Chronic social stress reduces dendritic arbors in CA3 of hippocampus and decreases binding to serotonin transporter sites

Male rats housed in mixed-sex groups in a visible burrow system (VBS) form a dominance hierarchy in which subordinate animals show stress-related chan ges in behavior, endocrine function and neurochemistry. Dominants also appe ar to be moderately stressed compared to controls, although these animals d o not develop the more pronounced behavioral and physiological deficits see n in the subordinates. In the present study, we examined the effects of chr onic psychosocial stress on the morphology of Golgi-impregnated CA3 pyramid al neurons. In addition, since serotonin has been implicated in the mechani sms mediating the dendritic remodeling seen with other chronic stress regim ens, we used quantitative autoradiography to measure binding to the seroton in transporter 5HTT) in hippocampus and dorsal and median raphe. Chronic so cial stress led to a decrease in the number of branch points and total dend ritic length in the apical dendritic trees of CA3 pyramidal neurons in domi nant animals compared to unstressed controls; subordinates also had a decre ased number of dendritic branch points. [H-3]paroxetine binding to the 5HTT was decreased in Ammon's horn in both dominants and subordinates compared to controls, while 5HTT binding remained unchanged in dentate gyrus and rap he. The similarity of the changes in 5HTT binding and dendritic arborizatio n between both groups of VBS animals, despite apparent differences in stres sor severity, suggests that these changes may be part of the normal adaptiv e response to chronic social stress. The mechanisms underlying dendritic re modeling in CA3 pyramidal neurons are likely to involve stress-induced chan ges in glucocorticoids and in 5HT and other transmitters. (C) 2000 Wiley-Li ss, Inc.