Transcriptomic changes following chronic administration of selective serotonin reuptake inhibitors: a review of animal studies.

The review focuses on transcriptomic changes following treatment with serotonin reuptake inhibitor (SSRI) antidepressants. We aimed to overview results of the most established methods for the investigation of the gene expression alterations including northern blotting, in situ hybridization, quantitative reverse transcriptase polymerase chain reaction (qRT-PCR), microarray and RNAseq in various brain regions and after chronic treatment protocols. In spite of some measurable changes in serotonin system mRNA expression, serotonin transporter levels remained mostly unaltered following various treatment protocols. In contrast, tryptophan hydroxylase 2 appeared to be downregulated in serotonergic nuclei, and upregulated in the midbrain regions. Alterations in serotonin receptors lack clear conclusions and changes probably reflect animal strain/substance related- and brain region dependent effects. Brain derived neurotrophic factor was upregulated following many, but not all chronic treatment regimens. GABA and glutamate genes also showed heterogeneous changes, with a surprising NMDA receptor downregulation in areas including the striatum and amygdala, known to be involved in depressive states and stress reactions. The review of the above studies suggests alterations in multiple processes, reflecting the heterogeneity of the action depending on brain area and type of SSRI, and raises the possibility of a novel grouping of antidepressant medications based on their chronic molecular profile rather than on their initial actions.