Release of exogenously-supplied and endogenous serotonin from tissue slices of Hymenolepis diminuta

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.

Immunology and biochemistry of Hymenolepis diminuta

This review is an account of modern research into the immunology and biochemistry of the rat tapeworm, Hymenolepis diminuta. The first half of the review is devoted to the immunological responses of the host to the parasite. It describes the specific responses that occur when the host is exposed to a primary infection, and the changes that occur when further infections are superimposed on the primary one. The aquisition of immunity to the tapeworm and its persistence in the absence of the infection are also discussed, as well as the non-specific responses of the host to the parasite. The second half of the review is concerned with biochemistry, summarizing the early biochemical work that has been carried out on the tapeworm and describing the metabolic pathways now thought to be characteristic of the parasite. What little information that exists on intermediary metabolism in eggs and larvae is summarized here. Much of this section is concerned with the role of mitochondria in H. diminuta, especially the control of the critical branchpoint (PK/PEPCK), which partitions carbon into either the cytosol or the mitochondrion. The role of 5-hydroxytryptamine in controlling both worm behaviour and metabolism is discussed, followed by a brief look at some other effectors that may prove in the future to have great significance in regulating the parasite. Finally, there is a detailed consideration of strain variation within H. diminuta and of the impact on the tapeworm of components of the immune system, formerly described as the 'crowding effect'. The review concludes with a brief discussion of evolutionary aspects of the rat-tapeworm relationship and a comprehensive bibliography.

The stimulatory effect of L-glutamate and related agents on inositol 1,4,5-trisphosphate production in the cestode Hymenolepis diminuta

The effects of L-glutamate, acetylcholine, and serotonin (5HT) were examined on generation of inositol 1,4,5-triphosphate [Ins(1,4,5)P3], in membrane preparations of the cestode Hymenolepis diminuta. Only L-glutamate and acetylcholine stimulated a significant elevation in Ins(1,4,5)P3. The response to L-glutamate was stereospecific; D-glutamate or L-aspartate were not as potent. A role for G-protein(s) was supported by the observations that sodium fluoride stimulated Ins(1,4,5)P3 generation, and the L-glutamate response was potentiated by GTP and GTP-S and was suppressed by GDPS. However, studies with pertussis and cholera toxins indicated that the putative G-protein(s) was not pertussis or cholera toxin sensitive. The pharmacological profile of the L-glutamate response was examined partially. Trans-ACPD was a very effective agonist at 10(-5)M. While 10(-3)M L-glutamate, NMDA, and AMPA significantly elevated Ins(1,4,5)P3 levels, quisqualate and kainate did not. The elevation of Ins(1,4,5)P3 levels by L-glutamate and NMDA was antagonized by the specific glutamatergic antagonists AP-5, AP-7, CNQX, and CPP. While the response to ACPD was antagonized by AP5, CPP and CPG, CNQX was without effect. Collectively, the data support the hypothesis that in the cestode H. diminuta, L-glutamate activation of a metabotropic (ACPD) and/or ionotropic-like AMPA/NMDA receptor subtypes proceeds via a G protein(s) to enhance phospholipase C activity, ultimately resulting in the elevation of Ins(1,4,5)P3 levels in the tissues.

Immunocytochemical localization of serotonin (5-HT) in the nervous system of the hydatid organism, Echinococcus granulosus (Cestoda, Cyclophyllidea)

The localization and distribution of the serotoninergic components of the nervous system in the hydatid organism, Echinococcus granulosus, were determined by immunocytochemical techniques in conjunction with confocal scanning laser microscopy (CSLM). The distribution of serotonin immunoreactivity (IR) paralleled that previously described for cholinesterase activity, although it was more widespread. Nerve cell bodies and nerve fibres immunoreactive for 5-HT were present throughout the central nervous system (CNS), occurring in the paired lateral, posterior lateral and rostellar ganglia, their connecting commissures and nerve rings in the scolex and in the ten longitudinal nerve cords that run posteriorly throughout the body of the worm. A large population of nerve cell bodies was associated with the lateral nerve cords. In the peripheral nervous system (PNS), immunoreactive nerve fibres occurred in well-developed nerve plexuses innervating the somatic musculature and the musculature of the rostellum and suckers. The genital atrium and associated reproductive ducts were richly innervated with serotoninergic nerve cell bodies and nerve fibres.

Serotonin stimulates protein phosphorylation in the cestode Hymenolepis diminuta

1. Serotonin stimulated the incorporation of 32P from [gamma-32P] ATP into crude membrane preparations (P2) of Hymenolepis diminuta in a dose-dependent manner (EC50 of approximately 0.79 microM). 2. This response was seen with several serotonin agonists, and was inhibited by several serotonin antagonists, which were identical to the previously described activation and inhibition of serotonin-sensitive adenylate cyclase. 3. Cyclic AMP produced a dose-dependent stimulation of 32P incorporation into the P2 fraction, with an EC50 of approximately 2.51 microM. 4. The targets for the serotonin stimulated incorporation of 32P were found to be in trypsin-labile proteins with Mr's of 134,000, 110,000, 82,000, 80,000 and 31,000.