Summary of Association Research

The results outlined in the previous sections can be summarized as follows. Despite some nonreplications and qualifications, research with diverse methodologies links low serotonergic function to elevated symptoms of depression and to clinical depression. Depressed persons have displayed a blunted response to drug challenge (compared with other persons), and manipulations that reduce available serotonin have induced symptoms among previously depressed persons. Similarly, the short allele of the 5-HTTLPR has been linked to elevated risk of depression, though that link has often depended on the additional presence of adverse life experiences. Thus, there seems to be solid evidence that connects low serotonergic function to depression.

Gender

An issue that should be mentioned in this context concerns the gender difference in depression. Women are roughly twice as likely as men to experience clinical depression in their lifetimes (Kessler et al., 2003). Heritability estimates for depression are also higher among women than among men (Kendler, Gatz, Gardner, & Pedersen, 2006). This suggests that at least some of the gender difference in depression risk may reflect biological vulnerabilities.

In light of this difference, it is of considerable interest that gender differences also exist pertaining to serotonergic function. For example, there is considerable evidence that women are more susceptible than are men to negative mood changes after acute tryptophan depletion (Booij & Van der Does, 2007; Booij et al., 2002; Ellenbogen, Young, Dean, Palmour, & Benkelfat, 1996; Moreno, McGahuey, Freeman, & Delgado, 2006; K. A. Smith et al., 1997; Walderhaug et al., 2007). Also, as noted earlier, two studies relating the short allele of the 5-HTTLPR polymorphism in interaction with stress to depressive symptoms found this association among women but not men (Grabe et al., 2005; Sjoberg et al., 2006). A recent analysis pooling nine studies found that tryptophan depletion creates greater memory impairments among women than among men (Sambeth et al., 2007).

This is not to say that the short allele has behavioral consequences only among women. However, the pattern of consequences may differ by gender. For example, one study has found that the short allele predicts greater aggression in response to stress among men but not women (Verona, Joiner, Johnson, & Bender, 2006). Another found that the short allele of the serotonin transporter gene interacted with adverse childhood environment among men to produce violent adult behavior (Reif et al., 2007). Perhaps the effects of low serotonin function depend partly on interactions of serotonin with sex hormones (L. H. O’Connor & Fischette, 1986).

Дата добавления: 2015-11-14