Hiporresponsividade frente ao desafio imunológico nos parâmetros termorregulatórios, hormonais e comportamentais em períodos finais da gestação

Abstract

The administration of Escherichia coli Lipopolysaccharide (LPS), a gram-negative bacterial cell wall product, mimics inflammation, culminating in the production of proinflammatory cytokines such as IL-1β, IL-6 and TNF-α. Moreover, LPS administration promotes sickness behavior, set of behavioral changes, which is characterized by anorexia frames, anhedonia, decreased locomotion and exploratory activity and induces similar behavior to depression and anxiety. There is also the HPA axis activation with consequent production of glucocorticoid hormones, due to the administration of LPS. Nonetheless, pregnancy is a time when there are drastic changes in the HPA axis, and the plasma concentration of glucocorticoids is decreased at the beginning of the same. However, there is an increase in glucocorticoid levels from the second half of gestation. Furthermore, it is known to hyporesponsiveness of the HPA axis during pregnancy, particularly in its final period before the stressors. They are still rare in the literature studies about sickness behavior during pregnancy and the influence of glucocorticoids in hyporesponsiveness in face of stress. This study was proposed with the aim to evaluate the responsiveness of pregnant animals to immune stress caused by LPS administration. For this purpose, saline or LPS (200 μg / kg) were given in pregnant rats (N=8-20; CEUA 644/2015) on the following days of gestation (DG): 6, 9, 12, 15, 18 and 20. Through the open field test, the locomotor activity of the animals was evaluated. It was also evaluated the pattern of food intake after the application of LPS. The social interaction was also evaluated after 2 hours the application of LPS in addition to evaluate the anecdotal status of pregnant females through the analysis of sucrose preference. After the observation that in the 20DG there was no behavioral response, besides the observation that in 12DG there is greater responsiveness to the immunological challenge in behavioral parameters, these two points were taken in order to investigate changes in thermoregulation by telemetry sensors implants, changes in c-Fos labeling in neurons in several brain regions, as well as cytokine and plasma corticosterone levels, also measuring protein levels of IBA-1 and GFAP. It was found in 20DG was not observed any change in temperature of the animals. 12DG there is a biphasic temperature response since the LPS caused hypothermia in the first two hours followed by a drastic rise in temperature. No changes were observed as the neuronal activation in areas such as BNST, MPOA, LS, CPx, SON and PVN when LPS was administered 2 hours before perfusion and collection of the brain in pregnant animals 20DG. In the 12DG, greater expression of c-fos was observed in all brain regions analyzed. No changes were observed in the production of cytokines in 20DG. However, there was an increase in the plasma concentration of TNF-α in pregnant animals after 2 hours the immunological challenge by LPS in 12DG. An increase in the plasma concentration of corticosterone in pregnant animals in 12DG is observed, with no changes in 20DG. Expression of proteins related to the activation of astrocytes (GFAP) and microglia (IBA-1) in the hypothalamus of pregnant rats subjected to LPS in the12DG and 20DG was analyzed by Western Blot technique, with no changes in these parameters were observed. Thus, with the results obtained, there is a hyporesponsiveness to the immunological challenge of LPS in 20DG, since no changes in behavioral parameters were observed, nor did changes in the production of plasma cytokines and corticosterone. In addition, there is no neuronal activation in central areas due to LPS administration in the prepartum period. However, hyperresponsiveness to endotoxemia by LPS in 12DG was observed, since it evoked sickness behavior verified by the deficit in exploratory / locomotor capacity, anorexia, drop in social interaction, anhedonia, alterations in thermoregulatory parameters, since its initial hypothermia followed by increase in body temperature and increased c-Fos expression in brain areas related to sickness behavior, and increase the plasma concentration of TNF-α and corticosterone.