Linking Predator Responses to Alkaloid Variability in Poison Frogs.

Many chemically-defended/aposematic species rely on diet for sequestering the toxins with which they defend themselves. This dietary acquisition can lead to variable chemical defenses across space, as the community composition of chemical sources is likely to vary across the range of (an aposematic) species. We characterized the alkaloid content of two populations of the Dyeing Poison Frog (Dendrobates tinctorius) in northeastern French Guiana. Additionally, we conducted unpalatability experiments with naive predators, Blue Tits (Cyanistes caeruleus), using whole-skin secretion cocktails to assess how a model predator would respond to the defense of individuals from each population. While there was some overlap between the two D. tinctorius populations in terms of alkaloid content, our analysis revealed that these two populations are markedly distinct in terms of overall alkaloid profiles. Predator responses to skin secretions differed between the populations. We identified 15 candidate alkaloids (including three previously undescribed) in seven classes that are correlated with predator response in one frog population. We describe alkaloid profile differences between populations for D. tinctorius and provide a novel method for assessing unpalatability of skin secretions and identifying which toxins may contribute to the predator response. In one population, our results suggest 15 alkaloids that are implicated in predator aversive response. This method is the first step in identifying the causal link between alkaloids and behavioral responses of predators, and thus makes sense of how varying alkaloid combinations are capable of eliciting consistent behavioral responses, and eventually driving evolutionary change in aposematic characters (or characteristics).

Weak warning signals can persist in the absence of gene flow.

Aposematic organisms couple conspicuous warning signals with a secondary defense to deter predators from attacking. Novel signals of aposematic prey are expected to be selected against due to positive frequency-dependent selection. How, then, can novel phenotypes persist after they arise, and why do so many aposematic species exhibit intrapopulation signal variability? Using a polytypic poison frog (Dendrobates tinctorius), we explored the forces of selection on variable aposematic signals using 2 phenotypically distinct (white, yellow) populations. Contrary to expectations, local phenotype was not always better protected compared to novel phenotypes in either population; in the white population, the novel phenotype evoked greater avoidance in natural predators. Despite having a lower quantity of alkaloids, the skin extracts from yellow frogs provoked higher aversive reactions by birds than white frogs in the laboratory, although both populations differed from controls. Similarly, predators learned to avoid the yellow signal faster than the white signal, and generalized their learned avoidance of yellow but not white. We propose that signals that are easily learned and broadly generalized can protect rare, novel signals, and weak warning signals (i.e., signals with poor efficacy and/or poor defense) can persist when gene flow among populations, as in this case, is limited. This provides a mechanism for the persistence of intrapopulation aposematic variation, a likely precursor to polytypism and driver of speciation.

Diversity of warning signal and social interaction influences the evolution of imperfect mimicry.

Mimicry, the resemblance of one species by another, is a complex phenomenon where the mimic (Batesian mimicry) or the model and the mimic (Mullerian mimicry) gain an advantage from this phenotypic convergence. Despite the expectation that mimics should closely resemble their models, many mimetic species appear to be poor mimics. This is particularly apparent in some systems in which there are multiple available models. However, the influence of model pattern diversity on the evolution of mimetic systems remains poorly understood. We tested whether the number of model patterns a predator learns to associate with a negative consequence affects their willingness to try imperfect, novel patterns. We exposed week-old chickens to coral snake (Micrurus) color patterns representative of three South American areas that differ in model pattern richness, and then tested their response to the putative imperfect mimetic pattern of a widespread species of harmless colubrid snake (Oxyrhopus rhombifer) in different social contexts. Our results indicate that chicks have a great hesitation to attack when individually exposed to high model pattern diversity and a greater hesitation to attack when exposed as a group to low model pattern diversity. Individuals with a fast growth trajectory (measured by morphological traits) were also less reluctant to attack. We suggest that the evolution of new patterns could be favored by social learning in areas of low pattern diversity, while individual learning can reduce predation pressure on recently evolved mimics in areas of high model diversity. Our results could aid the development of ecological predictions about the evolution of imperfect mimicry and mimicry in general.

Differential responses of avian and mammalian predators to phenotypic variation in Australian Brood Frogs.

Anti-predator signaling is highly variable with numerous examples of species employing cryptic coloration to avoid detection or conspicuous coloration (often coupled with a secondary defense) to ensure detection and recollection. While the ends of this spectrum are clear in their function, how species use intermediate signals is less clear. Australian Brood Frogs (Pseudophryne) display conspicuous coloration on both their dorsum and venter. Coupled with the alkaloid toxins these frogs possess, this coloration may be aposematic, providing a protective warning signal to predators. We assessed predation rates of known and novel color patterns and found no difference for avian or mammalian predators. However, when Pseudophryne dorsal phenotypes were collectively compared to the high-contrast ventral phenotype of this genus, we found birds, but not mammals, attacked dorsal phenotypes significantly less frequently than the ventral phenotype. This study, importantly, shows a differential predator response to ventral coloration in this genus which has implications for the evolution of conspicuous signaling in Pseudophryne.

Avian learning favors colorful, not bright, signals.

A few colors, such as red and yellow, are commonly found in aposematic (warning) signaling across taxa, independent of evolutionary relationships. These colors have unique traits (i.e., hue, brightness) that aid in their differentiation, and perhaps, their effectiveness in promoting avoidance learning. This repeated use calls into question the influence of selection on specific warning colors adopted by aposematic prey-predator systems. To disentangle the influence of color characteristics on this process, we trained week-old chickens (Gallus gallus domesticus) to learn to avoid distasteful food that was associated with one of three color signals (yellow, white, red) that varied in both hue and in brightness in order to assess which of these traits most influenced their ability to learn avoidance. Our results show that while chicks learned to avoid all three colors, avoidance was based on the hue, not brightness of the different signals. We found that yellow was the most effective for avoidance learning, followed by red, and finally white. Our results suggest that while these three colors are commonly used in aposematic signaling, predators' ability to learn avoidance differs among them. These results may explain why yellow is among the most common signals across aposematic taxa.

Rapid diagnostic evaluation of bronchial washings in patients with suspected coccidioidomycosis.

Coccidioidomycosis is a regionally common fungal infection, primarily affecting the lung. While in the majority of cases the tempo of the disease allows for a more leisurely diagnostic plan, including multiple serologic tests and culture of respiratory secretions, occasionally, patients will present with rapidly progressive, life-threatening pulmonary illness, in whom there is an urgent need for rapid diagnosis. Evaluation of respiratory secretions including expectorated sputum as well as bronchial washings are frequently available or obtained for diagnosing pulmonary infiltrates. We compared the sensitivity of the Papanicolaou stain with 10% potassium hydroxide digestion (10% KOH) and with calcofluor white (cw). The Papanicolaou test performed the best and should be used in the evaluation of suspected patients with coccidioidomycosis.

Effects of epidermal growth factor and Clostridium difficile toxin B in a model of mucosal injury.

Numerous factors have been advocated as being paramount to the development of necrotizing enterocolitis (NEC) including hypoxia, abnormal bacterial flora, and by products of enteral feedings. In an effort to better understand mechanisms involved at the level of the intestinal mucosal barrier the authors have chosen the CACO-2 cell line to model the neonatal intestinal epithelium. By growing CACO-2 cells in transwell inserts, the authors have investigated the ability of Clostridium difficile toxin B, epidermal growth factor (EGF), and a model of mechanical injury to alter transepithelial resistance of CACO-2 monolayers. The findings show that toxin B diminishes resistance in this setting, and EGF can alter that resistance drop.

Pyocolpos: diagnosis and treatment.

Pyocolpos is a rare complication of hydrocolpos. Hydrocolpos usually presents during adolescence and is associated with an imperforate hymen. The following is a case of a 3-month-old girl with pyocolpos. Her history was significant for a urinary tract infection (UTI) at 7 weeks of age. The authors believe that her UTI was caused by urinary retention secondary to hydrocolpos. A complete evaluation may have prevented the complication of pyocolpos.

Tenidap inhibits replication of the human immunodeficiency virus-1 in cultured cells.

Interleukin-6 (IL-6) may be important in the pathogenesis of HIV-1 because of its ability to induce HIV-1 expression in infected cells in vitro. Tenidap, a structurally and functionally novel antirheumatic drug affecting diverse biologic processes, has been shown to reduce IL-6 production by peripheral blood mononuclear cells stimulated with lipopolysaccharide. Tenidap also inhibits the activity of chloride-bicarbonate exchangers and causes acidification of the cytoplasmic compartment that is similar to the effect of the anion transport inhibitor UK5099. Furthermore, tenidap inhibits the cyclooxygenase-mediated pathway of arachidonic acid metabolism as do the nonsteroidal antiinflammatory drugs (NSAIDs). Here we show that tenidap decreased HIV-1 replication as measured by p24 core antigen in the acutely infected CD4+ T-lymphocyte lines H9 and Jurkat, in the acutely infected monocyte line U937, and in its chronically infected subclone U1.8/HIV. These effects were seen at concentrations in the range of 3 to 15 microM, well below those toxic to cells. The antiviral effects of tenidap may be independent of its ability to reduce IL-6 production based on the observations that these effects were as prominent in IL-6 nonresponsive lines as in IL-6 responsive lines and that the inhibition of p24 production was not reversed by exogenous IL-6.

Button device for antegrade enema in the treatment of incontinence and constipation.

Antegrade enema through an appendicostomy is effective in improving the quality of life for patients with incontinence or severe constipation. For patients without an appendix, a conventional gastrostomy button was used to create a cecostomy (or ileostomy) that served as a port for the administration of enema solutions.

Anteriorly located anus: is constipation caused by abnormal location of the anus?

Anteriorly located anus (ALA) is frequently associated with severe constipation accompanied by defecation pain. Between 1988 and 1994, the authors treated 27 children (26 girls, 1 boy; age range, 0 to 11 years) to surgically correct ALA. The operation was performed according to a uniform protocol to longitudinally divide the internal sphincter muscle from the anal skin level to 2 cm above the dentate line on the posterior wall of the anorectum. For anal reconstruction, any of the conventional procedures was employed. Twenty-two of the 27 patients have had follow-up in our clinic for 12 months to 6 years (mean, 2.75 years). Eighteen are completely free of constipation and defecation pain and have regular spontaneous bowel movements. The other four require occasional use of enemas or laxatives. Anal incontinence did not occur in any patient. The results of this study suggest that abnormal function of the internal sphincter is the most likely cause of constipation or defecation pain in patients with ALA and that internal sphincterotomy is the cornerstone of surgical treatment.

Rejection after pediatric liver transplantation is not the limiting factor to survival.

Liver transplantation became a very successful therapy when cyclosporin A was introduced as an immunosuppressive agent. In an effort to evaluate the contribution of difficult or uncontrolled allograft rejection to mortality, the authors determined the most important factors that limited survival after liver transplantation. Eighty-two children received a total of 94 liver transplants from January 1987 to the present. Patients' records were reviewed for complications that contributed to morbidity and mortality and to assess which complications were preventable. Twelve patients died (15%), nine within 6 weeks of liver transplantation. The chief contributing cause of death was hepatic artery thrombosis (one patient), brain death after liver transplantation for fulminant hepatic failure (two patients), primary allograft nonfunction or dysfunction (two patients), allograft rejection (three patients), or other problems (four patients). Overall, hepatic artery thrombosis occurred in 3.1%, allograft rejection in 57%, fulminant hepatic failure in 7%, and donor organ dysfunction in 7%. Allograft rejection contributed directly to the cause of death in three children (4%). The authors conclude that few deaths after pediatric liver transplantation are caused by failure of immunosuppression. A high survival rate can be achieved after transplantation by eliminating the correctable complications that most frequently occur in the early postoperative period.

Isolated liver transplantation for liver failure in patients with short bowel syndrome.

The ultimate prognosis for patients with short bowel syndrome (SBS) has become progressively more favorable over the past decade. Advances in long-term total parenteral nutrition (TPN) have allowed this group of patients to meet nutritional needs while the process of intestinal adaptation occurs. Unfortunately, a subgroup of patients with SBS have hepatic failure (HF), most often secondary to TPN-induced cholestasis. Combined small bowel and liver transplantation (LT) offers a sound anatomic solution for cases of HF with SGS, but it remains experimental at this time. We propose that an isolated LT is a viable alternative mode of therapy for the patient with HF and SBS. The following characteristics were reviewed for five patients with SBS and HF who underwent LT: age at transplantation, weight, liver function, survival, intestinal length, volume of feeding before surgery, and current feeding tolerance and liver function. Four boys and one girl, aged 5.5 to 15 months (average, 11.9), had LT. The total bilirubin level at the time of transplantation was 14.4 to 37 mg/dL (average, 24.7). The patients weighed between 3.8 and 12 kg (average, 8.0), and feeding tolerance ranged from no enteric to complete enteric feeding (average, < 33% of calories by enteric feeding). Bowel loss was attributed to necrotizing enterocolitis in two cases, volvulus in two, and birth hypoxia in one. Bowel length ranged from 60 to 120 cm (average, 88.6). Four children (80%) survived LT, and the average follow-up period was 9.3 months. Three (75%) are home; one is on combined hyperalimentation and enteral feeding, and two are on full enteric feeding. One remains in a chronic care facility, on combined enteral and intravenous feeding. The average daily enteral feeding now comprises more than 70% of caloric requirements. The total bilirubin level is .6 to .8 mg/dL (average, .71). Isolated LT for HF in the patient with SBS effectively restores liver function, allowing time for further intestinal adaptation.

Glycosylphosphatidylinositol-anchored CD4 supports human immunodeficiency virus type 1 replication, but not cytopathic effect, in T-cell transfectants.

Despite equivalent p24 antigen production, HSB-2 T cells expressing glycosylphosphatidylinositol (GPi)-linked CD4 were productively infected without cell death or syncytium formation, unlike HSB-2 transfectants expressing wild-type CD4 (wtCD4). HSB-2 transfectants dually expressing wtCD4 and GPi-linked CD4 formed syncytia and died. Thus, wtCD4 expression is critical for human immunodeficiency virus cytopathic effect in HSB-2 transfectants.

Monotherapy with cyclosporine for chronic immunosuppression in pediatric liver transplant recipients.

Children who survive liver transplantation (LT) suffer the adverse effects of life-long immunosuppression. In an attempt to minimize these effects, we have instituted a program of tapering immunosuppression, resulting in chronic monotherapy for children after LT. Seventy-three children ages 4 months to 19 years received LT between January 1987 and December 1992. Patient survival was 85% (62/73), with graft survival of 73%, at one year. Triple therapy with prednisone, cyclosporine, and azathioprine begun at transplant was tapered as follows: 1-2 mg/kg prednisone at discharge was reduced by .2 mg/kg every 2 months until a .2 mg/kg total was reached. Alternate-day steroids (.2 mg/kg) were begun at 1 year and discontinued at 1.5 years. AZA (1 mg/kg) was begun posttransplant and discontinued after any serious viral illness or by 1 year. Currently 37 survivors are > 18 months post-LT and were considered candidates for monotherapy. Monotherapy was attempted in 28 (76%), and 25 of these remain on monotherapy an average of 2 years later. All have normal liver function. After monotherapy and alternate-day steroids were achieved, 66% of children < 5th percentile for height at the time of transplant improved to greater than the 5th percentile. There were 3 (11%) patients who rejected while on monotherapy an average of 1.15 years after it was started. These patients had the following predisposing factors that decreased cyclosporine levels and led to rejection: common bile duct stricture, chronic and intermittent antibiotic administration for urinary tract infection, and noncompliance. In the 9 potential candidates not tapered to monotherapy, 6 have had recurrent acute or chronic rejection; 2 of these now receive FK506. We conclude that the majority of stable pediatric LT recipients may be safely tapered to chronic cyclosporine monotherapy. Increased growth is a major benefit of decreased steroid dosing in these children. Cyclosporine absorption and adequate levels are crucial for success of this approach.

Persistence of the circadian variation and altered response to hepatectomy of hepatic ornithine decarboxylase activity with malignant tumor burden.

We measured the effect of MC-26 mouse colon cancers (of different sizes) on the circadian rhythm of hepatic ornithine decarboxylase (ODC) activity and hepatic ODC activity during the 24 hr after 60% hepatectomy. Tumor-free control mice showed a normal circadian rhythm of ODC activity with the highest levels at 1100 hr and the lowest levels at 2300 hr. The amplitude of the rhythm was diminished significantly in mice with a large tumor burden (3% of their body weight), and hepatic ODC activity was significantly less than in the tumor-free mice at every point during the 24 hr of the study. In mice with "early" tumors (0.3% of body weight), basal activity of ODC was normal and there was no reactive increase in activity following hepatectomy. In contrast, mice with "late" (3% of body weight) tumors had significantly lower basal ODC activities and the increase in ODC activity following hepatectomy was prolonged and exaggerated. We concluded that tumor burden is associated with abnormal ODC activity and that these differences are exaggerated after hepatectomy. Furthermore, although average ODC concentrations in tumor-bearing mice fell precipitously, the circadian rhythm in hepatic ODC persisted. This finding indicates early recognition by the host of tumor presence, which has a profound negative regulatory effect on hepatic ODC. Apparently, this effect does not impinge on circadian control mechanisms, indicating that these signals act independently.

Aging and the trophic effects of cholecystokinin, bombesin and pentagastrin on the rat pancreas.

We examined the effect of age on the trophic response of the pancreas to chronic treatment with cholecystokinin (CCK), bombesin, or pentagastrin. Three age groups (3-, 12-, and 24-months) male F344 rats received saline; CCK-8 (5 ng/kg), bombesin (10 micrograms/kg), or pentagastrin (100 micrograms/kg) by intraperitoneal injection t.i.d. for 2 weeks. Rats were then killed and the pancreases excised, weighed, and assayed for DNA, RNA, protein, and polyamine (putrescine, spermidine, and spermine) concentrations and contents. We found that none of the treatments altered body weight at any age. All three hormones increased pancreas size and cell number in 3-month old rats, but by 12 months, all three had increased only pancreatic RNA content. Pancreatic spermidine concentration was decreased by all three hormone regimens in 3- but not in 12-month old rats, and pancreatic putrescine concentration and content were increased in 12-month old rats receiving all three hormones. There was no change in any parameter following any of the three hormones, tested at 24 months of age. We conclude that, at the dosages tested, the trophic response of pancreas to chronic administration of CCK, bombesin, and pentagastrin, which is normally present in young adult rats, is lost with aging.

The effect of somatostatin on 5-hydroxytryptamine release from a carcinoid tumor.

One of the major manifestations of the carcinoid syndrome is secretory diarrhea thought to be due to overproduction of 5-hydroxytryptamine (5-HT). Synthetic somatostatin analogues have proved to be clinically effective in controlling this diarrhea. We have established a continuous cell line from a human pancreatic carcinoid tumor that secretes 5-HT. We examined the ability of the somatostatin analogue, SMS 201-995, to inhibit 5-HT release in vitro. Tumor cells were exposed to SMS 201-995 (10(-6) mol/L), pentagastrin (10(-9) mol/L), acetylcholine (10(-5) mol/L), and isoproterenol (10(-5) mol/L) alone and in combination; 5-HT release was assayed with high pressure liquid chromatography. We found that pentagastrin (6.43 +/- 0.64 ng/ml), isoproterenol (20.24 +/- 2.17 ng/ml), and acetylcholine (12.39 +/- 1.10 ng/ml) each stimulated release of 5-HT compared to control values (4.38 +/- 0.42 ng/ml). SMS 201-995 significantly reduced release of 5-HT in response to isoproterenol and acetylcholine but did not inhibit the effect of pentagastin. These data suggest that different agents do not act through the same pathway to stimulate 5-HT release from human pancreatic carcinoid cells.

Bone density distribution within the femoral head and neck. An examination by high-resolution computed tomography.

The upper portions of three cadaveric femora were examined by high-resolution computed tomography. Analysis of the resulting images provided both quantitative and spatial distributions of bone density within the femoral head and neck. The information obtained provides new insights into aspects of proximal femoral architecture for both normal and osteoporotic bone. The study also points the way towards a clinical technique for measuring the material properties of proximal femoral bone.