Significance of the cerebral dopaminergic neurotransmission for the individual differences in learning and memory...

Using the step-down method for passive avoidance with punishment electroshock reinforcement, the experimental rats were divided according to their individual differences in the capacity for learning and retention into two groups: good learners (GL) and poor learners (PL). Stereotypy and catalepsy methods were used in order to clarify the role of the central dopaminergic (DA-ergic) transmitter mechanisms for the individual differences. Stereotypic motor behaviour was induced by applying the following DA-ergic agonists: apomorphine (2 mg/kg. i.p.), amphetamine (6 mg/kg, s.c.) and elymoklavine (2 mg/kg, i.p.). The stereotypic behaviour was recorded on a 5-point scale. A set of catalepsy tests was used to determine the cataleptic effect of the DA-ergic antagonist haloperidol (1 mg/kg, i.p.). Our experimental results showed that the intensity and duration of the stereotypy caused by the three agents were significantly increased in GL compared with PL. Catalepsy in the PL group appeared later than in the GL group, and its total duration was shorter. The data obtained suggest that in the GL group there is a marked tendency towards a higher level of sensitivity of the brain dopamine receptors, compared with the PL group.