Identifying homologous recombination deficiency in breast cancer: genomic instability score distributions differ among breast cancer subtypes.

PURPOSE: A 3-biomarker homologous recombination deficiency (HRD) score is a key component of a currently FDA-approved companion diagnostic assay to identify HRD in patients with ovarian cancer using a threshold score of ≥ 42, though recent studies have explored the utility of a lower threshold (GIS ≥ 33). The present study evaluated whether the ovarian cancer thresholds may also be appropriate for major breast cancer subtypes by comparing the genomic instability score (GIS) distributions of BRCA1/2-deficient estrogen receptor-positive breast cancer (ER + BC) and triple-negative breast cancer (TNBC) to the GIS distribution of BRCA1/2-deficient ovarian cancer. METHODS: Ovarian cancer and breast cancer (ER + BC and TNBC) tumors from ten study cohorts were sequenced to identify pathogenic BRCA1/2 mutations, and GIS was calculated using a previously described algorithm. Pathologic complete response (pCR) to platinum therapy was evaluated in a subset of TNBC samples. For TNBC, a threshold was set and threshold validity was assessed relative to clinical outcomes. RESULTS: A total of 560 ovarian cancer, 805 ER + BC, and 443 TNBC tumors were included. Compared to ovarian cancer, the GIS distribution of BRCA1/2-deficient samples was shifted lower for ER + BC (p = 0.015), but not TNBC (p = 0.35). In the subset of TNBC samples, univariable logistic regression models revealed that GIS status using thresholds of ≥ 42 and ≥ 33 were significant predictors of response to platinum therapy. CONCLUSIONS: This study demonstrated that the GIS thresholds used for ovarian cancer may also be appropriate for TNBC, but not ER + BC. GIS thresholds in TNBC were validated using clinical response data to platinum therapy.

The landscape of BRCA1 and BRCA2 large rearrangements in an international cohort of over 20 000 ovarian tumors identified using next-generation sequencing.

BACKGROUND: Approximately half of ovarian tumors have defects within the homologous recombination repair pathway. Tumors carrying pathogenic variants (PVs) in BRCA1/BRCA2 are more likely to respond to poly-ADP ribose polymerase (PARP) inhibitor treatment. Large rearrangements (LRs) are a challenging class of variants to identify and characterize in tumor specimens and may therefore be underreported. This study describes the prevalence of pathogenic BRCA1/BRCA2 LRs in ovarian tumors and discusses the importance of their identification using a comprehensive testing strategy. METHODS: Sequencing and LR analyses of BRCA1/BRCA2 were conducted in 20 692 ovarian tumors received between March 18, 2016 and February 14, 2023 for MyChoice CDx testing. MyChoice CDx uses NGS dosage analysis to detect LRs in BRCA1/BRCA2 genes using dense tiling throughout the coding regions and limited flanking regions. RESULTS: Of the 2217 PVs detected, 6.3% (N = 140) were LRs. Overall, 0.67% of tumors analyzed carried a pathogenic LR. The majority of detected LRs were deletions (89.3%), followed by complex LRs (5.7%), duplications (4.3%), and retroelement insertions (0.7%). Notably, 25% of detected LRs encompassed a single or partial single exon. This study identified 84 unique LRs, 2 samples each carried 2 unique LRs in the same gene. We identified 17 LRs that occurred in multiple samples, some of which were specific to certain ancestries. Several cases presented here illustrate the intricacies involved in characterizing LRs, particularly when multiple events occur within the same gene. CONCLUSIONS: Over 6% of PVs detected in the ovarian tumors analyzed were LRs. It is imperative for laboratories to utilize testing methodologies that will accurately detect LRs at a single exon resolution to optimize the identification of patients who may benefit from PARP inhibitor treatment.

Pharmacogenomic Profiling of Pediatric Patients on Psychotropic Medications in an Emergency Department.

OBJECTIVE: The aim of the study was to evaluate the ability of a combinatorial pharmacogenomic test to predict medication blood levels and relative clinical improvements in a selected pediatric population. METHODS: This study enrolled patients between ages 3 to 18 years who presented to a pediatric emergency department with acute psychiatric, behavioral, or mental health crisis and/or concerns, and had previously been prescribed psychotropic medications. Patients received combinatorial pharmacogenomic testing with medications categorized according to gene-drug interactions (GDIs); medications with a GDI were considered "incongruent," and medications without a GDI were considered "congruent." Blood levels for escitalopram, fluoxetine, aripiprazole, and clonidine were evaluated according to level of GDI. Relative clinical improvements in response to the prescribed psychotropic medications were measured using a parent-rated Clinical Global Impression of Improvement (CGI-I) assessment, where lower scores corresponded with greater improvement. RESULTS: Of the 100 patients enrolled, 73% reported taking ≥1 incongruent medication. There was no significant difference in CGI-I scores between patients prescribed congruent versus incongruent medications (3.37 vs 3.68, P = 0.343). Among patients who presented for depression or suicidal ideation, those prescribed congruent medications had significantly lower CGI-I scores compared with those taking incongruent medications ( P = 0.036 for depression, P = 0.018 for suicidal ideation). There was a significant association between medication GDI and blood levels for aripiprazole (n = 15, P = 0.01) and escitalopram (n = 10, P = 0.01). CONCLUSIONS: Our preliminary findings suggest that combinatorial pharmacogenomic testing can predict medication blood levels and relative outcomes based on medication congruency in children presenting to an emergency department with acute psychiatric/behavioral crises. Additional studies will be needed to confirm these findings.

Review and Meta-analysis on the Impact of the ADRA2A Variant rs1800544 on Methylphenidate Outcomes in Attention-Deficit/Hyperactivity Disorder.

Background: Methylphenidate is among the most prescribed medications for treating attention-deficit/hyperactivity disorder (ADHD). However, nearly half of pediatric patients with ADHD do not respond to methylphenidate treatment. Pharmacogenetic testing can aid in identifying patients for whom methylphenidate is unlikely to be safe or effective, leading to improved methylphenidate outcomes and increased use of alternative treatment options for ADHD. This article aimed to summarize findings from studies of the ADRA2A gene variant, rs1800544, and its association with methylphenidate outcomes in ADHD. Methods: We systematically reviewed and meta-analyzed available literature on the impact of rs1800544 on methylphenidate outcomes in ADHD. Results: Fourteen studies met inclusion criteria for review, 9 of which were eligible for meta-analysis. The included studies compared methylphenidate outcomes in patients with ADHD categorized by rs1800544 genotype. G-allele carriers experienced significantly greater improvements in ADHD symptom scores (Swanson, Nolan, and Pelham Version-IV Scale or ADHD Rating Scale-IV) relative to noncarriers (odds ratio 3.08, 95% confidence interval 1.71-5.56, p = .0002) and greater response rates as measured by a ≥50% improvement in symptom scores (odds ratio 2.68, 95% confidence interval 1.23-5.82, p = .01); no significant difference in response rate as measured by Clinical Global Impressions score ≤2 was found. Stouffer's z-score method showed significant improvement across all methylphenidate outcomes in G-allele carriers relative to noncarriers (z = 3.03, p = .002). Conclusions: These findings suggest that carriers of rs1800544 may have improved ADHD outcomes following methylphenidate treatment. However, the extent to which these improvements are clinically impactful remain unclear. Additional studies are required to determine if rs1800544 carrier status should influence clinical recommendations for treatment of ADHD symptoms.

Characterisation of seven medications approved for attention-deficit/hyperactivity disorder using in vitro models of hepatic metabolism.

The metabolism of most medications approved for the treatment of attention deficit/hyperactivity disorder (ADHD) is not fully understood.In vitro studies using cryopreserved, plated human hepatocytes (cPHHs) and pooled human liver microsomes (HLMs) were performed to more thoroughly characterise the metabolism of several ADHD medications.The use of enzyme-specific chemical inhibitors indicated a role for CYP2D6 in atomoxetine (ATX) metabolism, and roles for CYP3A4/5 in guanfacine (GUA) metabolism.The 4-hydroxy-atomoxetine and N-desmethyl-atomoxetine pathways represented 98.4% and 1.5% of ATX metabolism in cPHHs, respectively. The 3-OH-guanfacine pathway represented at least 2.6% of GUA metabolism in cPHHs, and 71% in HLMs.The major metabolising enzyme for methylphenidate (MPH) and dexmethylphenidate (dMPH) could not be identified using these methods because these compounds were too unstable. Hydrolysis of these medications was spontaneous and did not require the presence of protein to occur.Clonidine (CLD), amphetamine (AMPH), and dextroamphetamine (dAMPH) did not deplete substantially in cPHHs nor HLMs, suggesting that these compounds may not undergo considerable hepatic metabolism. The major circulating metabolites of AMPH and dAMPH (benzoic acid and hippuric acid) were not observed in either system, and therefore could not be characterised. Additionally, inhibition experiments suggested a very minimal role for CYP2D6 in CLD and AMPH metabolism.

Hereditary cancer risk assessment and genetic testing in the community urology practice setting.

OBJECTIVES: To evaluate the feasibility of integrating a hereditary cancer risk assessment (HCRA) process in the community urology practice setting for patients with prostate cancer (PCa). METHODS: In this prospective intervention, an HCRA process was implemented across six different community urology clinics between May 2019 and April 2020. The intervention included a process integration during which the workflow at each site was refined, a post-integration period during which HCRA was conducted in all patients with PCa, and a follow-up period during which healthcare providers and patients reported their satisfaction with the HCRA and genetic testing process. RESULTS: Among patients who completed a family history assessment during the post-integration period, 23.6% met guideline criteria for genetic testing. Of all patients seen at the clinic during the post-integration period, 8.7% completed genetic testing; this was a twofold increase over the period immediately preceding process integration (4.2%), and a sevenfold increase over the same period 1 year prior (1.2%). The majority of providers reported that the HCRA was as important as other regularly performed assessments (61.0%) and planned to continue using the process in their practice (68.3%). Most patients believed that the genetic test results were important for their future cancer care (84.7%) and had already shared their test results with at least one family member (63.2%). CONCLUSIONS: This study demonstrated that implementing an HCRA process in the community urology practice setting was feasible, generally favored by providers and patients, and resulted in an increase in the number of patients with PCa who completed genetic testing.

Clinical utility of combinatorial pharmacogenomic testing in depression: A Canadian patient- and rater-blinded, randomized, controlled trial.

The pharmacological treatment of depression consists of stages of trial and error, with less than 40% of patients achieving remission during first medication trial. However, in a large, randomized-controlled trial (RCT) in the U.S. ("GUIDED"), significant improvements in response and remission rates were observed in patients who received treatment guided by combinatorial pharmacogenomic testing, compared to treatment-as-usual (TAU). Here we present results from the Canadian "GAPP-MDD" RCT. This 52-week, 3-arm, multi-center, participant- and rater-blinded RCT evaluated clinical outcomes among patients with depression whose treatment was guided by combinatorial pharmacogenomic testing compared to TAU. The primary outcome was symptom improvement (change in 17-item Hamilton Depression Rating Scale, HAM-D17) at week 8. Secondary outcomes included response (≥50% decrease in HAM-D17) and remission (HAM-D17 ≤ 7) at week 8. Numerically, patients in the guided-care arm had greater symptom improvement (27.6% versus 22.7%), response (30.3% versus 22.7%), and remission rates (15.7% versus 8.3%) compared to TAU, although these differences were not statistically significant. Given that the GAPP-MDD trial was ultimately underpowered to detect statistically significant differences in patient outcomes, it was assessed in parallel with the larger GUIDED RCT. We observed that relative improvements in response and remission rates were consistent between the GAPP-MDD (33.0% response, 89.0% remission) and GUIDED (31.0% response, 51.0% remission) trials. Together with GUIDED, the results from the GAPP-MDD trial indicate that combinatorial pharmacogenomic testing can be an effective tool to help guide depression treatment in the context of the Canadian healthcare setting (ClinicalTrials.gov NCT02466477).

Combinatorial pharmacogenomic algorithm is predictive of sertraline metabolism in patients with major depressive disorder.

Pharmacogenomic testing can be used to guide medication selection in patients with major depressive disorder (MDD). Currently, there is no consensus on which gene or genes to consider in medication management. Here, we assessed the clinical validity of the combinatorial pharmacogenomic algorithm to predict sertraline blood levels in a subset of patients enrolled in the Genomics Used to Improve DEpression Decisions (GUIDED) trial. Patients who reported taking sertraline within ≤2 weeks of the screening blood draw were included. All patients received combinatorial pharmacogenomic testing, which included a weighted assessment of individual phenotypes for multiple pharmacokinetic genes relevant for sertraline (CYP2C19, CYP2B6, and CYP3A4). Sertraline blood levels were compared between phenotypes based on: 1) the pharmacokinetic portion of the combinatorial pharmacogenomic algorithm, and 2) individual genes. When evaluated separately, individual genes (for CYP2C19 and CYP2B6) and the combinatorial algorithm were significant predictors of sertraline blood levels. However, in multivariate analyses that included individual genes and the combinatorial pharmacogenomic algorithm, only the combinatorial pharmacogenomic algorithm remained a significant predictor of sertraline blood levels. These findings support the clinical validity of the combinatorial pharmacogenomic algorithm, in that it is a superior predictor of sertraline blood levels compared to individual genes.

Calcium-permeable AMPA receptor activity and GluA1 trafficking in the basolateral amygdala regulate operant alcohol self-administration.

Addiction is viewed as maladaptive glutamate-mediated neuroplasticity that is regulated, in part, by calcium-permeable AMPA receptor (CP-AMPAR) activity. However, the contribution of CP-AMPARs to alcohol-seeking behavior remains to be elucidated. We evaluated CP-AMPAR activity in the basolateral amygdala (BLA) as a potential target of alcohol that also regulates alcohol self-administration in C57BL/6J mice. Operant self-administration of sweetened alcohol increased spontaneous EPSC frequency in BLA neurons that project to the nucleus accumbens as compared with behavior-matched sucrose controls indicating an alcohol-specific upregulation of synaptic activity. Bath application of the CP-AMPAR antagonist NASPM decreased evoked EPSC amplitude only in alcohol self-administering mice indicating alcohol-induced synaptic insertion of CP-AMPARs in BLA projection neurons. Moreover, NASPM infusion in the BLA dose-dependently decreased the rate of operant alcohol self-administration providing direct evidence for CP-AMPAR regulation of alcohol reinforcement. As most CP-AMPARs are GluA1-containing, we asked if alcohol alters the activation state of GluA1-containing AMPARs. Immunocytochemistry results showed elevated GluA1-S831 phosphorylation in the BLA of alcohol as compared with sucrose mice. To investigate mechanistic regulation of alcohol self-administration by GluA1-containing AMPARs, we evaluated the necessity of GluA1 trafficking using a TET-ON AAV encoding a dominant-negative GluA1 c-terminus (GluA1ct) that blocks activity-dependent synaptic delivery of native GluA1-containing AMPARs. GluA1ct expression in the BLA reduced alcohol self-administration with no effect on sucrose controls. These results show that CP-AMPAR activity and GluA1 trafficking in the BLA mechanistically regulate the reinforcing effects of sweetened alcohol. Pharmacotherapeutic targeting these mechanisms of maladaptive neuroplasticity may aid medical management of alcohol use disorder.

Chronic intermittent ethanol exposure dysregulates a GABAergic microcircuit in the bed nucleus of the stria terminalis.

Neuroadaptations in brain regions that regulate emotional and reward-seeking behaviors have been suggested to contribute to pathological behaviors associated with alcohol-use disorder. One such region is the bed nucleus of the stria terminalis (BNST), which has been linked to both alcohol consumption and alcohol withdrawal-induced anxiety and depression. Recently, we identified a GABAergic microcircuit in the BNST that regulates anxiety-like behavior. In the present study, we examined how chronic alcohol exposure alters this BNST GABAergic microcircuit in mice. We selectively targeted neurons expressing corticotropin releasing factor (CRF) using a CRF-reporter mouse line and combined retrograde labeling to identify BNST projections to the ventral tegmental area (VTA) and lateral hypothalamus (LH). Following 72 h of withdrawal from four weekly cycles of chronic intermittent ethanol (CIE) vapor exposure, the excitability of a sub-population of putative local CRF neurons that did not project to either VTA or LH (CRFnon-VTA/LH neurons) was increased. Withdrawal from CIE also increased excitability of non-CRF BNST neurons that project to both LH and VTA (BNSTnon-CRF-proj neurons). Furthermore, both populations of neurons had a reduction in spontaneous EPSC amplitude while frequency was unaltered. Withdrawal from chronic alcohol was accompanied by a significant increase in spontaneous IPSC frequency selectively in the BNSTnon-CRF-proj neurons. Together, these data suggest that withdrawal from chronic ethanol dysregulates local CRF-GABAergic microcircuit to inhibit anxiolytic outputs of the BNST which may contribute to enhanced anxiety during alcohol withdrawal and drive alcohol-seeking behavior. This article is part of the special issue on 'Neuropeptides'.

Divergent behavioral responses in protracted opioid withdrawal in male and female C57BL/6J mice.

Persons suffering from opioid use disorder (OUD) experience long-lasting dysphoric symptoms well into extended periods of withdrawal. This protracted withdrawal syndrome is notably characterized by heightened anxiety and hyperkatifeia. Here, we investigated if an exacerbated withdrawal model of acute morphine dependence results in lasting behavioral adaptation 6 weeks into forced abstinence in C57BL/6J mice. We found that our exacerbated morphine withdrawal paradigm produced distinct alterations in behavior in elevated plus maze (EPM), open field, and social interaction tests in male and female mice. Following protracted withdrawal male mice showed enhanced exploration of the open arms of the EPM, reduced latency to enter the corner of the OF, and a social interaction deficit. In contrast, female mice showed enhanced thigmotaxis in the OF. In both sexes, protracted withdrawal enhanced locomotor behavior in response to subsequent morphine challenge, albeit at different doses. These findings will be relevant for future investigation examining the neural mechanisms underlying these behaviors and will aid in uncovering physiological sex differences in response to opioid withdrawal.

Inhibitory transmission in the bed nucleus of the stria terminalis in male and female mice following morphine withdrawal.

The United States is experiencing an opioid crisis imposing enormous fiscal and societal costs and driving the staggering overdose death rate. While prescription opioid analgesics are essential for treating acute pain, cessation of use in individuals with a physical dependence induces an aversive withdrawal syndrome that promotes continued drug use to alleviate/avoid these symptoms. Additionally, repeated bouts of withdrawal often lead to an increased propensity for relapse. Understanding the neurobiology underlying withdrawal is essential for providing novel treatment options to alleviate physiological and affective components accompanying the cessation of opiate use. Here, we administered morphine and precipitated withdrawal with naloxone to investigate behavioral and cellular responses in C57BL/6J male and female mice. Following 3 days of administration, both male and female mice demonstrated sensitized withdrawal symptoms. Since the bed nucleus of the stria terminalis (BNST) plays a role in mediating withdrawal-associated behaviors, we examined plastic changes in inhibitory synaptic transmission within this structure 24 hours following the final precipitated withdrawal. In male mice, morphine withdrawal increased spontaneous GABAergic signaling compared with controls. In contrast, morphine withdrawal decreased spontaneous GABAergic signaling in female mice. Intriguingly, these opposing GABAergic effects were contingent upon activity-dependent dynamics within the ex vivo slice. Our findings suggest that male and female mice exhibit some divergent cellular responses in the BNST following morphine withdrawal, and alterations in BNST inhibitory signaling may contribute to the expression of behaviors following opioid withdrawal.

Manipulations of Central Amygdala Neurotensin Neurons Alter the Consumption of Ethanol and Sweet Fluids in Mice.

The central nucleus of the amygdala plays a significant role in alcohol use and other affective disorders; however, the genetically-defined neuronal subtypes and projections that govern these behaviors are not well known. Here we show that neurotensin neurons in the central nucleus of the amygdala of male mice are activated by in vivo ethanol consumption and that genetic ablation of these neurons decreases ethanol consumption and preference in non-ethanol-dependent animals. This ablation did not impact preference for sucrose, saccharin, or quinine. We found that the most robust projection of the central amygdala neurotensin neurons was to the parabrachial nucleus, a brain region known to be important in feeding behaviors, conditioned taste aversion, and alarm. Optogenetic stimulation of projections from these neurons to the parabrachial nucleus is reinforcing, and increases ethanol drinking as well as consumption of sucrose and saccharin solutions. These data suggest that this central amygdala to parabrachial nucleus projection influences the expression of reward-related phenotypes and is a novel circuit promoting consumption of ethanol and palatable fluids.SIGNIFICANCE STATEMENT Alcohol use disorder (AUD) is a major health burden worldwide. Although ethanol consumption is required for the development of AUD, much remains unknown regarding the underlying neural circuits that govern initial ethanol intake. Here we show that ablation of a population of neurotensin-expressing neurons in the central amygdala decreases intake of and preference for ethanol in non-dependent animals, whereas the projection of these neurons to the parabrachial nucleus promotes consumption of ethanol as well as other palatable fluids.

Role of RGS12 in the differential regulation of kappa opioid receptor-dependent signaling and behavior.

Kappa opioid receptor (KOR) agonists show promise in ameliorating disorders, such as addiction and chronic pain, but are limited by dysphoric and aversive side effects. Clinically beneficial effects of KOR agonists (e.g., analgesia) are predominantly mediated by heterotrimeric G protein signaling, whereas ß-arrestin signaling is considered central to their detrimental side effects (e.g., dysphoria/aversion). Here we show that Regulator of G protein Signaling-12 (RGS12), via independent signaling mechanisms, simultaneously attenuates G protein signaling and augments ß-arrestin signaling downstream of KOR, exhibiting considerable selectivity in its actions for KOR over other opioid receptors. We previously reported that RGS12-null mice exhibit increased dopamine transporter-mediated dopamine (DA) uptake in the ventral (vSTR), but not dorsal striatum (dSTR), as well as reduced psychostimulant-induced hyperlocomotion; in the current study, we found that these phenotypes are reversed following KOR antagonism. Fast-scan cyclic voltammetry studies of dopamine (DA) release and reuptake suggest that striatal disruptions to KOR-dependent DAergic neurotransmission in RGS12-null mice are restricted to the nucleus accumbens. In both ventral striatal tissue and transfected cells, RGS12 and KOR are seen to interact within a protein complex. Ventral striatal-specific increases in KOR levels and KOR-induced G protein activation are seen in RGS12-null mice, as well as enhanced sensitivity to KOR agonist-induced hypolocomotion and analgesia-G protein signaling-dependent behaviors; a ventral striatal-specific increase in KOR levels was also observed in ß-arrestin-2-deficient mice, highlighting the importance of ß-arrestin signaling to establishing steady-state KOR levels in this particular brain region. Conversely, RGS12-null mice exhibited attenuated KOR-induced conditioned place aversion (considered a ß-arrestin signaling-dependent behavior), consistent with the augmented KOR-mediated ß-arrestin signaling seen upon RGS12 over-expression. Collectively, our findings highlight a role for RGS12 as a novel, differential regulator of both G protein-dependent and -independent signaling downstream of KOR activation.

Disrupting reconsolidation: memory erasure or blunting of emotional/motivational value?

When memories are retrieved they become labile, and subject to alteration by a process known as reconsolidation. Disruption of memory reconsolidation decreases the performance of learned responses, which is often attributed to erasure of the memory; in the case of Pavlovian learning, to a loss of the association between a conditioned stimulus (CS) and unconditioned stimulus (US). However, an alternative interpretation is that disrupting reconsolidation does not erase memories, but blunts their emotional/motivational impact. It is difficult to parse the predictive vs. emotional/motivational value of CSs in non-human animals, but studies on variation in the form of conditioned responses (CRs) in a Pavlovian conditioned approach task suggest a way to do this. In this task a lever-CS paired with a food reward (US) acquires predictive value in all rats, but is attributed with emotional/motivational value to a greater extent in some rats (sign-trackers) than others (goal-trackers). We report that the post-retrieval administration of propranolol selectively attenuates a sign-tracking CR, and the associated neural activation of brain "motive circuits", while having no effect on conditioned orienting behavior in sign-trackers, or on goal-tracking CRs evoked by either a lever-CS or a tone-CS. We conclude that the disruption of reconsolidation by post-retrieval propranolol degrades the emotional/motivational impact of the CS, required for sign-tracking, but leaves the CS-US association intact. The possibility that post-retrieval interventions can reduce the emotional/motivational aspects of memories, without actually erasing them, has important implications for treating maladaptive memories that contribute to some psychiatric disorders.

Stress-Induced Alterations of Norepinephrine Release in the Bed Nucleus of the Stria Terminalis of Mice.

Stress can drive adaptive changes to maintain survival during threatening stimuli. Chronic stress exposure, however, may result in pathological adaptations. A key neurotransmitter involved in stress signaling is norepinephrine. Previous studies show that acute stress elevates norepinephrine levels in the bed nucleus of the stria terminalis (BNST), a critical node regulating anxiety and upstream of stress responses. Here, we use mice expressing channelrhodopsin in norepinephrine neurons to selectively activate terminals in the BNST, and measure norepinephrine release with optogenetics-assisted fast-scan cyclic voltammetry (FSCV). We demonstrate that while corticosterone habituates to chronic restraint stress, cFos activation of medullary norepinephrine neurons shows equivalent activation under both acute and chronic stress conditions. Mice exposed to a single restraint session show an identical optically stimulated norepinephrine release profile compared to that of unexposed mice. Mice experiencing 5 days of restraint stress, however, show elevated norepinephrine release across multiple stimulation parameters, and reduced sensitivity to the α2-adrenergic receptor (AR) antagonist idazoxan. These data are the first to examine norepinephrine release in the BNST to tonic and phasic stimulation frequencies, and confirm that repeated stress alters autoreceptor sensitivity.

The form of a conditioned stimulus can influence the degree to which it acquires incentive motivational properties.

There is considerable individual variation in the extent to which food- and drug-associated cues (conditioned stimuli, CSs) acquire incentive salience, as indicated by whether they elicit approach towards them, and/or act as conditioned reinforcers. Here we asked whether this variation is influenced by properties of the CS itself. In rats, we assessed both the attractiveness and conditioned reinforcing properties of two CSs: a manipulable lever CS versus an auditory (tone) CS. There was considerable individual variation in the extent to which a lever CS acquired incentive motivational properties, as indicated by whether it became attractive (evoked a sign-tracking or goal-tracking conditioned response) or acted as a conditioned reinforcer. However, with a tone CS all rats learned a goal-tracking response, and the tone CS was an equally effective conditioned reinforcer in sign-trackers and goal-trackers. Even when presented in compound (a lever-tone CS), the two elements of the compound differentially acquired motivational properties. In contrast, amphetamine and stress potentiated the conditioned reinforcing properties of both visual and auditory CSs similarly in rats that primarily sign-tracked or goal-tracked. We conclude that variation in the to the ability of CSs to acquire incentive salience, and thus their ability to act as incentive stimuli capable of motivating behavior, is determined in part by properties of the CS itself.

On the motivational properties of reward cues: Individual differences.

Cues associated with rewards, such as food or drugs of abuse, can themselves acquire motivational properties. Acting as incentive stimuli, such cues can exert powerful control over motivated behavior, and in the case of cues associated with drugs, they can goad continued drug-seeking behavior and relapse. However, recent studies reviewed here suggest that there are large individual differences in the extent to which food and drug cues are attributed with incentive salience. Rats prone to approach reward cues (sign-trackers) attribute greater motivational value to discrete localizable cues and interoceptive cues than do rats less prone to approach reward cues (goal-trackers). In contrast, contextual cues appear to exert greater control over motivated behavior in goal-trackers than sign-trackers. It is possible to predict, therefore, before any experience with drugs, in which animals specific classes of drug cues will most likely reinstate drug-seeking behavior. The finding that different individuals may be sensitive to different triggers capable of motivating behavior and producing relapse suggests there may be different pathways to addiction, and has implications for thinking about individualized treatment. This article is part of a Special Issue entitled 'NIDA 40th Anniversary Issue'.