Synapse-specific expression of mu opioid receptor long-term depression in the dorsomedial striatum

The dorsal striatum is a brain region involved in action control, with dorsomedial striatum (DMS) mediating goal-directed actions and dorsolateral striatum (DLS) mediating habitual actions. Presynaptic long-term synaptic depression (LTD) plasticity at glutamatergic inputs to dorsal striatum mediates many dorsal striatum-dependent behaviors and disruption of LTD influences action control. Our previous work identified mu opioid receptors (MORs) as mediators of synapse-specific forms of synaptic depression at a number of different DLS synapses. We demonstrated that anterior insular cortex inputs are the sole inputs that express alcohol-sensitive MOR-mediated LTD (mOP-LTD) in DLS. Here, we explore mOP-LTD in DMS using mouse brain slice electrophysiology. We found that contrary to DLS, DMS mOP-LTD is induced by activation of MORs at inputs from both anterior cingulate and medial prefrontal cortices as well as at basolateral amygdala inputs and striatal cholinergic interneuron synapses on to DMS medium spiny neurons, suggesting that MOR synaptic plasticity in DMS is less synapse-specific than in DLS. Furthermore, only mOP-LTD at cortical inputs was sensitive to alcohol’s deleterious effects. These results suggest that alcohol-induced neuroadaptations are differentially expressed in a synapse-specific manner and could be playing a role in alterations of goal-directed and habitual behaviors

Genetic Selection for Alcohol Preference in Mice Alters Dorsal Striatum Neurotransmission

Background Although it is widely acknowledged that the risk of developing an alcohol use disorder (AUD) is strongly influenced by genetic factors, very little is known about how this genetic predisposition may alter neurotransmission in a way that promotes AUD susceptibility. The dorsal striatum has garnered increased attention as a brain region of interest in AUD development given its significant roles in goal‐directed and habitual behavior. Methods In the present work, dorsal striatal neurotransmission parameters were measured in preclinical mouse models of high and low AUD risk. We performed brain slice whole‐cell patch clamp electrophysiological recordings from medium spiny neurons (MSNs) in the dorsomedial (DMS) and dorsolateral (DLS) striatum of naïve adult male and female selectively bred high‐ and low‐alcohol–preferring lines of mice (HAP and LAP). Results We found that MSNs of HAP mice were significantly more excitable than those of LAP mice, specifically in the DLS. Additionally, the frequencies of spontaneous glutamate‐ and GABA‐mediated currents were both elevated in HAP mice relative to LAP mice in both dorsal striatal subregions, whereas amplitude differences were more variable between lines and subregions. AMPAR/NMDAR current ratios were significantly lower in HAP mice in both DLS and DMS. Conclusions Collectively, these results suggest that genetic predisposition for high or low alcohol consumption produces significantly different basal functional states within both DLS and DMS which may be important factors in the behavioral phenotypes of HAP and LAP mice

Prenatal Opioid Exposure Enhances Responsiveness to Future Drug Reward and Alters Sensitivity to Pain: A Review of PreclinicalModels and Contributing Mechanisms

The opioid crisis has resulted in an unprecedented number of neonates born with prenatal opioid exposure (POE); however, the long-term effects of POE on offspring behavior and neurodevelopment remain relatively unknown. The advantages and disadvantages of the various preclinical POE models developed over the last several decades are discussed in the context of clinical and translational relevance. Although considerable and important variability exists among preclinical models of POE, the examination of these preclinical models has revealed that opioid exposure during the prenatal period contributes to maladaptive behavioral development as offspring mature including an altered responsiveness to rewarding drugs and increased pain response. The present review summarizes key findings demonstrating the impact of POE on offspring drug self-administration (SA), drug consumption, the reinforcing properties of drugs, drug tolerance, and other reward-related behaviors such as hypersensitivity to pain. Potential underlying molecular mechanisms which may contribute to this enhanced addictive phenotype in POE offspring are further discussed with special attention given to key brain regions associated with reward including the striatum, prefrontal cortex (PFC), ventral tegmental area (VTA), hippocampus, and amygdala. Improvements in preclinical models and further areas of study are also identified which may advance the translational value of findings and help address the growing problem of POE in clinical populations

A High-fat, High-sugar ‘Western’ Diet Alters Dorsal Striatal Glutamate, Opioid, and Dopamine Transmission in Mice

Understanding neuroadaptations involved in obesity is critical for developing new approaches to treatment. Diet-induced neuroadaptations within the dorsal striatum have the capacity to drive excessive food seeking and consumption. Five-week-old C57BL/6J mice consumed a high-fat, high-sugar ‘western diet’ (WD) or a control ‘standard diet’ (SD) for 16 weeks. Weight gain, glucose tolerance, and insulin tolerance were measured to confirm an obese-like state. Following these 16 weeks, electrophysiological recordings were made from medium spiny neurons (MSNs) in the medial (DMS) and lateral (DLS) portions of dorsal striatum to evaluate diet effects on neuronal excitability and synaptic plasticity. In addition, fast-scan cyclic voltammetry evaluated dopamine transmission in these areas. WD mice gained significantly more weight and consumed more calories than SD mice and demonstrated impaired glucose tolerance. Electrophysiology data revealed that MSNs from WD mice demonstrated increased AMPA-to-NMDA receptor current ratio and prolonged spontaneous glutamate-mediated currents, specifically in the DLS. Evoked dopamine release was also significantly greater and reuptake slower in both subregions of WD striatum. Finally, dorsal striatal MSNs from WD mice were significantly less likely to demonstrate mu-opioid receptor-mediated synaptic plasticity. Neuronal excitability and GABAergic transmission were unaffected by diet in either striatal subregion. Our results demonstrate that a high-fat, high-sugar diet alters facets of glutamate, dopamine, and opioid signaling within the dorsal striatum, with some subregion specificity. These alterations within a brain area known to play a role in food motivation/consumption and habitual behavior are highly relevant for the clinical condition of obesity and its treatment

Input-selective adenosine A1 receptor-mediated synaptic depression of excitatory transmission in dorsal striatum

The medial (DMS) and lateral (DLS) dorsal striatum differentially drive goal-directed and habitual/compulsive behaviors, respectively, and are implicated in a variety of neuropsychiatric disorders. These subregions receive distinct inputs from cortical and thalamic regions which uniquely determine dorsal striatal activity and function. Adenosine A1 receptors (A1Rs) are prolific within striatum and regulate excitatory glutamate transmission. Thus, A1Rs may have regionally-specific effects on neuroadaptive processes which may ultimately influence striatally-mediated behaviors. The occurrence of A1R-driven plasticity at specific excitatory inputs to dorsal striatum is currently unknown. To better understand how A1Rs may influence these behaviors, we first sought to understand how A1Rs modulate these distinct inputs. We evaluated A1R-mediated inhibition of cortico- and thalamostriatal transmission using in vitro whole-cell, patch clamp slice electrophysiology recordings in medium spiny neurons from both the DLS and DMS of C57BL/6J mice in conjunction with optogenetic approaches. In addition, conditional A1R KO mice lacking A1Rs at specific striatal inputs to DMS and DLS were generated to directly determine the role of these presynaptic A1Rs on the measured electrophysiological responses. Activation of presynaptic A1Rs produced significant and prolonged synaptic depression (A1R-SD) of excitatory transmission in the both the DLS and DMS of male and female animals. Our findings indicate that A1R-SD at corticostriatal and thalamostriatal inputs to DLS can be additive and that A1R-SD in DMS occurs primarily at thalamostriatal inputs. These findings advance the field’s understanding of the functional roles of A1Rs in striatum and implicate their potential contribution to neuropsychiatric diseases

TREM2 is required for microglial instruction of astrocytic synaptic engulfment in neurodevelopment

Variants in the microglial receptor TREM2 confer risk for multiple neurodegenerative diseases. However, it remains unknown how this receptor functions on microglia to modulate these diverse neuropathologies. To understand the role of TREM2 on microglia more generally, we investigated changes in microglial function in Trem2−/− mice. We found that loss of TREM2 impairs normal neurodevelopment, resulting in reduced synapse number across the cortex and hippocampus in 1-month-old mice. This reduction in synapse number was not due directly to alterations in interactions between microglia and synapses. Rather, TREM2 was required for microglia to limit synaptic engulfment by astrocytes during development. While these changes were largely normalized later in adulthood, high fat diet administration was sufficient to reinitiate TREM2-dependent modulation of synapse loss. Together, this identifies a novel role for microglia in instructing synaptic pruning by astrocytes to broadly regulate appropriate synaptic refinement, and suggests novel candidate mechanisms for how TREM2 and microglia could influence synaptic loss in brain injury and disease

Mu opioid receptors on vGluT2‐expressing glutamatergic neurons modulate opioid reward

The role of Mu opioid receptor (MOR)-mediated regulation of GABA transmission in opioid reward is well established. Much less is known about MOR-mediated regulation of glutamate transmission in the brain and how this relates to drug reward. We previously found that MORs inhibit glutamate transmission at synapses that express the Type 2 vesicular glutamate transporter (vGluT2). We created a transgenic mouse that lacks MORs in vGluT2-expressing neurons (MORflox-vGluT2cre) to demonstrate that MORs on the vGluT2 neurons themselves mediate this synaptic inhibition. We then explored the role of MORs in vGluT2-expressing neurons in opioid-related behaviors. In tests of conditioned place preference, MORflox-vGluT2cre mice did not acquire place preference for a low dose of the opioid, oxycodone, but displayed conditioned place aversion at a higher dose, whereas control mice displayed preference for both doses. In an oral consumption assessment, these mice consumed less oxycodone and had reduced preference for oxycodone compared with controls. MORflox-vGluT2cre mice also failed to show oxycodone-induced locomotor stimulation. These mice displayed baseline withdrawal-like responses following the development of oxycodone dependence that were not seen in littermate controls. In addition, withdrawal-like responses in these mice did not increase following treatment with the opioid antagonist, naloxone. However, other MOR-mediated behaviors were unaffected, including oxycodone-induced analgesia. These data reveal that MOR-mediated regulation of glutamate transmission is a critical component of opioid reward

Deletion of Abi3 gene locus exacerbates neuropathological features of Alzheimer's disease in a mouse model of Aβ amyloidosis

Recently, large-scale human genetics studies identified a rare coding variant in the ABI3 gene that is associated with an increased risk of Alzheimer’s disease (AD). However, pathways by which ABI3 contributes to the pathogenesis of AD are unknown. To address this question, we determined whether loss of ABI3 function affects pathological features of AD in the 5XFAD mouse model. We demonstrate that the deletion of Abi3 locus significantly increases amyloid β (Aβ) accumulation and decreases microglia clustering around the plaques. Furthermore, long-term potentiation is impaired in 5XFAD;Abi3 knockout (“Abi3−/−”) mice. Moreover, we identified marked changes in the proportion of microglia subpopulations in Abi3−/− mice using a single-cell RNA sequencing approach. Mechanistic studies demonstrate that Abi3 knockdown in microglia impairs migration and phagocytosis. Together, our study provides the first in vivo functional evidence that loss of ABI3 function may increase the risk of developing AD by affecting Aβ accumulation and neuroinflammation

saeRS and sarA Act Synergistically to Repress Protease Production and Promote Biofilm Formation in Staphylococcus aureus

Mutation of the staphylococcal accessory regulator (sarA) limits biofilm formation in diverse strains of Staphylococcus aureus, but there are exceptions. One of these is the commonly studied strain Newman. This strain has two defects of potential relevance, the first being mutations that preclude anchoring of the fibronectin-binding proteins FnbA and FnbB to the cell wall, and the second being a point mutation in saeS that results in constitutive activation of the saePQRS regulatory system. We repaired these defects to determine whether either plays a role in biofilm formation and, if so, whether this could account for the reduced impact of sarA in Newman. Restoration of surface-anchored FnbA enhanced biofilm formation, but mutation of sarA in this fnbA-positive strain increased rather than decreased biofilm formation. Mutation of sarA in an saeS-repaired derivative of Newman (P18L) or a Newman saeRS mutant (ΔsaeRS) resulted in a biofilm-deficient phenotype like that observed in clinical isolates, even in the absence of surface-anchored FnbA. These phenotypes were correlated with increased production of extracellular proteases and decreased accumulation of FnbA and/or Spa in the P18L and ΔsaeRS sarA mutants by comparison to the Newman sarA mutant. The reduced accumulation of Spa was reversed by mutation of the gene encoding aureolysin, while the reduced accumulation of FnbA was reversed by mutation of the sspABC operon. These results demonstrate that saeRS and sarA act synergistically to repress the production of extracellular proteases that would otherwise limit accumulation of critical proteins that contribute to biofilm formation, with constitutive activation of saeRS limiting protease production, even in a sarA mutant, to a degree that can be correlated with increased enhanced capacity to form a biofilm. Although it remains unclear whether these effects are mediated directly or indirectly, studies done with an sspA::lux reporter suggest they are mediated at a transcriptional level

Expression of G protein-coupled receptors and related proteins in HEK293, AtT20, BV2, and N18 cell lines as revealed by microarray analysis

<p>Abstract</p> <p>Background</p> <p>G protein coupled receptors (GPCRs) are one of the most widely studied gene superfamilies. Thousands of GPCR research studies have utilized heterologous expression systems such as human embryonic kidney cells (HEK293). Though often treated as 'blank slates', these cell lines nevertheless endogenously express GPCRs and related signaling proteins. The outcome of a given GPCR study can be profoundly influenced by this largely unknown complement of receptors and/or signaling proteins. Little easily accessible information exists that describes the expression profiles of the GPCRs in cell lines. What is accessible is often limited in scope - of the hundreds of GPCRs and related proteins, one is unlikely to find information on expression of more than a dozen proteins in a given cell line. Microarray technology has allowed rapid analysis of mRNA levels of thousands of candidate genes, but though often publicly available, the results can be difficult to efficiently access or even to interpret.</p> <p>Results</p> <p>To bridge this gap, we have used microarrays to measure the mRNA levels of a comprehensive profile of non-chemosensory GPCRs and over a hundred GPCR signaling related gene products in four cell lines frequently used for GPCR research: HEK293, AtT20, BV2, and N18.</p> <p>Conclusions</p> <p>This study provides researchers an easily accessible mRNA profile of the endogenous signaling repertoire that these four cell lines possess. This will assist in choosing the most appropriate cell line for studying GPCRs and related signaling proteins. It also provides a better understanding of the potential interactions between GPCRs and those signaling proteins.</p