Estudo das relações entre idade, parâmetros cognitivos espaciais e atividade do sistema serotonérgico no hipocampo de ratos

Abstract

Three groups of Wistar male rats were used to study the effects of age on: (i) performance in a spatial cognitive task: Barnes Maze (BM) and (ii) serotonergic parameters in the hippocampus.Training: for learning the task, the rats have to use extra-spatial cues cognitive map. Theaversive stimuli were the height and luminosity on the platform of BM. The reinforce and (ii) serotonergic parameters in the hippocampus.Training: for learning the task, the rats have to use extra-spatial cues cognitive map. The aversive stimuli were the height and luminosity on the platform of BM. The reinforcement was an escape-chamber (EC), which was the only escape among twelve possibilities (eleven ofthem were false escapes) in the BM. The EC was placed in the same position (target quadrant=TQ) in relation to the spatial cues placed on the room walls. Animal performances were expressed as latency (s) and path length (cm) to find the EC. There was a significant effect of age on animal performance during training. However, in the last session, afterconsecutive trials, aged rats performance was similar to the adult and young rats. Statistical analyzes of path length data adjusted for rats ambulation speed showed that the observed aged effect was on cognitive aspect and not on rats motility. Probe trial: twenty-four hours aftertraining, all rats were given a 120-s probe trial, in which the EC was removed and its entrance closed. There was no group effect on memory, expressed as the preference for the TQ (TQP=target quadrant preference) measured during the 1st min (considered as 100%) of theprobe. However, aged rats showed a median of TQP below 50%, while adult and young rats spend more than 60% of the 1st min in the TQ. It indicates they were able to remember, at least partly, the place where the EC was during the training. For assessing behavioural flexibility(BF), an Index of Extinction (IE) was worked out by dividing the TQP in the 1st min by TQP in the 2nd min of the trial. There was no age effect on IE, though the young, but not aged and adult rats, spent shorter time (p=0,025) in TQ during the 2nd min, indicating BF. On the firstday after probe trial, all rats were killed and their hippocampus separated for biochemical assays (5-HT and 5-HIAA) using the High Performance Liquid Chromatography method. There was significant effect of group on the extracellular 5-HIAA levels in both normal and depolarized (high potassium) conditions. There were no significant correlations betweenbehavioural and neurochemical parameters, except between path length (cm) measured during the 3th session of training and total [5-HIAA] for aged rats. The present data show that age affects both the kinetic of spatial learning process and the hippocampal 5-HIAA levels. Inaddition, they indicate that 5-HIAA seems to play a role in the neurobiological mechanism of the observed cognitive change.