Effects of dopamine modulation on chronic stress-induced deficits in reward learning

Restorative properties of chronic lurasidone treatment on emotional dysfunction in rats exposed to chronic unavoidable stress: A role for medial prefrontal cortex - nucleus accumbens network

Anhedonia, a transdiagnostic symptom prevalent in depressive and psychotic disorders, poses a significant challenge for pharmacological intervention due to its association with impaired motivation. Understanding how psychotropic drugs can modulate this pathological domain and elucidating the molecular mechanisms underlying such effects are crucial endeavors in psychiatric research. In this study, we aimed to investigate the pro-motivational properties of lurasidone in a rat (Sprague Dawley males) model of anhedonia and to unravel the interplay between lurasidone and the brain regions critical for reward processing. Exposure to unpredictable chronic stress (UCS) led to a marked reduction in motivation, a deficit that was restored by lurasidone treatment at 3 mg/kg, but not at 10 mg/kg. Interestingly, the stress-induced decrease in reactivity to negative stimuli was reversed by both doses of lurasidone. At the molecular level, stressed animals exhibited reduced expression of neuroplastic markers, that was increased following lurasidone administration. Furthermore, UCS exposure impaired the activation of the medial prefrontal cortex (mPFC) and nucleus accumbens (NAc) in response to hedonic stimuli, an effect amended by lurasidone treatment. Additionally, lurasidone restored the impaired phosphorylation of DARPP-32, a key regulator of dopamine signaling, in mPFC and NAc of UCS rats exposed to a hedonic stimulus. These findings underscore the potential of lurasidone in improving various psychopathological domains, like impaired motivation and emotional reactivity, core elements contributing to the disability associated with mental disorders. These effects highlight the therapeutic potential of lurasidone in addressing the intricate behavioral and neurochemical alterations associated with anhedonia and related mood disorders.

Models developed to explain the effects of stress on brain and behavior

There is an integral relationship between stress, brain function and behavior. Over the year's extensive research has led to the development of various models to explain the intricate intersection between brain and stress. This chapter delves into some of the theoretical frameworks that explains the neurobiological and behavioral responses to stress using key models of stress such as the allostatic load model, which is the most common model that describes how chronic stress affect brain structure and function resulting in long-term changes in regions such as the hippocampus, amygdala, and prefrontal cortex which phenotypically express as cognitive impairments, emotional dysfunction seen in various forms of neurological disorder. The neuro-endocrine model, follows the glucocorticoid cascade hypothesis, that associates prolonged stress exposure to hippocampal damage and cognitive decline via alteration in the hypothalamic-pituitary-adrenal (HPA) axis and the overproduction of stress hormones like cortisol which can induce hippocampal atrophy, impair learning and memory, and promote depressive-like behaviors. The neurobiological stress model addresses the role of the hypothalamic-pituitary-adrenal (HPA) axis and stress-related neurotransmitters in shaping behavioral responses, emphasizing alterations in neuroplasticity and synaptic function. These models demonstrate how chronic stress can alter neural plasticity, neurotransmitter systems, and synaptic connectivity, affecting behavior and cognitive function. Hence by integrating molecular, neurobiological, and behavioral perspectives, these models offer a comprehensive understanding of how stress alters brain activity and behavior. The chapter further showcase how these models direct the development of medical interventions, shedding light on potential therapies that target the underlying molecular mechanisms of stress-induced brain changes.

Oxytocin Protects Against Corticosterone-Induced DA Dysfunction: An Involvement of the PKA/CREB Pathway

Chronic stress disrupts dopamine (DA) transmission, adversely affecting mood and contribution to neuropsychiatric disorders like ADHD, autism, schizophrenia, anxiety, depression, and drug addiction. The neuropeptide oxytocin (OXT) plays a key role in social cognition, bonding, attachment, and parenting behaviors. In addition, OXT can modulate the activity of the HPA axis, counteracting the effects of stress, and alleviating fear and anxiety. However, whether OXT can mitigate stress-induced DA dysfunction and the underlying mechanisms remains unclear. This study investigated the neuroprotective effects of OXT on corticosterone (CORT) induced DA dysfunction in the neuroblastoma cell line SH-SY5Y. The results revealed that CORT decreases the levels of intracellular signaling molecules associated with DA function, including phosphorylated tyrosine hydroxylase (pTH), phosphorylated cAMP response element-binding protein (pCREB), and protein kinase A (PKA). Interestingly, pretreatment with OXT mitigated CORT-induced DA dysfunction through its potent PKA activator properties. In addition, the neuroprotective effect of OXT was abolished by atosiban (an OXT receptor antagonist) or H89 (a PKA inhibitor). Our results suggest that OXT protects dopaminergic neuroblastoma cells from CORT-induced DA dysfunction, potentially through the involvement of oxytocin receptors and the PKA/CREB signaling pathway. These findings contribute to the understanding of the neurobiological mechanisms underlying stress resilience and highlight potential pathways for developing targeted treatments that leverage the neuroprotective properties of OXT to address disorders characterized by DA dysregulation and impaired stress responses.

A U-shaped relationship between chronic academic stress and the dynamics of reward processing

Despite the potential link between stress-induced reward dysfunctions and the development of mental problems, limited human research has investigated the specific impacts of chronic stress on the dynamics of reward processing. Here we aimed to investigate the relationship between chronic academic stress and the dynamics of reward processing (i.e., reward anticipation and reward consumption) using event-related potential (ERP) technology. Ninety healthy undergraduates who were preparing for the National Postgraduate Entrance Examination (NPEE) participated in the study and completed a two-door reward task, their chronic stress levels were assessed via the Perceived Stress Scale (PSS). The results showed that a lower magnitude of reward elicited more negative amplitudes of cue-N2 during the anticipatory phase, and reward omission elicited more negative amplitudes of FRN compared to reward delivery especially in high reward conditions during the consummatory phase. More importantly, the PSS score exhibited a U-shaped relationship with cue-N2 amplitudes regardless of reward magnitude during the anticipatory phase; and FRN amplitudes toward reward omission in high reward condition during the consummatory phase. These findings suggest that individuals exposed to either low or high levels of chronic stress, as opposed to moderate stress levels, exhibited a heightened reward anticipation, and an augmented violation of expectations or affective response when faced with relatively more negative outcomes.

A narrative review of non-racemic amisulpride (SEP-4199) for treatment of depressive symptoms in bipolar disorder and LB-102 for treatment of schizophrenia

INTRODUCTION

The challenges posed by treatment-resistant schizophrenia and depressive symptoms have led to ongoing difficulties despite the availability of antipsychotics and antidepressants. This review addresses the potential of amisulpride analogs, particularly SEP-4199, in addressing these challenges through enhanced efficacy and reduced side effects.

AREAS COVERED

This review focuses on the pharmacological profile of amisulpride analogs, exemplified by LB-102 and its derivative SEP-4199. PubMed gathered articles (up to 10 March 2023) on 'amisulpride,' 'schizophrenia,' 'bipolar disorder,' and 'major depressive disorder;' ClinicalTrials.gov tracked SEP-4199 and LB-102 trials. LB-102, a newly identified N-methylated analog of amisulpride, exhibits enhanced lipophilicity at lower doses, as demonstrated in a phase 1 study, indicating significant promise for therapeutic applications. The discovery of SEP-4199, a non-racemic analog composed of R- and S-enantiomers in an 85:15 ratio, is discussed, emphasizing its potential to enhance antidepressant effects while minimizing extrapyramidal side effects via selective D2 receptor binding. Recent phase 2 trials have demonstrated SEP-4199's efficacy in treating depressive symptoms in bipolar disorder I, capitalizing on D2-mediated anti-anhedonic and D3-mediated reward effects.

EXPERT OPINION

The development of SEP-4199 presents a potential breakthrough for managing depressive symptoms in bipolar disorder I. Further exploration of D2 and D3 receptor-mediated effects could lead to improved treatment strategies.

Electrophysiological signatures of reward learning in the rodent touchscreen-based Probabilistic Reward Task

Blunted reward learning and reward-related activation within the corticostriatal-midbrain circuitry have been implicated in the pathophysiology of anhedonia and depression. Unfortunately, the search for more efficacious interventions for anhedonic behaviors has been hampered by the use of vastly different preclinical and clinical assays. In a first step in addressing this gap, in the current study, we used event-related potentials and spectral analyses in conjunction with a touchscreen version of the rodent Probabilistic Reward Task (PRT) to identify the electrophysiological signatures of reward learning in rats. We trained 11 rats (5 females and 6 males) on the rodent touchscreen-based PRT and subsequently implanted them with deep electrodes in the anterior cingulate cortex (ACC) and nucleus accumbens (NAc) for local field potentials recordings during the PRT. Behaviorally, the expected responsivity-to-reward profile was observed. At the electrophysiological level, we identified a negative amplitude deflection 250-500 ms after feedback in the ACC and NAc electrodes, as well as power increase in feedback-locked delta (1-5 Hz) and alpha/beta (9-17 Hz) bands in both electrodes for rewarded trials. Using a reverse-translational approach, we identified electrophysiological signatures of reward learning in rats similar to those described in humans. These findings and approaches might provide a useful translational platform to efficiently evaluate novel therapeutics targeting anhedonia.