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.