Obstetric outcomes of IVF trichorionic triamniotic triplets which are spontaneously or electively reduced to twins.

PURPOSE: To assess the obstetric outcome of IVF triplets which are spontaneously or electively reduced to twins. METHODS: Retrospective study of trichorionic triplets (TT) and dichorionic twins (DT) conceived with IVF. RESULTS: Compared to TT without reduction, TT with spontaneous reduction (SR) (OR: 5.6, 95% CI: 1.6-19.9) or elective reduction (ER) (OR: 14.0, 95% CI: 3.92-50.02) to twins were significantly more likely to be delivered at ≥34 weeks. Compared to DT likelihood of delivery ≥34 weeks was similar for SR and ER. Compared to TT without reduction, the risk of pregnancy loss before 24 weeks was not increased with SR or ER. Compared to DT the risk of pregnancy loss before 24 weeks was not significantly increased for SR or ER. CONCLUSION: Obstetric outcome of IVF triplets with SR is better than ongoing triplets and is similar to that of ER of TT and DT.

Fixed behaviours and migration in parasitic flatworms.

This paper considers how fixed behaviours may play a role in post-larval migrations of Entobdella soleae. A general argument is that a shift away from the paradigm of orientation is required to elucidate the mechanisms that parasites use to navigate on the surface of their hosts. Some migrations may rely on fixed behaviours (genetically programmed stereotyped behaviours) that often evolve under predictable environmental conditions with reliable signals. In turbulent and stochastic free-living environments, homeostatic hosts present very predictable topological substrates and physico-chemical characteristics to their parasites. Over the course of evolution on these predictable host substrates, adaptive behaviours in the parasites can become fixed. Examples of endoparasite migration behaviour, particularly that of the common liver fluke, Fasciola hepatica, will be used to develop an approach based on the perceptual worlds of migrating parasites. An important conclusion is that multi-disciplinary approaches, firmly rooted in an understanding of each parasite's natural history, are requisite to successful interpretation of migration behaviours on the host.

Mesenchyme cells in Fasciola hepatica (platyhelminthes): primitive glia?

Mesenchyme cells and their processes are found in the cerebral ganglia of the parasitic flatworm, Fasciola hepatica. The mesenchyme cell processes are found in two specialized associations within the ganglion: (i) as lamellae-like multilayer sheaths encircling the cerebral ganglia and separating it from the surrounding parenchyma cells, and (ii) invaginated into the surface of large diameter ('giant') nerve processes to form trophospongium-like relationships. Based on morphological criteria, these mesenchyme cells resemble general invertebrate glial cells suggesting that the mesenchyme cells of these flatworms may represent the earliest glial-like cell.

FMRFamide-related peptides in Hymenolepis diminuta: immunohistochemistry and radioimmunoassay.

The localization of FMRFamide-related peptide (FaRP) immunoreactivity was determined during different stages of development of the rat tapeworm Hymenolepis diminuta. In the adult worm (14 days old), FaRP immunostaining was most intense in the scolex and concentrated in the central nervous system (cerebral ganglia and transverse commissures) and around the lips of the suckers. In the strobila, medial and lateral longitudinal nerve cords (LNCs) and ladder-like connecting commissures were the only tissue stained. Immunoreactivity in the medial LNCs of the adult tapeworms extended only to and included proglottides containing developing testis and seminal receptacle but disappeared in proglottides in which primordial ovaries were first detected. Radioimmunoassay confirmed that FaRPs were concentrated in the scolex/neck region of the adult worm (3.9 +/- 1.5 pmol mg protein-1), whereas the lowest concentrations (0.2 +/- 0.19 pmol mg protein-1) were recovered from the regions of the strobila containing shelled eggs. The pattern of FaRP immunoreactivity observed in 5- and 7-day-old worms was similar to that seen in adult worms, but in 2- and 3-day-old worms the pattern of immunoreactivity observed in the cerebral ganglia, transverse commissures, and LNCs differed significantly as compared with that seen in older worms. These results indicate differential utilization and/or roles for FaRPs during development and suggest both central and sensory roles in this tapeworm.

Optimal habitat selection by helminths within the host environment.

Helminth parasites of vertebrates usually select very specific regions or habitats in their hosts, and this is often preceded by a tortuous migration through various host organs. However, the proximate mechanisms of migration and habitat selection have remained enigmatic despite considerable effort by parasitologists. In this paper a new approach to studying helminth behaviour in the host is proposed. The core idea is that behaviour strategies must be considered from the perspective of the parasites and their perceptions of their environment. A guiding principle is that the environmental features to which an animal responds, and the actions which are required for responding to the environment, form a fundamental unit of behaviour. Thus, we can deduce an animal's behavioural strategy from the details of its response to environmental signals and from its sensory capabilities. The evidence presented suggests that helminth behaviours in the host often occur as fixed (or modal) action patterns which are usually seen in response to constant, or predictable environmental features. Thus, a working hypothesis is that the mechanisms of physiological and biochemical homeostasis within the host provide an extremely predictable environment for the parasite. Under these conditions, a parasite needs to perceive only small subsets of the total information available from the environment to respond appropriately. Studies on sensory and nervous systems of these organisms are critical to understanding parasite perception, but there are formidable technical obstacles that prevent easy access to parasite nervous systems. Therefore, a multidisciplinary approach, using ideas from parasitology, ecology, evolutionary biology and neuroethology, is considered requisite for reconstructing the parasites' behaviour strategies. It is suggested that future directions should pursue integration of studies on sensory physiology with the behavioural ecology of these organisms.

Abdominal postural motor responses initiated by the muscle receptor organ in lobster depend upon centrally generated motor activity.

1. Stretch stimulation of the abdominal muscle receptor organ of the lobster Homarus americanus initiated spike discharge of its tonic sensory neuron (SR1). This sensory response evoked a series of tonic postural reflex responses in the motor neurons that innervate the superficial extensor and flexor muscles of the abdominal postural system. The type of motor response depended on whether a flexion or extension pattern of spontaneous activity was being generated by the postural efferents. Spontaneous shifts between these centrally generated motor activities completely changed the SR1-evoked reflex responses. 2. During spontaneous centrally initiated flexion activity, tonic SR1 neuron discharge elicited an assistance response that included excitation of a medium-sized flexor excitor (f3) and the peripheral extensor inhibitor (e5), and inhibition of at least one extensor excitor. Neither the other flexor excitors nor the peripheral flexor inhibitor (f5) were affected by SR1 excitation. 3. During spontaneous centrally initiated extension activity, SR1 activity elicited a response that included excitation of the extensor excitors and the flexor peripheral inhibitor (f5) only, f3 and e5 spontaneous activities were unchanged. This response was a resistance reflex, since SR1 discharge normally resulted from an imposed abdominal flexion. 4. The SR1-initiated control of postural motor activity in lobster differs from previously published results in the crayfish Procambarus clarkii.

Ontogenetic development of the brain of the platyhelminth Fasciola hepatica.

During ontogenetic development in the definitive host, the cerebral ganglia of the parasitic flatworm Fasciola hepatica lose their cell rind integrity and develop specialized nerve processes. The organization and cytological features of the central nervous system were examined during three developmental stages in the parasitic life cycle of F. hepatica to determine when the changes occur. The cerebral ganglion cell bodies of migrating juvenile worms (5 days post-infection) are organized into a one-cell-thick rind that surrounds a central neuropile composed of small unmyelinated nerve processes (less than 3 microns in diameter). In young, sexually-immature adult worms (30 days post-infection), the cell bodies of the ganglia are no longer organized into a complete or tight cell rind around the ganglia. In addition, large diameter ('giant') unmyelinated nerve processes (greater than 12 microns) are found in the neuropile area. These giant nerve processes are also found in the transverse commissure and the longitudinal nerve cords. In mature adult worms (4-6 months post-infection), the rind of nerve cell bodies has completely disappeared and cell bodies are scattered around and within the neuropile. More than half of the volume of the mature adult neuropile is composed of giant nerve processes. The three developmental stages of the parasite that were used in this study differ significantly in their sizes, behaviours and microhabitat locations in the host. The results suggest that the organizational and morphological changes in the ganglia reflect selective adaptations to changes in the parasitic microenvironment.

Gastrointestinal hormones: environmental cues for Fasciola hepatica?

The effects of pharmacological concentrations of several gastrointestinal hormones on the rate of sucker activity and the frequency and the amplitude of spontaneous longitudinal muscle contractions have been examined in adult Fasciola hepatica. Caerulein and serum decrease the rate of oral sucker activity; motilin decreases and CCK-PZ increases ventral sucker activity when compared to controls. Caerulein, serum and motilin significantly inhibit the frequency of contractions while bile, caerulein and motilin decrease the amplitude of contractions. These results suggest that F. hepatica can recognize and respond to certain gastrointestinal hormones and there may be adaptive value in these behavioural responses.

Histochemical localization of acetylcholinesterase in the cerebral ganglia of Fasciola hepatica, a parasitic flatworm.

Acetylcholinesterase activity was found in the cell bodies and extracellularly in the neuropile of the cerebral ganglia of the adult trematode parasite, Fasciola hepatica. Within neuronal cell bodies of the cerebral ganglion, acetylcholinesterase reaction product was found in the endoplasmic reticulum, in the cisternae of the Golgi apparatus, and in secretory vesicles near the inner (releasing face) cisternae. Acetylcholinesterase reaction product was not seen intracellularly within any nerve processes. The reaction product was found around the somatic cell membranes and in the extracellular space between closely apposed nerve processes in the neuropile. Acetylcholinesterase reaction product was associated with synaptic endings that contained clear spheroidal synaptic vesicles, and the reaction product was localized at the site of synaptic contact between the zone of apposition of the pre- and postsynaptic terminals. This intracellular and extracellular distribution of the enzyme is consistent with its function as the degrading enzyme in cholinergic transmission.

Neurocytology of the cerebral ganglion of Fasciola hepatica (Platyhelminthes).

An ultrastructural study of the organization and fine structure of the nervous system of the parasitic flatworm Fasciola hepatica was undertaken. The brain consists of paired cerebral ganglia, located just posterior to the oral sucker, that are connected by a transverse commissure which crosses over the dorsal surface of the pharynx. The cell bodies of the cerebral ganglia are not organized into a clearly defined rind around the neuropile but are loosely scattered around and within the neuropile area. The neuropile consists of two morphologically distinct types of unmyelinated nerve processes. The small nerve processes, with smooth cell membranes, are less than 2 micron in diameter, whereas the "giant" processes are greater than 12 micron in diameter and have extensively invaginated cell membranes. Giant processes make up the bulk of the nerve fibers in the transverse commissure and longitudinal nerve cords. Four morphological types of vesicles are present in the small processes; small clear vesicles (which were found associated with synapses), spheroidal and ellipsoidal dense vesicles, and dense-core vesicles. Two types of synapses are found in the neuropile: simple synapses characterized by pre- and postsynaptic membrane densities, clusters of small clear vesicles, and a clear synaptic cleft; and wedge-shaped synapses or divergent diads each having one presynaptic process synapsing onto two postsynaptic processes. Synaptic contacts were observed only between small processes; no synapses were observed on the cell bodies or on giant processes.

Immunohistochemical and electrochemical detection of serotonin in the nervous system of Fasciola hepatica, a parasitic flatworm.

The head region of the trematode parasite Fasciola hepatica contains 3.47 +/- 0.42 pmol/mg wet wt. of serotonin as measured by high-performance liquid chromatography coupled to electrochemical detection. The head region includes the cerebral ganglia, the transverse commissure and associated nervous tissue that innervates the musculature of the oral sucker, pharynx and body wall. Tissue from the tail, which contains little nervous innervation, has approximately 20 times less serotonin (0.18 +/- 0.01 pmol/mg wet wt.). Immunohistochemistry was used to identify serotonin-like immunoreactive cells. Bipolar and multipolar cell bodies in the cerebral ganglia show serotonin-like immunoreactivity. Also evident are serotonin-like immunoreactive processes in the neuropile and in the transverse commissure that connects the ganglia, and immunoreactive peripheral bipolar cell bodies innervating the musculature of the pharynx and body wall. The cell bodies containing serotonin are organized in bilateral symmetry with homologous cell bodies and processes represented in each ganglion and on both sides of the pharynx.

Effects of cholinergic drugs on longitudinal muscle contractions of Fasciola hepatica.

Acetylcholine, cholinergic agonists and acetylcholinesterase inhibitors significantly decrease the amplitude and frequency of spontaneous longitudinal muscle contractions in Fasciola hepatica. In order of their effects on the inhibition of muscle contractions, the cholinergic agonists can be ranked as nicotine greater than carbachol greater than acetylcholine. High calcium ion concentration also causes a significant inhibition of contractions. Atropine, a cholinergic antagonist that acts on muscarinic receptors, significantly increases the amplitude and frequency of spontaneous contractions and completely reverses the effects of cholinomimetic drugs, including nicotine. In adult F. hepatica, the levels of acetylcholine and its precursor choline are 3.14 +/- 0.55 and 13.75 +/- 3.72 pmol/mg wet weight, respectively. The activities of choline acetyltransferase, specific acetylcholinesterase and the nonspecific cholinesterase are 1.25 +/- 0.19, 238.0 +/- 13.0, and 83.0 +/- 33.0 nmol/hr/mg protein, respectively.