Précipitation et prévention de l'abstinence chez le rat et la souris en état de dépendance aiguë. Comparaison de la naloxone,de la naltrexone et de la diprenorphine

Summary Abstinence signs were precipitated in rats by naloxone (1 mg·kg^-1 s.c.) injected at various times (from 1.5 to 16 h) after a single dose of morphine hydrochloride (15 or 50 mg·kg^-1 s.c.) administered incaqueous solution. Increasing the dose of morphine increased the latency of the phenomena and the duration of the underlying state shifts of signs as described by Bläsig et al. (1974) in chronically morphinized rats also occurred when increasing the dose of morphine and the time interval between the injections of morphine and of naloxone. Naltrexone and diprenorphine were also effective. These three antagonists, given before morphine, were able to prevent precipitated abstinence: however, naloxone was almost ineffective when the higher dose of morphine was used and when the time interval was long. In these latter conditions, naltrexone was definitely more effective and longer acting and diprenorphine still more so. The same characteristics were found for the protective action of the three antagonists in acutely morphinized mice and the same order for their potencies in precipitating abstinence in acutely morphinized mice. Like naloxone, naltrexone and diprenorphine facilitated a nociceptive reaction in normal mice.The abstinence signs precipitated in acutely morphinized rats or mice are probably not unmasked excitatory effects of morphine as such effects should have been increased rather than inhibited by previous administration of specific antagonists; they might correspond to potentiated effects of the antagonists themselves. The prevention by specific antagonists of the abstinence syndrome is most simply interpreted by antagonism (direct or indirect) of dependence induction, but other interpretations are not excluded.

     

Détection des entérobactéries productrices de bêta-lactamases à spectre étendu par biologie moléculaire : avantages,limites

Extended-spectrum beta-lactamases or ESBL are enzymes produced by gram-negative bacilli responsible for hydrolysis of third-generation cephalosporins and aztreonam. However, their susceptibility in vitro to clavulanic acid, tazobactam and sulbactam generally remains unaffected. Considered as resistance threat, they have been involved in many outbreaks and can be related to enhanced morbidity and mortality rates. Described for the first time in 1983, they are encoded by plasmids more frequently isolated from Escherichia coli, Klebsiella pneumoniae or Enterobacter aerogenes. They are derived from TEM-1 or SHV-2 beta-lactamases by mutations responsible for modifications of the active site. Though, the beta-lactamase affinity toward its substrates is modulated and the enzyme displays variable activity against the different third-generation cephalosporins. However, even if cephalosporins MICs against ESBL-producer bacteria are generally higher compared to non-ESBL rods, these values are not always superior to critical values (breakpoints), which could lead to detection impairment when using synergy-based techniques. In this context, a great deal of effort was devoted into developing molecular methods which could avoid phenotypic variations.The aim of this article was to review the different techniques presently available and to point out their relative advantages and limits.     

Mécanismes moléculaires de l’émergence de souches de Neisseria meningitidis responsables d’infections invasives

Neisseria meningitidis is a commensal bacterium of the human nasopharynx that occasionally provokes invasive disease (meningitis and septicemia). Virulence factors facilitate the ability of the bacteria to multiply in its host and to invade sterile sites such as the blood, the cerebrospinal fluid or other sites such as the synovial or pericardial fluids. However, meningococcal disease is not a part of the transmission cycle. Moreover, N. meningitidis is highly variable due to frequent DNA exchanges between strains. New variants that are modified in their virulence and/or transmissibility are continually generated. New genotypes of N. meningitidis may exhibit enhanced virulence that enables them to escape the host immune defense (short term evolution). Variants with a selective advantage in transmissibility may spread rapidly among susceptible hosts (long term evolution).     

Virus émergents ou menaces à répétition

Emergent viruses have attracted attention during years 2003 and 2004. Ancient fears have reappeared regarding pathogenic agents, capable to result in epidemics with high mortality rates. Such events constitute really repeated threats. The analysis of mechanisms permitting emergence of these viruses has shown that they are not random phenomenons, but they result from accumulated factors leading to transmission from animals to men. Several modes of transmission of infection include: either direct transmission, or by intermediate vectors (mosquitoes, ticks and other (mammals) animals). Convergence of ecologic, economic and epidemiologic factors confer to the epidemics potential ability do spread widely. With the development of surveillance networks and improvement in diagnostic technologies, these “new” viruses are better identified. Recent occurrence of SARS and of the avian influenza are best examples of such experiences.     

Action de la Noradrénaline et de la Réserpine sur l'Analgésie expérimentale

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