Sex-Dependent Changes in miRNA Expression in the Bed Nucleus of the Stria Terminalis Following Stress

Anxiety disorders disproportionately affect women compared to men, which may arise from sex differences in stress responses. MiRNAs are small non-coding RNAs known to regulate gene expression through actions on mRNAs. MiRNAs are regulated, in part, by factors such as stress and gonadal sex, and they have been implicated in the pathophysiology of multiple psychiatric disorders. Here, we assessed putative sex differences in miRNA expression in the bed nucleus of the stria terminalis (BNST) – a sexually dimorphic brain region implicated in anxiety – of adult male and female rats that had been exposed to social isolation (SI) stress throughout adolescence. To assess the translational utility of our results, we assessed if childhood trauma in humans resulted in changes in blood miRNA expression that are similar to those observed in rats. Male and female Sprague-Dawley rats underwent SI during adolescence or remained group housed (GH) and were tested for anxiety-like behavior in the elevated plus maze as adults. Small RNA sequencing was performed on tissue extracted from the BNST. Furthermore, we re-analyzed an already available small RNA sequencing data set from the Grady Trauma Project (GTP) from men and women to identify circulating miRNAs that are associated with childhood trauma exposure. Our results indicated that there were greater anxiogenic-like effects and changes in BNST miRNA expression in SI versus GH females compared to SI versus GH males. In addition, we found nine miRNAs that were regulated in both the BNST from SI compared to GH rats and in blood samples from humans exposed to childhood trauma. These studies emphasize the utility of rodent models in studying neurobiological mechanisms underlying psychiatric disorders and suggest that rodent models could be used to identify novel sex-specific pharmacotherapies for anxiety disorders

Detection of Intranasally Delivered Bone Marrow-Derived Mesenchymal Stromal Cells in the Lesioned Mouse Brain: A Cautionary Report

Bone marrow-derived mesenchymal stromal cells (MSCs) hold promise for autologous treatment of neuropathologies. Intranasal delivery is relatively noninvasive and has recently been reported to result in transport of MSCs to the brain. However, the ability of MSCs to migrate from nasal passages to sites of neuropathology and ultimately survive has not been fully examined. In this paper, we harvested MSCs from transgenic mice expressing enhanced green fluorescent protein (cells hereafter referred to as MSC-EGFP) and delivered them intranasally to wild-type mice sustaining mechanical lesions in the striatum. Using fluorescent, colorimetric, and ultrastructural detection methods, GFP-expressing cells were undetectable in the brain from 3 hours to 2 months after MSC delivery. However, bright autofluorescence that strongly resembled emission from GFP was observed in the olfactory bulb and striatum of lesioned control and MSC-EGFP-treated mice. In a control experiment, we directly implanted MSC-EGFPs into the mouse striatum and detected robust GFP expression 1 and 7 days after implantation. These findings suggest that—under our conditions—intranasally delivered MSC-EGFPs do not survive or migrate in the brain. Furthermore, our observations highlight the necessity of including appropriate controls when working with GFP as a cellular marker

The effects of Δ9-tetrahydrocannabinol on the dopamine system

Δ(9)-tetrahydrocannabinol (THC), the main psychoactive ingredient in cannabis, is a pressing concern to global mental health. Patterns of use are changing drastically due to legalisation, availability of synthetic analogues (‘spice’), cannavaping and aggrandizements in the purported therapeutic effects of cannabis. Many of THC’s reinforcing effects are mediated by the dopamine system. Due to complex cannabinoid-dopamine interactions there is conflicting evidence from human and animal research fields. Acute THC causes increased dopamine release and neuron activity, whilst long-term use is associated with blunting of the dopamine system. Future research must examine the long-term and developmental dopaminergic effects of the drug

Overexpression of miR-9 in the Nucleus Accumbens Increases Oxycodone Self-Administration

Background: There is an urgent need to identify factors that increase vulnerability to opioid addiction to help stem the opioid epidemic and develop more efficient pharmacotherapeutics. MicroRNAs are small non-coding RNAs that regulate gene expression at a posttranscriptional level and have been implicated in chronic drug-taking in humans and in rodent models. Recent evidence has shown that chronic opioid treatment regulates the microRNA miR-9. The present study was designed to test the hypothesis that miR-9 in the nucleus accumbens potentiates oxycodone addictive-like behavior. Methods: We utilized adeno-associated virus (AAV) to overexpress miR-9 in the nucleus accumbens of male rats and tested the effects on intravenous self-administration of the highly abused prescription opioid, oxycodone, in 1-hour short-access followed by 6-h long-access sessions, the latter of which leads to escalation of drug intake. In separate rats, we assessed the effects of nucleus accumbens miR-9 overexpression on mRNA targets including RE1-silencing transcription factor (REST) and dopamine D2 receptor (DRD2), which have been shown to be regulated by drugs of abuse. Results: Overexpression of miR-9 in the nucleus accumbens significantly increased oxycodone self-administration compared with rats expressing a control, scrambled microRNA. Analysis of the pattern of oxycodone intake revealed that miR-9 overexpression increased "burst" episodes of intake and decreased the inter-infusion interval. Furthermore, miR-9 overexpression decreased the expression of REST and increased DRD2 in the nucleus accumbens at time points that coincided with behavioral effects. Conclusions: These results suggest that nucleus accumbens miR-9 regulates oxycodone addictive-like behavior as well as the expression of genes that are involved in drug addiction

Induction of stereotypy in dopamine-deficient mice requires striatal D1 receptor activation

Motor stereotypies are abnormally repetitive behaviors that can develop with excessive dopaminergic stimulation and are features of some neurologic disorders. To investigate the mechanisms required for the induction of stereotypy, we examined the responses of dopamine-deficient (DD) mice to increasing doses of the dopamine precursor l-DOPA. DD mice lack the ability to synthesize dopamine (DA) specifically in dopaminergic neurons yet exhibit robust hyperlocomotion relative to wild-type (WT) mice when treated with l-DOPA, which restores striatal DA tissue content to ≈10% of WT levels. To further elevate brain DA content in DD mice, we administered the peripheral l-amino acid decarboxylase inhibitor carbidopa along with l-DOPA (C/l-DOPA). When striatal DA levels reached >50% of WT levels, a transition from hyperlocomotion to intense, focused stereotypy was observed that was correlated with an induction of c-fos mRNA in the ventrolateral and central striatum as well as the somatosensory cortex. WT mice were unaffected by C/l-DOPA treatments. A D1, but not a D2, receptor antagonist attenuated both the C/l-DOPA-induced stereotypy and the c-fos induction. Consistent with these results, stereotypy could be induced in DD mice by a D1, but not by a D2, receptor agonist, with neither agonist inducing stereotypy in WT mice. Intrastriatal injection of a D1 receptor antagonist ameliorated the stereotypy and c-fos induction by C/l-DOPA. These results indicate that activation of D1 receptors on a specific population of striatal neurons is required for the induction of stereotypy in DD mice