Animal tests of anxiety

Phytoconstituents of Chloranthus elatior as a potential adjunct in the treatment of anxiety disorders: In vivo and in silico approaches

Traditional plants have played a vital role in civilization and medicine throughout history. Chloranthus elatior, a plant used in South Asian traditional medicine, has various medicinal applications but limited research on its impact on the central nervous system (CNS). This study analyzed the methanolic leaf extract of Chloranthus elatior (MECE) for secondary metabolites and conducted experiments to evaluate the sedative, and anxiolytic effect of MECE on a mice model. To assess anxiolytic effects, elevated plus maze (EPM) and light-dark box (LDB) tests were performed. Sedative effects were explored in open field and hole-cross tests. Additionally, in silico investigations included molecular docking and ADME/T property assessments for 40 secondary metabolites. The phytochemical analysis of MECE revealed the presence of alkaloids, tannins, flavonoids, and glycosides. MECE exhibited significant anxiolytic effects in both the EPM and LDB tests, with statistical significance (P < 0.001). The open field and hole-cross tests demonstrated significant sedative potential (P < 0.05) compared to the standard Diazepam. Furthermore, molecular docking was performed to evaluate the potential of the compounds with a potassium channel protein. Among them, Chloramultilide C, 4-dimethoxyflavanone, and Neolitacumone B were identified as potential against the target protein with a binding score of -8.8 kcal/mol, -6.5 kcal/mol, and -6.4 kcal/mol, respectively. Additionally, pharmacokinetic attributes and ADMET analysis emphasized promising properties for drug development. These findings suggest that MECE possesses sedative and anxiolytic properties that could be valuable for addressing insomnia and anxiety associated with various psychiatric disorders.

Single-Dose P2 X4R Single-Chain Fragment Variable Antibody Permanently Reverses Chronic Pain in Male Mice

Non-opioid single-chain variable fragment (scFv) small antibodies were generated as pain-reducing block of P2X4R receptor (P2X4R). A panel of scFvs targeting an extracellular peptide sequence of P2X4R was generated followed by cell-free ribosome display for recombinant antibody selection. After three rounds of bio-panning, a panel of recombinant antibodies was isolated and characterized by ELISA, cross-reactivity analysis, and immunoblotting/immunostaining. Generated scFv antibodies feature binding activity similar to monoclonal antibodies but with stronger affinity and increased tissue penetrability due to their ~30% smaller size. Two anti-P2X4R scFv clones (95, 12) with high specificity and affinity binding were selected for in vivo testing in male and female mice with trigeminal nerve chronic neuropathic pain (FRICT-ION model) persisting for several months in untreated BALBc mice. A single dose of P2X4R scFv (4 mg/kg, i.p.) successfully, completely, and permanently reversed chronic neuropathic pain-like measures in male mice only, providing retention of baseline behaviors indefinitely. Untreated mice retained hypersensitivity, and developed anxiety- and depression-like behaviors within 5 weeks. In vitro P2X4R scFv 95 treatment significantly increased the rheobase of larger-diameter (>25 µm) trigeminal ganglia (TG) neurons from FRICT-ION mice compared to controls. The data support use of engineered scFv antibodies as non-opioid biotherapeutic interventions for chronic pain.

Oligophrenin-1 moderates behavioral responses to stress by regulating parvalbumin interneuron activity in the medial prefrontal cortex

Ample evidence indicates that individuals with intellectual disability (ID) are at increased risk of developing stress-related behavioral problems and mood disorders, yet a mechanistic explanation for such a link remains largely elusive. Here, we focused on characterizing the syndromic ID gene oligophrenin-1 (OPHN1). We find that Ophn1 deficiency in mice markedly enhances helpless/depressive-like behavior in the face of repeated/uncontrollable stress. Strikingly, Ophn1 deletion exclusively in parvalbumin (PV) interneurons in the prelimbic medial prefrontal cortex (PL-mPFC) is sufficient to induce helplessness. This behavioral phenotype is mediated by a diminished excitatory drive onto Ophn1-deficient PL-mPFC PV interneurons, leading to hyperactivity in this region. Importantly, suppressing neuronal activity or RhoA/Rho-kinase signaling in the PL-mPFC reverses helpless behavior. Our results identify OPHN1 as a critical regulator of adaptive behavioral responses to stress and shed light onto the mechanistic links among OPHN1 genetic deficits, mPFC circuit dysfunction, and abnormalities in stress-related behaviors.

Effect of acetyl-L-carnitine on hypersensitivity in acute recurrent caerulein-induced pancreatitis and microglial activation along the brain’s pain circuitry

BACKGROUND

Acute pancreatitis (AP) and recurring AP are serious health care problems causing excruciating pain and potentially lethal outcomes due to sepsis. The validated caerulein- (CAE) induced mouse model of acute/recurring AP produces secondary persistent hypersensitivity and anxiety-like behavioral changes for study.

AIM

To determine efficacy of acetyl-L-carnitine (ALC) to reduce pain-related behaviors and brain microglial activation along the pain circuitry in CAE-pancreatitis.

METHODS

Pancreatitis was induced with 6 hly intraperitoneal (i.p.) injections of CAE (50 µg/kg), 3 d a week for 6 wk in male C57BL/6J mice. Starting in week 4, mice received either vehicle or ALC until experiment’s end. Mechanical hyper-sensitivity was assessed with von Frey filaments. Heat hypersensitivity was determined with the hotplate test. Anxiety-like behavior was tested in week 6 using elevated plus maze and open field tests. Microglial activation in brain was quantified histologically by immunostaining for ionized calcium-binding adaptor molecule 1 (Iba1).

RESULTS

Mice with CAE-induced pancreatitis had significantly reduced mechanical withdrawal thresholds and heat response latencies, indicating ongoing pain. Treatment with ALC attenuated inflammation-induced hypersensitivity, but hypersensitivity due to abdominal wall injury caused by repeated intraperitoneal injections persisted. Animals with pancreatitis displayed spontaneous anxiety-like behavior in the elevated plus maze compared to controls. Treatment with ALC resulted in increased numbers of rearing activity events, but time spent in “safety” was not changed. After all the abdominal injections, pancreata were translucent if excised at experiment’s end and opaque if excised on the subsequent day, indicative of spontaneous healing. Post mortem histopathological analysis performed on pancreas sections stained with Sirius Red and Fast Green identified wide-spread fibrosis and acinar cell atrophy in sections from mice with CAE-induced pancreatitis that was not rescued by treatment with ALC. Microglial Iba1 immunostaining was significantly increased in hippocampus, thalamus (intralaminar nuclei), hypothalamus, and amygdala of mice with CAE-induced pancreatitis compared to naïve controls but unchanged in the primary somatosensory cortex compared to naïves.

CONCLUSION

CAE-induced pancreatitis caused increased pain-related behaviors, pancreatic fibrosis, and brain microglial changes. ALC alleviated CAE-induced mechanical and heat hypersensitivity but not abdominal wall injury-induced hypersensitivity caused by the repeated injections.

HIV-1 Tat promotes age-related cognitive, anxiety-like, and antinociceptive impairments in female mice that are moderated by aging and endocrine status

Hypogonadism is a common comorbidity associated with HIV-1 that is more prevalent among infected individuals over the age of 45. The underlying mechanisms are unknown, but both combined antiretroviral therapeutics and HIV-1 proteins, such as trans-activator of transcription protein (Tat), dysregulate steroid-synthetic mechanisms including lipid storage/synthesis and mitochondrial function. Thus, Tat expression may accelerate age-related comorbidities partly by impairing endocrine function. Few studies exist of Tat-mediated behavioral deficits in aged animals and effects of endocrine status have not been investigated. Accordingly, we tested whether conditional Tat expression in aged (~ 1.5 years old), female, Tat-transgenic [Tat(+)] mice increases anxiety-like behavior, impairs cognition, and augments mechanical allodynia, when compared to age-matched controls that do not express Tat protein [Tat(-)]. We further tested whether aged mice that maintained their endocrine status (pre-estropausal) were more resilient to Tat/age-related comorbidities than peri- or post-estropausal mice. Tat and endocrine aging status exerted separate and interacting effects that influenced anxiety-like and cognitive behaviors. Peri- and post-estropausal mice exhibited greater anxiety-like behavior in the elevated plus-maze and impaired learning in the radial arm water maze compared to pre-estropausal mice. Irrespective of estropause status, Tat(+) mice demonstrated impaired learning, reduced grip strength, and mechanical allodynia compared to Tat(-) mice. Tat exposure reduced circulating estradiol in post-estropausal mice and increased the estradiol-to-testosterone ratio in pre-estropausal mice. Changes in circulating estradiol, testosterone, and progesterone correlated with grip strength. Thus, endocrine status is an important factor in age-related anxiety, cognition, neuromuscular function, and allodynia that can be accelerated by HIV-1 Tat protein.

N-acetyl cysteine reverses bio-behavioural changes induced by prenatal inflammation, adolescent methamphetamine exposure and combined challenges

RATIONALE

Schizophrenia is associated with prenatal inflammation and/or postnatal stressors such as drug abuse, resulting in immune-redox dysfunction. Antioxidants may offer therapeutic benefits.

OBJECTIVES

The objective of this study is to investigate N-acetyl cysteine (NAC) as a therapeutic antioxidant to reverse schizophrenia-like bio-behavioural changes in rats exposed to maternal immune activation (MIA), adolescent methamphetamine (MA) or a combination thereof.

METHODS

Sprague-Dawley offspring prenatally exposed to saline/lipopolysaccharide (LPS) received saline or MA (0.2-6 mg kg^-1 twice daily × 16 days) during adolescence and divided into LPS, MA and LPS + MA groups. Vehicle/NAC (150 mg kg^-1 × 14 days) was administered following MA/saline exposure on postnatal day 51-64. Social interaction, novel object recognition and prepulse inhibition (PPI) of startle, as well as regional brain monoamines, lipid peroxidation, plasma reactive oxygen species (ROS) and pro- and anti-inflammatory cytokines (TNF-α; IL-10), were assessed.

RESULTS

NAC reversed LPS, MA and LPS + MA-induced anxiety-like social withdrawal behaviours, as well as MA and LPS + MA-induced deficits in recognition memory. PPI deficits were evident in MA, LPS and LPS + MA models, with NAC reversing that following LPS + MA. NAC reversed LPS, MA and LPS + MA-induced frontal cortical dopamine (DA) and noradrenaline (NA) elevations, LPS and LPS + MA-induced frontal cortical 3,4-dihydroxyphenylacetic acid (DOPAC), serotonin (5-HT) and striatal NA deficits as well as LPS + MA-induced frontal cortical 5-HT turnover. Decreased IL-10 in the LPS, MA and LPS + MA animals, and increased TNF-α in the LPS and MA animals, was reversed with NAC. NAC also reversed elevated lipid peroxidation and ROS in the LPS and LPS + MA animals.

CONCLUSIONS

Prenatal LPS, LPS + postnatal MA challenge during adolescence, and to a lesser extent MA alone, promotes schizophrenia-like bio-behavioural changes later in life that are reversed by NAC, emphasizing therapeutic potential for schizophrenia and MA-associated psychosis. The nature and timing of the dual-hit are critical.

Benzodiazepine and neuroactive steroid combinations in rats: anxiolytic-like and discriminative stimulus effects

RATIONALE

Benzodiazepines are effective anxiolytics, hypnotics, and anticonvulsants but unwanted side effects, including abuse potential, limit their use. A possible strategy to increase the therapeutic index of this drug class is to combine benzodiazepines with neuroactive steroids.

OBJECTIVES

The present study evaluated the extent to which combinations of benzodiazepines (triazolam, clonazepam) and neuroactive steroids (pregnanolone, ganaxolone) induced additive, supra-additive, or infra-additive effects in an elevated zero maze and a drug discrimination procedure in rats.

METHODS

Male Sprague-Dawley rats (N = 7/group) were placed into an elevated zero maze apparatus following injections of multiple doses of triazolam and pregnanolone, alone and combined, or clonazepam and ganaxolone, alone and combined. These drugs/drug combinations also were evaluated in rats (N = 8) trained to discriminate triazolam (0.1 mg/kg, i.p.) from vehicle. Drug interactions were evaluated using isobolographic and dose-addition analysis.

RESULTS

In the elevated zero maze, all drugs engendered dose-dependent increases in time spent in the open quadrant when administered alone. Triazolam and pregnanolone, as well as clonazepam and ganaxolone combinations produced additive or supra-additive effects depending on the fixed-proportion that was tested. In triazolam discrimination, all drugs engendered dose-dependent increases in triazolam-lever responding. In combination, triazolam and pregnanolone and clonazepam and ganaxolone produced predominantly additive discriminative stimulus effects, except for one fixed proportion of clonazepam and ganaxolone which had supra-additive effects.

CONCLUSIONS

Although drug interactions depended on the constituent drugs, the combination tested, and the behavioral endpoint; a combination was identified that would be predicted to result in supra-additive anxiolytic-like effects with predominantly additive discriminative stimulus effects.

5α-reduced progestogens ameliorate mood-related behavioral pathology, neurotoxicity, and microgliosis associated with exposure to HIV-1 Tat

Human immunodeficiency virus (HIV) is associated with motor and mood disorders, likely influenced by reactive microgliosis and subsequent neural damage. We have recapitulated aspects of this pathology in mice that conditionally express the neurotoxic HIV-1 regulatory protein, trans-activator of transcription (Tat). Progestogens may attenuate Tat-related behavioral impairments and reduce neurotoxicity in vitro, perhaps via progesterone's 5α-reductase-dependent metabolism to the neuroprotective steroid, allopregnanolone. To test this, ovariectomized female mice that conditionally expressed (or did not express) central HIV-1 Tat were administered vehicle or progesterone (4mg/kg), with or without pretreatment of a 5α-reductase inhibitor (finasteride, 50mg/kg). Tat induction significantly increased anxiety-like behavior in an open field, elevated plus maze and a marble burying task concomitant with elevated protein oxidation in striatum. Progesterone administration attenuated anxiety-like effects in the open field and elevated plus maze, but not in conjunction with finasteride pretreatment. Progesterone also attenuated Tat-promoted protein oxidation in striatum, independent of finasteride pretreatment. Concurrent experiments in vitro revealed Tat (50nM)-mediated reductions in neuronal cell survival over 60h, as well as increased neuronal and microglial intracellular calcium, as assessed via fura-2 AM fluorescence. Co-treatment with allopregnanolone (100nM) attenuated neuronal death in time-lapse imaging and blocked the Tat-induced exacerbation of intracellular calcium in neurons and microglia. Lastly, neuronal-glial co-cultures were labeled for Iba-1 to reveal that Tat increased microglial numbers in vitro and co-treatment with allopregnanolone attenuated this effect. Together, these data support the notion that 5α-reduced pregnane steroids exert protection over the neurotoxic effects of HIV-1 Tat.

Central HIV-1 Tat exposure elevates anxiety and fear conditioned responses of male mice concurrent with altered mu-opioid receptor-mediated G-protein activation and β-arrestin 2 activity in the forebrain

Co-exposure to opiates and HIV/HIV proteins results in enhanced CNS morphological and behavioral deficits in HIV(+) individuals and in animal models. Opiates with abuse liability, such as heroin and morphine, bind preferentially to and have pharmacological actions through μ-opioid-receptors (MORs). The mechanisms underlying opiate-HIV interactions are not understood. Exposure to the HIV-1 transactivator of transcription (Tat) protein causes neurodegenerative outcomes that parallel many aspects of the human disease. We have also observed that in vivo exposure to Tat results in apparent changes in morphine efficacy, and thus have hypothesized that HIV proteins might alter MOR activation. To test our hypothesis, MOR-mediated G-protein activation was determined in neuroAIDS-relevant forebrain regions of transgenic mice with inducible CNS expression of HIV-1 Tat. G-protein activation was assessed by MOR agonist-stimulated [(35)S]guanosine-5'-O-(3-thio)triphosphate ([(35)S]GTPγS) autoradiography in brain sections, and in concentration-effect curves of MOR agonist-stimulated [(35)S]GTPγS binding in membranes isolated from specific brain regions. Comparative studies were done using the MOR-selective agonist DAMGO ([D-Ala(2), N-MePhe(4), Gly-ol]-enkephalin) and a more clinically relevant agonist, morphine. Tat exposure reduced MOR-mediated G-protein activation in an agonist, time, and regionally dependent manner. Levels of the GPCR regulatory protein β-arrestin-2, which is involved in MOR desensitization, were found to be elevated in only one affected brain region, the amygdala; amygdalar β-arrestin-2 also showed a significantly increased association with MOR by co-immunoprecipitation, suggesting decreased availability of MOR. Interestingly, this correlated with changes in anxiety and fear-conditioned extinction, behaviors that have substantial amygdalar input. We propose that HIV-1 Tat alters the intrinsic capacity of MOR to signal in response to agonist binding, possibly via a mechanism involving altered expression and/or function of β-arrestin-2.

AAV1/2-mediated BDNF gene therapy in a transgenic rat model of Huntington's disease

Reduced expression and disrupted corticostriatal transportation of brain-derived neurotrophic factor (BDNF) is proposed to contribute to the selective vulnerability of medium spiny striatal projection neurons (MSNs) in Huntington's disease (HD). We have previously demonstrated that BDNF overexpression in the quinolinic acid lesioned rat striatum attenuates motor impairment and reduces the extent of MSN cell loss. To further investigate the potential therapeutic properties of BDNF for HD, the current study examines the effect of bilateral AAV1/2-mediated BDNF expression in the striatum of a transgenic rat model of HD. Transfer of the BDNF gene to striatal neurons using an AAV1/2 serotype vector enhanced BDNF protein levels in the striatum. Bilateral BDNF expression attenuated the impairment of both motor and cognitive function when compared with AAV1/2-vehicle- or YFP-treated transgenic HD rats. Interestingly, a gender effect was apparent with female transgenic HD rats exhibiting less functional impairment than males. Quantification of NeuN and DARRP32 immunoreactivity and striatal volume revealed limited disease phenotype between wild type and transgenic HD animals. However, AAV1/2-BDNF-treated transgenic HD rats showed evidence of greater striatal volume and increased NeuN+ cell numbers compared with wild-type vehicle- and AAV1/2-vehicle- or YFP-treated transgenic HD rats. We propose BDNF holds considerable therapeutic potential for alleviating behavioral dysfunction and neuronal degeneration in HD, with further work required to examine the role of BDNF-TrkB signaling and the preservation of axonal and synaptic function.

Immediate ketamine treatment does not prevent posttraumatic stress responses in an animal model for PTSD

Clinical studies suggest that administration of ketamine hydrochloride-an antagonist at the N-methyl-d-aspartate ionophore-provides short-term amelioration for depressive symptoms. The effects of a brief course of ketamine given immediately following exposure to psychogenic stress on the behavioral stress responses were assessed in an animal model of posttraumatic stress disorder. Animals exposed to stress were treated 1h later with ketamine (0.5, 5, and 15 mg/kg) or vehicle for three days (N = 107). Outcome measures included behavior in the elevated plus maze (EPM) and acoustic startle response (ASR) tests 30 days after initial exposure and freezing behavior upon exposure to a trauma-cue on day 31. Pre-set cut-off behavioral criteria classified exposed animals according to their EPM and ASR response-patterns into "extreme," "minimal," or "partial" behavioral response for analysis of prevalence rates of "PTSD-like behavior." Circulating corticosterone levels were assessed 20 min after injection of ketamine in exposed and unexposed animals (N = 62). The dexamethasone suppression test was used to assess negative feedback inhibition of the HPA axis. Prevalence rates of extremely-, partially-, or minimally-disrupted behavior demonstrated that ketamine administered immediately following stress exposure was ineffective in alleviating "PTSD-like behavior" at day 30 after exposure. Administration of ketamine was associated with increase in freezing behavior after exposure to a trauma-cue on day 31. Corticosterone levels were significantly suppressed by ketamine only in the exposed animals. Administration of ketamine immediately following trauma-exposure may not only be ineffective but actually detrimental in the long term. A disruption of the post-stress HPA-response has been raised as a contributing factor.