Hypothalamic norepinephrine (NE) release regulates arterial pressure by altering sympathetic nervous system activity. Because angiotensin (Ang) (1–7) decreases hypothalamic NE release and this effect may be correlated with a diminished NE synthesis, we hypothesize that Ang‐(1–7) down‐regulates tyrosine hydroxylase (TH), the rate‐limiting enzyme in catecholamines biosynthesis. We investigated the effect of Ang‐(1–7) on centrally TH activity and expression. TH activity was evaluated by the release of tritiated water from 3H‐l‐tyrosine. TH expression and phosphorylation were determined by western blot. Hypothalami from normotensive or spontaneously hypertensive rats pre‐incubated with Ang‐(1–7) showed a significant decrease in TH specific activity. Ang‐(1–7) caused a decrease in TH phosphorylation at Ser19 and Ser40 residues. The heptapeptide induced a decrease in TH expression that was blocked by an AT2 receptor antagonist and not by an AT1 or Mas receptor antagonist, suggesting the involvement of AT2 receptors. The proteasome inhibitor MG132 blocked the Ang‐(1–7)‐mediated TH reduction. In addition, Ang‐(1–7) increased the amount of TH–ubiquitin complexes, indicating that the Ang‐(1–7)‐mediated TH degradation involves ubiquitin conjugation prior to proteasome degradation. We conclude that Ang‐(1–7) down‐regulates TH activity and expression centrally leading to a decrease in the central NE system activity.

The results indicate that the phosphorylation of CREB and expression of Fos protein, as indicators of neural activity, accompany the acquisition and maintenance of nicotine-induced CPP but not CPA in mesolimbic areas (NAc, VTA, PFC, and DStr) as well as in memory consolidation structures (hippocampus and amygdala) and nicotinic receptor are involved in this process. Taken together, these studies identify the brain regions where pCREB activity is essential for nicotine preference.

Since angiotensin (Ang) (1-7) injected into the brain blocked Ang II pressor actions in rats made hypertensive by aortic coarctation (CH), we examined systemic and tissue angiotensin peptide levels, specifically concentrating on the hypothalamic Ang-(1-7) levels. Plasma, heart and kidney isolated from CH rats showed increased levels of Ang I, Ang II and Ang-(1-7) compared with the normotensive group, with Ang II being the predominant peptide in heart and kidney. In the hypothalamus, equimolar amounts of Ang II and Ang-(1-7) were found in the sham group, whereas only Ang-(1-7) levels increased in CH rats. We conclude that aortic coarctation activates systemic and tissue renin-angiotensin system. The increased central levels of Ang-(1-7) in the CH rats suggest a potential mitigating role of this peptide in central control of the hypertensive process.

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