Acute stress induced modification of calcium signaling in learned helpless rats

Previous reports have demonstrated reduced elevations of free intracellular calcium concentration in blood cells of depressed patients after various stimuli. Therefore, a disturbance of intracellular calcium (Ca²⁺) homeostasis has been postulated to be involved in the pathophysiology of mood disorders. It was the aim of the present study to investigate whether Ca²⁺ signaling was affected in spleen T-lymphocytes of rats submitted to a learned helplessness paradigm, an animal model of depression with a high level of construct, face and predictive validity. In addition, we tested for effects of acute stress on the Ca²⁺ signaling in helpless rats, as compared to non-stressed rats. It was found that mitogen-induced Ca²⁺ signaling only tended to be reduced in helpless rats. However, when helpless rats were submitted to acute immobilization stress, Ca²⁺ signaling appeared to be significantly blunted, whereas the same stressor did not affect Ca²⁺ signaling in the non-helpless control rats. These acute stress-induced differences in Ca²⁺ signaling, were not paralleled by a differential increase in plasma corticosterone. It is hypothesized that blunted Ca²⁺ signaling, as assessed in spleen T-lymphocytes of helpless rats, may be a correlate of the increased vulnerability of helpless rats to acute stressors.