Stress response in the freshwater snail Planorbarius corneus (L.) (Gastropoda, Pulmonata): interaction between CRF, ACTH, and biogenic amines

Determining the effectiveness of using dermal swabs to evaluate the stress physiology of laboratory cephalopods: A preliminary investigation

To better comprehend the physiology of cephalopods, we used a minimal invasive technique of skin mucus swabs to measure immunoreactive corticosteroids in three cephalopod species commonly kept in captivity and promoted as new model organisms: Euprymna berryi, Sepia bandensis, and Octopus chierchiae. We compared results between sexes and age classes and then evaluated their stress responses during acclimation to a new habitat. To better understand glucocorticoid production, we conducted an adrenocorticotropic hormone, using Cosyntropin (an adrenocorticotropin (ACTH) analogue) challenge with a saline control and swabbed their mantles at 15-minute intervals for 2 h. Results showed cortisol was higher for younger individuals. Additionally, cortisol and corticosterone concentrations decreased by 2-fold after 2 to 4 days of acclimation to a new habitat. We were able to successfully measure 2-fold increase in immunoreactive corticosteroids which reacted with cortisol and corticosterone assays for all the species following ACTH injection, although not all individuals responded similarly. With further investigation, this technique can increase our understanding and management of cephalopods in captivity.

RNAi-mediated knock-down of the dopamine beta-hydroxylase gene changes growth of razor clams

Dopamine beta-hydroxylase (DβH) plays an essential role in the synthesis of catecholamines (CA) in neuroendocrine networks. In the razor clam, Sinonovacula constricta a novel gene for DβH (ScDβH-α) was identified that belongs to the copper type II ascorbate-dependent monooxygenase family. Expression analysis revealed ScDβH-α gene transcripts were abundant in the liver and expressed throughout development. Knock-down of ScDβH-α in adult clams using siRNA caused a reduction in the growth rate compared to control clams. Reduced growth was associated with strong down-regulation of gene transcripts for the growth-related factors, platelet derived growth factors A (PDGF-A) (P < 0.001) 24 h after ScDβH-α knock-down, vascular endothelial growth factor (VEGF1) (P < 0.001) and platelet derived growth factor B (PDGF-B-2) (P < 0.001) 24 h and 48 h after ScDβH-α knock-down and transforming growth factor beta (TGF-β1) (P < 0.001) 48 h and 72 h after ScDβH-α knock-down. Taken together the results suggest that the novel ScDβH-α gene through its role in CA synthesis is involved in growth regulation in the razor clam and possibly other bivalves.

Independent and simultaneous effect of crustacean hyperglycemic hormone and dopamine on the hemocyte intracellular signaling pathways and immune responses in white shrimp Litopenaeus vannamei

Immune responses and intracellular signaling pathways were examined after hemolymph of Litopenaeus vannamei being incubated in Crustacean hyperglycemic hormone (CHH), dopamine (DA) and DA antagonist (Y). The results showed that the effect CHH and CHH + DA + Y on viability of hemocytes were no significant changes compared to the control group. However, in DA, DA + Y and CHH + DA groups, the viability of hemocytes decreased significantly. The phagocytic activity and the antibacterial activity of CHH group were increased significantly within 12h. Whereas the CHH + DA, DA were significantly lower than the control. PO in haemolymph was up-regulated after CHH and DA incubation. The proPO has the opposite change in all groups. In addition, DA + Y, CHH + DA + Y has a similar trend with the DA and CHH respectively. Furthermore, a significant increase of cAMP, CaM and cGMP were found in treatment groups except for the CaM concentration of the CHH group and the cGMP concentration of DA group. There is no significant change observed in the CHH group about CaM concentration. Whereas the cGMP of DA group decreased within 12h. The results suggest that DA could depress the immune responses by cAMP-, CaM-pathways. However, the CHH is on the contrary, which transduced the signals from cAMP, cGMP to PKA, PKC and PKG to enhance the immune response parameters.

Rotational stress influences sensitized, but not habituated, exploratory behaviors in the woodlouse, Porcellio scaber

Terrestrial isopods (or woodlice), like the members of the other arthropod taxa, have a sophisticated nervous system that makes them sensitive to specific environmental factors. They can search for survival-related opportunities (e.g., approaching food sources or avoiding sunny areas). Two experiments examined how rotational stress could influence the propensity of common woodlice, Porcellio scaber to exhibit survival-related behaviors such as traveling and rearing up in a hostile environment. Experiment 1 assessed the behaviors of stressed and nonstressed woodlice exposed to a familiar or a novel environment without rewards. Experiment 2 assessed the effects of stress in woodlice given a free choice between a familiar and a novel environment without rewards. In the nonstressed individuals, the results showed a decrease in locomotor activity (habituation) and an increase in the time spent rearing up (sensitization) on the arena's walls over time. In the stressed individuals, repeated rotation had a detrimental effect on the time spent rearing up, but locomotion was decreased only in the stressed individuals that were not preexposed to the test environment beforehand. In addition, immobilization periods-as a plausible indicator of stress-were longer in the absence of preexposure. It is suggested that preexposure had some antistress protective effects on habituated but not on sensitized, exploratory behaviors in woodlice.

Immune-Neuroendocrine Interactions: Evolution, Ecology, and Susceptibility to Illness

The integration between immune and neuroendocrine systems is crucial for maintaining homeostasis from invertebrates to humans. In the first, the phagocytic cell, i.e., the immunocyte, is the main actor, while in the latter, the principle player is the lymphocyte. Immunocytes are characterized by the presence of pro-opiomelanocortin (POMC) peptides, CRH, and other molecules that display a significant similarity to their mammalian counterparts regarding their functions, as both are mainly involved in fundamental functions such as immune (chemotaxis, phagocytosis, cytotoxicity, etc.) and neuroendocrine (stress) responses. Furthermore, the immune-neuroendocrine system provides vital answers to ecological and immunological demands in terms of economy and efficiency. Finally, susceptibility to disease emerges as the result of a continuous dynamic interaction between the world within and the world outside. New fields such as ecological immunology study the susceptibility to pathogens in an evolutionary perspective while the field of neuro-endocrine-immunology studies the susceptibility from a more immediate perspective.

Age-dependent effects of predation risk on reproductive success in a freshwater snail

Reproductive performance is often age-dependent, showing patterns of improvement and/or senescence as well as trade-offs with other traits throughout the lifespan. High levels of extrinsic mortality (e.g., from predators) have been shown to sometimes, but not always, select for accelerated actuarial senescence in nature and in the lab. Here, we explore the inductive (i.e., plastic) effects of predation risk (i.e., nonlethal exposure to chemical cues from predators) on the reproductive success of freshwater snails (Physa acuta). Snails were reared either in the presence or absence of chemical cues from predatory crayfish and mated early in life or late in life (a 2 × 2 factorial design); we measured egg hatching and early post-hatching survival of their offspring. Both age and predation risk reduced reproductive success, illustrating that predation risk can have a cross-generational effect on the early survival of juveniles. Further, the decline in reproductive success was over three times faster under predation risk compared to the no-predator treatment, an effect that stemmed from a disproportionate, negative effect of predation risk on the post-hatching survival instead of hatching rate. We discuss our results in terms of a hypothesized consequence of elevated stress hormone levels.

In hemocytes from Mytilus galloprovincialis Lmk., treatment with corticotropin or growth factors conditions catecholamine release

The cells in charge of the innate immune response in the sea mussel Mytilus galloprovincialis Lmk. are the hemocytes, which have the capacity to release catecholamines when subjected to stressing conditions. Hemocytes were kept in culture before stimulation. That is, their behaviour was not studied immediately after extraction from the mollusc, as happens in most studies. This avoids the interference and variability caused by the conditions in which mussels may be when collected. This work describes the great variability found in the pattern of catecholamine release when the hemocytes are stimulated with either corticotropins or growth factors. Dopamine, adrenaline and noradrenaline release differs with each of the inducers assayed, with stimulation time and with the season of hemocyte collection. One of the results presented is particularly remarkable; such is the great amount of adrenaline and noradrenaline released to the medium when the hemocytes obtained in summer are stimulated with transforming growth factor-beta1 (TGF-beta1) for 60 min.

In vitro effects of LPS, IL-2, PDGF and CRF on haemocytes of Mytilus galloprovincialis Lmk

The cells in charge of the innate immune response in the marine mussel Mytilus galloprovincialis Lmk. are the haemocytes. These cells respond in different ways to agents such as lipopolysaccharide (LPS), interleukin-2 (IL-2), platelet-derived growth factor (PDGF) and corticotropin releasing factor (CRF). After stimulation of the haemocytes, the expression of molecules reactive with monoclonal antibodies raised to the alpha chain of the IL-2 receptor, present in their membrane, differed depending on the agent used. The same happened with regard to the levels of dopamine, adrenaline and noradrenaline released to the medium by the haemocytes. It should also be noted that no catecholamine release was detected and the level of expression of IL-2Ralpha showed no significant variation in cultured cells that had not been treated with inducers. These facts would indicate that most haemocytes were in the same starting condition at the moment that the stimulation was performed. Therefore, cultured haemocytes can be a highly reliable model in the study of the innate immune system.

Comparative distribution of urocortin- and CRF-like immunoreactivities in the nervous system of the earthworm Lumbricus terrestris

Corticotropin-releasing factor (CRF) and urocortin (Ucn) are both members of the CRF neuropeptide family. The distribution of Ucn- and CRF-like immunoreactive (ir) structures in the central nervous system of several vertebrate species has been studied, but little is known about that in non-vertebrates. We used a highly specific polyclonal antibody against rat Ucn and CRF to determine and compare the distribution of Ucn- and CRF-like immunoreactivity in the earthworm nervous system. Several Ucn- and CRF-like ir perikarya were described in the cerebral ganglion, subesophageal and ventral cord ganglia. The majority of Ucn-like ir cells were found in the ventral ganglia, whereas CRF-like ir cells were most abundant in the cerebral ganglion. Scattered Ucn- and CRF-like ir varicose fiber terminals were seen in all areas of the earthworm central nervous system. Ucn-like ir cell bodies and fiber terminals were also demonstrated in the pharyngeal wall. No co-localization of Ucn- and CRF-like ir nervous structures were observed. This study provided morphological evidence that Ucn- and CRF-like neurosecretory products exist in the earthworm central nervous system. Furthermore, both the distribution and morphology of Ucn- and CRF-like ir structures were distinct, therefore, it can be hypothesized that these neuropeptides exert different neurendocrine functions in the earthworm nervous system.

Invertebrate Humoral Factors: Cytokines as Mediators of Cell Survival

The presence and the different functional aspects of cytokine-related molecules in invertebrates are described. Cytokine-like factors affect immune functions, such as cell motility, chemotaxis, phagocytosis and cytotoxicity. In particular, cell migration shows a species-specific effect for IL-1alpha and TNF-alpha and a dose-correlated effect for IL-8, PDGF-AB and TGF-beta1. Apart from some exceptions, the phagocytic effect increases significantly at all the concentrations tested and with all the species used. PDGF-AB, TGF-beta1 and IL-8 provoke conformational changes in mollusk immunocytes, involving the signaling transduction pathways of phosphatidylinositol and cAMP. PDGF-AB and TGF-beta1 partially inhibit the induced programmed cell death in an insect cell line, and the survival effect is mediated by the activation of phosphatidylinositol 3-kinase, PKA and PKC. The exogenous administration of these growth factors in an invertebrate wound repair model showed that they are able to control the wound environment and promote the repair process by accelerating the coordinated activities involved. Moreover, IL-1alpha, IL-2 and TNF-alpha are able to induce nitric oxide synthase. PDGF-AB and TGF-beta1 provoke an increase in neutral endopeptidase-24.11 (NEP)-like activity in membrane preparations from mollusk immunocytes, while NEP deactivates the PDGF-AB- and TGF-beta1-induced cell shape changes. Cytokines are also involved in invertebrate stress response in a manner extremely similar to that in vertebrates. Several studies suggest the existence on the mollusk immunocyte membrane of an ancestral receptor capable of binding both IL-2 and CRH. Furthermore, the competition found between CRH and a large number of cytokines supports the idea that invertebrate cytokine receptors show a certain degree of promiscuity. The multiple functions of cytokines detected in invertebrates underline another characteristic of mammalian cytokines, i.e. their great pleiotropicity. Altogether, the studies on the function of the invertebrate humoral factors show a close overlapping with those found in vertebrates, and the hypothesized missing correlation between invertebrate and vertebrate cytokine genes that is emerging from the limited molecular biology data present in literature might represent a very peculiar strategy followed by Nature in the evolution of cytokines.

Air exposure and functionality of Chamelea gallina haemocytes: effects on haematocrit, adhesion, phagocytosis and enzyme contents

The Venus clam Chamelea gallina is fairly common along the western coasts of the Adriatic and is subjected to intense fishing. Since over the last 20 years extensive hypoxic and anoxic conditions have repeatedly damaged this natural resource, we decided to study the effects of anoxic stress on the functionality of clam haemocytes and the consequences on immune responses. Clams, exposed to air, close their valves and tissues become anoxic and metabolism processes switch to anaerobiosis. In these conditions, a significant decrease in the haematocrit value and in the percentage of acid phosphatase-positive haemocytes was observed, while the number of cells with beta-glucuronidase significantly increased after day 1. The above indices generally returned to control values when clams were re-immersed in seawater after 1 day of treatment. Clams exposed to air for 2 days and then re-immersed, attempted to recover in the subsequent 3 days. Animals had fully recovered on day 4. Three-day-exposed clams did not recover. Phagocytic and adhesion indices decreased significantly after the first day of air exposure. The change in frequency of three types of circulating cells (spreading, round, apoptotic) was also monitored.

Inflammation Causes a Long-Term Hyperexcitability in the Nociceptive Sensory Neurons of Aplysia

Nerve injury, tissue damage, and inflammation all cause hyperalgesia. A factor contributing to this increased sensitivity is a long-term (>24 hr) hyperexcitability (LTH) in the sensory neurons that mediate the responses. Using the cluster of nociceptive sensory neurons in Aplysia californica as a model, we are examining how inflammation induces LTH. A general inflammatory response was induced by inserting a gauze pad into the animal. Within 4 days, the gauze is enmeshed in an amorphous material that contains hemocytes, which comprise a cellular immune system. Concurrently, LTH appears in both ipsilateral and contralateral sensory neurons. The LTH is manifest as increased action potential discharge to a normalized stimulus. Immunocytochemistry revealed that hemocytes have antigens recognized by antibodies to TGFβ1, IL-6, and 5HT. When a localized inflammation was elicited on a nerve, hemocytes containing the TGFβ1 antigen were present near axons within the nerve and those containing the IL-6 were on the surface. Western blots of hemocytes, or of gauze that had induced a foreign body response, contained a 28-kD polypeptide recognized by the anti-TGFβ1 antibody. Exposure of the nervous system to recombinant human TGFβ1 elicited increased firing of the nociceptive neurons and a decrease in threshold. The TGFβ1 also caused an activation of protein kinase C (PKC) in axons but did not affect a kinase that is activated in axons after injury. Our findings, in conjunction with previous results, indicate that a TGFβ1-homolog can modulate the activity of neurons that respond to noxious stimuli. This system could also contribute to interactions between the immune and nervous systems via regulation of PKC.

Regulation of the hypothalamic-pituitary-adrenal axis by cytokines: actions and mechanisms of action

Glucocorticoids are hormone products of the adrenal gland, which have long been recognized to have a profound impact on immunologic processes. The communication between immune and neuroendocrine systems is, however, bidirectional. The endocrine and immune systems share a common "chemical language," with both systems possessing ligands and receptors of "classical" hormones and immunoregulatory mediators. Studies in the early to mid 1980s demonstrated that monocyte-derived or recombinant interleukin-1 (IL-1) causes secretion of hormones of the hypothalamic-pituitary-adrenal (HPA) axis, establishing that immunoregulators, known as cytokines, play a pivotal role in this bidirectional communication between the immune and neuroendocrine systems. The subsequent 10-15 years have witnessed demonstrations that numerous members of several cytokine families increase the secretory activity of the HPA axis. Because this neuroendocrine action of cytokines is mediated primarily at the level of the central nervous system, studies investigating the mechanisms of HPA activation produced by cytokines take on a more broad significance, with findings relevant to the more fundamental question of how cytokines signal the brain. This article reviews published findings that have documented which cytokines have been shown to influence hormone secretion from the HPA axis, determined under what physiological/pathophysiological circumstances endogenous cytokines regulate HPA axis activity, established the possible sites of cytokine action on HPA axis hormone secretion, and identified the potential neuroanatomic and pharmacological mechanisms by which cytokines signal the neuroendocrine hypothalamus.

A new theory on the common evolutionary origin of natural immunity, inflammation and stress response: the invertebrate phagocytic immunocyte as an eye-witness

Data in favor of the hypothesis of the common evolutionary origin of natural immunity inflammation and stress response are presented. These phenomena seem to be mediated by a common pool of molecules (POMC-derived peptides, cytokines, biogenic amines, glucocorticoids, and nitric oxide). Macrophages are able to release all the above mentioned molecules. They play a primary role in defence mechanisms. Thus, we argue that this cell can be considered the eye-witness of the common evolutionary origin of the immune and neuroendocrine systems.

The CRH-ACTH-biogenic amine axis in invertebrate immunocytes activated by PDGF and TGF-beta

In immunocytes from the mollusc Mytilus galloprovincialis, the major pathway followed by platelet-derived growth factor (PDGF)-AB and transforming growth factor (TGF)-beta1 in provoking the release of norepinephrine, epinephrine and dopamine into cell-free hemolymph (serum) is mediated by a corticotropin-releasing hormone-adrenocorticotropin hormone (CRH-ACTH) biogenic amine axis. This axis not only annulled the inhibiting properties of PDGF-AB, it even reversed the latter's effect, while the inducing effect of TGF-beta1 was amplified. These findings show that non-classical immune-neuroendocrine molecules, such as PDGF-AB and TGF-beta1, are involved in building stress response, using the same conserved mechanisms present from invertebrates to vertebrates.

Presence of immunoreactive corticotropin-releasing hormone and cortisol molecules in invertebrate haemocytes and lower and higher vertebrate thymus

Corticotropin-releasing hormone- and cortisol-like molecules are present in the haemocytes of different molluscan species and in the epithelial cells, interdigitating cells and macrophages - but not in the lymphocytes - of fish, frog, chicken and rat thymus. Taking into account the fact that other pro-opiomelanocortin-derived peptides, such as adrenocorticotropin hormone, are present in the haemocytes and thymus of the same species, these results complete the list of stress mediators present in molluscan haemocytes and further support the hypothesis that, although the prototype stress response we have demonstrated in invertebrates is concentrated in a single cell, i.e. the haemocyte, it is similar to the response seen in vertebrates. Moreover, the data presented here are compatible with the hypothesis that an evolutionary, conserved stress response can occur locally with a single organ, e.g. the thymus, in which all the main mediators of this biological response, such as corticotropin-releasing hormone, adrenocorticotropin hormone and glucocorticoids, are present. The implications of these findings for the physiology of thymus and stress response may be far reaching.

Corticotropin-releasing factor in antinociception and inflammation

Corticotropin-releasing factor (CRF) plays a major role at the level of the hypothalamus and pituitary to control the body's response mechanisms to stressful stimuli. The recent discovery of CRF outside the central nervous system suggests that CRF may well play a similar role in peripheral tissues, most likely in a paracrine manner. While its effects in many other peripheral tissues is not known yet, CRF and its receptors are upregulated in inflammatory pain states pointing to a key role under these circumstances. Indeed, locally expressed CRF seems to act on CRF receptors on immune cells which have migrated into the area of the inflamed tissue, and induce the release of opioid peptides synthesized within these immune cells. These opioids subsequently act on peripheral opioid receptors located on peripheral sensory nerves to inhibit the transmission of painful stimuli. CRF may also affect the inflammatory response; however, these data are still controversial. The peripheral paracrine effects of CRF may be similar to those of hypothalamic CRF, i.e., to counterbalance local stressful events, such as inflammation and pain, so that they do not threaten the homeostasis of the body. Interestingly, CRF-like peptides have been identified not only in mammalians, but also in species such as the frog (Stenzel-Poore et al., 1992, Mol. Endocrinol. 6, 1716) and the teleost fish (Okawara et al., 1988, Proc. Natl. Acad. Sci. USA 85, 8439) indicating that this is a peptide that has been conserved over a long period (200 million years) across species (Lederis et al., 1990, Prog. Clin. Biol. Res. 342, 467) and that the release of ACTH-like peptides by peptides of the CRF family may represent an ancestral type of stress response (Ottaviani et al., 1992, Gen. Comp. Endocrinol. 87, 354; Tran et al., 1990, Gen. Comp. Endocrinol. 78, 351).

Pro-opiomelanocortin-derived peptides, cytokines, and nitric oxide in immune responses and stress: an evolutionary approach

In vertebrates, including man, the study of stress has contributed substantially to unravelling the complex relationship between immune-neuroendocrine interactions and the systems involved. On the basis of data on the presence and distribution of the main actors (POMC products, cytokines, biogenic amines, and steroid hormones) in different species and taxa from invertebrates to vertebrates, we argue that these responses have been deeply connected and interrelated since the beginning of life. Moreover, the study of nitric oxide suggests that the inflammatory reaction is located precisely between the immune and stress responses, sharing the same fundamental evolutionary roots. The major argument in favor of this hypothesis is that the immune, stress, and inflammation responses appear to be mediated by a common pool of molecules that have been conserved throughout evolution and that from a network of adaptive mechanisms. One cell type, the macrophage, appears to emerge as that most capable of supporting this network critical for survival; it was probably a major target of selective pressure. All these data fit the unitarian hypothesis we propose, by which evolution favors what has been conserved, rather than what has changed, as far as both molecules and functions are concerned.

Induction of ACTH- and TNF-alpha-like molecules in the hemocytes of Calliphora vomitoria (Insecta, Diptera)

Three basic cell types are described in the hemolymph of newly enclosed adult Calliphora vomitoria: prohemocytes, plasmatocytes, and granular cells. In addition, anucleate cellular fragments with some inclusions are observed. Cell division is found only in the prohemocytes. Plasmatocytes and granular cells are capable of in vitro bacterial phagocytosis and take part in capsule formation. Adrenocorticotropin hormone (ACTH)-like molecules are found in both cell types. The staining of the plasmatocytes is related to the functional activation of the cells. Indeed, positive staining is only observed during capsule formation, suggesting an induction of ACTH expression. The behaviour of tumor necrosis factor (TNF)-alpha-like molecules is similar. In conclusion, these data provide further support for the close, evolutionary relationship between the immune and the neuroendocrine systems.

Immunocytochemical evidence of PDGF- and TGF-beta-like molecules in invertebrate and vertebrate immunocytes: an evolutionary approach

Immunoreactive platelet-derived growth factor-AB and transforming growth factor-beta 1 were demonstrated in invertebrate and vertebrate immunocytes by an immunocytochemical procedure. These factors are only present in phagocytic cells among invertebrate immunocytes, whereas in vertebrate immunocytes they are found in monocytes, granulocytes, lymphocytes, thrombocytes and platelets. These results, in agreement with previous reports, represent further evidence in favour of the hypothesis that Nature has followed a conservative strategy in using a common pool of signal molecules that have been highly conserved throughout evolution.

Biogenic monoamines in the freshwater snail, Biomphalaria glabrata: influence of infection by the human blood fluke, Schistosoma mansoni

The biogenic monoamines, serotonin (5-HT), dopamine (DA) and L-dopa were measured using high performance liquid chromatography with electrochemical detection (HPLC-ED) in the extracts of the central nervous system (CNS) and plasma of uninfected freshwater snails, Biomphalaria glabrata, and in snails at 7, 14, 21 and 28 days postexposure (PE) to the miracidia of the human blood fluke, Schistosoma mansoni. Relative to age-matched uninfected snails, a general depression of biogenic amine levels was observed in the plasma (cell-free haemolymph) and the CNS of infected snails, especially during the latter phase of the prepatency period. Significant decreases were first observed in the CNS of infected snails beginning at Day 14 PE for DA and 5-HT and Day 21 PE for L-dopa. Parasite-exposed snails also exhibited an early and persistent suppression of plasma 5-HT concentrations, starting at 7 days PE and continuing throughout the infection test period. In order to determine the effect of 5-HT on reproduction and, thereby, establish a possible relationship between the observed parasite-induced reduction in 5-HT levels and parasitic castration, the effect of exogenous 5-HT on individual infected and uninfected B. glabrata was investigated. Repeated treatment with 10 microM 5-HT promoted both ovulation and oviposition in B. glabrata. Snails treated with 5-HT consistently layed more eggs than did sham-treated controls. Infected snails that were treated with 5-HT exhibited similar egg-laying rates as those of both serotonin-treated and untreated, uninfected snail groups, thus reversing the castrating effects of larval infection. These findings suggest that 5-HT acts as a stimulant for egg production in B. glabrata, and that parasitic castration may be due, at least in part, to larval-induced suppression of 5-HT in the snail's CNS and plasma during the course of infection with S. mansoni.

Modulation of catecholamine storage and release by the pituitary-interrenal axis in the rainbow trout, Oncorhynchus mykiss

This study examined the effects of pituitary-interrenal hormones on catecholamine storage and release in the rainbow trout Oncorhynchus mykiss. An extract of trout pituitary elicited the release of adrenaline, but not noradrenaline, using an in situ perfusion preparation. A variety of doses of adrenocorticotropic hormone (2-2000 mU) caused the release of both catecholamines in situ which was unaffected by pre-treatment with the ganglion blocker, hexamethonium, or the serotonergic receptor antagonist, methysergide, but was abolished in calcium-free media. Intra-arterial injections of adrenocorticotrophic hormone in vivo caused an elevation of plasma adrenaline but not noradrenaline levels. Injections of cortisol in situ did not elicit catecholamine release. Trout given an intraperitoneal implant of cortisol (50 mg.kg-1 body weight) had significantly higher plasma cortisol concentrations when compared to controls after 7 days of implantation. Increases in the levels of stored catecholamines were observed in various regions of the kidney and posterior cardinal vein following 3 and 7 days of cortisol treatment. The ability of the chromaffin cells to release catecholamines in response to cholinergic stimulation was assessed in situ after 7 days of treatment. Basal (non-stimulated) adrenaline outflowing perfusate levels were greater in the cortisol-treated fish. Cortisol treatment increased the responsiveness of the catecholamine release process to low doses of the cholinoceptor agonist carbachol. Three or 7 days of cortisol treatment did not alter the in vitro activity of the enzyme phenylethanolamine-N-methyl transferase. The results of this study demonstrate that interactions within the pituitary-adrenal axis can influence both catecholamine storage and release in the rainbow trout.

How schistosomes profit from the stress responses they elicit in their hosts

Results obtained with the model Trichobilharzia ocellata-Lymnaea stagnalis have confirmed the hypothesis that the physiological effects evoked by schistosomes in their snail host--castration and giant growth--are brought about by them interfering with the neuroendocrine systems (NES) regulating the physiological processes concerned. As soon as differentiating cercariae are present in the daughter sporocysts a factor can be detected in the haemolymph of the snail host, called schistosomin, which acts both at the central and the peripheral parts of the NES involved in regulation of reproduction and growth. Schistosomin appears to be a host-derived factor, which is probably released by cells of the internal defence system, the haemocytes, and by connective tissue cells, the telo-glial cells. It meets the criteria of having a cytokine-like function although its molecular structure does not show sequence homology with any of the vertebrate-type cytokines identified to date. Its cytokine nature explains why schistosomin can interfere with different neuroendocrine regulatory systems both at the central and peripheral--target--level, namely after binding to its own receptor. Schistosomin is probably not only responsible for the effects exerted by the parasite on female reproduction but also for those on male reproduction and on growth so that energy and space become available for the continuous production of cercariae. The nature of the humoral cercarial factor, which induces schistosomin release, is as yet unknown. Based on its hydrophobic character and on the fact that it can pass through the wall of the daughter sporocyst, it is supposed to be a diffusible molecule or a protonephridial excretion product. It does not seem to be a vertebrate-type steroid, an ecdysteroid or an eicosanoid. Results obtained in vitro have indicated that schistosomin might have a suppressive effect on haemocyte activity. Plasma from snails 5-6 weeks post-exposure showed a tendency to inhibit phagocytic activity of haemocytes from non-infected snails, that is preparatory to the escape and migration of cercariae. Once shedding has started this effect of schistosomin is overrruled by a strong activation of haemocyte activity coinciding with the tissue damage that the cercariae cause in the host. The cercariae escape from being attacked by masking their surface coat with host molecules. As the physiological effects caused by schistosomes resemble those observed during stress in mammals, experiments were carried out to find out whether schistosomin is also released in non-parasitized snails during stress resulting in an inhibiting effect on reproduction.(ABSTRACT TRUNCATED AT 400 WORDS)

Immunoendocrine reshaping with age

The interaction of the endocrine, immune, and nervous systems in modulating each other's activity opens the track for a new way of looking to the effects ongoing on each of the three systems. This new approach finds it bases in old times, since evolution shows how we missed for many years a relation between the three systems that was clearly manifested in lower species. In this chapter, the effects of aging on the immune, endocrine and nervous systems are proposed as the consequence of the influences of each system on the others.

Microglia in invertebrate ganglia

The results of this study lend strong support to the concept of the existence in insects and molluscs of a distinctive class of neuroglial cells comparable to vertebrate microglia. The evidence presented is as valid as that used in reference to the separate status of vertebrate microglia--i.e., the demonstration of a close structural and functional relationship of these cells with cells of the immune system. As in vertebrates, the excision of ganglia from three invertebrate species (the molluscs Planorbarius corneus and Mytilus edulis and the insect Leucophaea maderae) and their maintenance in incubation media led to an exodus of small cells and their accumulation in the culture dish. During this process, they underwent conformational changes from stellate to rounded, and then to more or less ameboid, comparable to those indicative of the process of activation in the animals' immunocytes. Functional characteristics which these translocated microglia-like cells share with immunocytes are motility, phagocytotic activity, and adherence to the culture dish. Furthermore, the two cells have certain biochemical features in common--e.g., the presence of certain cytokines and (at least in Planorbarius) that of corticotropin. An additional phenomenon of particular interest for the classification of microglial elements is their response to morphine. At 10(-6) M, this drug decreases not only the number of cells emerging from the excised ganglia but also the degree of their transformation to the "active" ameboid form. This dose-dependent and naloxone-sensitive effect of morphine on microglial cells parallels that on activated immunocytes of the same species. Corresponding results demonstrating an inhibitory effect of morphine on mobilized microglial cells of the frog Rana pipiens indicate that this relationship between the two cell types under consideration also exists in vertebrates. Binding and displacement experiments with membrane homogenates of microglial cells as well as immunocytes of Mytilus have shown that the effects of morphine on both cell types are mediated by the same special opiate receptor (mu 3).

Relationship between corticotropin-releasing factor and interleukin-2: evolutionary evidence

The addition of corticotropin-releasing factor (CRF) to molluscan hemocytes induces the release of biogenic amines (norepinephrine, epinephrine, dopamine), a phenomenon we have considered as an ancestral type of stress response [(1992) Gen. Comp. Endocrinol. 87, 354-360]. A similar but less significant response was observed following the addition of interleukin-2 (IL-2). Pre-incubation of hemocytes with IL-2 or anti-IL-2 monoclonal antibody significantly reduced or completely eliminated the CRF-induced release of biogenic amines. Further direct evidence of competition between CRF and IL-2 was revealed by immunocytochemical and cytofluorimetric analysis. The data are compatible with the presence of a unique (ancestral?) receptor on molluscan hemocytes, capable of binding both CRF and IL-2, two key molecules of the neuroendocrine and immune system, respectively.

Differential modulation of invertebrate hemocyte motility by CRF, ACTH, and its fragments

Various reports have shown that invertebrate hemocytes are responsive to mammalian neuropeptides and cytokines. In the present study, we demonstrate that corticotropin-releasing factor (CRF) and adrenocorticotropin (ACTH) fragments (1-24), (1-4), (4-9), (1-13), (1-17), and (11-24) significantly stimulate molluscan hemocyte migration, and the whole sequence (1-39) and the fragment (4-11) have an inhibitory effect. Differences between species were found with respect to the response to individual fragments. Additionally, the (4-11) fragment was able to antagonize some of the stimulatory fragments (4-9) as well as tumor necrosis factor (TNF-alpha)-induced chemotaxis. Our results suggest that invertebrate hemocytes are able to respond to CRF and ACTH fragments that in turn provide further evidence of the complexity of intercellular signaling within the immune system in relatively primitive animals. Thus, auto- and neuroimmunoregulatory activities in mammals must have had an earlier beginning than previously believed.

The presence of immunoreactive vertebrate bioactive peptide substances in hemocytes of the freshwater snail Viviparus ater (Gastropoda, Prosobranchia)

1. Using an immunocytochemical procedure a wide range of immunoreactive vertebrate bioactive peptides (BAPs) has been found in hemocytes of Viviparus ater: bombesin, calcitonin, CCK-8, CCK-39, GH, glucagon, insulin, oxytocin, neurotensin, secretin, serotonin, somatostatin, substance P, vasopressin, and VIP. 2. No immunostaining was observed for antigastrin and antithyroglobulin antibodies. 3. The presence of BAP-like molecules in hemocytes suggests a correlation between hemocyte and APUD cells and is evidence of a relationship between the neuroendocrine and the immune systems.