Hits and misses with animal models of narcolepsy and the implications for drug discovery.

INTRODUCTION: Narcolepsy is a chronic and rare neurological disorder characterized by disordered sleep. Based on animal models and further research in humans, the dysfunctional orexin system was identified as a contributing factor to the pathophysiology of narcolepsy. Animal models played a larger role in the discovery of some of the pharmacological agents with established benefit/risk profiles. AREAS COVERED: In this review, the authors examine the phenotypes observed in animal models of narcolepsy and the characteristics of clinically used pharmacological agents in these animal models. Additionally, the authors compare the effects of clinically used pharmacological agents on the phenotypes in animal models with those observed in narcolepsy patients. EXPERT OPINION: Research in canine and mouse models have linked narcolepsy to the O×R2mutation and orexin deficiency, leading to new diagnostic criteria and a drug development focus. Advancements in pharmacological therapies have significantly improved narcolepsy management, with insights from both clinical experience and from animal models having led to new treatments such as low sodium oxybate and solriamfetol. However, challenges persist in addressing symptoms beyond excessive daytime sleepiness and cataplexy, highlighting the need for further research, including the development of diurnal animal models to enhance understanding and treatment options for narcolepsy.

Usmarapride (SUVN-D4010), a 5-HT4 receptor partial agonist for the potential treatment of Alzheimer's disease: Behavioural, neurochemical and pharmacological profiling.

Alzheimer's disease (AD) is a progressive neurodegenerative disorder which affects cognitive functions with negative impact on day to day activities and an ultimate loss of independent living. Current standard of care (SOC) for AD, viz. donepezil, rivastigmine, galantamine, memantine etc. either alone or in combination show modest efficacy without changing the course of the disease. On prolonged treatment, side effects are more common with an eventual loss of efficacy. Aducanumab, a monoclonal antibody is a disease modifying therapeutic agent targeting the toxic amyloid beta (Aß) proteins for its clearance. However, it is found to have only modest efficacy in AD patients and its approval by FDA is controversial. Alternate, effective and safe therapeutics are need of the hour, as AD cases are expected to be doubled by 2050. Recently, 5-HT4 receptors have been envisioned as target for alleviating AD associated cognitive impairment with potential disease modifying ability impacting disease progression. Usmarapride is a 5-HT4 receptor partial agonist, being developed for the possible treatment of AD with symptomatic and disease modifying potential. Usmarapride demonstrated promising effects in ameliorating cognitive deficits in diverse animal models of episodic, working, social, and emotional memories. Usmarapride produced elevation in cortical acetylcholine levels in rats. Furthermore, usmarapride increased levels of soluble amyloid precursor protein alpha, a potential mechanism to reverse toxic Aß peptide pathology. Usmarapride also potentiated the pharmacological effects of donepezil in animal models. To conclude, usmarapride may be a promising intervention for alleviating the cognitive dysfunction in AD patients with disease modifying potential.

Progress in Investigational Agents Targeting Serotonin-6 Receptors for the Treatment of Brain Disorders.

Serotonin (5-HT) plays an important role in the regulation of several basic functions of the central and peripheral nervous system. Among the 5-HT receptors, serotonin-6 (5-HT6) receptor has been an area of substantial research. 5-HT6 receptor is a G-protein-coupled receptor mediating its effects through diverse signaling pathways. Exceptional features of the receptors fueling drug discovery efforts include unique localization and specific distribution in the brain regions having a role in learning, memory, mood, and behavior, and the affinity of several clinically used psychotropic agents. Although non-clinical data suggest that both agonist and antagonist may have similar behavioral effects, most of the agents that entered clinical evaluation were antagonists. Schizophrenia was the initial target; more recently, cognitive deficits associated with Alzheimer's disease (AD) or other neurological disorders has been the target for clinically evaluated 5-HT6 receptor antagonists. Several 5-HT6 receptor antagonists (idalopirdine, intepirdine and latrepirdine) showed efficacy in alleviating cognitive deficits associated with AD in the proof-of-concept clinical studies; however, the outcomes of the subsequent phase 3 studies were largely disappointing. The observations from both non-clinical and clinical studies suggest that 5-HT6 receptor antagonists may have a role in the management of neuropsychiatric symptoms in dementia. Masupirdine, a selective 5-HT6 receptor antagonist, reduced agitation/aggression-like behaviors in animal models, and a post hoc analysis of a phase 2 trial suggested potential beneficial effects on agitation/aggression and psychosis in AD. This agent will be assessed in additional trials, and the outcome of the trials will inform the use of 5-HT6 receptor antagonists in the treatment of agitation in dementia of the Alzheimer's type.

Potential beneficial effects of masupirdine (SUVN-502) on agitation/aggression and psychosis in patients with moderate Alzheimer's disease: Exploratory post hoc analyses.

OBJECTIVES: The effects of masupirdine on the neuropsychiatric symptoms were explored. METHODS: Masupirdine (SUVN-502) was evaluated for its effects on cognition in patients with moderate AD. The prespecified primary outcome showed no drug-placebo difference. Post hoc analyses of domains of the 12-item neuropsychiatric inventory scale were carried out. RESULTS: In a subgroup of patients (placebo, n = 57; masupirdine 50 mg, n = 53; masupirdine 100 mg, n = 48) with baseline agitation/aggression symptoms ≥1, a statistically significant reduction in agitation/aggression scores was observed in masupirdine 50 mg (95% confidence interval (CI), -1.9 to -0.5, p < 0.001) and masupirdine 100 mg (95% CI, -1.7 to -0.3, p = 0.007) treated arms at Week 13 in comparison to placebo and the effect was sustained for trial duration of 26 weeks in the masupirdine 50 mg treatment arm (95% CI, -2.3 to -0.8, p < 0.001). Similar observations were noted in the subgroup of patients (placebo, n = 29; masupirdine 50 mg, n = 30; masupirdine 100 mg, n = 21) with baseline agitation/aggression symptoms ≥3. In the subgroup of patients (placebo, n = 28; masupirdine 50 mg, n = 28; masupirdine 100 mg, n = 28) who had baseline psychosis symptoms and/or symptom emergence, a significant reduction in psychosis scores was observed in the masupirdine 50 mg (Week 4: 95% CI, -2.8 to -1.4, p < 0.001; Week 13: 95% CI, -3.3 to -1.3, p < 0.001) and masupirdine 100 mg (Week 4: 95% CI, -1.4 to 0, p = 0.046; Week 13: 95% CI, -1.9 to 0.1, p = 0.073) treatment arms in comparison to placebo. CONCLUSION: Further research is warranted to explore the potential beneficial effects of masupirdine on NPS.

A Case of Lymphomatoid Granulomatosis in a Lymph Node with Unique Clinical and Histopathologic Features.

BACKGROUND Lymphomatoid granulomatosis (LyG) is a rare lymphoproliferative disorder associated with Epstein-Barr virus (EBV) in which there is an infection of B cells and numerous reactive T cells. The lymphoproliferative disorder progresses to organ infiltration and resultant dysfunction of affected organs. Histologically, it is characterized by a triad of polymorphic lymphoid infiltrate, angiitis, and granulomatosis. The lungs are the most commonly involved sites for lymphomatoid granulomatosis, but other sites that can be involved include the liver, skin, and central nervous system. The signs and symptoms of LyG can vary, and can produce generalized symptoms such as cough, shortness of breath, and chest tightness, but can vary depending on the location of LyG. CASE REPORT We report a case of a 60-year-old man who presented with altered mental status. Cross-sectional imaging of the brain was negative for any acute intracranial process, but a fine-needle biopsy of a retroperitoneal lymph node revealed nodular polymorphous mononuclear infiltrates containing atypical large EBV-positive B cells with positive EBER and CD30, consistent with lymphomatoid granulomatosis. The patient was started on a regimen of brentuximab/bendamustine, and instructed to follow up with Oncology on an outpatient basis. CONCLUSIONS Treatment options for lymphomatoid granulomatosis are based on the disease grading. Lymphomatoid granulomatosis can be classified by using a grading system determined by the number of EBV-positive large B cell malignant cells, along with necrosis. The most effective treatment for lymphomatoid granulomatosis is unknown, but at this time treatment protocols are based on the grade of the disease. The clinical and histological features of lymphomatoid granulomatosis are discussed in this case report.

Ropanicant (SUVN-911), an α4ß2 nicotinic acetylcholine receptor antagonist intended for the treatment of depressive disorders: pharmacological, behavioral, and neurochemical characterization.

RATIONALE: Ropanicant (SUVN-911) (3-(6-Chloropyridine-3-yloxymethyl)-2-azabicyclo (3.1.0) hexane hydrochloride) is a novel α4ß2 nicotinic acetylcholine receptor (nAChR) antagonist being developed for the treatment of depressive disorders. OBJECTIVES: Pharmacological and neurochemical characterization of Ropanicant to support a potential molecule for the treatment of depressive disorders. METHODS: Ropanicant was assessed for antidepressant-like activity using the rat forced swimming test (FST) and differential reinforcement of low rate -72 s (DRL-72 s). Alleviation of anhedonia was assessed in chronic mild stress model using sucrose preference test. To understand the mechanism of action, serotonin levels, ionized calcium-binding adaptor molecule 1 (Iba1), and brain-derived neurotrophic factor (BDNF) were determined. The onset of antidepressant-like activity was determined using the reduction in submissive behavior assay. The effects on cognition and sexual functions were assessed using the object recognition task and sexual dysfunction assay respectively. Interaction of Ropanicant, TC-5214, and methyllycaconitine (MLA) with citalopram was investigated individually in mice FST. RESULTS: Ropanicant exhibited antidepressant like properties in the FST and DRL-72 s. A significant reduction in anhedonia was observed in the sucrose preference test. Oral administration of Ropanicant produced a significant increase in serotonin and BDNF levels, with a reduction in the Iba1 activity. The onset of antidepressant like effect with Ropanicant was within a week of treatment, and was devoid of cognitive dulling and sexual dysfunction. While Ropanicant potentiated the effect of citalopram in FST, such an effect was not observed with MLA or TC-5214. CONCLUSIONS: Preclinical studies with Ropanicant support the likelihood of its therapeutic utility in the treatment of depressive disorders.

Acute suppurative thyroiditis seeded from infective endocarditis and intravenous drug use.

Acute suppurative thyroiditis (AST) is a rare infection of the thyroid gland, and most patients are euthyroid upon presentation. We present an interesting case of a 42-year-old man with a history of intravenous drug use (IVDU) and poorly controlled type 2 diabetes mellitus who was admitted for sepsis and thyrotoxicosis from infective endocarditis (IE), AST, prostate abscess, and pyelonephritis. He suffered from a cerebral vascular accident (CVA) from septic embolic showering. Thyroid-stimulating hormone (TSH) was <0.10 mIU/L, and free thyroxine (T4) levels were>90 pmol/L. Methicillin-resistant Staphylococcus aureus (MRSA) was cultured in the patient's blood and urine. He was treated with prompt intravenous (IV) antimicrobials and source control from a transurethral resection of the prostate. This case demonstrates that AST can be a potential complication of IE and IVDU.

Discovery and Preclinical Characterization of Usmarapride (SUVN-D4010): A Potent, Selective 5-HT4 Receptor Partial Agonist for the Treatment of Cognitive Deficits Associated with Alzheimer's Disease.

A series of oxadiazole derivatives were synthesized and evaluated as 5-hydroxytryptamine-4 receptor (5-HT4R) partial agonists for the treatment of cognitive deficits associated with Alzheimer's disease. Starting from a reported 5-HT4R antagonist, a systematic structure-activity relationship was conducted, which led to the discovery of potent and selective 5-HT4R partial agonist 1-isopropyl-3-{5-[1-(3-methoxypropyl) piperidin-4-yl]-[1,3,4]oxadiazol-2-yl}-1H-indazole oxalate (Usmarapride, 12l). It showed balanced physicochemical-pharmacokinetic properties with robust nonclinical efficacy in cognition models. It also showed disease-modifying potential, as it increased neuroprotective soluble amyloid precursor protein alpha levels, and dose-dependent target engagement and correlation of efficacy with oral exposures. Phase 1 clinical studies have been completed and projected efficacious concentration was achieved without any major safety concerns. Phase 2 enabling long-term safety studies have been completed with no concerns for further development.

Histamine 3 receptor inverse agonist Samelisant (SUVN-G3031): Pharmacological characterization of an investigational agent for the treatment of cognitive disorders.

BACKGROUND: Central histamine H3 receptors are a family of presynaptic auto and heteroreceptors. Blockade of the presynaptic H3 receptors activates the downstream pathway(s) involved in the processes of learning and memory, making it a potential therapeutic option for ameliorating cognitive dysfunction. Samelisant (SUVN-G3031) is a potent and selective inverse agonist at the H3 receptors. AIM: The aim of this research is to study the effects of Samelisant in diverse animal models of cognitive functions. METHODS: The effects of Samelisant on cognitive functions were studied using social recognition, object recognition and Morris water maze tasks. Neurochemical and electrophysiological effects of Samelisant were monitored using microdialysis and electroencephalography techniques. RESULTS: Samelisant showed procognitive effects in diverse animal models of cognition at doses ranging from 0.3 to 3 mg/kg, per os (p.o.) (social recognition and object recognition task). Samelisant significantly increased the brain acetylcholine levels in the cortex at doses of 10 and 20 mg/kg, p.o. In the Morris water maze task, combined administration of suboptimal doses of Samelisant and donepezil resulted in procognitive effects significantly larger than the either treatment. Similarly, Samelisant significantly potentiated the effects of donepezil on pharmacodynamic biomarkers of cognition i.e. acetylcholine levels in brain and neuronal theta oscillations. CONCLUSION: Samelisant may have potential utility in the treatment of cognitive deficits associated with hypocholinergic state.

Discovery and Development of 3-(6-Chloropyridine-3-yloxymethyl)-2-azabicyclo[3.1.0]hexane Hydrochloride (SUVN-911): A Novel, Potent, Selective, and Orally Active Neuronal Nicotinic Acetylcholine α4ß2 Receptor Antagonist for the Treatment of Depression.

A series of chemical optimizations guided by in vitro affinity at the α4ß2 receptor in combination with selectivity against the α3ß4 receptor, pharmacokinetic evaluation, and in vivo efficacy in a forced swim test resulted in identification of 3-(6-chloropyridine-3-yloxymethyl)-2-azabicyclo[3.1.0]hexane hydrochloride (9h, SUVN-911) as a clinical candidate. Compound 9h is a potent α4ß2 receptor ligand with a Ki value of 1.5 nM. It showed >10 µM binding affinity toward the ganglionic α3ß4 receptor apart from showing selectivity over 70 other targets. It is orally bioavailable and showed good brain penetration in rats. Marked antidepressant activity and dose-dependent receptor occupancy in rats support its potential therapeutic utility in the treatment of depression. It does not affect the locomotor activity at doses several folds higher than its efficacy dose. It is devoid of cardiovascular and gastrointestinal side effects. Successful long-term safety studies in animals and phase-1 evaluation in healthy humans for safety, tolerability, and pharmacokinetics paved the way for its further development.

SUVN-502, a novel, potent, pure, and orally active 5-HT6 receptor antagonist: pharmacological, behavioral, and neurochemical characterization.

Research in Alzheimer's disease is going through a big turnaround. New palliative therapies are being reconsidered for the effective management of disease because of setbacks in the development of disease-modifying therapies. Serotonin 6 (5-HT6) receptor has long been pursued as a potential target for the symptomatic treatment of Alzheimer's disease. SUVN-502 is a novel 5-HT6 receptor antagonist (Ki=2.04 nmol/l) with high receptor affinity and high degree of selectivity. SUVN-502 at doses ranging from 1 to 10 mg/kg, per os (p.o.) demonstrated procognitive effects in various behavioral animal models (object recognition task, water maze, and radial arm maze), and it acts on three phases of cognition, viz., acquisition, consolidation, and retention (object recognition task). SUVN-502 (3 and 10 mg/kg, p.o.) modulated glutamate levels when administered alone (microdialysis). At doses ranging from 1 to 10 mg/kg p.o., SUVN-502 potentiated the effects of donepezil (microdialysis). SUVN-502 [1 mg/kg, intravenous (i.v.)] also potentiated pharmacological effects of memantine (1 mg/kg, i.v.) and/or donepezil (0.3 mg/kg, i.v.) (θ modulation). The beneficial effects of SUVN-502 on learning and memory might be mediated through the modulation of cholinergic and/or glutamatergic neurotransmission in relevant brain regions. In summary, behavioral, neurochemical, and electrophysiological outcomes indicate that SUVN-502 may augment the beneficial effects of donepezil and memantine combination.

Prognostic Utility of Tumor-Infiltrating Lymphocytes in Noncolorectal Gastrointestinal Malignancies.

BACKGROUND: Tumor-infiltrating lymphocytes (TILs) and mismatch repair gene mutation (MMR) status are emerging biomarkers in immunotherapy. MMR status and TILs have significant clinical implications with regard to treatment with checkpoint inhibitors. We designed a study to determine the frequency and prognostic utility of TILs and MMR in advanced unresectable noncolorectal gastrointestinal (NCGI) malignancies. METHODS: This is a retrospective cohort study of patients who were diagnosed with advanced noncolorectal gastrointestinal tumors. Biopsy specimens were tested for MMR status by immunohistochemistry along with evaluation of TILs. Kaplan-Meier analysis was performed to determine the impact of TILS and MMR on survival. RESULTS: We analyzed 146 patients; the mean age at diagnosis was 66.4 ± 11.2 years. 65.8% patients were male, and 62.3% patients had stage 4 disease. All cases had proficient MMR status. The percentage of patients with TILs >5 was 50.7%. There was no statistically significant difference in median overall survival (OS) by TILs when stratified by stage of tumor. When stratified by type of tumor, median OS by TILs level was significantly different for hepatocellular cancers (⩽5 TILs, 86 days versus >5 TILs 312 days, P = .031). CONCLUSIONS: Our study suggests that MMR-deficient tumors are quite rare in advanced NCGI malignancies. More than 5 TILs per high power field, evaluated simply on a routine hematoxylin and eosin-stained glass slide confer a better prognosis to most noncolorectal gastrointestinal malignancies, especially hepatocellular carcinoma. This has immense clinical utility with regard to eligibility for immunotherapy.

Benzamide derivatives and their constrained analogs as histamine H3 receptor antagonists.

A series of 4-(1-substituted piperidin-4-yloxy) benzamides and 6-(1-substituted piperidin-4-yloxy)-3,4-dihydro-2H-isoquinolin-1-one derivatives have been synthesized and tested for their binding affinity towards H3 receptor. Most of these synthesized compounds have displayed potent binding affinity for H3 receptor when tested in in vitro binding assay. Preliminary SAR studies, functional activity, pharmacokinetic profile and efficacy profile constitute the subject matter of this communication.

Low-dose prazosin in combination with 5-HT6 antagonist PRX-07034 has antipsychotic effects.

An extensive amount of research has focused on the development of new pharmacological agents to treat schizophrenia. Varying from person to person, schizophrenia is a heterogeneous disease with symptoms of positive, negative, and cognitive deficits. PRX-07034, a 5-hydroxytryptamine6 (5-HT6) receptor antagonist has been evaluated for its potential in treating obesity and cognitive deficits. This study evaluated PRX-07034 (0.1, 0.3, and 1.0 mg/kg body mass, by intraperitoneal (i.p.) injection), in combination with a low dose of prazosin (0.3 mg/kg, i.p.), for its antipsychotic potential. The research utilized a stereotypy assay, an open field test, an object recognition task, and prepulse inhibition. Dizocilpine, a non-competitive N-methyl-d-aspartate (NMDA) antagonist, was also administered in the above-mentioned assays as a psychomimetic. The combination of PRX-07034 and prazosin alleviated stereotypy and hyperlocomotor activity while enhancing memory in an object recognition task, and reversed sensory-gating deficits induced by dizocilpine. Examination of the medial prefrontal cortex revealed that a combination of PRX-07034 and prazosin reduced the dizocilpine-mediated increase of 5-HT. These results suggest that the combination of a 5-HT6 antagonist with low doses of prazosin could have therapeutic potential in the treatment of schizophrenia.

Role of glutamate and advantages of combining memantine with a 5HT6 ligand in a model of depression.

BACKGROUND: It is a well-known fact that 5HT6 ligands increase glutamate levels. In the current study we investigated whether a 5HT6 antagonist, SB399885 would show antidepressant like property at a dose which would significantly increase the glutamate levels. Further we studied if the combination of a 5HT6 antagonist and N-methyl-D-aspartate (NMDA) antagonist, memantine would restore the antidepressant property. As dementia and depression are co-morbid, we evaluated if this combination would have an effect on cognition. METHODS: The antidepressant like property of SB399885 alone and in combination with memantine was investigated using the forced swim test (FST). Object recognition task (ORT) was used to investigate the combination therapy on cognition. Additionally, glutamate levels in prefrontal cortex and corresponding brain concentration of SB399885 were determined. RESULTS: Brain concentrations of SB399885 equal to or greater than 553 nM significantly increased brain glutamate levels and reduced immobility time in FST. When combined with memantine, glutamate levels and immobility time in FST was reduced. A dose dependent increase in the discriminative index was observed in ORT. CONCLUSION: Loss of antidepressant like property seen at the highest tested dose of SB399885 could be due to increased glutamate levels which was reversed by memantine. Combining memantine and SB399885 offers the advantage of extending the therapeutic window of antidepressant like property of SB399885 as well as having procognitive effect. The combination therapy holds promise in treatment of dementia associated with depression.

α4ß2* neuronal nicotinic receptor ligands (agonist, partial agonist and positive allosteric modulators) as therapeutic prospects for pain.

α4ß2* neuronal nicotinic acetylcholine receptor are ligand-gated ion channels and widely expressed throughout the central and peripheral nervous system. α4ß2* neuronal nicotinic acetylcholine receptor play crucial role in pain signaling via modulation of multiple neurotransmitters like acetylcholine, dopamine, γ-amino butyric acid (GABA) and norepinephrine. Both spinal and supraspinal pathways are involved in the mechanisms by which α4ß2* neuronal nicotinic acetylcholine receptor ligands modulate the neuropathic and inflammatory pain. Selective α4ß2* neuronal nicotinic acetylcholine receptor ligands are being developed for the treatment of neuropathic and inflammatory pain as they show considerable efficacy in a wide range of preclinical pain models. Agonists/partial agonists of α4ß2* neuronal nicotinic acetylcholine receptor show efficacy in animal models of pain and their anti-nociceptive properties are blocked by nicotinic antagonists. Positive allosteric modulators are being developed with the aim to increase the potency or therapeutic window of agonists/partial agonists. Accumulating evidences suggest that anti-nociceptive effects of nicotinic acetylcholine receptor ligands may not be mediated solely by α4ß2* neuronal nicotinic acetylcholine receptor. We have also reviewed the stage of clinical development of various α4ß2* neuronal nicotinic acetylcholine receptor ligands.

Aripiprazole in an animal model of chronic alcohol consumption and dopamine D2 receptor occupancy in rats.

BACKGROUND: Epidemiologic studies and clinical assessment of schizophrenic population have revealed a high incidence of overlap between schizophrenia and addictive disorders. OBJECTIVE: The aim of the present investigation was to study the effect of aripiprazole in a preclinical animal model of chronic alcohol self-administration (CASA) and also to evaluate the influence of CASA on plasma pharmacokinetics and dopamine D2 receptor (D2R) occupancy in rats. METHODS: The effect of oral administration of aripiprazole (1, 3, and 10 mg/kg) on 4% alcohol intake in CASA was studied for a period of 45 min after a post-dosing interval of 60 min. Brain penetration, pharmacokinetics, and D2R occupancy of aripiprazole were evaluated in normal and CASA rats. RESULTS: Aripiprazole reduced alcohol consumption in CASA rats by 13, 28, and 86% at 1, 3, and 10 mg/kg, respectively, and the effect reached statistical significance at 10 mg/kg (p < .01). At this behavioral effective dose, a decrease (75%) in total plasma apparent clearance and an increase in oral area under the concentration-time curve (3.98-fold) and bioavailability (3.50-fold) of aripiprazole was observed in CASA rats. Striatal D2R occupancy and brain exposure of aripiprazole were significantly higher (∼twofold) in CASA rats when compared to normal rats (p < .01). CONCLUSION: Chronic alcohol intake results in a significant increase in exposure of aripiprazole in plasma and brain and striatal D2R occupancy. SCIENTIFIC SIGNIFICANCE: Chronic alcohol intake would increase aripiprazole exposure, thus aripiprazole dose might have to be decreased (assuming this same phenomenon occurs in humans).

Design, synthesis and pharmacological evaluation of 4-(piperazin-1-yl methyl)-N1-arylsulfonyl indole derivatives as 5-HT6 receptor ligands.

4-(Piperazin-1-yl methyl)-N(1)-arylsulfonyl indole derivatives were designed and synthesized as 5-HT(6) receptor (5-HT(6)R) ligands. The lead compound 6a, from this series shows potent in vitro binding affinity, good PK profile, no CYP liabilities and activity in animal models of cognition.

Comparison of manual and automated filaments for evaluation of neuropathic pain behavior in rats.

INTRODUCTION: The most commonly used Von Frey filaments are productive in evaluating behavioral responses of neuropathic pain in preclinical and clinical research. To reduce the potential experimenter bias, automated instruments are being developed for behavioral assessment. In preclinical research, neuropathic pain models of nerve injury with varied etiology like partial sciatic nerve ligation (PNL), chronic constricted injury (CCI) and spinal nerve ligation (SNL) are employed to screen the analgesic drugs to treat symptoms like allodynia and hyperalgesia. The current study was aimed to validate and compare conventionally used Von Frey monofilaments and automated dynamic plantar aesthesiometer using three different pain models. METHODS: PNL, CCI and SNL rats were used to compare and validate the assessment of neuropathic pain using Von Frey monofilaments and automated dynamic plantar aesthesiometer. RESULTS: Mechanical allodynia was assessed at various time points to mimic drug testing conditions in neuropathic pain models and anticipated to observe reliable and reproducible paw withdrawal threshold measurements across these models. Consistent paw withdrawal thresholds were observed in all the three models of neuropathic pain with Von Frey monofilaments, whereas variable paw withdrawal thresholds were noticed in PNL and CCI models but not in SNL model with dynamic plantar aesthesiometer. DISCUSSION: Manually used Von Frey filaments can be used in assessment of mechanical allodynia in all the three models, whereas dynamic plantar aesthesiometer is suitable for assessing mechanical allodynia in SNL but not in PNL and CCI models. The reason for variable paw withdrawal thresholds during assessment of mechanical allodynia in PNL and CCI models with dynamic plantar aesthesiometer may be due to the paw deformity and change in foot posture.

Difference in the norepinephrine levels of experimental and non-experimental rats with age in the object recognition task.

In the present study, we investigated the performance of adult and juvenile rats in the Object Recognition Task (ORT). While it is well known that the performance of rat in ORT differs with age, the reason for the difference as well as the underlying neurotransmitter that may have led to these differences were investigated. In the present study, juvenile rats of postnatal day 40-45 (PND 40-45) and adult rats of postnatal day 60+ (PND 60+) were subjected to a two trial ORT. The juvenile rats did not discriminate between the novel object and the familiar object, while the adult rats discriminated the novel from the familiar object. On estimating brain concentrations of norepinephrine (NE), it was observed that the NE level in MTL (medial temporal lobe) of adult experimental rats was significantly higher than the adult non-experimental rats. In juvenile rats, no significant difference was observed in the NE levels of experimental rats in comparison to its non-experimental counterparts. Administration of yohimbine (α(2A) adrenergic receptor antagonist) enhanced the level of NE in juvenile rats and reversed the difference seen with age. From the present study, we conclude that the deficit in memory seen is likely due to the difference in NE levels with task and this can be reversed by yohimbine which enhance NE levels.