An increasing number of states are legalizing marijuana (Cannabis sativa), yet the neurobiological consequences are largely unknown. During pregnancy, the human fetus is particularly vulnerable to exogenous insults, such as exposure to drugs. To date, cannabis is the most commonly abused illicit drug by pregnant mothers in North America. Epidemiological studies have documented a significant link between repeated early cannabis exposure and an increased risk for subsequent neuropsychiatric abnormalities, including drug addiction and schizoafective disorders. Cannabis is known to target cannabinoid receptors, which are involved in hardwiring the brain during the prenatal period and are expressed on neurons that control dopamine neurotransmission in the nucleus accumbens (NAc). Data from both our unique human fetal brain collection and rat model show a significant decrease in dopaminergic D2 receptor (Drd2) gene expression in the NAc folowing prenatal cannabis/THC exposure. Interestingly, our animal studies demonstrated that this D2 receptor reduction is caused by altered mRNA expression and it persists into adulthood, thus indicating a molecular mechanism, which can sustain a long- term temporal effect that canot be explained by individual genotype. The epigenome controls gene regulation and is influenced by the environment, thus it is a highly relevant biological candidate capable of maintaining aberrant D2 receptor function as a result of developmental drug exposure. A major epigenetic mechanism known to be crucial for neurodevelopment is covalent modifications of nucleosomal histones on chromatin that regulate gene transcription. Preliminary data indicate that the Drd2 gene contains abnormal histone H3 methylation marks in adult rats that were exposed to THC prenatally. The purpose of this proposal is to evaluate how prenatal THC exposure alters chromatin methylation through histone modifying enzymes that disrupt the regulation and function of D2 receptors, leading to increased sensitivity to develop addiction later in life. To investigate the mechanisms underlying histone modification disruption, mRNA and protein levels of histone modifying enzymes will be determined by qPCR and western blot analysis in rats exposed to THC prenatally. The striatal anatomical pattern of the identified histone modifying enzyme mRNA levels will be examined in cannabis and control subjects from our unique human fetal brain bank. To determine the specific histone modifying enzymes behind Drd2 reduction, candidate proteins wil be manipulated via knock-down or overexpression in a neuronal cell line and consequences on the chromatin structure and Drd2 expression will be studied. Lentiviral-mediated modulation of the expression of the relevant histone modifer identified will be conducted in the NAc of rats with prenatal THC exposure and the behavioral consequences evaluated in relation to heroin self- administration to gain insight into the relationship between THC-induced molecular changes and phenotype.
Marijuana is the most commonly abused drug among pregnant women, despite studies that report that fetuses exposed to this drug have an increased susceptibility to psychiatric diseases later in life, including a drug addiction. We have found that marijuana changes chromatin structure in specific brain regions that results in abnormalities in neurotransmitter systems linked to addiction risk. This project serves to evaluate how marijuana causes these irregularities, through the investigation of underlying proteins, to ultimately better understand the mechanism behind addiction vulnerability.
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