The effects of MDMA on gene expression in rat cortex were studied after a single injection of 20 mg/kg MDMA. Rats were killed 0.5, 1, 2, 4, 8, and 16 hours, 1 day or 7 days after MDMA administration, and RNA was isolated from frontal cortex. The RNA was used to determine the code DNA related to RNA, indicating gene activation. Genes were identified from a rat gene atlas. After locating genes showing changed expression after MDMA, the authors clustered genes on the basis of direction of expression (upregulated or downregulated) after MDMA administration and the time course of this change, with clustering performed by the GeneSpring computer program. Five clusters were identified; the initial analysis was confirmed with a sample of five representative genes via reverse transcriptase and real time polymerase chain reaction (RT-PCR). Cluster A contained 6 genes with decreased expression 4 h and 1 day after MDMA, and included two genes for types of macrophage inflammatory protein (MIPAlpha, MIP3). Cluster B contained 9 genes with increased expression 1 to 2 hours after MDMA, including genes such as cellular glutathione peroxidase-1 (Gpx-1) that are involved in cellular detoxification, Genes involved in protein synthesis and cellular stress responses were also in this cluster. Cluster C contained 6 genes that were maximally expressed 30 minutes after MDMA, and slowly returned to saline values afterwards, and included genes for nerve growth factor-induced protein 1-A and nerve growth factor-induced protein 1-B (NGF1A and NGF1B). Activity at these Cluster C genes may be related to or triggered by direct activation of serotonin receptors (as through serotonin release and direct activity at 5HT2A receptors). Cluster D contained 3 genes that increased expression, with peak expression 8 hours after drug administration, and included the gene for cell adhesion kinase-Beta (CAKB), a protein that interacts with the extracellular matrix. The 3 genes in Cluster E had a triphasic gene expression profile, with small increases appearing 8 and 16 hours after MDMA, followed by a decrease 1 day after drug followed by another increase 7 days after drug administration. Cluster E genes included the prostoglandin D2 gene (potentially involved in sleep regulation) and laminin, another element of the extracellular matrix. Confirmation of initial analysis was performed on NGFI-1A, NGFI-1B, Gpx-1, heme oxygenase 2 (Hmox2) and serotonin 5HT3 receptor gene (5HTR3). The authors note that while only 5HTR3 gene expression was changed after MDMA, non-significant changes were seen in all serotonin 5HT2 receptor family genes (2A, 2B, 2C), and in 5HT1F, 5HT5A, 5HT5B, 5HT4 and 5HT6 receptor genes. There were no changes in 5HT1A gene expression. Profiles obtained through RT-PCR were similar to profiles obtained through array studies. However, Hmox2 (Cluster B) increase was delayed in RT-PCR studies, increasing at 2-4 hours rather than at 1-2 hours after MDMA, and 5HTR3 expression (cluster not identified, possibly B) was biphasic, increasing at 4 hours after MDMA and then showing smaller increases in expression 3 and 7 days later. Changes in gene expression are interpreted as arising from the following causes; acute effects, responses to receptor stimulation and responses to oxidative stress. Changes in 5HTR3 may indicate response to 5HT depletion after release by MDMA. Several genes (such as NGFI-1A and 1B) may be connected to secondary messenger stimulation, and other genes may indicate changes in serotonin receptors after MDMA. The authors note that expression of some of the identified genes might relate to neuroplasticity, including changes in cell function. Lastly, some genes may be expressed in response to oxidative stress and responses to protect neurons from oxidizing agents. It is difficult to establish the cause for gene expression, since changed gene expression may be both directly or indirectly produced by the reasons already listed by the authors, and others as well, such as effects arising from physiological drug effects (such as locomotion, hyperthermia). It should also be noted that a dose of 20 mg/kg MDMA may influence gene expression differently than lower doses, with lower doses more closely matching doses used by humans. http://www.maps.org/w3pb/new/2002/2002_thiriet_6000_1.pdf