L-thyroxine and L-triiodothyronine in the cerebral tissues of the adult rat. Effect of hypothyroidism]

The L-thyroxine and L-triiodothyronine concentrations in several brain areas (cerebral cortex, brain stem, hypothalamus, total brain and hypophysis) in normal and hypothyroid rats have been studied. Results show that L-thyroxine values at tissue level are inferior in the hypothyroid group, although non-significant with respect to the control group, whereas L-triiodothyronine presents values similar to the hypothyroid group and its control in all the brain regions studied with the exception of hypophysis. These results show that in hypothyroid situations exist a compensatory mechanism for maintaining the adequate L-triiodothyronine levels in several brain areas, although the serum levels are strongly decreased in hypothyroid animals.     

Transmitter release in hippocampal slices from rats with limbic seizures produced by systemic administration of kainic acid

The systemic injection of kainic acid (KA) has been shown to destroy neurons in the hippocampus and to induce limbic-type seizure activity. However, little is known on the neurochemical events that are associated with this convulsant effect. In the present work we studied the spontaneous and the K⁺-stimulated release of labeled -aminobutyric acid (GABA), glutamate, serotonin and dopamine, in hippocampal slices of KA-treated rats, at the moment of clinical seizures (2 h) and 72 h later. At the onset of convulsions we found a 40–45% decrease in the K⁺-stimulated release of GABA. The release of the other neurotransmitters was not significantly affected by KA treatment. After 72 h GABA release was still reduced by 30–40%. It is concluded that the epileptogenic effect of KA in the hippocampus is probably related to a diminished inhibitory GABAergic neurotransmission.     

Patterns of frugivore species richness and abundance in forest islands and in agricultural habitats at Los Tuxtlas,Mexico

Destruction and fragmentation of tropical rain forest result in a loss of species and of generating capacity of the ecosystem via animal vectors such as seed dispersal agents. To gather quantitative data regarding this ecological problem, birds and mammals were censused in 30 forest fragments, 15 agricultural islands representing five types of vegetation (coffee, cacao, citrus, pepper and mixed-crops) and in three pastures in Los Tuxtlas, southern Veracruz, Mexico. More than 6000 animals of 257 species were detected thus suggesting the existence of a rich species pool in the fragmented landscape. Frugivores accounted for 60% of species, for 72% of individuals censured and for 85% of the total animal biomass recorded. Clusters of small forest fragments (<100 ha) were richer in species and individuals than clusters of large area (>100 ha) forest islands. Pastures were especially poor in forest birds and mammals. While the agricultural islands studied contributed to only 1% of the total area of vegetation sampled, they contained 58% of all species detected and 34% of all individual birds and mammals censured. Recaptures indicated inter-island movements of forest birds and mammals. Forty percent of the species were detected in forest habitats only, the rest were detected in forest and in agricultural habitats. Seeds of forest interior plants dispersed by birds and bats were detected in the agricultural habitats. The value of agricultural islands as landscape features providing some degree of biotic connectivity among fragmented animal populations is discussed.     

Effects of two different experimental situations of hypothyroidism on serum aldosterone concentration and plasma renin in rats

When hypothyroidism is induced surgically in early steps of development in the rat, an increase in serum aldosterone concentration (AC), in absence of changes in plasma renin activity (PRA), is observed. In contrast, in propylthiouracil (PTU) induced hypothyroidism, in adult animals, both AC and PRA decrease. Potassium iodide (KI) or triiodo-L-thyronine (T3) administration to thyroidectomized rats restores AC to normal levels, increasing PRA during the latter treatment. A close relationship between AC and plasma renin concentration (PRC) is observed in these experimental situations. The decrease in urinary aldosterone concentration (ACu), and the relation found between AC/ACu ratio and T3 concentration, suggest that metabolic clearance of aldosterone might be related to peripheric T3 levels in thyroidectomized animals, treated with KI or T3. These observations support the hypothesis, previously reported, which suggests different mechanisms involved in the control of aldosterone and renin release during the two different types of hypothyroidism.     

Scanning isoelectric focusing of cholera enterotoxin in polyacrylamide gels

Scanning isoelectric focusing has been employed for continuous monitoring of the isoelectric spectrum of highly purified cholera enterotoxin in 4% polyacrylamide gels containing 2% ampholytes pH 3–10. The resolution obtained by this technique is of high order because at no instance during focusing interruption of current occurs and thus diffusion of the isolated protein moieties is suppressed. An added aspect of scanning isoelectric focusing was that it allowed estimation of the minimal focusing time of cholera enterotoxin. Thus under the standard assay procedure, the main basic component of cholera enterotoxin was focused in 5800 sec, while the other at least 3 minor acidic and anodic components were focused in approximately 19000 sec. Focusing of cholera enterotoxin in the presence of 6m urea allowed the visualization of 5 well defined and about equal components. The proteinaceous nature of the observed peaks was verified by scanning at wavelengths other than 280 nm, staining of gels for protein, and varying the concentration of the enterotoxin. The design of scanning isoelectric focusing equipment is presented. Reproducibility, economy of sample, and ampholytes and simplicity of experimental technique were some of the features of this apparatus. The resolution of scanning isoelectric focusing was found to be superior to that of ordinary disc and SDS gel electrophoresis.     

Cytokinin treated microcalli of Phelipanche ramosa: an efficient model for studying haustorium formation in holoparasitic plants

The ability of Orobanchaceae to establish a parasitic relationship is based on the development of a specific organ called haustorium. Previous studies in Phelipanche aegyptiaca and P. ramosa have underlined the interest of producing calli from germinated seeds as an efficient genetic transformation system, but they also pointed the need to improve the attachment rate of infectious calli to the host plant as well as the seed yield of the regenerated plants following attachment. It was previously shown that haustorium formation in P. ramosa is triggered by cytokinins. The present work demonstrates that one month-old microcalli produced from germinated seeds displayed a response to c/tZ similar to germinated seeds, as shown by the temporal expression profile of markers genes of cytokinin-related haustorium initiation, including PrRR5, PrCKX2, PrCKX4, PrTRN2 and PrZFP6. In addition, a 48 h treatment of microcalli with c/tZ (10^?7 M) before infestation triggered a 4-fold increase in the attachment rate of microcalli to tomato roots after 18 days in minirhizotrons when compared to untreated microcalli. Finally, it also outlines that increasing the aggressiveness of microcalli with a c/tZ treatment followed by the transfer of parasitized tomato plants into pots significantly improved seed yield of regenerated P. ramosa plants. Indeed, high amounts of viable seeds which germinated at more than 90% in response to GR24 were harvested after a 10 weeks-co-cultivation period. According to these results, cytokinin treated P. ramosa microcalli thus appear to be a good tool for further functional studies in holoparasitic plants, especially on haustorium formation.

     

First Report of Peronospora belbahrii on Sweet Basil in Baja California Sur,México

In Baja California Sur, Mexico, a foliar disease occurred on sweet basil which seriously affected its quality and yield. The most common symptoms were yellowing and necrosis on leaves, caused by a downy mycelium growth on the lower leaf surface. Symptomatic leaves from two sampling sites were collected for morphological studies and molecular analysis of pathogen DNA. Based on morphological characteristics (sporangiophore size of 240–530 × 7–11 μm, branches of 5–8 order and a sporangia size of 27–31 × 21–25 μm) and molecular analysis (the GenBank blast of the PCR assays showed unique rDNA sequence data with 99% similarity to P. belbahrii), the pathogen was identified as Peronospora belbahrii, the causal agent of basil downy mildew. This is the first report of P. belbahrii affecting sweet basil in Mexico.