After a single injection of cholinergic neurotoxin ethylcholine aziridinium (AF64A, 3 nmol intracerebroventricularly (i.c.v.)), rats failed to perform the tasks in the active avoidance (learning and retention paradigms) and water maze tests. N-Acetylserotonin (NAS), melatonin and their newly synthesized derivatives, CA-15 and CA-18, (0.3-3.0 mg/kg daily for 12-14 days) reversed the effect of AF64A in a dose-dependent manner with CA-18 being the most active. Melatonin and NAS caused sedation absent in CA-18-treated rats. The studied compounds (25-500 microM for 72 hr) protected against beta-amyloid peptide (beta AP) fragment 25-35-induced neurotoxicity in cerebellar granule cell culture. Our results suggest that neuroprotecting properties of these compounds might mediate their cognition-enhancing effects. The results obtained warrant the further search for the novel types of safe neuroprotectors among the synthetic NAS/melatonin derivatives.

No abstract

It was shown for the first time that estrogens 17 beta- and 17 alpha-estradiols compensate impaired cognitive functions in rats with partial chronic deprivation of cholinergic functions in the central nervous system induced by intracerebral administration of selective cholinergic neurotoxin AF64A. 17 beta-Estradiol produced strong dose-dependent changes in the weights of hormone-sensitive endocrine glands, while 17 alpha-estradiol did not affect the weight of the gonads and slightly influenced (in high concentration) the weights of the adrenal glands and thymus. The positive effects of exogenous 17 beta- and 17 alpha-estradiols on cognitive functions are due to their antioxidant properties, rather than due to specific action on hormone-sensitive endocrine glands.