Figure 2.

Illustration of a mechanistic model linking sleep length (horizontal) and genotype (vertical) in the expression of depressed mood. The 5-HTTLPR polymorphisms (S′S′ and L′L′) are associated with differences in transporter expression³⁰ and number of presynaptic and postsynaptic 5-HT1A receptors.³⁹ Shorter sleep is associated with blunting of 5-HT1A receptor function.²² The synergy between these 2 influences may place those with S′S′ genotype at greater risk for depressed mood symptoms under circumstances of prolonged short sleep, as illustrated by the diagram in the lower right region in which short sleep blunting of 5-HT1A receptors is noted as exacerbating the 5-HT deficits.