Estudo da pressão arterial média basal e de respostas cardiovasculares em ratos submetidos à mudança no ciclo claro/escuro

Abstract

The sympathetic and parasympathetic autonomic nervous system (ANS) adjusts finely the cardiovascular system because the maintenance of Mean Arterial Pressure (MAP) is important for the homeostasis. On the other hand, these fine adjustments on the cardiovascular system can be impaired by different pathologies, acquired genetically or throughout life. Among some pathologies, psychosocial disorders such as high anxiety and depression may cause changes in ANS activity and thus influence these fine adjustments on blood pressure. The rat is an animal very used in laboratories for experiments because its physiological mechanisms resemble that of the human being. It is known that some protocols of changes in the light-dark cycle may affect rat behavior inducing anxiety and depression. The objective of this project was to study the baseline MAP and Heart Rate (HR) as well as the autonomic responses in rats subjected to changes in their light-dark cycle. Groups of rats were placed in a cabinet with 5 hours of exposure to light and 19 hours of exposure to the dark (group 5/19) and the control groups were placed in a different cabinet with a usual light-dark cycle [(12 hours each) group 12/12]. Both groups (5/19 and 12/12) were subdivided and received daily an intraperitoneal injection of N-acetylcysteine [NAC (1 mL/100 g) an antidepressant agent or PBS (control injection)]. After the end of the treatment, MAP and HR were recorded in unanesthetized rats that had polyethylene tubing implanted into the abdominal aorta through the femoral artery one day before the experiments. A second polyethylene tubing was inserted in the femoral vein for baroreflex and chemoreflex tests. At the end of the experiments and to study the cardiovascular responses to acute anxiety, a test called the "neighboring rat" was made by placing close to the animal 5/19 or 12/12 a box containing another rat, considered "neighbor". The results showed that the 5/19 light-dark cycle did not alter the baseline MAP and HR of the rat. On the other hand, it cycle was able to enhance the pressor response to chemoreflex activation without changes in baroreflex responses. Important, the enhanced pressor response to chemoreflex activation was not restored by chronic NAC treatment. In addition to the test of the "neighboring rat" the animals from 12/12 light dark-cycle presented an increase in the HR and this increase was also enhanced in the animals from 5/19 light-dark cycle. It is noteworthy that before the cardiovascular tests, behavioral tests such as open field, sucrose consumption and forced swim were also performed.