Influence of the early stress of maternal separation on the prefrontal cortex transcriptome

Exposure to early stress (ES) is known to enhance adult vulnerability for anxiety and depressive behaviors. The molecular and cellular pathways altered in response to ES that contribute to the establishment of a substrate for susceptibility to adult psychopathology are not well understood. Focusing on the prefrontal cortex (PFC), a brain region implicated in the modulation of emotional responses, we examined the consequences of the early stress experience of maternal separation (MS) on the adult PFC transcriptome. Microarray analysis identified alterations in genes associated with signal transduction, neuronal excitability, G-protein signaling and stress responses in the PFC of adult animals previously exposed to ES. Our results also indicated that the pattern of gene expression changes observed in ES animals contains a component in common with that induced by 5-HT2A/C receptor stimulation in control animals, suggesting enhanced 5-HT2A/C receptor-mediated signaling in ES animals. Further, our microarray results reveal that a history of ES alters the DOI-induced transcriptome in the PFC. We used the early stress (ES) paradigm of maternal separation (MS), which was performed as described below. In brief, post birth the litters were assigned to either the control or the MS group. Pups from the MS litters were separated from their mother every day for a period of 3 hours from postnatal day 2 (p2) to postnatal day 14 (p14), while the control litters were left undisturbed. After p14, the MS pups were left undisturbed and all litters were weaned at postnatal day 30. Experiments on adult control and MS rats were performed at postnatal day 60. To determine transcriptome alterations that arise in the PFC following a history of ES, a microarray analysis was performed. Further, to address gene expression changes that arise following 5-HT2 stimulation, we used the 5-HT2 partial agonist, DOI. We further compared to the DOI-induced transcriptome in the PFC of control animals with the ES induced transcriptome. Control and MS animals (3 - Control and 4 - Maternally Separated) were examined in adulthood. In addition, control animals were injected with with 8 mg/kg DOI, a 5Ht2a agonist. The groups included Control (Control rats injected with saline; n=3), DOI (control rats injected with 8 mg/kg DOI; n=4), MS (MS rats injected with saline, n=4). Rats were sacrificed 2 hours after the injection by decapitation. The prefrontal cortex was quickly dissected out and stored at -70 till further use. Total RNA from each rat was extracted, labeled with Cy3 and hybridized onto Agilent Custom Rat Array 8X15K (AMADID: G2509F_16352). Each biological replicate was hybridized onto one array, making the total number of arrays 11.