Structural and segregational stability of various replicons in Actinobacillus actinomycetemcomitans.

Few vectors suitable for cloning in Actinobacillus actinomycetemcomitans, a periodontal pathogen, have been described. These plasmids were based either on the native A. actinomycetemcomitans replicon, pVT736-1, or derivatives of the IncP and IncQ family of plasmids. Their usefulness as cloning vectors is limited because of instability or size. Therefore, the ability of additional replicons to function in A. actinomycetemcomitans was evaluated. Derivatives of p15A, ColE1/f1, and pWV01 transformed A. actinomycetemcomitans efficiently and exhibited no structural instability in the new host. The stable maintenance of A. actinomycetemcomitans-specific DNA fragments inserted into the p15A derivative, pDMG4, demonstrated the ability of this plasmid to function as a cloning vector. In addition, pVT736-1 was used to clone selectable markers directly into A. actinomycetemcomitans. These constructs were structurally and segregationally stable.

Losartan reduces ethanol intoxication in the rat.

Results of a previous study showed that ethanol inhibition of hippocampal long-term potentiation (LTP) induction was mediated by angiotensin II (AII) and the AT1 subtype receptor because it was blocked by losartan, a specific AT1 antagonist. Because LTP is an important hippocampal function involved in the memory process and other behaviors, it is possible that losartan might block some of the directly observable ethanol-induced changes in rat behavior. Results demonstrate that losartan can effectively block some of the intoxicating effects of low doses of ethanol, 2 g/kg PO or IP. However, even a high dose of losartan 20 mg/kg IP, did not reduce significantly any of the intoxicating effects of the higher dose of 4 g/kg administered by gavage. Higher doses of ethanol might be more difficult to block because of a direct effect on the post synaptic membrane.

Role of angiotensin II and AT1 receptors in hippocampal LTP.

Results of a previous study showed that angiotensin II (AII) inhibited the induction of long-term potentiation (LTP) in hippocampal granule cells in response to dorsomedial perforant path stimulation in urethane-anesthetized rats. The results of present experiments demonstrate a dose-dependent inhibition of LTP induction under the same conditions due to ethanol (EtOH) administered by stomach tube and diazepam (DZ) injected IP. The inhibition of LTP induction by EtOH and DZ can be blocked by saralasin (SAR) applied directly to the dorsal hippocampus and by lorsartan (DuP 753) administered IP. Lorsartan or a metabolite crosses the blood-brain barrier because it also blocks the inhibition of LTP induction due to AII administration directly into the dorsal hippocampus. Lorsartan is a competitive antagonist of the AT1 subtype AII receptor. Therefore, the AII and the EtOH and DZ inhibition of LTP induction are mediated by the AII subtype receptor AT1. AIII and the AT2 antagonist PD123319 did not produce any significant effects. These in vivo effects can be reproduced in brain slices and therefore cannot be attributed to other factors, such as the urethane. In addition, electrical stimulation of the lateral hypothalamus (LH) inhibits LTP induction, and the inhibition can be blocked by SAR. These data on LH stimulation indicate that LH AII-containing neurons send axons into the hippocampus that inhibit the induction of LTP. These results not only provide new information on a neurotransmitter involved in the amnesic effects of benzodiazepines and ethanol-induced memory blackouts, but also testable hypotheses concerning recent observations that angiotensin converting enzyme (ACE) inhibitors elevate mood and improve certain cognitive processes in the elderly.

Ethanol and diazepam inhibition of hippocampal LTP is mediated by angiotensin II and AT1 receptors.

Angiotensin II (AII) inhibits the induction of hippocampal long-term potentiation (LTP), a frequency-dependent model of learning and memory. These results demonstrate that the dose-dependent inhibition of LTP due to ethanol (EtOH) and diazepam (DZ) involves AII. Inhibition of LTP induction by AII, EtOH, and DZ can be blocked by AII receptor antagonists saralasin and lorsartan (DuP 753). Lorsartan is a competitive antagonist of the AT1 subtype AII receptor. Therefore, the EtOH and DZ inhibition of LTP induction is mediated by AT1 receptors. These results indicate a new role for AII in the brain in the possible mediation of memory deficits associated with alcohol and the benzodiazepines.