Efeitos da pinealectomia na plasticidade neuronal: impacto no comportamento tipo-ansioso e na memória de ratos

Abstract

Melatonin is a hormone, produced mainly by the pineal gland, which acts in various physiological processes. In particular, it plays a role in the phenomena of plasticity in the hippocampus, memorization and mood regulation. Objectives: To investigate the effects of plasticity alterations induced by pinealectomy and how these alterations may interfere with anxiety-like behavior and memory in rats. Methods: The study was carried out with the approval of the UFS Animal Use Ethics Committee (Nº 3490280722). Fifty-four male Wistar rats were used. The animals were divided into: Memory control (CTR-MM); Memory sham (SHAM-MM); Memory pinealectomized (PIN-MM); Anxiety control (CTR-ANS); Anxiety sham (SHAM-ANS); Anxiety pinealectomized (PIN-ANS). The animals underwent stereotactic surgery and subsequently behavioral and immunohistochemical evaluation of the brain was performed. Results: In the open field test, the two-month-old animals in the PIN group spent less time in the center of the apparatus compared to CTR and SHAM. The fourmonth-old PIN group spent less time in the center compared to CTR and SHAM. In the elevated cross maze test, the two-month-old PIN-ANS group spent less time in the open arm compared to CTR-ANS and SHAM-ANS. The PIN-ANS group remained longer in the closed arm compared to CTR-ANS and SHAM-ANS. At four months, the animals in the PIN-ANS group spent less time in the open arm compared to CTR-ANS and SHAM-ANS. In the closed arm, the PIN-ANS group stayed longer compared to CTR-ANS and SHAM-ANS. In the modified elevated cross maze PIN-MM stayed less in the safe arm compared to CTR-MM and SHAMMM. The PIN-MM group remained longer in the aversive arm compared to CTR-MM and SHAM-MM. In the context-conditioned fear in the conditioning phase, there was an increase in the freezing time of PIN-MM compared to CTR-MM. In the same test, PIN-MM showed an increase in freezing time compared to CTR-MM and SHAM-MM. Immunohistochemistry for BDNF showed a reduction in densitometry in the CA1 region compared to CTR. In the memory experiment, an increase in BDNF was observed in the CA1; CA3; dentate gyrus; entorhinal cortex and amygdala regions, with their controls. It is concluded that pinealectomy was capable of causing alterations in the anxiety-like behavior and memory of rats, as well as alterations in plasticity.