Effects of prenatal cocaine exposure on social development in mice

Prenatal cocaine exposure (PCE) in humans and animals has been shown to impair social development. Molecules that mediate synaptic plasticity and learning in the medial prefrontal cortex (mPFC), specifically brain-derived neurotrophic factor (BDNF) and its downstream signaling molecule, early growth response protein 1 (egr1), have been shown to affect the regulation of social interactions (SI). In this study we determined the effects of PCE on SI and the corresponding ultrasonic vocalizations (USVs) in developing mice. Furthermore, we studied the PCE-induced changes in the constitutive expression of BDNF, egr1 and their transcriptional regulators in the mPFC as a possible molecular mechanism mediating the altered SI. In prenatal cocaine-exposed (PCOC) mice we identified increased SI and USV production at postnatal day (PD) 25, and increased SI but not USVs at PD35. By PD45 the expression of both social behaviors normalized in PCOC mice. At the molecular level, we found increased BDNF exon IV and egr1 mRNA in the mPFC of PCOC mice at PD30 that normalized by PD45. This was concurrent with increased EGR1 protein in the mPFC of PCOC mice at PD30, suggesting a role of egr1 in the enhanced SI observed in juvenile PCOC mice. Additionally, by measuring the association of acetylation of histone 3 at lysine residues 9 and 14 (acH3K9,14) and MeCP2 at the promoters of BDNF exons I and IV and egr1, our results provide evidence of promoter-specific alterations in the mPFC of PCOC juvenile mice, with increased association of acH3K9,14 only at the BDNF exon IV promoter. These results identify a potential PCE-induced molecular alteration as the underlying neurobiological mechanism mediating the altered social development in juvenile mice.