Effects of an Acute Treatment with L-Thyroxine on Memory, Habituation, Danger Avoidance, and on Na+, K+-ATPase activity in Rat Brain

Eleonora   Araujo dos   Reis-Lunardelli; Maria   Rosana   Ramirez; Cibele   Canal   Castro; Adriana   Simon   Coitinho; Caren      Bavaresco; Laura   Schumacher Schuh   da Trindade; Myriam   Fortes   Perrenoud; Angela   Terezinha de Souza   Wyse; Joao   Jose Freitas   Sarkis; Ivan      Izquierdo

doi:10.2174/156720207782446360

Abstract

Thyroid hormones (THs) have a relevant action on brain development and maintenance. By using an acute treatment to induce a hyperthyroid animal model, we aimed at investigating the effect of an altered THs levels on learning and memory and on the activity of Na+, K+-ATPase in the rat brain. Our results have shown that the acute treatment with L-T4 did not alter the retrieval of the inhibitory avoidance task, but had a significant effect on the elevated plus maze and on open-field performance in rats. We suggest that animals subjected to L-T4 administration improved the habituation to a novel environment as well as a better evaluation of a dangerous environment, respectively. Na+, K+-ATPase activity is increased in parietal cortex (30%), but it is not altered in hippocampus in L-T4 treated group. These both brain structures are involved in memory processing and it was previously demonstrated that there is a double dissociation between them for spatial location information, perceptual and episodic memory. We propose the hypothesis that this increase of Na+, K+- ATPase activity in parietal cortex may be correlated to our results in behavior tests, which suggest a role of THs as well as of the Na+, K+-ATPase in the cognitive process.

Keywords: Hyperthyroidism, inhibitory avoidance, open-field, plus maze, Na+, K+-ATPase, hippocampus, parietal cortex