Sex, but not juvenile stress, affects reversal learning and DRL performance following cocaine administration.

INTRODUCTION: Early adversity, impulsivity and sex all contribute to the risk of developing substance use disorder. Using rats, we examined how juvenile stress interacts with sex and cocaine to affect performance on a serial reversal task and a differential reinforcement of low rates 10 s (DRL10) task. The expression of dopamine-related proteins in several brain areas was also assessed. METHODS: From postnatal days (PND) 25-29, rats were exposed to a variable stress protocol. In adulthood, rats were trained on the reversal task and the effects of cocaine (0, 10, or 20 mg/kg, IP) on performance were assessed. Next, rats were trained on the DRL10 task and the effects of cocaine on performance were assessed. Finally, brains were extracted, and Western blot analyses conducted. RESULTS: Juvenile stress did not affect behavior. Sex did not affect baseline performance in either task. In the reversal task, cocaine decreased % high probability responses and the number of rewards earned in both sexes. Cocaine had sex-dependent effects on omissions, low probability responses and response latencies. In the DRL10 task, cocaine decreased the peak latency to respond and the number of rewards earned in both sexes. Cocaine had sex-dependent effects on peak rate of responding, response efficiency, burst responses and long responses. Female rats exhibited increased expression of DRD1 receptors in the striatum. DISCUSSION: These data contribute to the growing literature demonstrating sex differences in the behavioral effects of cocaine and suggest that DRD1 receptors could contribute to the observed behavioral sex differences.

Prenatal alcohol exposure results in brain region- and sex-specific changes in circHomer1 expression in adult mouse brain.

Circular RNAs (circRNAs) are a novel category of covalently-closed non-coding RNAs mainly derived from the back-splicing of exons or introns of protein-coding genes. In addition to their inherent high overall stability, circRNAs, have been shown to have strong functional effects on gene expression via a multitude of transcriptional and post-transcriptional mechanisms. Furthermore, circRNAs, appear to be particularly enriched in the brain and able to influence both prenatal development and postnatal brain function. However, little is known about the potential involvement of circRNAs in the long term influence of prenatal alcohol exposure (PAE) in the brain and their relevance for Fetal Alcohol Spectrum Disorders (FASD). Using circRNA-specific quantification, we have found that circHomer1, an activity-dependent circRNA derived from Homer protein homolog 1 (Homer1) and enriched in postnatal brain, is significantly down-regulated in the male frontal cortex and hippocampus of mice subjected to modest PAE. Our data further suggest that the expression of H19, an imprinted embryonic brain-enriched long non-coding RNA (lncRNA), is significantly up-regulated in the frontal cortex of male PAE mice. Furthermore, we show opposing changes in the developmental- and brain region specific- expression of circHomer1 and H19. Lastly, we show that knockdown of H19 results in robust increases in circHomer1 but not linear HOMER1 mRNA expression in human glioblastoma cell lines. Taken together, our work uncovers notable sex- and brain region-specific alterations in circRNA and lncRNA expression following PAE and introduces novel mechanistic insights with potential relevance to FASD.

A bidirectional competitive interaction between circHomer1 and Homer1b within the orbitofrontal cortex regulates reversal learning.

Although circular RNAs (circRNAs) are enriched in the brain, their relevance for brain function and psychiatric disorders is poorly understood. Here, we show that circHomer1 is inversely associated with relative HOMER1B mRNA isoform levels in both the orbitofrontal cortex (OFC) and stem-cell-derived neuronal cultures of subjects with psychiatric disorders. We further demonstrate that in vivo circHomer1 knockdown (KD) within the OFC can inhibit the synaptic expression of Homer1b mRNA. Furthermore, we show that circHomer1 directly binds to Homer1b mRNA and that Homer1b-specific KD increases synaptic circHomer1 levels and improves OFC-mediated behavioral flexibility. Importantly, double circHomer1 and Homer1b in vivo co-KD results in a complete rescue in circHomer1-associated alterations in both chance reversal learning and synaptic gene expression. Lastly, we uncover an RNA-binding protein that can directly bind to circHomer1 and promote its biogenesis. Taken together, our data provide mechanistic insights into the importance of circRNAs in brain function and disease.

Circular RNA circCCNT2 is upregulated in the anterior cingulate cortex of individuals with bipolar disorder.

Gene expression dysregulation in the brain has been associated with bipolar disorder, but little is known about the role of non-coding RNAs. Circular RNAs are a novel class of long noncoding RNAs that have recently been shown to be important in brain development and function. However, their potential role in psychiatric disorders, including bipolar disorder, has not been well investigated. In this study, we profiled circular RNAs in the brain tissue of individuals with bipolar disorder. Total RNA sequencing was initially performed in samples from the anterior cingulate cortex of a cohort comprised of individuals with bipolar disorder (N = 13) and neurotypical controls (N = 13) and circular RNAs were identified and analyzed using "circtools". Significant circular RNAs were validated by RT-qPCR and replicated in the anterior cingulate cortex in an independent cohort (24 bipolar disorder cases and 27 controls). In addition, we conducted in vitro studies using B-lymphoblastoid cells collected from bipolar cases (N = 19) and healthy controls (N = 12) to investigate how circular RNAs respond following lithium treatment. In the discovery RNA sequencing analysis, 26 circular RNAs were significantly differentially expressed between bipolar disorder cases and controls (FDR < 0.1). Of these, circCCNT2 was RT-qPCR validated showing significant upregulation in bipolar disorder (p = 0.03). This upregulation in bipolar disorder was replicated in an independent post-mortem human anterior cingulate cortex cohort and in B-lymphoblastoid cell culture. Furthermore, circCCNT2 expression was reduced in response to lithium treatment in vitro. Together, our study is the first to associate circCCNT2 to bipolar disorder and lithium treatment.

Prenatal Alcohol Exposure Results in Sex-Specific Alterations in Circular RNA Expression in the Developing Mouse Brain.

Fetal alcohol spectrum disorders (FASD) are heterogeneous disorders associated with alcohol exposure to the developing fetus that are characterized by a range of adverse neurodevelopmental deficits. Despite the numerous genomics and genetic studies on FASD models, the comprehensive molecular understanding of the mechanisms that underlie FASD-related neurodevelopmental deficits remains elusive. Circular RNAs (circRNAs) are a subtype of long non-coding RNAs that are derived from back-splicing and covalent joining of exons and/or introns of protein-coding genes. Recent studies have shown that circRNAs are highly enriched in the brain, where they are developmentally regulated. However, the role of the majority of brain-enriched circRNAs in normal and pathological brain development and function has not been explored yet. Here we carried out the first systematic profiling of circRNA expression in response to prenatal alcohol exposure (PAE) in male and female embryonic day 18 (E18) whole brains. We observed that the changes in circRNA expression in response to PAE were notably sex-specific and that PAE tended to erase most of the sex-specificity in circRNA expression present in control (saccharin-treated) mice. On the other hand, RNA sequencing (RNA-seq) in the same samples showed that changes in protein-coding gene expression were not predominantly sex-specific. Using circRNA quantitative real-time PCR (qRT-PCR), we validated that circSatb2, which is generated from the special AT-rich sequence-binding protein 2 (Satb2) gene, is significantly upregulated in the brain of E18 male PAE mice. We also show that circPtchd2, a circRNA synthesized from dispatched RND transporter family member 3 (Disp3, also known as Ptchd2), exhibits significantly higher expression in E18 control but not PAE female mouse brain relative to males. Taken together, our results demonstrate that PAE differentially alters circRNA expression in the developing brain in a sex-specific manner.