Reevaluation of the effects of growth hormone and prolactin on anuran tadpole growth and development

The effects of ovine prolactin (oPRL) and ovine (o) or porcine (p) growth hormone (GH) on growth of anuran larvae were compared. In grass frog tadpoles (Rana pipiens), injections of oPRL (10 micrograms/gm/day) increased tail growth and body weight but had no effect on hindlimb growth or development. The same dose of oGH did not significantly affect the tail or body weight but it caused a striking increase in limb length and development. In bullfrog tadpoles (Rana catesbeiana) given an ergot drug (bromocriptine) to induce metamorphic changes, significant tail regression and loss of body weight occurred. Treatment with oPRL reversed these effects but had no effect on hindlimb growth or development. The pGH was much less effective than the oPRL in blocking tail regression and body weight loss but it significantly increased limb growth and development. These results show that GH and PRL can differentially regulate growth and development of structures in larval anurans. The effects of GH on limb growth and development can not be explained simply by a thyrotropic effect.     

Effect of vasotocin on locomotor activity in bullfrogs varies with developmental stage and sex

Although neurohypophysial peptides are present in many regions of the developing and adult bullfrog (Rana catesbeiana) brain, the function of these peptides remains unclear. To investigate possible behavioral actions, we examined locomotor activity following peptide injection in bullfrogs at various developmental stages. An intraperitoneal (ip) injection of arginine vasotocin (AVT) in tadpoles (stages V, X, or XVII) produced an immediate and dose-dependent inhibition of locomotor activity. On the other hand, AVT stimulated activity when administered ip to juvenile or adult female bullfrogs, but did not influence activity in juvenile or adult males. The minimum effective dose of AVT, when injected directly into the brain of tadpoles, was 100-fold less than that observed when injected ip, suggesting a central nervous system site of action for this peptide. A vasopressin receptor antagonist (d(CH2)5[Tyr(Me)2]AVP administered ip or icv) significantly increased locomotor activity in tadpoles, compared to controls. Oxytocin, vasopressin, and AVP4-9 inhibited activity in tadpoles while mesotocin, des Gly(NH2)AVP, and pressinoic acid had no significant effect. Injection of PGF2 alpha also significantly decreased activity levels in tadpoles. However, pretreatment of tadpoles with indomethacin, a prostaglandin synthesis inhibitor, did not prevent the behavioral effects of AVT, suggesting that prostaglandin synthesis is not required for this response. In summary, AVT influenced locomotor activity in bullfrog tadpoles and female frogs. This effect shifted during development from an inhibitory action in tadpoles to a stimulatory effect in metamorphosed female frogs. The effect of AVT on juvenile and adult frog locomotion was sexually dimorphic, as this peptide altered female behavior but not male behavior.     

Growth hormone and prolactin actions on osmoregulation and energy metabolism of gilthead sea bream (Sparus auratus)

The gilthead sea bream (Sparus auratus) is an euryhaline fish where prolactin (PRL) and growth hormone (GH) play a role in the adaptation to different environmental salinities. To find out the role of these pituitary hormones in osmoregulation and energy metabolism, fish were implanted with slow release implants of ovine GH (oGH, 5 microg g(-1) body mass) or ovine prolactin (oPRL, 5 microg g(-1) body mass), and sampled 7 days after the start of the treatment. GH increased branchial Na(+),K(+)-ATPase activity and decreased sodium levels in line with its predicted hypoosmoregulatory action. GH had metabolic effects as indicated by lowered plasma protein and lactate levels, while glucose, triglycerides and plasma cortisol levels were not affected. Also, GH changed liver glucose and lipid metabolism, stimulated branchial and renal glucose metabolism and glycolytic activity, and enhanced glycogenolysis in brain. PRL induced hypernatremia. Furthermore, this hormone decreased liver lipid oxidation potential, and increased glucose availability in kidney and brain. Both hormones have opposite osmoregulatory effects and different metabolic effects. These metabolic changes may support a role for both hormones in the control of energy metabolism in fish that could be related to the metabolic changes occurring during osmotic acclimation.     

Ovine placental lactogen specifically binds to endometrial glands of the ovine uterus

A hormonal servomechanism has been proposed to regulate differentiation and function of the endometrial glandular epithelium (GE) in the ovine uterus during pregnancy. This mechanism involves sequential actions of estrogen, progesterone, ovine interferon tau (IFNtau), placental lactogen (oPL), and placental growth hormone (oGH). The biological actions of oPL in vitro are mediated by homodimerization of the prolactin receptor (oPRLR) and heterodimerization of the oPRLR and oGH receptor. The objectives of the study were to determine the effects of intrauterine oPL, oGH, and their combination on endometrial histoarchitecture and gene expression and to localize and characterize binding sites for oPL in the ovine uterus in vivo using an in situ ligand binding assay. Intrauterine infusion of oPL and/or oGH following IFNtau into ovariectomized ewes treated with progesterone daily differentially affected endometrial gland number and expression of uterine milk proteins and osteopontin. However, neither hormone affected PRLR, insulin-like growth factor (IGF)-I, or IGF-II mRNA levels in the endometrium. A chimeric protein of placental secretory alkaline phosphatase (SEAP) and oPL was used to identify and characterize binding sites for oPL in frozen sections of interplacentomal endometrium from pregnant ewes. Specific binding of SEAP-oPL was detected in the endometrial GE on Days 30, 60, 90, and 120 of pregnancy. In Day 90 endometrium, SEAP-oPL binding to the endometrial GE was displaced completely by oPL and prolactin (oPRL) but only partially by oGH. Binding experiments using the extracellular domain of the oPRLR also showed that iodinated oPL binding sites could be competed for by oPRL and oPL but not by oGH. Collectively, results indicate that oPL binds to receptors in the endometrial glands and that oPRL is more effective than oGH in competing for these binding sites. Thus, effects of oPL on the endometrial glands may be mediated by receptors for oPRL and oGH.     

Differential effects of placental lactogen,growth hormone and prolactin on rat liver ornithine decarboxylase activity in the perinatal period

Ovine placental lactogen, (oPL), ovine growth hormone, (oGH), and ovine prolactin, (oPRL) are present in high concentrations in the fetal circulation late in gestation. To determine if these hormones stimulate the activity of ornithine decarboxylase (ODC), an enzyme widely implicated in the control of cellular growth, rat fetuses were injected $\text{in utero}$ with 100 μg of oPL, oGH, oPRL, rat growth hormone (rGH) or rat prolactin (rPRL) and ODC activity in the livers, hearts, and brains of the fetuses was measured 2, 4, and 6 hours after injection. OPL stimulated fetal liver ODC activity by 282 ± 45% (mean ± SEM) as compared to litter mates injected with buffer alone but oGH, oPRL, rGH and rPRL had no effect on fetal liver ODC activity. However, in neonatal rats 24–48 hours old all five hormones significantly increased liver ODC activity. ODC activities in the hearts and brains of the fetuses and neonates were unaffected by any of the five hormones. In other experiments 50 μg of oPL significantly stimulated fetal liver ODC activity while 250 μg of oGH were without effect. However 25 μg of oGH significantly stimulated liver ODC activity in rat pups 1–2 days after birth. These results suggest that oPL, by its stimulation of ODC activity, has somatotropic effects in the fetus and that rat liver ODC activity becomes responsive to growth hormone and prolactin in the perinatal period.     

Acute N-methyl-D,L-aspartate administration stimulates the luteinizing hormone releasing hormone pulse generator in the ovine fetus

To assess whether fetal luteinizing hormone releasing hormone (LH-RH) neurosecretory neurons have the capacity to respond to an exogenous stimulus, a synthetic excitatory amino acid analogue, N-methyl-D-L-aspartate (NMDA; 15 mg/kg), was given rapidly intravenously to 8 chronically catheterized fetuses (130-142 days of gestation; term 147 +/- 3 days). All 8 fetuses exhibited a rise in plasma ovine luteinizing hormone (oLH) and ovine follicle-stimulating hormone (oFSH) within 5 min. The mean maximal increments of oLH (2.25 +/- 0.36 ng/ml) and oFSH (1.21 +/- 0.32 ng/ml) were significantly greater than in 6 normal saline-injected controls (oLH p < 0.0002; oFSH p < 0.03). The secretion of ovine prolactin (oPRL) and ovine growth hormone (oGH) was unaffected. LH-RH (5 microg) evoked a greater oLH response (p < 0.0009) and a greater oFSH response (p < 0.03) than NMDA (n = 6). Desensitization of the fetal gonadotrope by a potent LH-RH agonist, D-Trp6Pro9NEt-LH-RH (10 microg/day i.v. x 4 days), abolished the fetal oLH and the oFSH response to NMDA (n = 5). Moreover, D, L-2-amino-5-phosphonovalerate, a specific competitive antagonist for the NMDA receptor, completely inhibited the fetal oLH and oFSH response to NMDA, whereas D-L-2-amino-5-phosphonovalerate alone did not affect the plasma oLH or oFSH levels, the gonadotropin response to LH-RH, or the release of oGH or oPRL (n = 3). In primary ovine fetal pituitary cell cultures, NMDA (10(-10) to 10(-6) M) had no effect on oLH, oFSH, oGH, or oPRL secretion, whereas LH-RH stimulated oLH (10(-8) M; p < 0.0004) and oFSH (10(-8) M; p < 0. 0001) release, evidence that NMDA did not have a direct pituitary effect. The results suggest that NMDA induces oLH and oFSH secretion by stimulation of the fetal LH-RH pulse generator and is mediated by central NMDA receptors. Fetal LH and FSH secretion and the response to LH-RH decrease in late gestation in the ovine and human fetus. The relative importance of sex steroid dependent and sex steroid independent central nervous system inhibition in this developmental change is unclear. It appears that central neural inhibition in addition to sex steroid negative feedback contributes to the decrease in fetal gonadotropin concentrations in late gestation. NMDA did not affect fetal oGH or oPRL secretion.     

Alternative life cycle strategies of Megalodiscus temperatus in tadpoles and metamorphosed anurans

Megalodiscus temperatus (Stafford, 1905) is a common paramphistome trematode of North American amphibians with a two host life cycle and has been reported to infect frogs and rarely tadpoles. In this study we document the alternative life cycle strategy of M. temperatus in tadpoles and metamorphosed anurans. We show through field work and experimental infections that M. temperatus can establish in both anuran life stages and worms become gravid and release eggs in both tadpoles and metamorphosed frogs. However, worms exhibit differences in route of infection, development, egg production, and diet in tadpoles and metamorphosed anurans. These alternative life history strategies of M. temperatus suggest different selective pressures on the development and reproductive success of these worms in tadpoles and metamorphosed anurans, and we discuss the evolutionary avenues for and constraints on amphibian trematode life cycles presented by these two different anuran life stages.     

Ovine placental lactogen stimulation of ornithine decarboxylase activity in brain and liver of neonatal rats

Ovine placental lactogen (oPL), growth hormone (oGH), prolactin (oPRL) and human placental lactogen (hPL) were administered intracisternally (ic) or intraperitoneally (ip) to 17 day old rats and brain and liver ODC activities determined four hours later. When given ic, oPL, oGH and oPRL caused significant increases in brain ODC activity, while hPL had no significant effect. After ip administration, oPL and oGH also caused a significant increase in brain as well as liver ODC activity but oPRL and hPL were without significant effect. The stimulation of polyamine metabolism by oPL together with earlier reports of its potent somatotropic effects and its high concentration in the fetus supports the hypothesis that oPL may be important in the regulation of fetal growth.     

Development of vasotocin pathways in the bullfrog brain

The brain of adult bullfrogs (Rana catesbeiana) contains six populations of cells which are immunoreactive for the neurohypophysial peptide arginine vasotocin (AVT). It is unknown when some of these cell populations first appear during development and when the sexual differences in AVT distribution first become apparent. We therefore used immunocytochemistry to examine development of AVT pathways in developing bullfrog tadpoles and in newly metamorphosed froglets of both sexes. AVT-immunoreactive (AVT-ir) cells were already present in the three diencephalic areas (magnocellular preoptic nucleus, suprachiasmatic nucleus and hypothalamus) at stage III (Taylor and Kollros stages), the earliest stage examined. Cell size in the magnocellular nucleus was not bimodally distributed in either tadpoles or froglets. AVT-ir cells in the telencephalic septal nucleus and amygdala did not appear until stage VI. There was no sexual difference in the density of AVT-ir cells or fibers in the amygdala of tadpoles or froglets. Finally, cells in the hindbrain pretrigeminal nucleus appeared much later-after stage XX. Thus, different populations of neurons begin to express AVT at unique times during development. The sexual dimorphism in AVT content observed in the amygdala of adult bullfrogs must appear during juvenile development or at adulthood.     

Canopy Closure,Competition, and the Endangered Dusky Gopher Frog

Abstract: A major challenge facing wildlife biologists is understanding why some species go extinct while others persist in the same habitat. To address this question, we investigated whether tree canopy closure over ponds affects growth and survival of rare and common tadpoles within ponds and mediates competitive interactions among species. We conducted 2 experiments to test whether canopy closure and competition may have contributed to the decline of the endangered dusky gopher frog (Rana sevosa), but allowed the persistence of the southern leopard frog (R. sphenocephala). We explored the response of both species to canopy closure in single-species and mixed- (1:1) species treatments of identical total tadpole density. An experiment using aquatic enclosures in temporary ponds showed that canopy closure reduced tadpole growth approximately 20% for both species. Survival of dusky gopher frog tadpoles was higher in mixed-species enclosures than in single-species enclosures. In a complementary experiment using artificial ponds, dusky gopher frogs had lower survival to metamorphosis, reduced size at metamorphosis, and produced a lower total biomass of metamorphosed juveniles in shaded ponds. Southern leopard frogs exhibited reduced body size at metamorphosis only when shaded. These studies suggest that pond canopy closure, not larval competition, may be contributing to the decline of the dusky gopher frog. The different responses to canopy closure suggest a potential mechanism for the loss of dusky gopher frogs and the persistence of southern leopard frogs. Removal of trees from historically open-canopy ponds may help facilitate the recovery of dusky gopher frogs and benefit similar species.     

Osmoregulatory effects of hypophysectomy and homologous prolactin replacement in hybrid striped bass

The effects of ovine prolactin (oPRL) and striped bass prolactin (sbPRL; Morone saxatilis) on plasma osmolality, electrolyte balance, and gill Na(+),K(+)-ATPase activity were investigated in hypophysectomized (Hx), freshwater (FW)-acclimated, hybrid striped bass (M. saxatilisxMorone chrysops). They were kept in dilute (isoosmotic) seawater for about 10 days after surgery. Seven days after transfer to FW, Hx fish had lower plasma osmolality and lower levels of Na(+), Cl(-), and Ca(2+) than sham-operated and intact fish. Fish were injected four times with oPRL (1, 5, or 20 microg/g body mass), sbPRL (10 or 100 ng/g), or hormone vehicle (0.9% NaCl) at 48-h intervals (days 0, 2, 4, and 6) in FW and then sampled for blood plasma 24 h after the fourth injection (day 7). In Hx fish, oPRL (5 and 20 microg/g) and sbPRL (10 and 100 ng/g) were effective in maintaining plasma osmolality and levels of Na(+), Cl(-), and Ca(2+) above values seen in saline-injected controls. Hypophysectomy did not affect branchial Na(+),K(+)-ATPase activity, but enzyme activity was significantly reduced in Hx fish receiving oPRL (20 mug/g) or sbPRL (10 or 100 ng/g). These results indicate that PRL acts to maintain plasma osmotic and ionic balance in FW-adapted hybrid striped bass, and that this may involve downregulation of branchial Na(+),K(+)-ATPase activity.     

Effects of induced variation in anuran larval development on postmetamorphic energy reserves and locomotion

Anuran larvae exhibit high levels of phenotypic plasticity in growth and developmental rates in response to variation in temperature and food availability. We tested the hypothesis that alteration of developmental pathways during the aquatic larval stage should affect the postmetamorphic performance of the Iberian painted frog (Discoglossus galganoi). We exposed tadpoles to different temperatures and food types (animal- vs. plant-based diets) to induce variation in the length of the larval period and body size at metamorphosis. In this species, larval period varied with temperature but was unaffected by diet composition. In contrast, size at metamorphosis was shaped by the interaction between food quality and temperature; tadpoles fed on an animal-based diet became bulkier metamorphs than those fed on plant-based food at high (22°C) but not at low (12°C) temperature. Body condition of newly metamorphosed frogs was unrelated to the temperature or food type experienced during the premetamorphic stage. Frogs maintained at high temperature during the larval period showed reduced jumping ability, especially when fed on the plant-based diet. However, when considering size-independent jumping ability, cold-reared individuals exhibited the lowest performance, and herbivores reared at 17°C the highest. Cold-reared (12°C) frogs accumulated larger amounts of energy reserves than individuals raised at 17°C or 22°C. This was still the case after correction for differences in body mass, thus indicating some size-independent effect of developmental temperature. Despite the higher lipid content of the carnivorous diet, the differences in energy reserves between herbivores and carnivores were relatively weak and associated with differences in body size. These results suggest that the consequences of environmental variation in the larval habitat can extend to the terrestrial phase and influence juvenile growth and survival.     

Plasma levels of arginine vasotocin,prolactin, aldosterone and corticosterone during prolonged dehydration in the domestic flowl: effect of dietary NaCl

Three groups of White Plymouth Rock laying hens were adapted to three levels of dietary NaCl: low-NaCl food with tap water (LOW), high-NaCl food (1% NaCl w/w added) with tap water (HT), and high-NaCl food with 0.5% NaCl for drinking (HS). The birds were subjected to water deprivation (dehydration) for 18 days. Blood sampling was done at 2-4 day intervals. Plasma concentrations of arginine vasotocin (AVT), prolactin (PRL), aldosterone (ALDO) and corticosterone (CS) were determined by radioimmunoassay. Plasma osmolality, sodium, chloride, and potassium were also determined. In the normally hydrated hens fully adapted to the diets, there was a stepwise increase from LOW to HS in plasma osmolality (305, 315, 332 mOsm, for LOW, HT and HS, respectively), [Na+] (144, 153, 161 mM) and [Cl-] (109, 119, 127 mM) as well as in [AVT] (6, 14, 18 pg/ml) and [PRL] (16, 24, 34 ng/ml). Regressing [AVT] on osmolality gave a slope of 0.30 pg . ml-1/mOsm and a threshold of 273 mOsm. The slope of [PRL] on osmolality was 0.73 ng . ml-1/mOsm. The correlation coefficient of [AVT] and [PRL] was 0.67. LOW had high [ALDO] (165 pg/ml) which was suppressed to low levels in HT and HS (5-8 pg/ml), while [CS] was the same in all groups (0.9-1.1 ng/ml). Plasma [K+] was decreased in the high-NaCl groups (5.8 mM in LOW, 4.4 and 4.7 mM in HT and HS). Dehydration resulted within 2 days generally in a sharp (5-15%) increase in osmolality, [Na+] and [Cl-], which thereafter increased more slowly during the remaining 16 days in all groups, with the slowest increase in LOW. The levels of osmolality [Na+] and [Cl-] were 5% lower in LOW than in HT and HS, which showed the same levels during the dehydration period. Plasma [AVT] and [PRL] increased 2-4 fold within 2 days of dehydration; [AVT] reached a plateau at 29 pg/ml in all groups, but [PRL] continued to rise in all groups, fastest in LOW, reaching similar levels in all groups after 14-18 days of dehydration, about 85 ng/ml. The correlation coefficient of [AVT] and [PRL] was decreased by half (to 0.32) during dehydration. Plasma [ALDO] increased in all groups with dehydration, 1.7 fold in LOW and 3-6 fold in HT and HS, but the levels reached in HT and HS were only 15-30% of that seen in LOW.(ABSTRACT TRUNCATED AT 400 WORDS)     

Effect of temperature and monensin on the level of intracellular sodium and pH in perfused RIF-1 cultured cells

The direct measurement of temperature in subcutaneously (sc) implanted tumors shows that the actual tumor temperature is by 3-4 degrees C lower than the normal body temperature. Thus, the temperatures usually used for tumor hyperthermia are in fact heating the sc-tumors from 33 to 37 degrees C. The temperature increase during the perfusion of radiation-induced fibrosarcoma (RIF-1) cells from 33 to 37 degrees C caused a reversible increase in intracellular 23Na ([Na+]i) NMR signal intensity by 50-60%. This heating significantly decreased the intracellular pH (pH) in 5 min, but it returned back to the baseline level during the heating period. The 3ATP/P(i) remained generally unchanged throughout the experiment. Monensin, an antitumoral drug and Na+ ionophor, increased [Na+]i by 20% during cell superfusion without heating. When combined, monensin did not increase the heating effect on [Na+]i. However, when monensin was added to the superfusion media, the [Na+]i level did not return to baseline during post-heating recovery, but instead started to increase again. Monensin did not significantly change pH(i) and betaATP/P(i). Our data and the literature show that monensin can accelerate the processes leading to the collapse of the transmembrane Na+ gradient and thus can increase the thermo-sensitivity of tumor cells.     

Transmission of Batrachochytrium dendrobatidis to wood frogs (Lithobates sylvaticus) via a bullfrog (L. catesbeianus) vector

Chytridiomycosis, an emerging infectious disease caused by the chytrid fungus Batrachochytrium dendrobatidis, threatens anuran populations worldwide. Effects of B. dendrobatidis on frog species are variable. Some species typically develop nonlethal infections and may function as carriers; others typically develop lethal infections that can lead to population declines. Nonlethal infections in the bullfrog (Lithobates catesbeianus) are well-documented. In contrast, recently metamorphosed wood frogs (L. sylvaticus) can die from chytridiomycosis. We conducted an ex-situ experiment between May and July 2010 to determine whether B. dendrobatidis-infected bullfrogs could transmit the fungus to wood frog tadpoles when the two species shared a body of water. We tested for B. dendrobatidis infections with quantitative polymerase chain reactions (qPCR) in a subsample of the wood frog tadpoles and in all metamorphosed wood frogs and compared risk of death of froglets exposed and unexposed to infected bullfrogs. We detected B. dendrobatidis sporadically in subsampled treatment tadpoles (nine of 90, 10%) and frequently in treatment froglets (112 of 113, 99.1%). Pooled risk of froglet death was higher (P<0.001) in treatment enclosures than in control enclosures. Our results indicate that, at the low infection loads bullfrogs tend to carry, swabbing for PCR analyses may underestimate prevalence of B. dendrobatidis in this species. We highlight bullfrog disease screening as a management challenge, especially in light of exotic bullfrog colonies on multiple continents and large-scale global trade in this species. We document the importance of quantifying lethal and sublethal effects of bullfrog vectors on B. dendrobatidis-susceptible species.     

Effect of prolactin on blood pressure and cardiovascular responsiveness in the rat

The effects of chronic ovine PRL (oPRL) infusion on resting systolic blood pressure (BP), heart rate, and pressor responsiveness to acute administration of norepinephrine and angiotensin were studied in adult male Sprague-Dawley rats. oPRL was administered over 7 days, via osmotic pump implanted ip on Day 1, at rates of 0, 0.15, 0.30, 0.60, 1.20, and 4.80 micrograms/hr. Resting BP and heart rate were indirectly determined in conscious rats by tail cuff technique on Days 1, 4, and 7 following pump implantation. In addition, acute pressor responses to ia norepinephrine (4.3 micrograms) and angiotensin (1.25 micrograms) were directly measured via arterial cannula in halothane-anesthetized rats on Day 7 of oPRL administration. oPRL infusion did not alter resting BP or heart rate over the 7 days. However, oPRL increased the BP response to norepinephrine at infusion rates of 0.60 and 4.80 micrograms/hr (P less than 0.01 vs controls). Body weight increases during the study were also greater in groups receiving 0.15, 0.30, 0.60, and 4.80 micrograms oPRL/hr (P less than 0.05) than those in control animals. oPRL decreased pressor responses to angiotensin at infusion rates of 0.30 and 1.20 micrograms/hr (P less than 0.01). These data suggest that, although the vascular effects of oPRL may not be evident under resting conditions, oPRL enhances vascular reactivity to norepinephrine infusion and depresses vascular reactivity to angiotensin infusion. Furthermore, at oPRL infusion rates which affect pressor responses to norepinephrine, oPRL increases body weight gain. These findings support a role for PRL in cardiovascular regulation during conditions of altered sympathetic activity.     

The effect of host age on Rana temporaria-gorgoderina vitelliloba interactions

Mitchell J. B. 1982. The effect of host age on Rana temporaria-Gorgoderina vitelliloba interactions. International Journal for Parasitology12: 601–604. Two age groups of tadpoles, and newly metamorphosed and adult male Rana temporaria were fed the metacercarial cysts of Gorgoderina vitelliloba. In the younger tadpoles metacercariae died in their cysts. In the older tadpoles excystment took place and juvenile flukes invaded the kidneys, killing the hosts within 72 h. In newly metamorphosed frogs, an immunological response resulted in some of the juvenile flukes in the kidneys being attacked by eosinophils which adhered to and dissolved the tegument, presumably killing the flukes. In contrast, some young frogs were harmed by flukes in their kidneys. Migration away from the kidneys to the bladder took place on about the twelfth day after infection. Juvenile flukes in the kidneys of adult frogs 7 and 14 days after infection, evoked an inflammatory reaction involving polymorphs and lymphocytes. These cells did not appear to damage the parasites.     

Comparative Pathology and Ecological Implications of Two Myxosporean Parasites in Native Australian Frogs and the Invasive Cane Toad

Myxosporean parasites Cystodiscus axonis and C. australis are pathogens of native and exotic Australian frog species. The pathology and ecological outcomes of infection with these parasites were investigated in this study. Gliosis was correlated to Cystodiscus axonis plasmodia in the brains of (9/60) tadpoles and (3/9) adult endangered Green and golden bell frogs using ordinal regression. Severe host reactions to C. axonis (haemorrhage, necrosis, and vasulitis) were observed in the brains of threatened Southern bell frogs (8/8), critically endangered Booroolong frogs (15/44) and Yellow spotted bell frogs (3/3). Severe brain lesions were associated with behavioural changes, neurological dysfunction, and spontaneous death. Both C. axonis and C. australis develop in the bile ducts of tadpoles, the plasmodia were significantly associated with biliary hyperplasia, inflammation and the loss of hepatocytes in (34/72) Green and golden bell frog tadpoles using ordinal regression. These lesions were so severe that in some cases 70% of the total liver was diseased. Normal liver function in tadpoles is necessary for metamorphosis, metabolism, and immune function. We postulate that this extensive liver damage would have significant host health impacts. Severe hepatic myxosporidiosis was more prevalent in tadpoles examined in autumn and winter (overwintered), suggestive of delayed metamorphosis in infected tadpoles, which would have serious flow-on effects in small populations. We compared the sensitivity of histopathology and species-specific PCR in the detection of C. australis and C. axonis. PCR was determined to be the most sensitive method (detection limit 1 myxospore equivalent of ribosomal DNA). Histology, however, had the advantage of assessing the impact of the parasite on the host. It was concluded that these parasites have the potential for significant ecological impacts, because of their high prevalence of infection and their ability to cause disease in some frogs.