecule(s) normally represses the expression of substance P responsiveness in this tissue. When the amniotic smooth muscle is separated from the basement membrane by dissociation, normally unresponsive cells exhibit a progressive increase in responsiveness to substance P, beginning within the first 24 hr in culture. The induction of substance P responses was completely inhibited when the cells were plated onto isolated amniotic basement membrane rather than onto polyornithine or collagen I. Similar changes in the responsiveness to another agonist, histamine, did not occur. The data demonstrate that extracellular matrix exerts a major instructive influence in determining the responsiveness of avian amniotic smooth muscle to specific ligands. We suggest that similar regulatory mechanisms may operate in other tissues.

Distribution and coexistence of urotensin I and urotensin II peptides in the cerebral ganglia of Aplysia californica

Urotensin I (UI) and urotensin II (UII) were demonstrated in the cerebral ganglia of Aplysia californica by applying immunocytochemical and radioimmunoassay procedures. Sequential analysis of adjacent sections of the cerebral ganglia of Aplysia demonstrated that the UI-immunoreactive (UI-IR) neurons of the F cluster of the cerebral ganglia also contained UII immunoreactivity (UII-IR). Both UI-IR and UII-IR were also observed in a cuff-like arrangement of fibers surrounding the proximal portion of the supralabial nerve, as well as in a few fibers in the anterior tentacular nerves. The UI-IR perikarya of the cerebral ganglia appeared to project to the entire CNS of Aplysia, but the UII-IR fibers appeared only in the neuropile and commissure of the cerebral ganglia. The UI-IR staining was abolished by previous immunoabsorption of the UI antiserum with sucker (Catastomus commersoni) UI, but not with ovine corticotropin-releasing factor (CRF), rat/human CRF, or goby (Gillichthys mirabilis) UII. Immunostaining with UII antiserum was quenched by goby UII, but not by sucker UII-A, UII-B, UII-A(6-12), or carp (Cyprinus carpio) UII-alpha and UII-gamma. The UII staining was not abolished by UI or somatostatin. The F cluster was not stained when a somatostatin antiserum was applied. Radioimmunoassay of dilutions of cerebral ganglia extract, using UII antiserum, revealed a parallel displacement curve to synthetic goby UII.(ABSTRACT TRUNCATED AT 250 WORDS)