Modulation of Serotonin 2C Receptor Editing by Sustained Changes in Serotonergic Neurotransmission

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Abstract
Serotonin 2C (5-HT2C) receptor pre-mRNA is a substrate for RNA editing enzymes that convert five adenosines (named A, B, C′, C, and D editing sites) to inosines. Editing of two of these sites (C′ and C) is crucial for decreasing the efficiency of the receptor to activate G-protein. Nucleotide sequence analysis of mouse forebrain neocortical 5-HT2C mRNA isoforms revealed that editing at these two sites is regulated in a serotonin-dependent manner. In serotonin-depleted mice, C′- and C-site editing is significantly decreased. This results in an increased expression of 5-HT2C mRNA isoforms encoding receptors with higher sensitivity to serotonin. In contrast, a 4 d treatment with the 5-HT2A/2C agonist (±)-1-(4-iodo-2,5-dimethoxyphenyl)-2-aminopropane significantly increases the editing frequency at the C′ site and leads to increased expression of 5-HT2C mRNA isoforms encoding receptors that activate G-protein least efficiently. None of the drug treatments led to alterations in cytoplasmic 5-HT2C mRNA levels. These data indicate that editing of 5-HT2C pre-mRNA is a mechanism that retains basic response properties of 5-HT2Creceptors in the face of changing synaptic input to keep receptor activation within an optimal range for information processing.