Memories that last in old age: motor skill learning and memory preservation.

Using an automated test panel, age-associated declines in learning, remembering and performing a novel visuomotor task were assessed in 497 normal adults ranging from 18 to 95 years old. As predicted, task performance times slowed with increasing age in the cross-sectional portion of the study. However in the subsequent longitudinal study, while motor learning was significantly slower in adults over 62 years old, motor memory was pristinely preserved in normal adults from 18 to 95 years old. When tested 2 years after the first training session and without intervening rehearsal, mean performance times were retained and continued to improve by 10% in young adults and 13% in aged adults, reflecting long lasting preservation of motor memories. While the maximum lifetime of an unpracticed, novel motor memory in humans is not known, the present study suggests that new motor memories can be retained for at least 2 years without rehearsal in normal aged adults. This age-resistant component of motor memory stands in contrast to the well-known decrements in other motor and cognitive processes with human aging.

What is a "low dose" of d-amphetamine for inducing behavioral effects in laboratory rats?

BACKGROUND: Because of the amphetamines' abuse potential and capability of exacerbating or inducing mood and psychotic disturbances, investigations of the behavioral effects of amphetamines commonly involve non-human animals, with the laboratory rat being by far the most common species used. Although investigators of the behavioral effects of amphetamine in rats sometimes refer to doses used as being "low", "moderate", "high", etc., it is not clear in what sense these terms apply. OBJECTIVES: To develop an operational definition of a low dose of amphetamine in rats, we reviewed studies that assessed the behavioral effects of dextroamphetamine (d-AMP) in rats in which some subset of doses, administered SC, IM or IP, was described as being "low". We then used the results of these studies to establish what the lowest effective dose ranges were across a variety of behavioral domains and compared these doses and their effects with those obtained with normal, healthy adult humans. RESULTS: While the range of the lowest doses used in the studies with rats was quite broad (0.025-2.0 mg/kg), the median lowest effective doses observed (in the studies using doses of 0.125 mg/kg or less) were between 0.125 and 0.165 mg/kg across the behavioral domains of consummatory behavior, unconditioned or spontaneous behavior, learned behavior, and drug discriminative control. This range of doses was also found to be comparable to the lowest behaviorally effective doses of d-AMP (SC or PO) in normal human adults, which suggests that the sensitivity to the behavioral effects of amphetamine in these two species is fairly comparable. CONCLUSIONS: Because of their ability to alter a wide variety of behaviors in rats, we conclude that low doses of d-AMP are in the 0.1-0.4 mg/kg range. Doses within this range typically: 1) constitute the ED50 in most drug discrimination/generalization procedures; 2) increase a variety of consummatory behaviors; 3) increase a variety of unconditioned or spontaneous motor activities; 4) increase low rate schedule-controlled behavior while exerting variable effects on high rate schedule controlled behavior; and 5) improve performance on some choice tasks, particularly those requiring sustained attention. Our analyses also indicate that, with respect to behavior, investigators do not always agree on what constitutes a low dose of amphetamine in rats and that doses assumed to be low for this species often are relatively high.

Effect of bradykinin-receptor blockade on the response to angiotensin-converting-enzyme inhibitor in normotensive and hypertensive subjects.

BACKGROUND: Angiotensin-converting-enzyme (ACE) inhibitors not only decrease the production of angiotensin II but also decrease the degradation of bradykinin. In this study, a specific bradykinin-receptor antagonist, icatibant acetate (HOE 140), was used to determine the contribution of bradykinin to the short-term effects of ACE inhibition on blood pressure and plasma renin activity in both normotensive and hypertensive subjects. METHODS: We compared the hemodynamic, renal, and endocrine effects of captopril alone (25 mg), captopril plus icatibant (100 microg per kilogram of body weight), the angiotensin II subtype 1-receptor antagonist losartan (75 mg), and placebo in 20 subjects with normal blood pressure and 7 subjects with hypertension. The subjects were studied while they were salt depleted (i.e., in balance on a diet in which they were allowed 10 mmol of sodium per day). The drugs were administered on four separate study days in a single-blind, randomized fashion. RESULTS: The coadministration of icatibant significantly attenuated the hypotensive effect of captopril (maximal decrease in mean arterial pressure for all subjects combined, 10.5+/-1.0 mm Hg, as compared with 14.0+/-1.0 mm Hg for captopril alone; P=0.001), in such a way that the decrease in blood pressure after the administration of captopril plus icatibant was similar to that after the administration of losartan (maximal decrease in mean arterial pressure, 11.0+/-1.7 mm Hg). Icatibant did not alter the renal hemodynamic response to captopril, but it significantly altered the change in plasma renin activity in response to ACE inhibition (-0.4+/-0.4 ng of angiotensin I per milliliter per hour, as compared with 2.0+/-0.7 ng per milliliter per hour for captopril alone; P=0.007). The magnitude of these effects was similar in both the normotensive and the hypertensive subjects, as well as in both the black subjects and the white subjects. CONCLUSIONS: These data confirm that bradykinin contributes to the short-term effects of ACE inhibition on blood pressure in normotensive and hypertensive persons and suggest that bradykinin also contributes to the short-term effects of ACE inhibition on the renin-angiotensin system.