Effect of L-DOPA on the Behavioral Activity of Wistar and Spontaneously Hypertensive (SHR) Rats in the Open-Field Test

We studied the effects of i.p. injections of L-DOPA (100 mg/kg) on the behavioral activity of Wistar rats and spontaneously hypertensive rats (SHR) in the open-field test, as well as on the content of catecholamines in the blood plasma of these animals. Prior to the administration of L-DOPA, the total level of locomotor/research activity in SHR was higher, as compared with that in Wistar rats. This was manifested in significantly greater values of the duration of moving of the animals in the center and on the periphery of the field and also in a greater number of rearings on the periphery of this field. At the same time, the episodes of grooming and sitting in Wistar rats were longer. After injections of L-DOPA, interstrain differences increased and became significant for most (9/10) indices of behavioral activity examined in our study. Injections of L-DOPA resulted in significant modifications of the behavioral activity of rats of the above strains, which is evidenced by changes in the number of visits to the peripheral squares of the open field and of rearings in the same field zones. Over repetitive test sessions, interstrain differences between most indices of behavioral activity (except the duration of research activity on the periphery and that of sitting) decreased. Injections of L-DOPA resulted in a significant increase in the content of this agent and dopamine in the blood plasma of rats of both strains; the level of noradrenaline in SHR also increased. The importance of a hereditary factor-determined increase in the activity of catecholaminergic brain systems (first of all, the dopaminergic system) in SHR for the specificity of locomotor behavior of these animals is discussed.