N. N. Klyueva - Ph.D. (Boil.), Research Scientist, Federal State Budgetary Institution «Research Institute of Experimental Medicine» under the North-West Branch of Russian Academy of Medical Sciences, Saint Petersburg
P. D. Shabanov - Dr. Sc.(Med.), Professor, Chief of Pharmacology Department, Federal State Budgetary Institution «Research Institute of Experimental Medicine» under the North-West Branch of Russian Academy of Medical Sciences, Saint Petersburg. E-mail: nnklyueva@gmail.com

Application of a diet enriched with cholesterol, which causes in male rats, individual differences in the accumulation of cholesterol in the blood serum and its distribution in lipoproteins, which may be due to genetically determined characteristics of animals. Hypersensitivity of rats to cholesterol-rich diet is inversely related to the ability of rats to the elaboration of a conditioned drinking reflex [1]. It is shown that in rats with hyperlipidemia it is difficult to develop a conditioned reflex as compared with control animals. Easily trained animals differ from poorly trained on the content of cholesterol in blood serum and in sympatic membranes of brain neurons [2]. Determination of lipids in blood serum and liver showed that the initial content of cholesterol in the blood serum of trainable rats differed significantly from that of untrainable animals. They were respectively 45.8 and 63.2 mg/dl. Application hyperholesterolemic diet showed that the trainable animals were less sensitive to increased concentrations of serum cholesterol compared with the untrainable animals. When hypercholesterolemic diet lasted 20 days content the cholesterol in blood serum in groups trainable animals was 51.1 mg/dl, while untrainable  84.4 mg/dl. Differences were observed in cholesterol and triglycerides levels in the liver also. Pre-selection of rats for their ability to develop a conditioned reflex (trainable and untrainable) gives untrainable animals sustained moderate hypercholesterolemia in 10 days.