Stress-induced changes in regional monoamine metabolism and behavior in rats

Groups of adult, male, Sprague-Dawley rats were subjected to either restraint at room temperature or cold restraint at 4 +/- 1 degree C for 2 h. Spontaneous motility, measured immediately after the stress, was decreased and defecation scores were increased in the cold restraint group but not in the restraint group. The rats were then sacrificed and prefrontal cortex, nucleus accumbens, and striatum dissected out. The levels of dopamine (DA), dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), serotonin (5-HT), and 5-hydroxyindole acetic acid (5-HIAA) were measured in these areas by high performance liquid chromatography (HPLC) with electrochemical detection. DA levels were decreased in the prefrontal cortex (-68%), nucleus accumbens (-40%), and striatum (-76%) of the cold restraint group when compared to the controls. DA levels were decreased only in the prefrontal cortex of the restraint rats (-31%) when compared to the controls. The cold restraint group also had increased levels of DOPAC in the prefrontal cortex (+66%) and nucleus accumbens (+65%) and increased levels of HVA in the prefrontal cortex (+43%) when compared to the control group. Our results therefore indicate that cold restraint activates DA metabolism in the prefrontal cortex, nucleus accumbens, and striatum while restraint activates DA metabolism in the prefrontal cortex alone. Thus, cold restraint may be a more potent stressor than restraint alone.