Psychosocial stress, glucocorticoids, and structural alterations in the tree shrew hippocampus

Animal models for chronic stress represent an indispensable preclinical app roach to human pathology since clinical data point to a major role of psych ological stress experiences, acute and/or chronic, to the development of be havioral and physiological disturbances. Chronic emotional arousal is a con sequence of various types of social interactions, and one major neurohumora l accompaniment is the activation of the classic stress circuit, the limbic -hypothalamic-pituitary-adrenocortical (LHPA) axis. The adrenocortical gluc ocorticoid hormones cortisol and corticosterone are principal effecters wit hin this circuit since they affect neurotransmission and neuroendocrine con trol, thus having profound effects on mood and behavior Using the experimen tal paradigm of chronic psychosocial stress in tree shrews, we investigated the impact of aversive chronic social encounters on hippocampal structure and function. In chronically stressed animals, we observed dendritic atroph y of hippocampal pyramidal neurons and an impairment of neurogenesis in the dentate gyrus. However, a stress-induced loss of hippocampal neurons was n ot observed in this animal model. This review summarizes our recent results on structural changes occurring during chronic stress in neurons of the hi ppocampus and their potential influence on learning and memory. We discuss whether these changes are reversible and to what extent glucocorticoids mig ht be responsible for the stress-induced effects. (C) 2001 Elsevier Science Inc. All rights reserved.