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

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.

Effects of experimentally induced maternal hypothyroidism and hyperthyroidism on the development of rat offspring: I. The development of the thyroid hormones–neurotransmitters and adenosinergic system interactions

“…Furthermore, the activity of Ca 2+ ‐ATPase elevated in cerebrum and medulla oblongata only at the end of the 1st week and in all investigated regions at the end of the 2nd and 3rd weeks in relation to control values. dos Reis‐Lunardelli et al (2007) found that Na + ,K + ‐ATPase activity is increased in parietal cortex in L‐T4 treated rat group. Hyperthyroidism, during the developing rat brain, results in a shift in the balance of inhibitory and excitatory modulation after T4 treatment (Bruno et al, 2003).…”

Nongenomic roles of thyroid hormones and their derivatives in adult brain: are these compounds putative neurotransmitters?

“…Three daily injections of 500 µg/Kg/day of T4 improve the performance of thyroidectomized rats in spatial memory tasks. Different memory tasks will give different outcomes, with an inhibitory avoidance task being less sensitive to THs than a spatial memory test ( 118 ). Effects of TH on spatial memory tasks were correlated with effects on NKA activity.…”