Influência da nicotina e da mecamelamina em teste de preferência condicionada por lugar em peixes da espécie Carassius auratus.

Abstract

Nicotine is a neuromodulator of the central nervous system, which has a wide variety of behavioural effects. The aim of this study is to investigate the role of nicotine and mecamylamine on the learning and memory mechanism through conditioning by a positive reinforcement process in 158 fish of the species Carassius auratus. For this purpose a rectangular aquarium was used (30×10×17 cm for total length, width and height, respectively). The aquarium was divided into two compartments, one black and one white. The experiment was done in five days: on the first day: habituation; on the second day: the natural preference of the animal was registered; on the third day: raining session number 1(T1), the animals were subjected to reinforcement in the white compartment; on the fourth day: training session number 2 (T2), the animals were subjected to reinforcement in the white compartment and were injected immediately after training; on the fifth day: test, the preference of the animals between the two compartments was registered once more. The animals were divided into eight groups according to the treatment. Four groups were injected immediately after training: vehicle (n=25); nicotine 2.0mg/kg (n=24); mecamylamine 1.0mg/kg (n=25); mecamylamine 2.0mg/kg (n=24); and four groups were injected three hours after training: vehicle (n=15); nicotine 2.0mg/kg; mecamylamine 1.0mg/kg (n=15); mecamylamine 2.0mg/kg (n=15). The statistical analysis was carried out using a two-way analysis of variance (ANOVA) followed by the Student-Newman-Keuls test or the Friedman test. The variables submitted to the analysis were: the time spent in each compartment; the latency and the number of times the fish crossed from one compartment to the other. The results show that in the groups, which were injected immediately the animals, showed a natural preference for the black compartment before training. In the post-training, the vehicle and mecamylamine 1,0mg/kg groups showed less preference for the black compartment, indicating learning. In the nicotine group there was a significant difference (P<0.01) between the time spent in the black and white compartments, however the animals of this group maintained the preference for the dark environment. In the mecamylamine 2.0mg/kg group, the animals changed the preference between the compartments showing facilitation of the learning process. In relation to latency the animals of the vehicle, mecamylamine 1.0 mg/kg and 2.0mg/kg groups, presented a significant reduction (P<0.05) of the L between the days showing that the animals learned by positive reinforcement and retained the task on the day of the test. In the animals of the nicotine group, there was a significant difference (P<0.05) of latency just between the T2 and the test days, showing a slower learning process. In relation to the number of times the fish crossed from one compartment to the other there was not a significant difference between the groups treated, suggesting that the drugs had no effect on the locomotor activity of the animals. In the groups injected after three hours, the animals still preferred the black compartment, showing that there was not any pro-active effect of the drugs on the memory consolidation process. With regards to latency, our results suggest that there was cholinergic drug action on unspecific neural systems. Thus, it suggests that concerning the immediate groups in this model there was an effect on the learning process.