Maternal cannabis use alters ventral striatal dopamine D2 gene regulation in the offspring

Abstract

Background: Prenatal cannabis exposure has been linked to addiction vulnerability, but the neurobiology underlying this risk is unknown.

Methods: Striatal dopamine and opioid-related genes were studied in human fetal subjects exposed to cannabis (as well as cigarettes and alcohol). Cannabis-related gene disturbances observed in the human fetus were subsequently characterized with an animal model of prenatal Δ-9-tetrahydrocannabinol (THC) (.15 mg/kg) exposure.

Results: Prenatal cannabis exposure decreased dopamine receptor D2 (DRD2) messenger RNA expression in the human ventral striatum (nucleus accumbens [NAc]), a key brain reward region. No significant alterations were observed for the other genes in cannabis-exposed subjects. Maternal cigarette use was associated with reduced NAc prodynorphin messenger RNA expression, and alcohol exposure induced broad alterations primarily in the dorsal striatum of most genes. To explore the mechanisms underlying the cannabis-associated disturbances, we exposed pregnant rats to THC and examined the epigenetic regulation of the NAc Drd2 gene in their offspring at postnatal day 2, comparable to the human fetal period studied, and in adulthood. Chromatin immunoprecipitation of the adult NAc revealed increased 2meH3K9 repressive mark and decreased 3meH3K4 and RNA polymerase II at the Drd2 gene locus in the THC-exposed offspring. Decreased Drd2 expression was accompanied by reduced dopamine D2 receptor (D(2)R) binding sites and increased sensitivity to opiate reward in adulthood.

Conclusions: These data suggest that maternal cannabis use alters developmental regulation of mesolimbic D(2)R in offspring through epigenetic mechanisms that regulate histone lysine methylation, and the ensuing reduction of D(2)R might contribute to addiction vulnerability later in life.

Copyright © 2011 Society of Biological Psychiatry. Published by Elsevier Inc. All rights reserved.

Figures

Figure 1

Dopamine receptor and opioid neuropeptide mRNA levels in human fetal striatum. (A) In situ hybridization autoradiograms showing the distribution pattern of DRD2 and DRD1 mRNA transcripts in the striatum. (B) DRD2 mRNA levels in the NAc and putamen of cannabis-exposed subjects. (C) Correlation of NAc DRD2 mRNA levels with maternal report of cannabis use. (D) DRD1 mRNA levels in the NAc and putamen of cannabis-exposed subjects. (E) Distribution pattern of PENK and PDYN mRNA transcripts in the human fetal striatum. (F) PENK and (G) PDYN mRNA levels in the NAc and putamen of cannabis-exposed subjects. Bar graphs show the cannabis-exposed group (black bars) expressed relative to control (white bars). Date are expressed as mean ± SEM. **, p <0.01 vs control subjects. N=17-24 subjects per group. NAc, nucleus accumbens; Put, putamen; ADJ, average daily joint; dpm/mg, disintegrations per minute per milligram.

Figure 2

Striatal Drd2 mRNA levels in rats exposed to THC in utero. Drd2 mRNA levels in the striatum of PND2 (A) and PND62 (B) rats with prenatal THC exposure. Bar graphs show the THC-exposed group (black bars) expressed relative to control (white bars). Data are expressed as mean ± SEM. *, p < 0.05; **, p < 0.01; ***, p < 0.001 vs control subjects. N=5-16 rats per group. PND, postnatal day.

Figure 3

Dopamine receptor gene regulation in the NAc of adult rats with prenatal THC exposure. (A) Analysis of 2meH3K9 at the Drd2 gene and Drd1 gene. (B) Analysis of 3meH3K4 at the Drd2 gene and Drd1 gene. (C) Analysis of Pol II binding in Drd2 and Drd1 gene. Values are expressed as mean ± SEM. *, p

Figure 4

D2R 3H-raclopride binding in the striatum of adult rats with prenatal THC exposure. Bar graphs show the THC-exposed group (black bars) expressed relative to the vehicle group (white bars). Values are expressed as mean ± SEM. *, p < 0.05 vs vehicle group. N=5 rats per group.

Figure 5

Place conditioning for morphine (4 mg/kg) in adult rats with prenatal THC or vehicle exposure. Data are represented as time spent on drug-paired side on test day. *, p