A Neurochemical Approach to the Search for Drugs for the Treatment of Symptoms of Alzheimer’s Disease

Abstract

We performed an analysis of the reciprocal influences of neurons involved in the rapid-eye-movement phase of sleep (REM sleep) under the conditions of changes in the concentrations of various neuromodulators that are characteristic of Alzheimer’s disease. Several approaches to the search for drugs for the weakening of disease symptoms have been proposed taking the results of this analysis into account. The antagonists of orexin receptors were recently suggested for the treatment of Alzheimer’s disease because the anomalously high concentration of orexin, which is specific for this pathology, results in impairment of REM sleep. However, our analysis shows that the treatment with the antagonists of orexin receptors is not appropriate because it may lead to depression of the excitation of cholinergic cells, an additional decrease in the cholinergic deficit, and aggravation of symptoms of the disease. For the same reason it is unlikely that one should apply the antagonists of histamine H1 receptors and the agonists of adenosine A1 receptors. Substances that can lead to reduced activity of orexinergic neurons may be helpful instead. These substances include melatonin and the agonists of melatonin M1 receptors. Administration of these substances should improve REM sleep because it decreases the efficacy of excitation of orexinergic and histaminergic cells. Melanin-concentrating hormone also should decrease the efficacy of excitation of orexinergic cells. Additionally, the antagonists of histamine H3 receptors may be used because they promote the increased efficacy of excitation of neurons that secrete the melanin-concentrating hormone. Experimental evidence exists that indicates the benefits of these substances for improvement of REM sleep and attenuation of cognitive impairments in Alzheimer’s disease. These drugs must be applied before nightfall and their action should not be prolonged because orexinergic cells must be active in the daytime.