Effects of some dopamine agents on modulation of memory processes performance in rats

Apomorphine is a potent dopamine receptor agonist which has been used as a neuro-protective agent in the treatment of Parkinson's disease. SCH-23390 is a synthetic compound that presents selective D1 dopamine receptors antagonist activity and possesses pharmacologic effects similar to standard antipsychotics.

Experimental researches on the effects of two substances acting on dopamine receptors on the cognitive processes in rats.

The experiment was carried out on white male Wistar rats (150-200 g) divided into 3 groups of 6 animals each, treated intraperitonealy with the same volume of solution as follows: Group I (Control): saline solution 0.3 ml; Group II (coded APO): apomorphine 2 mg/kbw; Group III (coded SCH): SCH-23390 0.3 mg/kbw. Working memory was assessed using the radial-arm maze. The following measures were recorded: the number of entering an arm containing food, but previously entered (working memory errors); the number of entering an arm that was not baited (reference memory errors); time taken to consume all five baits and the number of arms entered until a repeat entry was made (entries to repeat). The data were presented as mean +/- standard deviation and significance was tested by SPSS Statistics for Windows version 17.0 and ANOVA method. Experimental protocol was implemented according to the recommendations of the "Grigore T. Popa" University Committee for Research and Ethical Issues.

In our experimental conditions dopamine agonist apomorphine produced significantly (p < 0.05) more novel choices in the first eight-arm entries than the saline vehicle. The animals treated with apomorphine entered significantly (P < 0.05) more arms compared to the control group. D1 receptor antagonist SCH-23390 induced a significant decrease (p < 0.05) in the number of working memory errors (elements relevant for short-time memory quantification) and average time taken to consume all five baits (p < 0.05), but did not modify the number of reference memory errors (for long-time memory quantification) compared to the control group, suggesting a short-time memory retention enhancement and an improvement of discriminative spatial learning. SCH-23390 administration resulted in a not quite significant increase in the number of entries to repeat compared to control rats.

The administration of apomorphine also increased the search efficiency in total arm entries, suggesting that it facilitates the response in the test session of secondary reinforcement, more than rewarding, effect combined with a lack of discrimination. Our research revealed that D1 receptor antagonist SCH-23390 influenced short-time memory, without affecting long-time memory of experimented animals.