α2-adrenoceptor binding in Flinders-sensitive line compared with Flinders-resistant line and Sprague-Dawley rats

An Updated Bio-Behavioral Profile of the Flinders Sensitive Line Rat: Reviewing the Findings of the Past Decade

The Flinders sensitive line (FSL) rat is an accepted rodent model for depression that presents with strong face, construct, and predictive validity, thereby making it suitable to investigate novel antidepressant mechanisms. Despite the translatability of this model, available literature on this model has not been reviewed for more than ten years. The PubMed, ScienceDirect and Web of Science databases were searched for relevant articles between 2013 and 2024, with keywords relating to the Flinders line rat, and all findings relevant to treatment naïve animals, included. Following screening, 77 studies were included and used to create behavioral reference standards and calculate FSL favor ratios for the various behavioral parameters. The GRADE and SYRCLE risk of bias tools were used to scale the quality of these studies. Based on these results, FSL rats display reliable and reproducible depressive-like behavior in the forced swim test, together with hyperlocomotor activity across various behavioral tests. Despite reports of increased anhedonia, anxiety-like behavior, and cognitive dysfunction, the reviewed findings indicate that these parameters are comparable between strains. For the various neuro- and biological constructs, oxidative stress, energy production, and glutamatergic, noradrenergic and serotonergic neurotransmission received the most support for strain differences. Taken together, the FSL remains a reliable, popular, and translatable rodent model of depression, with strong face and construct validity. As for predictive validity, similar review approaches should be considered to establish whether the mentioned behavioral aspects and neurochemical constructs may be more sensitive (or resistant) to certain antidepressant strategies.

Anesthetic Influence on Electroconvulsive Therapy: A Comprehensive Review

The prevalence of severe mental disorders has been rising annually. Electroconvulsive therapy (ECT) is considered a valuable treatment option in psychiatry for conditions such as schizophrenia and medication-resistant depression, especially when other treatments have proven insufficient. ECT rapidly improves patients' mood, alleviates symptoms, and demonstrates significant therapeutic effects. Currently, the form of ECT used in clinical practice is modified electroconvulsive therapy (mECT), which is administered under general anesthesia. Accumulative evidence has confirmed that different anesthetic drugs, anesthetic-ECT time interval, anesthetic depth, and airway management can impact the outcomes of ECT. Therefore, this review aims to summarize the current impact of anesthesia factors on ECT, providing reference for clinical anesthesia during ECT procedures.

Increased depressive-like behaviour of postpartum Flinders sensitive and resistant line rats is reversed by a predictable postpartum stressor

During the peripartum period, women are at an increased risk to develop perinatal distress, presenting as symptoms of depression and/or anxiety. Yet, due to practical and ethical restrictions, our understanding of this condition remains limited. Animal studies that focus on the neuropsychiatric mechanisms associated with the postpartum period, often ignore the genetical predisposition factor. We therefore investigated whether pregnancy could alter the bio-behavioural profile of the Flinders sensitive and resistant line rats, and whether these effects are exacerbated by a postpartum stressor. Postpartum dams were compared to nulliparous controls in behavioural tests, analysing depressive- and anxiety-like behaviours. Next, postpartum dams were subjected to a maternal separation and early weaning (MSEW) regimen, with their behaviour and serotonergic and noradrenergic concentrations compared to rats not separated from their pups. Regardless of strain, pregnancy decreased time spent in the open arms of the elevated plus maze and hippocampal serotonin concentrations. Time spent immobile in the forced swim test was also increased, with a significant effect in the FRL and a strong trend in the FSL rats. MSEW reversed these behaviours in both strains and increased social interaction with a male counterpart in the FSL rats, without influencing hippocampal or cortical serotonin or norepinephrine. Taken together, these results suggest that pregnancy influences postpartum behaviour, in a strain-dependent manner. Contrary to what we expected, MSEW overall decreased depressive- and anxiety-like behaviours, with strain specific differences, indicating that a chronic, predictable stressor may not necessarily adversely affect postpartum behaviour.

Electroconvulsive Therapy in Psychiatric Disorders: A Narrative Review Exploring Neuroendocrine-Immune Therapeutic Mechanisms and Clinical Implications

Electroconvulsive therapy (ECT) is based on conducting an electrical current through the brain to stimulate it and trigger generalized convulsion activity with therapeutic ends. Due to the efficient use of ECT during the last years, interest in the molecular bases involved in its mechanism of action has increased. Therefore, different hypotheses have emerged. In this context, the goal of this review is to describe the neurobiological, endocrine, and immune mechanisms involved in ECT and to detail its clinical efficacy in different psychiatric pathologies. This is a narrative review in which an extensive literature search was performed on the Scopus, Embase, PubMed, ISI Web of Science, and Google Scholar databases from inception to February 2022. The terms "electroconvulsive therapy", "neurobiological effects of electroconvulsive therapy", "molecular mechanisms in electroconvulsive therapy", and "psychiatric disorders" were among the keywords used in the search. The mechanisms of action of ECT include neurobiological function modifications and endocrine and immune changes that take place after ECT. Among these, the decrease in neural network hyperconnectivity, neuroinflammation reduction, neurogenesis promotion, modulation of different monoaminergic systems, and hypothalamus-hypophysis-adrenal and hypothalamus-hypophysis-thyroid axes normalization have been described. The majority of these elements are physiopathological components and therapeutic targets in different mental illnesses. Likewise, the use of ECT has recently expanded, with evidence of its use for other pathologies, such as Parkinson's disease psychosis, malignant neuroleptic syndrome, post-traumatic stress disorder, and obsessive-compulsive disorder. In conclusion, there is sufficient evidence to support the efficacy of ECT in the treatment of different psychiatric disorders, potentially through immune, endocrine, and neurobiological systems.

Hippocampal monoamine changes in the Flinders sensitive line rat: A case for the possible use of selective α2C-AR-antagonists in stress and anxiety disorders in companion animals

Non-selective α₂-adrenoreceptor (AR) stimulation delivers favourable sedative, analgesic, muscle relaxant and anxiolytic actions in companion animals, but is associated with cardiovascular and respiratory side effects. Anxiety conditions underscore monoamine disturbances amenable to α₂-AR modulation. We investigated sub-chronic (14 day s.c.) treatment with the selective α_2C-AR antagonist, ORM-10921 (0.03, 0.1, 0.3 mg/kg/d) on hippocampal noradrenaline (NA), dopamine (DA), serotonin (5-HT) and their turnover levels in stress sensitive Flinders Sensitive Line (FSL) rats versus Flinders Resistant Line (FRL) controls, using high performance liquid chromatography. The effects of ORM-10921 were compared to the non-selective α₂-AR antagonist, idazoxan (IDAZ; 3 mg/kg/d), and to imipramine (IMI; 15 mg/kg/d), a reference antidepressant in this model. FSL rats displayed significantly reduced 5-HT (p = 0.03) and DA (p = 0.02) levels vs. FRL controls, while NA levels showed a similar trend. ORM-10921 significantly increased NA (all doses p ≤ 0.02), 5-HT (0.1 and 0.3 mg/kg p ≤ 0.03) and DA levels (all doses p ≤ 0.03), which correlated with decreased monoamine turnover. In contrast, IDAZ significantly elevated NA (p < 0.005) and DA (p < 0.004) but not 5-HT levels. IMI also significantly increased 5-HT (p < 0.009), with a tendency to increase NA (p = 0.09) but not DA. ORM-10921 exerts similar albeit broader effects on hippocampal monoamines than IDAZ, explaining earlier established efficacy associated with α_2C-AR antagonism in animal models of depression and cognitive dysfunction. These and the current studies encourage application of ORM-10921 in depression in humans, as well as raise the intriguing possibility that selective α_2C-AR antagonists may be beneficial in anxiety and stress-related disorders in companion animals. Both warrant further study.

Dexmedetomidine exerts neuroprotective effects during high glucose-induced neural injury by inhibiting miR-125b

Diabetic neuropathy (DNP) is the most common complication of diabetes mellitus affecting approximately 50% of diabetes patients. Studying the effect of potential drugs with antioxidant properties and minimal toxicities on neural cells may lead to the development of new and safe pharmacotherapy. Dexmedetomidine (DEX), a highly selective α2-adrenoceptor agonist, is a clinically used sedative also known to have neural protection effect. In the present study, we aimed to investigate the protective role of DEX in high glucose (HG)-induced neural injury and its potential miRNA-related mechanisms. Our results showed that DEX exerted neuroprotective effects during high glucose-induced damage to PC12 cells in a dose-dependent manner. DEX restored cell viability and repressed LDH, Caspase-3 activity, ROS production, and cell apoptosis in HG-treated PC12 cells. MiR-125b-5p was significantly up-regulated in PC12 cells upon HG treatment and it was demonstrated as an target for DEX. The neuroprotective effects of DEX on HG-induced cellular injury were reversed through miR-125b-5p overexpression, and vitamin D receptor (VDR) is a direct targeted of the miR-125b-5p. Together, our results indicate that DEX displays neuroprotective effects on PC-12 cells under high glucose through regulating miR-125b-5p/VDR axis. Our findings might raise the possibility of potential therapeutic application of DEX for managing diabetic neuropathy neural injuries.

Alpha2-adrenergic dysregulation in congenic DxH recombinant inbred mice selectively bred for a high fear-sensitized (H-FSS) startle response

Patients with anxiety disorders and posttraumatic stress disorder (PTSD) exhibit exaggerated fear responses and noradrenergic dysregulation. Fear-related responses to α₂-adrenergic challenge were therefore studied in DxH C3H/HeJ-like recombinant inbred (C3HLRI) mice, which are a DBA/2J-congenic strain selectively bred for a high fear-sensitized startle (H-FSS). C3HLRI mice showed an enhanced acoustic startle response and immobility in the forced swim test compared to DBA/2J controls. The α₂-adrenoceptor antagonist yohimbine (Yoh; 5.0 mg/kg) induced an anxiogenic and the α₂-adrenoceptor agonist clonidine (Clon; 0.1 mg/kg) an anxiolytic effect in the open field (OF) in C3HLRI but not DBA/2J mice. In auditory fear-conditioning, Yoh (5.0 mg/kg)-treated C3HLRI mice showed higher freezing during fear recall and extinction learning than DBA/2J mice, and a higher ceiling for the Yoh-induced deficit in fear extinction. No strain differences were observed in exploration-related anxiety/spatial learning or the Clon-induced (0.1 mg/kg) corticosterone surge. A global analysis of the behavioral profile of the two mouse strains based on observed and expected numbers of significant behavioral outcomes indicated that C3HLRI mice showed significantly more often fear- and stress-related PTSD-like behaviors than DBA/2J controls. The analysis of the robustness of significant outcomes based on false discovery rate (FDR) thresholds confirmed significant differences for the strain-Yoh-interactions in the OF center and periphery, the Yoh-induced general extinction deficit, strain differences in conditioned fear levels, and at the dose of 5.0 mg/kg for the Yoh-induced ceiling in freezing levels among others. The current findings are consistent with previous observations showing alterations in the central noradrenergic system of C3HLRI mice (Browne et al., 2014, Stress 17:471-83). Based on their behavioral profile and response to α₂-adrenergic stimulation, C3HLRI mice are a valuable genetic model for studying adrenergic mechanisms of anxiety disorders and potentially also of PTSD.

Individual differences in inflammatory and oxidative mechanisms of stress-related mood disorders

Emotional stress leads to the development of peripheral disorders and is recognized as a modifiable risk factor for psychiatric disorders, particularly depression and anxiety. However, not all individuals develop the negative consequences of emotional stress due to different stress coping strategies and resilience to stressful stimuli. In this review, we discuss individual differences in coping styles and the potential mechanisms that contribute to individual vulnerability to stress, such as parameters of the immune system and oxidative state. Initial differences in inflammatory and oxidative processes determine resistance to stress and stress-related disorders via the alteration of neurotransmitter content in the brain and biological fluids. Differences in coping styles may serve as possible predictors of resistance to stress and stress-related disorders, even before stressful conditions. The investigation of natural variabilities in stress resilience may allow the development of new methods for preventive medicine and the personalized treatment of stress-related conditions.

Monoaminergic System Modulation in Depression and Alzheimer's Disease: A New Standpoint?

The prevalence of depression has dramatically increased, and it has been estimated that over 300 million people suffer from depression all over the world. Depression is highly comorbid with many central and peripheral disorders. In this regard, depressive states have been associated with the development of neurological disorders such as Alzheimer's disease (AD). Accordingly, depression is a risk factor for AD and depressive symptomatology is common in pre-clinical AD, representing an early manifestation of this disease. Neuropsychiatric symptoms may represent prodromal symptoms of dementia deriving from neurobiological changes in specific cerebral regions; thus, the search for common biological substrates is becoming an imperative and intriguing field of research. Soluble forms of beta amyloid peptide (Aβ) have been implicated both in the development of early memory deficits and neuropsychiatric symptoms. Indeed, soluble Aβ species have been shown to induce a depressive-like phenotype in AD animal models. Alterations in monoamine content are a common feature of these neuropathologies. Interestingly, serotonergic system modulation has been implicated in alteration of Aβ production. In addition, noradrenaline is considered crucially involved in compensatory mechanisms, leading to increased Aβ degradation via several mechanisms, including microglia modulation. In further agreement, antidepressant drugs have also been shown to potentially modulate cognitive symptoms in AD and depression. Thus, the present review summarizes the main knowledge about biological and pathological substrates, such as monoamine and related molecules, commonly involved in AD and depression pathology, thus shading light on new therapeutic approaches.

Cortical and striatal serotonin transporter binding in a genetic rat model of depression and in response to electroconvulsive stimuli

Depression is a debilitating mental illness and two thirds of patients respond insufficiently to conventional antidepressants. Electroconvulsive therapy (ECT) remains the most effective treatment to alleviate drug-refractory depression, however the neurobiological mechanisms are mostly unknown. The serotonergic system plays an important role in depression and alterations in the serotonin transporter (SERT) are seen both in depression and response to antidepressant pharmacotherapies. The first aim of this study was to investigate SERT density in a genetic rat model of depression, Flinders Sensitive Line (FSL), compared to control Flinders Resistant Line (FRL) and Sprague-Dawley (SD) rats. The second aim was to investigate SERT density in response to electroconvulsive stimuli (ECS), an animal model of ECT. Female rats of each strain were treated with ECS or sham (ear-clip placement with no current) for 10 days before brains were removed, frozen and cut into 20 µm thick sections. SERT density was measured in striatal and cortical regions by quantitative in vitro autoradiography using the SERT-radioligand, [³H]-DASB. Higher SERT density was observed in FSL rats compared to SD rats by 36-48% in motor cortex and striatum under sham conditions. In response to ECS, SD rats displayed a significant effect of treatment, whereas no changes were observed in FRL and FSL rats. Increased SERT binding in FSL rats compared to SD supports a dysfunction of the serotonergic system in depression. The increased SERT density after ECS, seen in SD rats but not FSL rats, suggests a different mechanism of action between depressive-like rats and controls.

The α2C-adrenoceptor antagonist, ORM-10921, exerts antidepressant-like effects in the Flinders Sensitive Line rat

Depression involves deficits in monoaminergic neurotransmission. Differential roles for α2A, B and C subtypes of the α2-adrenoceptor (AR) are evident, with selective α2C-AR antagonists purported to have antidepressant and procognitive properties. However, this has not been demonstrated in a genetic animal model of depression. The role of the α2C-AR in modulating two key depression-related behaviours in the Flinders Sensitive Line (FSL) rat was studied using a dose-response analysis following subcutaneous administration with the selective α2C-AR antagonist ORM-10921 (0.03; 0.3 mg/kg), the nonselective α2-AR antagonist idazoxan (3 mg/kg), or vehicle once daily for 14 days. Behaviour in the novel object recognition test, forced swim test (FST) and locomotor activity test was assessed. To ratify the validity of the FSL model, the reference tricyclic antidepressant imipramine (15 mg/kg, intraperitoneally) was used as a comparator drug in the FST. FSL rats demonstrated significantly increased immobility and recognition memory deficits versus Flinders Resistant Line controls, with imipramine significantly reversing said immobility. Similarly, ORM-10921 at both doses but not idazoxan significantly reversed immobility in the FST as well as attenuated cognitive deficits in FSL animals. We conclude that selective α2C-AR antagonism has potential as a novel therapeutic strategy in the treatment of depression and cognitive dysfunction.

Electroconvulsive shocks decrease α2-adrenoceptor binding in the Flinders rat model of depression

Despite years of drug development, electroconvulsive therapy (ECT) remains the most effective treatment for severe depression. The exact therapeutic mechanism of action of ECT is still unresolved and therefore we tested the hypothesis that the beneficial effect of ECT could in part be the result of increased noradrenergic neurotransmission leading to a decrease in α2-adrenoceptor binding. We have previously shown that both the Flinders sensitive line (FSL) and Flinders resistant line (FRL) rats had altered α2-adrenoceptor binding compared to control Sprague-Dawley (SD) rats. In this study, we treated female FSL, FRL and SD rats with electroconvulsive shock (ECS), an animal model of ECT, or sham stimulation for 10 days before brains were removed and cut into 20µm thick sections. Densities of α2-adrenoceptors were measured by quantitative autoradiography in the hippocampus, thalamic nucleus, hypothalamus, amygdala, frontal cortex, insular cortex, and perirhinal cortex using the α2-adrenoceptor antagonist, [(3)H]RX 821002. ECS decreased the binding of α2-adrenoceptors in cortical regions in the FSL and cortical and amygdaloid regions in the control FRL rats compared to their respective sham treated group. The normal SD controls showed no significant response to ECS treatment. Our data suggest that the therapeutic effect of ECS may be mediated through a decrease of α2-adrenoceptors, probably due to a sustained increase in noradrenaline release. These data confirm the importance of the noradrenergic system and the α2-adrenoceptor in depression and in the mechanism of antidepressant treatments.