Experimental design
The rats were brought to the experimental room in their own cages. The animals were allowed at least 60 min to adapt to the experimental room conditions, such as sound and illumination, before starting the experiment. The experimental room was temperature-controlled (25 °C) and acoustically isolated from the other rooms.
After at least 30 min of basal cardiovascular recording, different sets of animals were subjected to bilateral microinjection into the IC of either the selective NMDA glutamate receptor antagonist LY235959 (1 nmol/100 nL), the selective non-NMDA glutamate receptor antagonist NBQX (1 nmol/100 nL) or vehicle (Adami, Barretto-de-Souza, Duarte, Almeida, & Crestani, 2017) (aCSF, 100 nL). Ten minutes after the IC treatment, the animals underwent a 30 min session of restraint stress.
Cardiovascular recordings began at least 30 min before the onset of the restraint and were performed throughout the period of exposure to the restraint stress. Tail skin temperature was recorded immediately after the IC treatment and 7 and 3 min before restraint stress onset (basal measurements). Tail skin temperature was also recorded immediately after restraint stress and every 10 min while the animal remained inside the tube.
The analysis of spontaneous baroreflex activity was performed in 5 min segments of recording at 4 points: before pharmacological treatment (basal), post-treatment and at two points during restraint stress. Analysis during the stress session was performed at 5–10 (point 1) and 20–25 (point 2) min after the onset of restraint. For serum corticosterone measurement, blood was collected immediately before the animal was placed in the restraint tube and 15 min after the onset of restraint stress. The corticosterone measurements were made in the same group of animals that was used for the cardiovascular and temperature measurements.