The effect of acute immobilization stress on the expression of synaptic proteins in serotonin transporter deficient mice

Depression and anxiety disorders are stress related disorders and they are associated with disturbances in the serotonergic system, in which the serotonin transporter (5-HTT) plays an important role. As 5-HTT-knockout mice represent an artificially hyperserotonergic environment, exhibit an anxious phenotype and exaggerated responses to stress they seem to be a practical model to investigate the role of the serotonergic system in the context of stress reactions and anxiety disorders. Synaptic proteins modulate the release of neurotransmitters into the synaptic cleft and seem to be involved in stress reactions. We focused our interest on the synaptic proteins Synaptotagmin (Syt) I & IV and Syntaxin (Stx) 1a. By the use of quantitative real time-PCR we previously showed differences in the expression of these synaptic proteins in different brain regions of 5-HTT-knockout and wild-type mice. In the present study we examined the effects of acute immobilization stress on synaptic protein expression. Exposure to acute stress primarily alters gene expression of Stx1a in hypothalamus and raphe of 5-HTT KO mice. Measurement of corticosterone plasma levels revealed increased levels in all 5-HTT-genotypes after stress. In conclusion, this could point to an important role of Syntaxin 1a in stress reactions. Our results support the notion that synaptic proteins play a significant role in the pathophysiology of stress related and affective disorders.