Enhanced Function of Prefrontal Serotonin 5-HT2 Receptors in a Rat Model of Psychiatric Vulnerability

Prefrontal serotonin 5-HT2 receptors have been linked to the pathogenesis and treatment of affective disorders, yet their function in psychiatric vulnerability is not known. Here, we examine the effects of 5-HT2 receptors in a rat model of psychiatric vulnerability using electrophysiology, gene expression, and behavior. Following the early stress of chronic maternal separation, we found that serotonin has atypical 5-HT2 receptor-mediated excitatory effects in the adult prefrontal cortex that were blocked by the 5-HT2A receptor antagonist MDL 100907. In the absence of a serotonergic agonist, the intrinsic excitability of the prefrontal cortex was not enhanced relative to controls. Yet, in response to stimulation of 5-HT2 receptors, adult animals with a history of early stress exhibit heightened prefrontal network activity in vitro, enhanced immediate early gene expression in vivo, and potentiated head shake behavior. These changes arise in the absence of any major alteration of prefrontal 5-HT2A/C mRNA expression or 5-HT2 receptor binding. Our microarray results and quantitative PCR validation provide insight into the molecular changes that accompany such enhanced 5-HT2 receptor function in adult animals following early stress. We observed persistent prefrontal transcriptome changes, with significant enrichment of genes involved in cellular developmental processes, regulation of signal transduction, and G-protein signaling. Specific genes regulated by early stress were validated in an independent cohort, and several altered genes were normalized by chronic blockade of 5-HT2 receptors in adulthood. Together, our results demonstrate enhanced prefrontal 5-HT2 receptor function and persistent alterations in prefrontal gene expression in a rat model of psychiatric vulnerability.