positions 156, 158 and 160. Several codon changes can occur due to A-to-I editing at these sites. Thirty-two different mRNA variants can occur leading to 24 different protein isoforms. An Isoleucine to Valine (I/V) at amino acid position 157,161. An Isoleucine to a Methionine(I/M) at amino acid position 157 An Aspartate to a Serine (N/S)at 159 An Aspartate to Asparagine(N/D) at 159 An Asparagine to a Glycine(N/G) at 159. These codon changes which can occur due to A to I editing at these sites can lead to a maximum of 32 different mRNA variants leading to 24 different protein isoforms. The number of protein isoforms is less than 32 since some amino acids are encoded by more than one codon. Another editing site, site F has also been located in the exon complementary sequence (ECS) of intron 5. The ECS required for formation of double stranded RNA structure is found within intron 5. Conservation RNA editing of this receptor occurs at 4 locations in the rat. Editing also occurs in the mouse. The initial demonstration of RNA editing in rat. The predominant isoform in rat brain is VNV which differs from the most common type found in humans. The editing complementary sequence is known to be conserved across Mammalia. Regulation The 5-HT2c receptor is the only serotonin receptor edited despite its close sequence similarities to other family members. 5HT2CR is different due to possessing an imperfect inverted repeat at the end of exon 5 and the beginning of intron 5 allowing formation of an RNA duplex producing the dsRNA required by ADARs for editing. Disruption of this inverted repeat was demonstrated to cease all editing. The different 5HT2CR mRNA isoforms are expressed differently throughout the brain, yet not all of the 24 have been detected perhaps due to tissue specific expression or low frequency editing of a particular type. Those isoforms that are not expressed at all or at a very low frequency are linked by being edited only at site C' and/or site B but not at site A. Some examples of differences in frequency of editing and site edited in different parts of the human brain of 5HT2CR include low frequency of editing in cerebellum and nearly all editing is at site D while in the hippocampus editing frequency is higher with site A being the main editing site. Site C' is only found edited in the thalamus.