Introduction The opioid receptor antagonist naltrexone (NTX) reduces goal-directed alcohol drinking in rats presumably by blunting alcohol reward. However, different operant conditioning behavior can be produced by different reinforcement schedules, with goal-directed operant behavior being more sensitive to changes in reward value than less flexible, habit-associated models. Objectives We tested the hypothesis that NTX more effectively reduces alcohol drinking and seeking in a goal-directed than in a habit-associated operant model, and more effectively reduces alcohol versus sucrose self-administration, consistent with diminished alcohol reward. Materials and Methods Rats were trained to self-administer 10% alcohol or 1.5% sucrose in a lever-press task and then underwent a within-subject assessment of NTX (0.1–1mg/kg) effects on operant behavior. A fixed-ratio (FR5) reinforcement schedule was used to model goal-directed behavior and a variable-interval (VI30) schedule was used to model habitual behavior. Results As predicted, NTX reduced fluid deliveries earned by the FR5-alcohol group significantly more than all other groups. However, NTX reduced lever presses during self-administration sessions in VI30-trained rats without reducing earned deliveries, due to the low contingency between rate of pressing and fluid deliveries under that schedule. Interestingly, when fluid delivery was withheld (extinction), NTX reduced reward-seeking in all rats. Finally, NTX blocked reinstatement of reward-seeking upon presentation of 0.2ml alcohol or sucrose and associated cues in the FR5-trained but not VI30-trained rats. Discussion NTX reduced goal-directed alcohol drinking compared to other operant conditions. In addition, NTX blocked reinstatement of reward-seeking in rats trained on the goal-directed FR5 reinforcement schedule but not in rats trained on the habit-like VI30 reinforcement schedule. However, NTX also exerted nonspecific effects on reward-seeking that were revealed under low-effort contingency conditions or absence of reward. Together, the data support the hypothesis that NTX is less effective in conditioning models that are more habit-associated.

Neurophysiological abnormalities in auditory deviance processing, as reflected by the mismatch negativity (MMN), have been observed across the course of schizophrenia. Studies in early schizophrenia patients have typically shown varying degrees of MMN amplitude reduction for different deviant types, suggesting that different auditory deviants are uniquely processed and may be differentially affected by duration of illness. To explore this further, we examined the MMN response to 4 auditory deviants (duration, frequency, duration + frequency “double deviant”, and intensity) in 24 schizophrenia-spectrum patients early in the illness (ESZ) and 21 healthy controls. ESZ showed significantly reduced MMN relative to healthy controls for all deviant types (p < 0.05), with no significant interaction with deviant type. No correlations with clinical symptoms were present (all ps > 0.05). These findings support the conclusion that neurophysiological mechanisms underlying processing of auditory deviants are compromised early in illness, and these deficiencies are not specific to the type of deviant presented.

The association between severe mental illness (SMI) and cardiovascular and metabolic disease (CMD) is poorly understood. PCSK9 is expressed in systems critical to both SMI and CMD and influences lipid homeostasis and brain function. We systematically investigated relationships between genetic variation within the PCSK9 locus and risk for both CMD and SMI. UK Biobank recruited ~500,000 volunteers and assessed a wide range of SMI and CMD phenotypes. Initially we used genetic data from white British ancestry individuals of UK Biobank. Genetic association analyses were conducted in PLINK, with statistical significance defined by the number of independent SNPs. Conditional analyses and linkage disequilibrium assessed the independence of SNPs and the presence of multiple signals. Two genetic risk scores of lipid-lowering alleles were calculated and used as proxies for putative lipid-lowering effects of PCSK9. PCSK9 variants were associated with central adiposity, venous thrombosis embolism, systolic blood pressure, mood instability, and neuroticism (all p&lt;1.16x10-4). No secondary signals were identified. Conditional analyses and high linkage disequilibrium (r2 =0.98) indicated that mood instability and central obesity may share a genetic signal, which was confirmed using trans-ancestry data from UK Biobank. Genetic risk scores suggested that the lipid-lowering effects of PCSK9 may be causal for greater mood instability and higher neuroticism. This is the first study to implicate the PCSK9 locus in mood-disorder symptoms and related traits, as well as the shared pathology of SMI and CMD. PCSK9 effects on mood may occur via lipid-lowering mechanisms. Further work is needed to understand whether repurposing PCSK9-targeting therapies might improve SMI symptoms and prevent CMD.

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