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Abstract
Mean arterial pressure (MAP), heart rate (HR), plasma epinephrine (E), plasma norepinephrine
(NE), and plasma corticosterone (CORT) were measured in 3-month- and 24-month-old
male Wistar rats exposed to a conditioned emotional stress response (CER) paradigm
and a conditioned defensive burying (CDB) paradigm. In the CER situation blood samples
were taken during reexposure to the training environment one day after a single inescapable
footshock (0.6 mA, AC for 3 s) had been administered. In the CER paradigm the young
rats displayed passive behavior (immobility) accompanied by an increase in plasma
levels of CORT and E, whereas both the control and conditioned animals showed increased
NE responses. Previously shocked aged rats exhibited an attenuated plasma NE response,
whereas levels of E remained elevated to a greater extent. Aged animals showed elevated
basal levels of CORT one day after footshock administration. Stress-induced immobility
was preserved in the aged rats. These animals had an increase in basal MAP values
and a decrease in basal HR values compared to young ones. In the CDB paradigm, rats
were exposed to a nonelectrified probe 1 day after the repeated shock (2 mA/contact)
procedure. Young rats displayed defensive burying accompanied by increments in MAP,
HR, CORT, and NE. The aged animals showed similar hormonal, autonomic, and behavioral
stress responses. Thus, the age-related alterations in neuroendocrine and autonomic
response patterns are apparent in stressed animals during behavioral passivity in
absence of control (CER) rather than during active control (defensive burying).