AGING PROLONGS THE STRESS-INDUCED RELEASE OF NORADRENALINE IN RAT HYPOTHALAMUS

A stress-induced increase in noradrenaline (NA) release was measured b y intracerebral microdialysis in the hypothalamic paraventricular nucl eus of freely moving Wistar-Kyoto rats at three different ages (6, 18 and 24 months). NA levels in 20-min dialysate samples were measured by high-performance liquid chromatography with electrochemical detection . Microdialysis sampling was done at the baseline during a 20-min immo bilization stress and for the next 100 min. Basal NA release was not s ignificantly different in the three age groups. The immobilization str ess increased NA levels (247, 197 and 234% of the baseline for the 6-, 18- and 24-month animals, respectively) which was not significantly d ifferent in the three groups. In the two younger groups NA returned to the baseline in the first sample after the end of the stress (t = 40 min) whereas in the 24-month group it remained significantly higher fo r longer (until t = 60 min). Stress-induced release of hypothalamic NA thus appears to be prolonged in old rats.