Stress-induced Atrophy of Apical Dendrites of Hippocampal CA3c Neurons: Comparison of Stressors

Repeated restraint stress induces an atrophy of apical dendrites of CA3c pyramidal neurons in the hippocampus, but the relationship between stress and adrenocortical activation has not been thoroughly investigated. In order to better understand the relationship between neural and non-neural indices of the severity of stress, we investigated the temporal relationship between CA3c dendritic atrophy and indices of adrenal steroid stress responsiveness. For this purpose, we used two different stress regimens: repeated restraint stress (6 h/day) and a chronic multiple stress paradigm (shaking, restraint and swimming, each day), differing in the degree of adrenal activation produced over 14 and 21 days. Atrophy of dendrites of CA3c neurons was found after 21 days of stress, but not after 14 days, and was of a similar magnitude for both stressors. However, non-neural measures differed between the two stress paradigms: (i) chronic restraint stress caused a significant habituation by day 21 in the corticosterone response to acute restraint, whereas chronic multiple stress exposure was not accompanied by habituation of the corticosterone response to restraint; (ii) chronic restraint stress caused neither adrenal hypertrophy nor thymus atrophy, but did reduce the rate of body weight gain throughout the 21 days, whereas chronic multiple stress caused a transient adrenal hypertrophy (on day 14), delayed suppression of thymus weight (on day 21) and transient reduction of body weight gain (on days 7 and 14, but not on day 21). Thus the non-neural indices of response to stress--although complex in their time course--suggest that the multiple stress regimen is a somewhat more potent chronic stressor for corticosterone and adrenal responses. Yet both stress regimens produced the same degree of apical dendritic atrophy in CA3c pyramidal neurons. These results are consistent with a model in which adrenocortical secretion plays a permissive role in enabling another agent, namely, excitatory amino acids, to produce the final effect.