IMPACT OF CORTICOTROPIN-RELEASING HORMONE ON EXTRACELLULAR NOREPINEPHRINE IN PREFRONTAL CORTEX AFTER CHRONIC COLD STRESS

We have previously demonstrated that exposing rats to cold (5 degrees C) for 3-4 weeks potentiates the increase in extracellular norepinephr ine (NE) in the medial prefrontal cortex produced by acute tail shock, In the present study, we used microdialysis to determine the duration of cold exposure required to produce this sensitization and explored the mechanism of the phenomenon. Tail shock elicited a twofold greater increase in extracellular NE in the medial prefrontal cortex of rats exposed to cold for 2 weeks than in naive control rats or in rats expo sed to cold for 1 week and tested either immediately or after a 2-week delay. Local infusion of 10 mu M D-amphetamine or 30 mM K+ increased extracellular NE in the medial prefrontal cortex (similar to 350 and 1 90%, respectively) comparably in control rats and rats exposed to cold for 3 weeks, In contrast, intraventricular administration of 3.0 mu g Of corticotropin-releasing hormone increased extracellular NE in the medial prefrontal cortex by 65% in rats exposed to cold for 2 weeks, b ut only 35% in control rats. These results indicate that an enhanced r esponsiveness of noradrenergic neurons to acute tail shock(1) requires similar to 2 weeks of cold exposure to develop and (2) may be mediate d by a change at the level of the noradrenergic cell bodies rather tha n the nerve terminals.