Efeito da sede intracelular nas respostas exploratórias e análogas a ansiedade em ratos: possível participação dos receptores AVPR1a e OTR.

Abstract

Thirst is a sensation that induces water intake. This behavior is essential for the maintenance of life, and the vertebrates resort to a set of neurohumoral mechanisms that constantly regulate the body water and sodium content. Different osmotic stimuli, such as water deprivation and salt loading, trigger the release of vasopressin (AVP) and oxytocin (OT) and, consequently, their systemic actions. Recent studies have demonstrated that magnocellular vasopressinergic paraventricular neurons project to extrahypothalamic regions, which include the lateral habenula and central amygdala. Thus, it is possible that these structures and neuropeptides are involved with the changes in anxiety-like/motivated behaviors under conditions of hyperosmolality. The objective of this study was to analyze the effect of the hyperosmolality induced by dehydration on anxiety-like behaviors and gene expression of the AVP and OT receptorsas well as, the enzyme glutamate decarboxylase (GAD) and the vesicular glutamate transporter (vGLUT) in amygdala and habenula. For this purpose, we used Wistar rats (~300g) separated into five different groups: control (CT), water deprivation for 24 hours (WD24) and 48hours (WD48) and salt loading wich NaCl 1.8% for 24 hours (SL24) and 48 hours (SL48). These groups were submitted to the open field test (OF) followed by the elevated plus maze (EPM) while another set of rats underwent the light/dark box test (LDB). All tests were carried out in the night period. To verify the influence of dehydration in gene expression we used RT-qPCR. All data are described as mean ± standard error of the mean and statistical significance was set at p<0.05. Plasma osmolality increased significantly in the PH48 (p=0.0039) and SS48 (p=0.0176) groups while hematocrit increased only in the WD48 group (p=0.0003). In the EPM there was an increased in the percentage of time spent in the open arms in WD48 (p=0,00124) and SL48 (p<0,0001), as well as, increased percentage of entries in the open arms, WD48 (p=0,0143) e SL48 (p<0,0001), indicating an anxiolytic response. In addition, the linear regression analysis showed a positive correlation between the increase in osmolality and the time spent in the open arms (p=0.0142; r=0.3631). In the OF test, no differences were observed, indicating that animals had no increase in spontaneous locomotor activity. Already in the LDB, only WD48 group increased the time in light area (p=0.0424). In relation to, gene expression we observed a significant increase in mRNA for OTR (p=0.0103) in WD48 in the central amygdala, as well as also increased vGLUT expression in habenula (p=0.0430). Our dada demonstrate that the plasma hyperosmolality induced by 48 hours of water deprivation and salt loading induces an anxiolytic-like behavior in rats independently of locomotor activity. This anxiolytic behavior was probably essential for the search for water in dehydrated animals and may involve the participation of OT signaling in the central amygdala.