Participação de neurotransmissores atípicos (endocanabinoides e sulfeto de hidrogênio) no comportamento doentio em ratos

Abstract

Lipopolysaccharide is a component of the cell wall of gram-negative bacteria, which is recognized by immune cells. Peripheral injections of this toxin are able to mimic an infection, generating an inflammatory process. In response to changes in the immune and endocrine levels in the face of an infectious- inflammatory stimulus, we observed behavioral and thermoregulatory changes in the animal, known as sickness behavior. Given this situation, agents that modulate the inflammatory response play an important role. The endocannabinoid system and the gaseous neurotransmitter, hydrogen sulfide (H2S), considered atypical neurotransmitters, have been addressed because participate in various physiological activities associated with the regulation of homeostasis, vascular contraction, anti-inflammatory effects, antioxidants, antiapoptotics, antidepressants and anxiolytics. Therefore, the aim of the present study was to evaluate the participation of atypical neurotransmitters in behavioral and neuroimmune changes observed during sickness behavior. Initially, we selected the dose of LPS, performed a dose-response curve and through behavioral tests, selected the dose of 200 µg / Kg for our study. Then, the animals were submitted to stereotaxis and after seven days, passed through 2 different parts. In Part I, the animals received AM251 (cannabinoid antagonist), or WIN55,212-2 (cannabinoid agonist), or VDM (cannabinoid reuptake inhibitor), or intracerebroventricular (icv) vehicle (V) and 15 minutes after injecting intraperitoneally (ip) saline (S) or LPS (200 µg / Kg). After two hours, submitted the animals to the tests of: open field (OF), food intake (FI) and forced swimming (FS). The animals in Part II also underwent the surgical procedure and after their recovery (5-7 days), received Na2S (H2S donor), or Aminooxyacetate (AOA, CBS enzyme inhibitor) or vehicle (V) i.c.v. and immediately afterwards inject i.p. saline or LPS. After two hours, submitted the animals for the tests of: open field (OF), food intake (FI), social interaction (SI) and forced swimming (FS), however in this second part, we collected the animals' plasma in order to quantify plasma cytokines and a brain structure, the prefrontal cortex, aiming to perform the Western Blotting technique, to quantify GFAP expression in animals pretreated with H2S or AOA, during endotoxemia. The animals in Part I showed a reduction in food intake in the groups treated with V + LPS, AM251 + LPS and VDM + LPS when compared to the control. However, in animals treated with WIN + LPS, we observed an increase in intake compared to the group that received V + LPS. In the OF and FS tests, only those who received V + LPS and AM251 + LPS showed a significant difference in relation to the V + S group, where observed a reduction in the distance traveled in the apparatus and an increase in immobility time, respectively, which allowed to suggest that the endocannabinoid system, via CB1 receivers, does not participate in the modulation of sickness behavior. In the animals in Part II, the group treated with V + LPS showed a reduction in the distance traveled and an increase in the immobility time in the OF, a reduction in the total interaction time in the SI, an increase in the immobility time and a reduction in the swimming time in the FS and reduced food intake compared to the V + S group. This picture was also observed in the group of animals that received AOA + LPS. In those who received Na2S + LPS, observed an increase in the total

interaction time in the SI, a reduction in the immobility time in the FS and an increase in food intake, however, we did not notice a significant difference in the parameters analyzed in the OF, in relation to the control group. As for cytokines, TNF-α and IL1β, observed an increase in their plasma concentrations in all groups when compared to the control group. Regarding the expression of GFAP, observed an increase in the expression of this protein in the groups V + LPS and AOA + LPS, however H2S was able to prevent the increase in GFAP expression induced by LPS. These results demonstrate the pre-treatment with Na2S (H2S donor, i.c.v.), before i.p. of LPS, was able to prevent behavioral changes and astrocyte activation in the face of the immune challenge, allowing to suggest that hydrogen sulfide may influence the manifestation of sickness behavior.