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How Depression Causes a Weak Leg to Stand On
This animal study suggests that depression might be a treatable risk factor for osteoporosis.
Osteoporosis and an increased incidence of fractures have been associated with major depression. The mechanism of these associations has not been defined, nor is it known whether treatment of depression would alleviate the problem. These researchers used an animal model of depression (mice subjected to chronic mild stress for 4 weeks) to investigate the issues.
Compared with control mice, stressed mice had bone loss and fewer osteoblasts, which are responsible for bone formation. Levels of physical activity, sex hormones, and inflammatory cytokines did not differ between stressed and nonstressed groups. However, levels of norepinephrine in bone and of serum glucocorticoids were elevated in stressed mice. Because of sympathetic innervation of bone, researchers gave stressed mice propranolol (a ß-adrenergic blocker); deficits in bone mass were decreased, although depression-like behavior did not change.
The researchers were unable to assess the role of corticosterone, which they attempted to do with adrenalectomized mice. When subjected to stress, these mice showed neither behavioral changes nor bone loss.
When stressed mice were treated with imipramine and exhibited less depression-like behavior, bone formation returned to control levels. Mice without behavioral response to imipramine (half of the sample) displayed no improvement in bone formation.
Comment: These findings linked improvement in bone mass to change in depression-like behavior, not simply to imipramine administration. The authors view the study as "setting the foundation for a discipline that we call ‘neuropsychosteology,’ which is aimed at elucidating the interactions among the brain, behavior, and the skeleton." The practical implication of this study is that treatment of depression might be important in preventing osteoporosis.
— Jonathan Silver, MD
Published in Journal Watch Psychiatry December 4, 2006
Citation(s):
Yirmiya R et al. Depression induces bone loss through stimulation of the sympathetic nervous system. Proc Natl Acad Sci U S A 2006 Nov 7; 103:16876-81.
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