Reproductive aspects of Oreochromis niloticus (Perciformes: Cichlidae) at Coatetelco Lake, Morelos, Mexico

Sex ratio, size at maturity, maturity stages, fecundity and egg diameter of Oreochromis niloticus from Coatetelco Lake, Morelos State, Mexico, were studied from January to December 1993. Sex ratio (male:female) was approximately 1:1.02. Length at maturity was 117 mm (males) and 120 mm (females). The fecundity ranged between 104 and 709 eggs, with egg diameter from 1,000 to 3,000 microns. The gonadosomatic and hepatosomatic index indicate that the species breeds during summer and winter.     

Evaluation of four methods for detecting the beta-lactamase activity in Neisseria gonorrhoeae isolated in Cuba

Four methods (chromogenic, acidimetric, inhibition, and iodometric) for demonstration of the beta-lactamase production by 70 isolates of Neisseria gonorrhoeae, were evaluated in Cuba. There was 100% correlation between all beta-lactamase methods and the standardized penicillin dilution susceptibility test for penicillinase-non-producing N. gonorrhoeae. For penicillinase-producing N. gonorrhoeae strains, there was a perfect correlation between the chromogenic method and penicillin susceptibility testing, but one and two strains failed to give a positive result for beta-lactamase with the inhibition/acidimetric and the iodometric methods, respectively. There was a high concordance between the chromogenic method, considered as gold standard and the rest of penicillinase tests evaluated: Kappa Index (KI) = 0.98 for inhibition/acidimetric methods and KI = 0.97 for the iodometric method. The four methods evaluated were accurate, reproducible, easily readable, economical, and ease to use for screening primary isolates of N. gonorrhoeae in Cuba. We recommended the use of the inhibition method, when testing the penicillinase activity in gonococcal isolates in provincial and municipal reference laboratories.     

Breakthrough performance of stacks of dye-cellulosic fabric in affinity chromatography of lysozyme

The breakthrough performance of stacks of dye-cellulosic fabric in affinity chromatography of lysozyme was investigated in batch and flow experiments. Breakthrough curves were significantly affected by flow rate and were not dependent on the feed solution concentration. System dispersion curves could not explain the flow-rate dependence. Breakthrough curves were analyzed by coupling the kinetic model for pore mass transfer as the only controlling resistance and a system dispersion model. From the analysis, pore film mass transfer resistance was found to be the leading rate-limiting factor when the residence time in the column is greater than 5 min. The model was used to predict the operating and design parameters needed to obtain sharp breakthrough curves. Selectivity studies using lysozyme and bovine serum albumin mixtures showed a high system selectivity for lysozyme.     

Macroscopic fungi from Sierra de Quila, Jalisco, Mexico: diversity and fungal similarity

Diversity and similarity of macrofungi of Sierra de Quila, Jalisco, México were analized in three different kinds of vegetation. Fungal diversity in the area is high. The pine-oak and cloud forests, were more diverse in their community structure than the oak forest. Similarity among the three kinds of vegetation was low, there are few species share among them; pine-oak and cloud forests show higher affinity than oak forests. This pattern of similarity is a general condition for others regions with environmental conditions similar to Sierra de Quila.     

Structural differences between the repertoires of mouse and human germline genes and their evolutionary implications

 Although human and mouse antibodies are similar when one considers their diversification strategies, they differ in the extent to which kappa and lambda light chains are present in their respective variable light chain repertoires. While the Igk-V germline genes are preponderant in mice (95% or more), they comprise only 60% in humans. This may account for differences in the structural repertoire encoded in the Igk-V germline genes of these species. However, this subject has not been properly investigated, partially because a systematic structural characterization of the mouse Igk-V germline genes has not been undertaken. In the present study we compiled all available information on mouse Igk-V germline genes to characterize their structural repertoire. As expected, comparison with the structural repertoire of human Igk-V germline genes indicates differences. The most interesting is that the mouse Igk-V germline gene repertoire is more diverse in structural terms than its human counterpart: the mouse encodes seven canonical structure classes (combination of canonical structures in L1 and L3). In contrast, the human encodes only four. Analysis of the evolutionary relationships of human and mouse Igk-V germline genes led us to propose that the difference reflects a strategy of mice to compensate for the small lambda chain contribution to the repertoire of their variable light chains. Received: 1 June 1997 / Revised: 6 October 1997     

Prenatal Stress Down-Regulates Reelin Expression by Methylation of Its Promoter and Induces Adult Behavioral Impairments in Rats

Prenatal stress causes predisposition to cognitive and emotional disturbances and is a risk factor towards the development of neuropsychiatric conditions like depression, bipolar disorders and schizophrenia. The extracellular protein Reelin, expressed by Cajal-Retzius cells during cortical development, plays critical roles on cortical lamination and synaptic maturation, and its deregulation has been associated with maladaptive conditions. In the present study, we address the effect of prenatal restraint stress (PNS) upon Reelin expression and signaling in pregnant rats during the last 10 days of pregnancy. Animals from one group, including control and PNS exposed fetuses, were sacrificed and analyzed using immunohistochemical, biochemical, cell biology and molecular biology approaches. We scored changes in the expression of Reelin, its signaling pathway and in the methylation of its promoter. A second group included control and PNS exposed animals maintained until young adulthood for behavioral studies. Using the optical dissector, we show decreased numbers of Reelin-positive neurons in cortical layer I of PNS exposed animals. In addition, neurons from PNS exposed animals display decreased Reelin expression that is paralleled by changes in components of the Reelin-signaling cascade, both in vivo and in vitro. Furthermore, PNS induced changes in the DNA methylation levels of the Reelin promoter in culture and in histological samples. PNS adult rats display excessive spontaneous locomotor activity, high anxiety levels and problems of learning and memory consolidation. No significant visuo-spatial memory impairment was detected on the Morris water maze. These results highlight the effects of prenatal stress on the Cajal-Retzius neuronal population, and the persistence of behavioral consequences using this treatment in adults, thereby supporting a relevant role of PNS in the genesis of neuropsychiatric diseases. We also propose an in vitro model that can yield new insights on the molecular mechanisms behind the effects of prenatal stress.