Comparative Study of the Behavior of Wistar Rats, Dopamine Transporter Heterozygous Rats and Rats after Long-Term Ethanol Consumption in the Morris Water Maze

Dysfunctions of the dopaminergic system are the basis of many neuropsychiatric diseases. A promising model for research is a model of moderate increase in DA system activity: DAT-HET rats heterozygous for the dopamine transporter gene knockout. They are characterized by higher motor activity and cognitive impairments, which allow them to be considered as a possible model of pathologies such as attention deficit hyperactivity disorder. It is known that chronic ethanol consumption leads to dopamine depletion, particularly in the striatum. We suggest that chronically ethanol-consuming rats may serve as a model of moderate hypodopaminergic state, as opposed to DAT-HET rats. The aim of this study was to explore the effect of such modulations of the dopaminergic system on learning and spatial navigation in the Morris water maze. A decrease in dopamine levels compared to DAT-HET rats was found only in rats with a higher level of ethanol preference. In the Morris water maze, the DAT-HET rats showed an unproductive strategy of thigmotaxis significantly more than the ethanol-consuming rats, which led to slower learning. It is possible that the observed impairments in the learning of the spatial task are related to their stress vulnerability, manifested, in particular, by a high level of defecation in the pool. Rats after the chronic ethanol exposure demonstrated a delayed purposeful search for a platform in comparison with the control group, which was expressed in less time spent in the target sector at the beginning of each learning session. The study allows us to conclude that the moderate multidirectional modulation of the activity of the dopaminergic system does not lead to the pronounced impairment in spatial navigation in the Morris water maze, but reduces cognitive flexibility evidenced by longer periods of using unproductive strategies.