The uptake and metabolism of 5-hydroxytryptamine by tissue slices of the cestode Hymenolepis diminuta

Serotonin Signalling in Flatworms: An Immunocytochemical Localisation of 5-HT7 Type of Serotonin Receptors in Opisthorchis felineus and Hymenolepis diminuta

The study is dedicated to the investigation of serotonin (5-hydroxytryptamine, 5-HT) and 5-HT₇ type serotonin receptor of localisation in larvae of two parasitic flatworms Opisthorchis felineus (Rivolta, 1884) Blanchard, 1895 and Hymenolepis diminuta Rudolphi, 1819, performed using the immunocytochemical method and confocal laser scanning microscopy (CLSM). Using whole mount preparations and specific antibodies, a microscopic analysis of the spatial distribution of 5-HT₇-immunoreactivity(-IR) was revealed in worm tissue. In metacercariae of O. felineus 5-HT₇-IR was observed in the main nerve cords and in the head commissure connecting the head ganglia. The presence of 5-HT₇-IR was also found in several structures located on the oral sucker. 5-HT₇-IR was evident in the round glandular cells scattered throughout the larva body. In cysticercoids of H. diminuta immunostaining to 5-HT₇ was found in flame cells of the excretory system. Weak staining to 5-HT₇ was observed along the longitudinal and transverse muscle fibres comprising the body wall and musculature of suckers, in thin longitudinal nerve cords and a connective commissure of the central nervous system. Available publications on serotonin action in flatworms and serotonin receptors identification were reviewed. Own results and the published data indicate that the muscular structures of flatworms are deeply supplied by 5-HT₇-IR elements. It suggests that the 5-HT₇ type receptor can mediate the serotonin action in the investigated species and is an important component of the flatworm motor control system. The study of the neurochemical basis of parasitic flatworms can play an important role in the solution of fundamental problems in early development of the nervous system and the evolution of neuronal signalling components.

Validation of internal controls for gene expression analysis in the intestine of rats infected with Hymenolepis diminuta

The non-invasive parasitic cestode Hymenolepis diminuta induces hypertrophy, hyperplasia and other changes in cell activity in the intestine of rats which are indicated in the expression of mRNA. We have investigated various house-keeping genes (GAPDH, beta-actin, 18S and HPRT) and other internal controls (total RNA/unit biomass, total RNA/unit length of intestine) to validate gene expression in the rat intestine after cestode infection and drug-induced neuromodulation. Variation in GAPDH, beta-actin, 18S and HPRT expression was observed in rat jejunal tissue according to treatment. Total RNA/unit length of intestine was found to be the most suitable internal control for normalizing target gene mRNA expression in both infected and/or drug-induced rat intestine. This normalization method may be applied to studies of gene expression levels in intestinal tissue where hypertrophy, hyperplasia, rapid growth and cell differentiation generally occur.

Classical transmitters and their receptors in flatworms

The flatworm nervous system employs a wide repertoire of neuroactive substances, including small chemical messengers, the so called classical transmitters, and several types of neuropeptides. A large body of research accumulated over four decades has provided a wealth of information on the tissue localization and effects of these substances, their biochemistry and, recently, their molecular modes of action in all major classes of flatworms. This evidence will be reviewed, with particular emphasis on the small (classical) transmitters and the receptors that mediate their effects. One of the themes that will emerge from this discussion is that classical transmitters regulate core activities such as movement, metabolism and transport, and thus are essential for survival of the organism. In addition, the evidence shows that flatworms have multiple neurotransmitter receptors, many with unusual pharmacological features, which make them particularly attractive as drug targets. Understanding the molecular basis of these distinctive properties, and developing new, more specific receptor agonists and antagonists will undoubtedly become a major challenge in future research.

Expulsion of the gastrointestinal cestode, Hymenolepis diminuta by tolerant rats: evidence for mediation by a Th2 type immune enhanced goblet cell hyperplasia, increased mucin production and secretion

The processes underlying expulsion of Hymenolepis diminuta in rats are not known. Expression levels of mRNAs of several cytokines revealed a Th2 response that differed between worm infection levels. IL-4 protein levels decreased while IL-13 levels increased in a 50-worm infection by 30 dpi; the converse was seen with a five-worm infection. A negative correlation was found between IL-4 or IL-13 mRNA expression and worm biomass, between IL-13 protein levels and worm number or worm biomass, and between IL-4 protein levels and worm biomass in 50-worm infections. A negative correlation between IL-4 mRNA or protein expression and worm biomass was observed with five-worm infections. A strong correlation between Muc2 mRNA expression and decreased worm number or biomass in a 50-worm infection was observed. Muc2 protein, goblet cell numbers and mucin decreased in a 50-worm infection by 20 days post-infection. These changes were not seen with five-worm infections where worms are not expelled. The data show that rats infected with 50 H. diminuta mount a Th2 response leading to high levels of IL-13, increased goblet cell numbers and increased mucin2 production and release. The mucus traps the worms, which are progressively expelled from the small intestine.

Localization of a sodium-dependent high-affinity serotonin transporter and recruitment of exogenous serotonin by the cestode Hymenolepis diminuta: an autoradiographic and immunohistochemical study

Uptake of serotonin by tissues of intact and hemitransected Hymenolepis diminuta was studied by autoradiography and immunohistochemistry. Hemitransected worms were incubated in balanced saline containing 10 µM [3H]serotonin and washed extensively. The density of silver grains over the serotonin-immunoreactive longitudinal nerve cords and commissural rings, male reproductive system, tissues surrounding the genital pouch, and deep longitudinal muscles was significantly greater than that over the parenchyma. The presence of serotonin in spermatozoa suggested a role for this amine in spermatozoon activity. In contrast, uptake of 10 µM [3H]serotonin in sodium-free saline was significantly reduced compared with that in balanced saline in all tissues examined except the parenchyma. Analysis of the data revealed that the sodium-dependent high-affinity serotonin transport system is localized primarily in the serotonergic-like neurons of H. diminuta, which suggests possible recycling of neuronally released serotonin. Following incubation of intact worms in vitro for 12 h in 5 µM [3H]serotonin, the density of silver grains was significantly higher over the serotonin-immunoreactive nerves, elements of the male reproductive system, tissues surrounding the genital pouch, and deep longitudinal muscles than over the parenchyma. These results demonstrate recruitment of exogenous serotonin by intact H. diminuta and suggest sequestration and concentration by the serotonin-immunoreactive neurons via the sodium-dependent high-affinity transporter. These data further suggest that although H. diminuta can synthesize serotonin, it may obtain serotonin from the host. Nonetheless, the amount of serotonin recruited by H. diminuta from the host in vivo compared with that which they synthesize is not known.

Transport of exogenous 5-hydroxytryptamine across the outer plasma membrane of the syncytial tegument ofHymenolepis diminutais by simple diffusion

The uptake of 5-hydroxytryptamine (5HT) from a 10 μM solution of exogenous [3H]5HT into the tegument of Hymenolepis diminuta was linear for the first 20 min of incubation. The rate of transport was 0.04 ± 0.01 pmol∙mg wet mass−1∙min−1, and there were no significant differences in the rate of uptake by the anterior, middle, and posterior regions of the body. The initial uptake was not Na+-dependent, was not saturable at up to 100 μM, was not highly temperature-dependent (Q10~ 1.2), and displayed activation energy of 11.8 kJ∙mol−1. Furthermore, uptake was not inhibited by p-chloromercuriphenyl sulphonic acid, imipramine, amiloride, or 5HT analogues, which collectively support a non-carrier-mediated uptake mechanism. Washing of the tissues with 10 mM 5HT after incubation in 10 μM [3H]5HT displaced less than 10% of the remaining [3H]5HT associated with the tissues, and little radioactivity was extracted by washing in acetone or chloroform. The uptake of [3H]5HT, however, was pH-dependent, the rate of uptake being closely correlated with the proportion of unprotonated 5HT. Only a small portion of the transported [3H]5HT was metabolized to a product associated with 5-hydroxyindoleacetic acid, and metabolism was significantly inhibited by the monoamine oxidase inhibitors iproniazid phosphate, deprenyl, and clorgyline. The present study showed that small amounts of [3H]5HT were taken up by H. diminuta by simple diffusion, little of the [3H]5HT was adsorbed to the surface of the worms or dissolved in the lipid phase of the plasma membrane, and some of the [3H]5HT taken up was metabolized by a monoamine oxidase-like enzyme.

An ontogenetic study of the cholinergic and serotoninergic nervous systems in Trilocularia acanthiaevulgaris (Cestoda, Tetraphyllidea)

The localisation and distribution of the cholinergic and serotoninergic components of the nervous system in the plerocercoid, adult and free proglottis stages of the tetraphyllidean tapeworm Trilocularia acanthiavulgaris were determined by enzyme histochemical and immunocytochemical techniques. The central nerve ring (CNR) in the scolex contains two lateral ganglia and gives rise to five pairs of longitudinal nerve cords (LNC's; three lateral, two median). The nerve cords run posteriorly throughout the bodies of the plerocercoid and adult worms and the free proglottis. Nerves from the CNR and accessory lateral LNC's pass to the bothridia, where they give rise to extensive nerve plexuses. As the individual proglottides develop along the strobila, a small nerve ring forms at the anterior end of each proglottis; within the nerve ring, distinct bilateral ganglia develop prior to the release of the proglottis. All ten LNC's are present in the free proglottis. The genital atrium and cirrus sac are innervated by cholinergic and serotoninergic elements. The cholinergic nervous system predominates in the CNS within the scolex, whereas there is a larger population of 5-HT-immunoreactive nerve cells associated with the LNC's and segmental ganglia along the strobila and within the free proglottis.

Praziquantel impairs the ability of exogenous serotonin to stimulate carbohydrate metabolism in intact Schistosoma mansoni

Praziquantel (PZQ) (Droncit, Biltricide) at 10 microM completely abolishes the stimulatory effect of serotonin on glucose uptake and lactate excretion of Schistosoma mansoni. Fluoxetine (FXT) exerts similar effects on the serotonin-induced stimulation of glucose uptake and lactate excretion, however, at 100-fold higher concentrations. In comparison with PZQ, which is inhibitory at 10 microM, FXT and other amphiphilic cationic drugs (amitriptyline, propranolol, imipramine, chlorpromazine) inhibit glucose uptake or lactate excretion in schistosomes at 1 mM; the strongest inhibitor is FXT. Glycogen breakdown is maximally stimulated by PZQ in the absence or presence of serotonin. There is an additive effect of 50 microM chlorpromazine or FXT and 0.01 to 0.1 microM PZQ on glycogen breakdown. The rate of sodium-sensitive or insensitive serotonin uptake in Schistosoma mansoni is reduced by 10 microM PZQ by about 40%, as is the sodium-sensitive excretion of serotonin. The results show that PZQ interferes with the ability of serotonin to stimulate carbohydrate metabolism. The possibility that PZQ may act through an effect on tegumental integrity is discussed.

Chlorpromazine, other amphiphilic cationic drugs and praziquantel: effects on carbohydrate metabolism of Schistosoma mansoni

The effects of the amphiphilic cationic drugs chlorpromazine, imipramine, amitriptyline, propranolol and fluoxetine and praziquantel were investigated on glucose uptake and lactate excretion of Schistosoma mansoni. While praziquantel enhances glucose uptake and lactate excretion at a concentration of 10(-7) M, all the other drugs exert the same effects at concentrations above 10(-5) M. Generally, a constant molar ratio of 1:2 is found between glucose uptake and lactate excretion. Above 10(-5) M, praziquantel inhibits glucose uptake and lactate excretion. Similar effects are caused by amphiphilic cationic drugs at 10(-3) M. Pre-incubation of S. mansoni with 10(-5) M praziquantel completely abolish the stimulation of carbohydrate metabolism by serotonin and by 5 X 10(-5) M chlorpromazine or fluoxetine. The action of praziquantel on S. mansoni resembles that of amphiphilic cationic drugs with respect to their influence on carbohydrate metabolism. This, together with data obtained from electrophysiological and electron microscopic studies, provides evidence for the hypothesis that praziquantel exerts its effect by interacting with membrane structures.