Cognitive enhancement

The term nootropic has been used to describe a class of compounds defined by the abibty of its members to facibtate learning (36). The compounds are most effective in animals that have had their cognitive abihties compromised in some way. The molecular mechanism undedying the cognitive-enhancing... 

DuP 753 is an orally active AT receptor antagonist and as of this writing is in clinical trials as an antihypertensive (see Cardiovascularagents). AT-11 antagonists affect the brain RAS system to enhance ACh release offering the possibiUty that these agents may function as cognition enhancers. 

However, clinical results with compounds enhancing cholinergic function have not been overly convincing (272). In the case of tacriae, however, the beneficial therapeutic iadex was sufficient to justify regulatory approval ia several countries. Psychostimulants such as pemoline, amphetamine, procaine, and methylphenidate have failed to show cognitive enhancing effects ia patients with dementia, except possibly as iadirect consequences of mood elevation. 

Table 6. Marketed Drugs Used as Cognition Enhancers...

Vasopressin is closely related to oxytocin and both peptides are cyclic in that they contain a disulphide bridge. Although much is known about the peripheral actions of the peptides the extent of our current knowledge of their possible CNS function is that vasopressin appears to act as a cognitive enhancer and has positive effects on learning processes in animals. Vasopressin acts on three receptors, Via and b and a V2 receptor. 

Riedel, W. and Jolles, J., Cognition enhancers in age related cognitive decline. Drugs Aging, 8(4), 245-474, 1996. 

Hsieh MT, Peng WH, Wu CR, Wang WH. The ameliorating effects of the cognitive-enhancing Chinese herbs on scopolamine-induced amnesia in rats. Phytother Res 2000 14 375-377. 

Revell, 1988). These studies were interpreted as showing that nicotine was a cognitive enhancer, boosting alertness through an increase in cholinergic activity (Parrott and Winder, 1989 Revell, 1988 Wesnes and Warburton, 1983 Wesnes and Parrott, 1992). 

Table 14.1. Nootropics the proposed modes of actions for several putative cognitive enhancers. 

The evidence cited here is only a very small sample of the vast quantity of research into putative cognitive enhancers. However, many of these compounds that have demonstrated positive effects are believed to influence cerebral metabolism, whether through increased blood flow, glucose metabolism or other indirect routes, as outlined above. Furthermore, these metabolic effects are hypothesised to be at least partly responsible for the cognitive improvements documented. Indeed, many of the putative cognitive enhancers currently available claim modes of influence (Table 14.1) that would fall in line with a metabolic model of cognitive enhancement. 

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