Angiotensin-converting enzyme inhibitors and the role of nitric oxide and excitatory amino acids in improvement of cognition and memory

Cognitive effects attributed to angiotensin II may result from its conversion to angiotensin IV

This study tests the hypothesis that the facilitation of learning and improvement of memory observed after an intracerebroventricular (i.c.v.) injection of angiotensin II (Ang II) is, in fact, caused by its derivative angiotensin IV (Ang IV). We ran two memory tests as well as an auxiliary test assessing motor performance in rats injected (i.c.v., 1 nmol in 2 microl saline) with Ang II or Ang IV. There were separate groups receiving peptide or saline five, 10 and 15 minutes before testing. Ang IV significantly increased step-through latencies in a passive avoidance paradigm as well as improved discrimination between familiar and unfamiliar objects in an object recognition test in all groups showing better retrieval of memory of aversive as well as appetitive stimuli in the peptide-treated groups regardless of the time of its injection. In contrast, rats treated with Ang II demonstrated significant improvement of memory of aversive and appetitive stimuli in the same tests only 15 minutes after its i.c.v. injection, with no effect in the groups injected five minutes before testing and slight efficacy in those injected 10 minutes before the test. Numbers of crossings, rearings and bar approaches in an open field were similar both in the peptide-treated and control groups making it unlikely that changes in motor performance affected the memory tests. In line with the present views on the intracellular metabolism of Ang II, these results suggest degradation to Ang IV by aminopeptidases A and N is necessary before the cognitive effects can occur.

Chronic ethanol intake modifies renin-angiotensin system-regulating aminopeptidase activities in mouse cerebellum

In developing cerebellum, where critical periods of vulnerability have been established for several basic substances, it has been extensively studied the wide array of abnormalities induced by exposure to ethanol (EtOH). However, little is known about the effects of EtOH consumption on cerebellar functions in adult individuals. Several studies show participation in cognitive activities to be concentrated in the lateral cerebellum (hemispheres), whereas basic motor functions such as balance and coordination are represented in the medial parts of the cerebellum (vermis and paravermis). In addition to the circulating renin angiotensin system (RAS), a local system has been postulated in brain. The effector peptides of the RAS are formed via the activity of several aminopeptidases (AP). The present work analyses the effect of chronic EtOH intake on the RAS-regulating AP activities in the soluble and membrane-bound fractions of two cerebellar locations: the hemispheres and the vermis. We hypothesize that cerebellar RAS is involved in basic motor functions rather than in cognitive activities.

Captopril and enalapril improve cognition and depressed mood in hypertensive patients

In this study, we evaluate the effects of two angiotensin converting enzyme inhibitors (ACEIs), captopril and enalapril given chronically as antihypertensive treatment, on certain cognitive and emotional processes in humans. Thirty-nine subjects with mild to moderate hypertension and fifteen normotensive controls were divided into four groups consisting of normotensive and hypertensive subjects taking captopril, enalapril, or no medication at all. The Rey Auditory Verbal Learning Test and the Wechsler Memory Scale were used to evaluate their cognitive functioning. Mood changes in all subjects were assessed using the Beck Depression Inventory and the Hopkins Symptom Check- list (HSC).

RESULTS

Untreated hypertensive patients scored lower than normotensive controls in cognitive tests and significantly worse in cumulative recall (P < 0.05) and paired words association (P < 0.01). When compared with normotensive subjects, untreated hypertensive patients also scored significantly higher on the depression with anxiety subscale in HSC (P < 0.05). No significant influence of hypertension was found in any other examined aspect of cognition and mood. In most cases captopril improved and enalapril reversed the adverse memory effects of hypertension. High arterial blood pressure is significantly associated with an impairment of cognition and the occurrence of depression with anxiety in humans. Enalapril and, to a lesser extent, captopril reversed these deficits.

Effects of six anti-hypertensive medications on cognitive performance

OBJECTIVE

To describe and compare the effects of six different antihypertensive medications on cognitive performance.

DESIGN

Prospective, randomized, and double-blind with treatment cross-over.

SETTING

University hypertension clinic and neuropsychology laboratory.

PARTICIPANTS

Ninety-eight Caucasian men between 25 and 55 years of age with mild-to-moderate essential hypertension (88 of whom completed the study), and 32 normotensive men with similar socio-demographic characteristics.

INTERVENTIONS

Six-week treatment periods with atenolol, metoprolol, hydrochlorothiazide, methyldopa, enalapril and verapamil, and 2-week placebo baseline and wash-out periods.

MAIN OUTCOME MEASURES

In-depth neuropsychological assessments and several mood questionnaires were completed during placebo (baseline) periods and active treatment periods. Practice effects due to repeated neuropsychological testing were estimated from data collected concurrently in the normotensive participants.

RESULTS

The antihypertensive treatments lowered blood pressure comparably and did not affect mood or anxiety. Small treatment effects were noted in four of seven domains of cognitive performance. Irrespective of medication type, treatment reduced the simple motor speed (P < 0.001), and slowed completion of two tests measuring perceptuo-motor speed and mental flexibility (P </= 0.05). Manual dexterity declined somewhat with metoprolol and methyldopa (P = 0.01). In contrast, all antihypertensive agents favorably affected performance on several tests that require working memory (P < 0.01). Performance on other tests assessing grip strength, learning and memory, attention and executive function was not affected.

CONCLUSION

Short-term treatment with standard antihypertensive medications was associated with some small decrements in psychomotor performance and small improvements in working memory, without notable drug-class differences. Long-term effects await further study.

Extracellular matrix molecules, long-term potentiation, memory consolidation and the brain angiotensin system

Considerable evidence now suggests an interrelationship among long-term potentiation (LTP), extracellular matrix (ECM) reconfiguration, synaptogenesis, and memory consolidation within the mammalian central nervous system. Extracellular matrix molecules provide the scaffolding necessary to permit synaptic remodeling and contribute to the regulation of ionic and nutritional homeostasis of surrounding cells. These molecules also facilitate cellular proliferation, movement, differentiation, and apoptosis. The present review initially focuses on characterizing the ECM and the roles of cell adhesion molecules (CAMs), matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs), in the maintenance and degradation of the ECM. The induction and maintenance of LTP is described. Debate continues over whether LTP results in some form of synaptic strengthening and in turn promotes memory consolidation. Next, the contribution of CAMs and TIMPs to the facilitation of LTP and memory consolidation is discussed. Finally, possible roles for angiotensins, MMPs, and tissue plasminogen activators in the facilitation of LTP and memory consolidation are described. These enzymatic pathways appear to be very important to an understanding of dysfunctional memory diseases such as Alzheimer's disease, multiple sclerosis, brain tumors, and infections.

Angiotensin IV enhances LTP in rat dentate gyrus in vivo

Angiotensins have been shown to play a significant role in a variety of physiological functions including learning and memory processes. Relatively recent evidence supports the increasing importance of angiotensin IV (Ang IV), in many of these functions previously associated only with Ang II, including learning and memory. An interesting hypothesis generated by these results has been that Ang II is a precursor for the production of a more active peptide fragment, Ang IV. Since Ang II impairs learning and memory, when administered directly or released into the hippocampal dentate gyrus, and inhibits long term potentiation (LTP) in medial perforant path-dentate granule cell synapses, as well; it remained to be seen what effects Ang IV had on LTP in these same synapses. Results of this study show clearly that Ang IV significantly enhances LTP, and the enhancement is both dose and time dependent. The following solutions of Ang IV were administered over a five min period, at the end of baseline and before the first tetanus was applied: 2.39, 4.78, and 9.56 nM. An inverted U-type dose related effect was observed. A complex time related effect was observed with a maximum at 5 min, a return to normal LTP at 30 min and a minimum below normal at 90 min, and a return to normal LTP at 120 min. The effects of the 4.78 nM solution were determined at the following intervals between administration and the first tetanus: 5, 15, 30, 60, 90, and 120 min. The enhancement of LTP can be prevented by pretreatment with Divalinal, an Ang IV antagonist, without any effect on normal LTP. Two solutions of Divalinal were used; 5 nM and 5 microM, and the 5 microM was more effective and completely blocked the enhancement of normal LTP. Results were also obtained with 4.78 nM Nle1-Ang IV (Norleucine), an Ang IV agonist. Norleucine was less effective than Ang IV in the enhancement of normal LTP and displayed a similar time course of activity. Both Ang IV and Norleucine produced a significant suppression of normal LTP at 90 min; that remains to be explained. However, the inhibition by Ang IV was dose dependent and was blocked by Divalinal. The fact that the Ang IV enhancement of normal LTP was blocked by losartan, an Ang II AT1 receptor antagonist, is puzzling since Divalinal had no effect on the inhibition of LTP by Ang II.

Signaling in unicellular eukaryotes

Aspects of intercellular and intracellular signaling systems in cell survival, proliferation, differentiation, chemosensory behavior, and programmed cell death in free-living unicellular eukaryotes have been reviewed. Comparisons have been made with both bacteria and metazoa. The central organisms were flagellates (Trypanosoma, Leishmania, and Crithidia), slime molds (Dictyostelium), yeast cells (Saccharomyces cerevisiae), and ciliates (Paramecium, Euplotes, and Tetrahymena). There are two novel aspects in this review. First, cellular responses are viewed in an evolutionary perspective, rather than from the more prevailing one, in which the unicellular eukaryotes are seen by the mammalian organisms. Second, results obtained with cell cultures in minimal, chemically defined nutrient media at low cell densities where intercellular signaling is strongly reduced are discussed. These results shed light on control mechanisms and their cooperation inside the living cell. Intracellular systems have many common features in unicellular and multicellular organisms.