Tn5 mutagenesis and insertion replacement in Azotobacter vinelandii

Tn5 insertion mutants of Azotobacter vinelandii were isolated using vectors pJB4JI (IncP) and pGS9 (IncN). A procedure to replace Tn5 (Kmr) by its nontransposing derivative Tn5-131 (Tcr) was developed. For the replacement, a ColEl derivative harboring Tn5-131 (pRZ131) was conjugally mobilized by the IncN plasmid pCU101 into A. vinelandii strains containing Tn5. Both plasmids are unable to be maintained in A. vinelandii, but the transient presence of pRZ131 allows recombination between the incoming and the resident Tn5 elements. Genetic and physical analysis showed that insertion replacements result in lower frequencies of Tn5-associated genomic rearrangements, thereby increasing the stability of Tn5-containing strains.

Differences in physical dependence induced by selective mu or delta opioid agonists and by endogenous enkephalins protected by peptidase inhibitors

The aim of the present study was to investigate if a physical dependence could be induced by chronic activation of the endogenous enkephalinergic system. We have therefore evaluated naloxone-induced withdrawal syndrome in rats after central infusion during 7 days of comparable antinociceptive doses of RB 38 A ((R,S)HONH-CO-CH2-CH(CH2C6H5)-CONH-CH(CH2C6H5)-COOH), a mixed enkephalin catabolism blocker and of the selective mu, DAGO (Tyr-D-Ala-Gly-(Me)Phe-Gly-ol) and delta, DSTBULET (Tyr-D-Ser(OtBu)-Gly-Phe-Leu-Thr), opioid agonists. The responses were compared to those induced by RB 38 B ((S,S)HONH-CO-CH2-CH(CH2C6H5)-CONH-CH(CH2C6H5)-COOH), a selective inhibitor of the 24.11 neutral endopeptidase (NEP) 'enkephalinase'. DAGO induced a severe withdrawal syndrome evidenced by a large weight loss, hypothermia, jumping, mastication, teeth chattering, diarrhoea, lacrimation and salivation. In contrast, DSTBULET and RB 38 A produced only a moderate physical dependence. Only two signs were statistically different in these two groups: wet dog shakes and temperature. Chronic i.c.v. administration of DAGO, DSTBULET and RB 38 A produced a time-dependent reduction in analgesia, but 120 h after continuous infusion only RB 38 A was able to still induce a significative antinociceptive effect. The present data suggest that even in the drastic conditions used here long-term complete inhibition of enkephalin catabolism induces a weak tolerance and a moderate physical dependence, similar to that produced by delta opioid agonists. This effect was not observed after chronic selective inhibition of NEP by RB 38 B.

Genomic imprinting in microorganisms

Genomic imprinting is an epigenetic mark introduced on a DNA molecule without alteration of the base sequence. Upon replication, the primary mark is propagated to the daughter DNA molecules. Epigenetic DNA modification often serves as a regulatory signal and may play a crucial role in many developmental processes. Although this mode of gene regulation was first discovered in multicellular eukaryotes, cases of imprinting have been recently found in lower eukaryotes, bacteria and phage. Thus it may be reasonable to list DNA modification among the major mechanisms that regulate gene expression.

Effects induced by chronic treatment with selective D1 or D2 antagonists on open-field behavior and colonic temperature

We have studied the behavioral responses in open-field and the changes in body temperature induced after chronic treatment with a selective D1 antagonist, SCH 23390, a selective D2+ antagonist, sulpiride, or a non specific but preferential D2 antagonist, haloperidol. After chronic treatment with SCH 23390 or sulpiride, rats were challenged with SKF 38393, selective D1 agonist, or LY 171555, selective D2 agonist, in order to study the responses of D1 and D2 stimulation. After chronic SCH 23390, an increase of the locomotion and of the number of rears were observed whereas, no changes were induced by chronic sulpiride or haloperidol. Acute treatment with sulpiride blocked the hyperlocomotion induced by chronic SCH 23390. In naive rats acute administration of SKF 38393 or LY 171555 did not produce any change in locomotion or rearing. In rats treated chronically with SCH 23390 this acute administration of LY 171555 induced an increase of the number of squares and of the number of rears. In these animals, acute administration of SKF 38393 also augmented the number of squares crossed. In contrast, chronic sulpiride did not modify behavioral responses obtained after acute SKF 38393 or LY 171555. Colonic temperature was not changed after acute SKF 38393 while acute LY 171555 induced a hypothermia. Chronic sulpiride did not modify the responses of SKF 38393 or LY 171555, but an increase in body temperature was observed after acute SKF 38393 in animals chronically treated with SCH 23390. The present results support a different behavioral expression of D1 and D2 supersensitivity in rats. Furthermore, chronic treatment with a D1 antagonist induced facilitatory effects on D2 behavioral responses; however, these D1-D2 interactions were not observed in body temperature responses.

Chronic blockade of D2 but not D1 dopamine receptors facilitates behavioural responses to endogenous enkephalins, protected by kelatorphan, administered in the accumbens in rats

It has previously been shown that kelatorphan, (R)-3-(N-hydroxycarboxamido-2-benzyl-propanoyl)-L-alanine, a mixed inhibitor of the catabolism of enkephalins, injected into the nucleus accumbens, induced a dose-dependent hyperlocomotion in rats. In this study, the consequence of chronic treatment with sulpiride, a selective D2 dopamine receptor antagonist, SCH 23390, a selective D1 dopamine receptor antagonist, or haloperidol, a nonspecific but preferential D2 receptor antagonist, on the behavioural response induced by acute administration of kelatorphan into the accumbens, has been investigated in rats. The drug SCH 23390 did not modify the behavioural response to kelatorphan, whereas sulpiride and haloperidol induced an increase which was maximal in the third week after the beginning of treatment, a period corresponding to the appearance of the antipsychotic effect of the neuroleptics. This facilitation was reversed by prior administration of the delta-selective antagonist, ICI 174864. These results suggest that the phasic activity of enkephalinergic neurones of the nucleus accumbens and the associated behavioural hyperactivity are facilitated after chronic blockade of the D2 but not the D1 subtypes of dopamine receptor.

Comparison of selective and complete inhibitors of enkephalin-degrading enzymes on morphine withdrawal syndrome

We investigated the effects of thiorphan, a selective inhibitor of endopeptidase 24.11 'enkephalinase', kelatorphan ((R)-3-(N-hydroxy-carboxamido-2-benzylpropanoyl)-L-alanine), and RB 38 A ((R)-3-(N-hydroxycarboxamido-2-benzylpropanoyl)-L-phenylalanine) two almost complete inhibitors of enkephalin metabolism, on the naloxone-precipitated morphine withdrawal syndrome in rats. Inhibitors administered intracerebroventricularly reduced several symptoms of the withdrawal syndrome. Jumping, chewing and tooth chattering were decreased by all drugs. The rise in plasma corticosterone and the hypothermia were reduced by kelatorphan and RB 38 A whereas rhinorrhea was blocked by thiorphan, tremor by kelatorphan and diarrhoea by RB 38 A. Other signs remained unchanged. These data suggest that an increase in opioid receptor occupancy by endogenous opioid peptides, protected from biotransformation specially by mixed inhibitors reduced the severity of the morphine abstinence symptoms in rats.

Comparative study in mice of flunitrazepam vs. diazepam on morphine withdrawal syndrome

1. There is some evidence that benzodiazepine may modify the opioid withdrawal syndrome. We have investigated the effect of two different benzodiazepines, diazepam and flunitrazepam, on the morphine withdrawal syndrome experimentally induced in mice. 2. Opiate dependence has been induced by administration of morphine s.c. over a period of five days. Two hours after last morphine administration withdrawal syndrome was induced by s.c. injection of naloxone (5mg/kg). The number of jumps, wet-dog-shakes and paw tremor, and the presence or absence of ptosis, diarrhea, teeth chattering and body tremor were evaluated after naloxone injection. 3. All the signs of morphine withdrawal syndrome was antagonized by flunitrazepam and diazepam, only wet-dog-shake was strongly increased by flunitrazepam.