Problem-based learning in veterinary medicine: protein metabolism

A problem-based approach to teaching biochemistry to veterinary students is described which aims to encourage the finding and learning of biochemical information that is relevant to real-life veterinary problems.     

Single exposure to stressors causes long-lasting, stress-dependent reduction of food intake in rats

A single exposure to severe stressors has been shown to cause anorexia in the next 24 h, but the duration of such alterations is not known. Male Sprague-Dawley rats were subjected to different stressors, and food intake was measured for several days after stress. In experiment 1, 2 h of immobilization (Imo) and lipopolysaccharide (LPS) administration (1,000 microgram/kg) caused a marked anorexia in the 24 h after stress, which persisted on poststress day 3. In experiment 2, changes in food intake after LPS and Imo were followed until total recovery. As in experiment 1, LPS caused initially a greater degree of anorexia than Imo, but normal food intake recovered much faster (poststress day 3 vs. poststress day 9). Changing the period of exposure to Imo between 20 min and 6 h (experiment 3) only slightly modified the pattern of response to the stressor. When different doses of LPS (50, 250, and 1,000 microgram/kg) were tested in experiment 4, a dose-dependent effect on food intake was observed, the greatest doses causing the most marked and lasting effect. The present results showed stressor-specific lasting changes in food intake caused by a single exposure to some stressors, the effect of a severe psychological stressor such as Imo being more lasting than that of LPS, despite a lower initial anorexia. A severe psychological stressor and a physical stressor such as LPS appear to change food intake in different ways.     

The cell cycle inhibitor p21 controls T-cell proliferation and sex-linked lupus development

Here we show that the cell-cycle regulator p21 is involved in immune system function. T lymphocytes from p21-/- mice exhibit significant proliferative advantage over wild-type cells following prolonged stimulation, but not after primary activation. Consistent with this, p21-deficient mice accumulate abnormal amounts of CD4+ memory cells, and develop loss of tolerance towards nuclear antigens. Similar to human lupus, female p21-deficient mice develop antibodies against dsDNA, lymphadenopathy, and glomerulonephritis, leading to decreased viability. These data demonstrate a specialized role for p21 in the control of T-cell proliferation, tolerance to nuclear antigens, and female-prone lupus. These findings could be the basis for new therapeutic approaches to lupus.     

Frequency of anti-Toxoplasma gondii antibodies in cats from Valdivia city, Chile

Toxoplasmosis is a parasitic zoonosis. The importance of the cat as related to this parasitosis lies in the fact that it is not only the definite host of the parasite, but responsible for its dissemination through the release of oocysts, which subsequently infect both humans and other animals. The objective of this study was to determine the serological prevalence of Toxoplasma gondii in the feline population of the city of Valdivia (Chile) and to establish the possible epidemiological implications of this prevalence. With these goals in mind the technique of indirect immunofluorescence was implemented to detect anti- T. gondii species--specific IgG. Blood samples from 97 cats (selected using a directed sampling process) from different sectors of Valdivia were collected. The sample included 46 males and 51 females of different ages, Positive and negative control sera obtained from de United States were used to verify the results, observed by UV microscopy. The anti-feline IgG antibody was used as directed by the manufacturer (Sigma). Of the 97 selected cats, 32 were found to be positive with a titre higher than 1:4, a prevalence of 33.0%. The number of infected males as compared to the number of infected females was found to be statistically insignificant, using the chi-square analysis with p less than 0.1. In contrast, a definite correlation between age and seropositivity was found; infection levels were higher in older animals. These results are consistent with those obtained in different studies on this topic that have been performed in different parts of the world. However, they would seem to be in conflict with other, similar studies that have been done recently in Chile; this may be due to the fact that the cats selected for this study were exposed to different climatic conditions than those examined in previous works. In conclusion, it has been determined that in Valdivia exist cats infected by T. gondii, which indicate the presence of the necessary epidemiological conditions for the persistence of this parasitic cycle and the source of infection for humans and other animals.     

Fish Communities in Central Amazonian White- and Blackwater Floodplains

In Amazonian floodplains, the flood cycle of the river is becoming the dominant seasonal factor, and fish communities are found to fluctuate greatly over the year. During inundation, fish migrate into floodplain forests to feed on fruits and seeds, in an area more than 300000km² in size. To document patterns of species diversity, distribution, abundance and temporal dynamics and in order to describe the ecological importance of the inundated forest, floodplain fish were captured using variously sized gill nets in white and black water areas inside and outside the floodplain forests during low, rising, high and falling water level in 1990 and 1991. Dominance varies to some extent in white water between floodplain forest (0.06) and open water (0.11) while it is unchanged in black water (0.04). Black water fish communities were more diverse. Most abundant among white water fish were Liposarcus pardalis, Pygocentrus nattereri, and Pellona flavipinnis, for example, or Plagioscion squamsissimus, Serrasalmus rhombeus, and Serrasalmus manueli in black water. Among the most abundant white water fish, Colossoma macropomum, Mylossoma duriventre and Osteoglossum bicirrhosum occurred almost exclusively in inundated forests. Of the black water species there were a large number of species which were captured only in inundated forest, such as Geophagus cf. altifrons, Hoplias malabaricus, Osteoglossum bicirrhosum and Uaru amphiacanthoides. Catches varied with sample site, water level and direction of water level change. The average CPUE in white and black water was 190 and 41g fishm^–2 and day, respectively, with maximum yields at low water and minimum yields at high water. Comparing rising and falling water levels, a significantly higher quantity of fishes was captured at falling water level. In black water, fish catches from the floodplain forest exceeded the open water catch by 183 to 550%, depending on season. Differences in respect of white water are smaller (106–281%). Fish communities in the area under investigation seem to be stochastically assembled, with significant differences between white and black water only. Many fishes move into the floodplain forest not only to feed but probably also for other reasons – to seek shelter, for example.     

Xanthan gum: production, recovery, and properties

Xanthan gum is a microbial polysaccharide of great commercial significance. This review focuses on various aspects of xanthan production, including the producing organism Xanthomonas campestris, the kinetics of growth and production, the downstream recovery of the polysaccharide, and the solution properties of xanthan.     

Effect of chronic hyperprolactinemia on daily changes of glutamate and aspartate concentrations in the median eminence and different hypothalamic areas of male rats

The 24h changes of glutamate (GLU) and aspartate (ASP) were studied in the median eminence (ME) and hypothalamic areas. It was analyzed whether prolactin may change their daily patterns. The hypothalamic concentration of these amino acids was measured by high-performance liquid chromatography (HPLC) with fluorometric detection. Plasma prolactin levels increased over the 24h light-dark cycle after pituitary grafting compared to controls, and its circadian rhythm was disrupted. In controls, aspartate and glutamate in the hypothalamic areas studied followed a specific daily variation or showed no rhythmicity. In the median eminence, hyperprolactinemia seem to phase advance the aspartate or glutamate peaks from 16:00 to 12:00. In the mediobasal hypothalamus, hyperprolactinemia altered daily changes of aspartate and significantly decreased its concentration. Also, it seems to delay the nocturnal glutamate peak compared to controls. In the posterior hypothalamus, hyperprolactinemia did not change aspartate and glutamate concentrations and their daily changes, although it increased the glutamine concentration. These data show the existence of 24h changes of amino acid concentration in three of the hypothalamic regions studied. Increased plasma prolactin levels differentially affected these patterns depending on the hypothalamic area analyzed. (Chronobiology International, 17(5), 631-643, 2000)