Effects of Some Dopamine Agents on Modulation

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. Aim: Experimental researches on the effects of two substances acting on dopamine receptors on the cognitive processes in rats. Material and methods: The experiment was carried out on white male Wistar rats (150-200g) divided into 3 groups of 6 animals each, treated intra-peritonealy with the same volume of solution as follows: Group I (Control): saline solution 0.3ml; Group II (coded APO): apomorphine 2mg/kbw; Group III (coded SCH): SCH-23390 0.3mg/kbw. Working memory was assessed using the radial-arm maze. The following measures were recorded: the number of entering an arm containing fo od, 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 AN O-VA method. Experimental protocol was implemented according to the recommendations of the " Grigore T. Popa " University Committee for Research and Ethical Issues. Results: 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 discrimin a-tive spatial learning. SCH-23390 administration resulted in a not quite significant increase in the number of entries to repeat compared to control rats. Conclusions: The administration of apomorphine also increased the search efficiency in total arm entries, suggestin g that it facilitates the response in the test session of secondary reinforcement, more than rewarding, e f-fect combined with a lack of discrimination. Our research revealed that D1 receptor antag o-nist SCH-23390 influenced short-time memory, without affecting long-time memory of experimented animals.