The four-plates test: anxiolytic or analgesic paradigm?

Nalbuphine-6-glucuronide is a potent analgesic with superior safety profiles by altering binding affinity and selectivity for mu-/kappa-opioid receptors

Although nalbuphine, a semi-synthetic analgesic compound, is less potent than morphine in terms of alleviating severe pain, our recent findings have revealed that nalbuphine-6-glucuronide (N6G), one of the glucuronide metabolites of nalbuphine, promotes a significantly more robust analgesic effect than its parent drug. Nevertheless, despite these promising observations, the precise mechanisms underlying the analgesic effects of nalbuphine glucuronides have yet to be determined. In this study, we aim to elucidate the mechanisms associated with the analgesic effects of nalbuphine glucuronides. Pharmacokinetic and pharmacodynamic studies were conducted to investigate the relationship between the central and peripheral compartments of nalbuphine and its derivatives. The analgesic responses of these compounds were evaluated based on multiple behavioral tests involving thermal and mechanical stimuli. Radioligand binding assays were also performed to determine the binding affinity and selectivity of these compounds for different opioid receptors. The results of these tests consistently confirmed that the heightened analgesic effects of N6G are mediated through its enhanced binding affinity for both mu- and kappa-opioid receptors, even comparable to those of morphine. Notably, N6G exhibited fewer side effects and did not induce sudden death, thereby highlighting its superior safety profile. Additionally, pharmacokinetic studies indicated that N6G could cross the blood-brain barrier when administered peripherally, offering pain relief. Overall, N6G provides great analgesic efficacy and enhanced safety. These findings highlight the potential value of nalbuphine glucuronides, particularly N6G, as promising candidates for the development of novel analgesic drugs.

Topiramate affords neuroprotection in diabetic neuropathy model via downregulating spinal GFAP/inflammatory burden and improving neurofilament production

The current study aimed to test the neuroprotective action of topiramate in mouse peripheral diabetic neuropathy (DN) and explored some mechanisms underlying this action. Mice were assigned as vehicle group, DN group, DN + topiramate 10-mg/kg and DN + topiramate 30-mg/kg. Mice were tested for allodynia and hyperalgesia and then spinal cord and sciatic nerves specimens were examined microscopically and neurofilament heavy chain (NEFH) immunostaining was performed. Results indicated that DN mice had lower the hotplate latency time (0.46-fold of latency to licking) and lower von-Frey test pain threshold (0.6-fold of filament size) while treatment with topiramate increased these values significantly. Sciatic nerves from DN control mice showed axonal degeneration while spinal cords showed elevated GFAP (5.6-fold) and inflammatory cytokines (∼3- to 4-fold) but lower plasticity as indicated by GAP-43 (0.25-fold). Topiramate produced neuroprotection and suppressed spinal cord GFAP/inflammation but enhanced GAP-43. This study reinforces topiramate as neuroprotection and explained some mechanisms included in alleviating neuropathy.

Novel GPR18 Ligands in Rodent Pharmacological Tests: Effects on Mood, Pain, and Eating Disorders

The lack of selective pharmacological tools has limited the full unraveling of G protein-coupled receptor 18 (GPR18) functions. The present study was aimed at discovering the activities of three novel preferential or selective GPR18 ligands, one agonist (PSB-KK-1415) and two antagonists (PSB-CB-5 and PSB-CB-27). We investigated these ligands in several screening tests, considering the relationship between GPR18 and the cannabinoid (CB) receptor system, and the control of endoCB signaling over emotions, food intake, pain sensation, and thermoregulation. We also assessed whether the novel compounds could modulate the subjective effects evoked by Δ⁹-tetrahydrocannabinol (THC). Male mice or rats were pretreated with the GPR18 ligands, and locomotor activity, depression- and anxiety-like symptoms, pain threshold, core temperature, food intake, and THC-vehicle discrimination were measured. Our screening analyses indicated that GPR18 activation partly results in effects that are similar to those of CB receptor activation, considering the impact on emotional behavior, food intake, and pain activity. Thus, the orphan GPR18 may provide a novel therapeutic target for mood, pain, and/or eating disorders, and further investigation is warranted to better discern its function.

Sex dependent alteration of epigenetic marks after chronic morphine treatment in mice organs

Epigenetic marks may be also affected by several factors, such as age, lifestyle, early life experiences and exposure to chemicals or drugs, such as opioids. Previous studies have focused on how morphine epigenetically regulates different regions of the brain that are implicated in tolerance, dependence and other psychiatric disorders more related to the physio-pathological effects of opioids. Nevertheless, a significant knowledge gap remains regarding the effect of chronic treatment on other organs and biological systems. Therefore, the aim of this work is to increase our knowledge about the impact of chronic morphine exposure on DNA methylation and histone modification levels in each of the organs of male and female model mice in vivo. Our results reveal, for the first time, that chronic morphine treatment induced changes in DNA methylation/hydroxymethylation and histone modification in-vivo at the systemic level, revealing a potential physiological effect on the regulation of gene expression. Notably, morphine-induced epigenetic modification occurs in a sex-dependent manner, revealing the existence of different underlying mechanisms of epigenetic modification in male and female mice.

LVV-hemorphin-7 (LVV-H7) plays a role in antinociception in a rat model of alcohol-induced pain disorders

Alcohol can increase the sensitivity to painful stimulation or convert insensibility to pain at different stages. We hypothesized that chronic alcohol consumption changes the level of LVV-hemorphin-7 (abbreviated as LVV-H7, an opioid-like peptide generated from hemoglobin β-chain), thereby affecting pain sensation. We established a chronic alcohol-exposed rat model to investigate the effects of LVV-H7. Adult male Sprague-Dawley rats were subjected to daily intraperitoneal injection of 10 % ethanol (w/v) at 0.5 g/kg for 15 days and subsequent alcohol withdrawal for 5 days. Using different pharmacological strategies to affect the LVV-H7 level, we investigated the correlation between LVV-H7 and pain-related behavior. Tail-flick and hot plate tests were employed to investigate alcohol-induced pain-related behavioral changes. The serum level of LVV-H7 was determined by ELISA. Our results showed that alcohol first induced an analgesia followed by a hyperalgesia during alcohol withdrawal, which could be driven by the quantitative change of LVV-H7. A positive correlation between the level of LVV-H7 and Δtail-flick latency (measured latency minus basal latency) confirmed this finding. Moreover, we revealed that the LVV-H7 levels were determined by the activity of cathepsin D and red blood cell/hemoglobin counts, which could be affected by alcohol. These results suggest that the deterioration of anti-nociception induced by alcohol is correlated to the decreased level of LVV-H7, and this could be due to alcohol-induced anemia. This study may help to develop LVV-H7 structure-based novel analgesics for treating alcohol-induced pain disorders and thus ameliorate the complications in alcoholics.

Anti-Nociceptive and Anti-Inflammatory Effects of Stem Bark Extract of Ficus Capensis Thunb (Moraceae) by Bioactivity Fractionation

OBJECTIVE

This study investigated the antinociceptive and anti-inflammatory activities of the aqueous extract of Ficus capensis (AEFC) by bio-guided fractionation.

METHODS

The anti-nociceptive and anti-inflammatory effects of AEFC (250, 500, 1000 mg/kg, i.p) were assessed using acetic acid-induced writhing, hot plate, tail-flick, formalin tests, and carrageenan- induced paw edema, respectively. The AEFC was fractionated base on polarity difference into butanol, ethyl acetate, and n-hexane fractions. The fractions (500 mg/kg) obtained were subjected to the same experimental procedures mentioned above. The EAF, which exerted the most productive activities, was further subjected to fractionation procedures that yielded six fractions (labeled CF1-CF6). These fractions (200 mg/kg) were tested for potential antinociceptive and anti-inflammatory activities. Notable antagonists (Naloxone and atropine) of the nociceptive pathway were used to evaluate the mechanism of the antinociceptive action of F. capensis.

RESULTS AND DISCUSSION

The AEFC, BF, EAF, and CF4 caused a significant (p<0.05) reduction in the number of abdominal writhes, an increase in reaction time against the hot plate, tail-flick tests, and a significant (p<0.05) inhibition in both phases of formalin test. The AEFC, BF, EAF, CF4, and CF6 caused a significant (p<0.05) inhibition of paw edema development due to carrageenan. Atropine significantly reversed the antinociceptive effect of CF4 in both phases of the formalin test. The results obtained revealed that CF4 produced central and peripheral antinociceptive effects, while CF6 is peripherally mediated.

CONCLUSION

The results support the traditional uses of F. capensis in the treatment of various diseases associated with pain and inflammation. The column fraction CF4 exhibited muscarinic receptor- mediated antinociceptive activity.

Increased NRSF/REST in anterior cingulate cortex contributes to diabetes-related neuropathic pain

Diabetic neuropathic pain is one of the most common complications of diabetes. Mechanisms underlying the central modulation are still unclear. Here, we investigated the role of the neuron-restricted silencing factor (NRSF/REST) in diabetic-related neuropathic pain. Mechanical allodynia and thermal hyperalgesia were assessed to evaluate painful behaviors. Our results found that in the anterior cingulate cortex (ACC) of db/db mice, NRSF/REST levels increased significantly. Reduction of NRSF/REST improved the painful sensation. Meanwhile, in vitro study found that high glucose and high palmitic acid treatment induced elevation of NRSF/REST and its cofactors (mSin3A, CoREST and HDAC1), whereas downregulation of GluR2 and NMDAR2B. Knockdown of NRSF/REST could attenuate the LDH release and partially reversed the expression changes of HDAC1 and NMDAR2B. Our results suggested that the elevation of NRSF/REST in the ACC area of db/db mice is one of the key mediators of diabetic neuropathic pain.

Inhibitory effect of valproate sodium on pain behavior in diabetic mice involves suppression of spinal histone deacetylase 1 and inflammatory mediators

Anti-epileptic medications are included in the international guidelines for managing neuropathic pain. Valproate sodium (VPS) was recently described as "the forgotten analgesic" and has been reported to relief pain in various models of neuropathic pain. Some studies reported anti-inflammatory and histone deacetylase 1 (HDA1) inhibitory properties for sodium valproate. The aim of the current study was to investigate the modulatory effect of VPS on pain behavior and inflammatory reactions in alloxan-induced diabetic neuropathy focusing on HDA1 inhibition and glia reactivity. 28 Male Swiss albino mice were allocated into four groups, (1) vehicle group, (2) alloxan-diabetic group, (3 & 4) alloxan+VPS (25 or 50 mg/kg) groups. VPS was given daily for 5 weeks by oral gavage. Pain behavior demonstrated increased allodynia (von-Frey filaments) and hyperalgesia (hot-plate test) in alloxan-diabetic mice that was reduced significantly by at least one of VPS doses. Sciatic nerves in diabetic mice showed increased histopathology score, increased silver staining for the nerves-indicating myelopathy- and a decrease in immunostaining for nerve growth factor. Spinal cord of diabetic mice showed greater histopathologic score, increased CD11b and glia fibrillary acidic protein (GFAP) immunostaining than vehicle treated mice. Molecular investigations highlighted greater content of spinal histone deacetylases, tumor necrosis factor-α (TNF-α) and interlukin-1β (IL1β) that were favorably modified by VPS. Overall, the current data confirmed that the pain killing and anti-inflammatory activity of VPS is at least partly mediated through inhibition of spinal HDA1 and glia reactivity. These findings support the view of inviting antiepileptics for treating neuropathies.

Uliginosin B presents antinociceptive effect mediated by dopaminergic and opioid systems in mice

Previous studies have shown that uliginosin B inhibits dopamine reuptake in rat brain. This compound occurs in Hypericum polyanthemum and H. caprifoliatum for which was reported to have antinociceptive effect sensitive to naloxone. The aim of this study was to assess the antinociceptive effect of uliginosin B and to evaluate the involvement of opioid and dopaminergic receptors activation. Uliginosin B presented antinociceptive effect in hot-plate and abdominal writhing tests, in mice, at doses that did not impair the motor coordination (15 mg/kg, i.p.). Uliginosin B in high dose (90 mg/kg, i.p.) presented ataxic effect in the rotarod apparatus. These effects seem to be mediated by distinct receptors since the effect on the hot-plate was completely abolished by naloxone and sulpiride, but it was unaffected by SCH 23390. On the other hand, the motor impairment induced by uliginosin B was completely prevented by naloxone and partially prevented by sulpiride and SCH 23390. However, the receptors' activation appears to be indirect since uliginosin B did not bind to opioid and dopaminergic receptors. Thus, uliginosin B effects probably are due to its ability to inhibit monoamine reuptake with consequent activation of dopamine receptors and indirect stimulation of opioid system.

The effects of diazepam on the behavioral structure of the rat's response to pain in the hot-plate test: anxiolysis vs. pain modulation

The aim of the present study was to evaluate, by means of quantitative and multivariate analyses, the effects of diazepam on the behavioral structure of the rat's response to pain in the hot-plate test as well as whether such changes are associated with drug-induced effects on anxiety and/or nociception. To this purpose, ten groups of male Wistar rats were intraperitoneally injected with saline, diazepam (0.25, 0.5 and 2 mg/kg), FG-7142 (1, 4 and 8 mg/kg) or morphine (3, 6 and 12 mg/kg). The mean number and mean latency to first appearance were calculated for each behavioral component. In addition, multivariate cluster and adjusted residual analyses based on the elaboration of transition matrices were performed. Three main behavioral categories were identified: exploratory (walking, sniffing), primary noxious-evoked (hind paw licking, front paw licking, shaking/stamping) and escape (climbing, jumping). Although no significant modifications in the latencies of the primary noxious-evoked components were induced by treatment with diazepam or FG-7142, significant effects were provoked by morphine treatment. Multivariate analyses showed that diazepam-induced anxiolysis redirected the rat's behavior toward a more purposeful and effective escape strategy. In contrast, the high level of anxiety induced by FG-7142 caused the behavioral structure to become disorganized and not purposefully oriented. Changes in the organization of behavioral components were observed in morphine-treated animals and mainly consisted of modifications in the primary noxious-evoked and escape components. The findings suggest that the effects of diazepam on the structure of the rat's response to pain in the hot-plate test are more likely attributable to anxiolysis than pain modulation.

The age of anxiety: role of animal models of anxiolytic action in drug discovery

Anxiety disorders are common, serious and a growing health problem worldwide. However, the causative factors, aetiology and underlying mechanisms of anxiety disorders, as for most psychiatric disorders, remain relatively poorly understood. Animal models are an important aid in giving insight into the aetiology, neurobiology and, ultimately, the therapy of human anxiety disorders. The approach, however, is challenged with a number of complexities. In particular, the heterogeneous nature of anxiety disorders in humans coupled with the associated multifaceted and descriptive diagnostic criteria, creates challenges in both animal modelling and in clinical research. In this paper, we describe some of the more widely used approaches for assessing the anxiolytic activity of known and potential therapeutic agents. These include ethological, conflict-based, hyponeophagia, vocalization-based, physiological and cognitive-based paradigms. Developments in the characterization of translational models are also summarized, as are the challenges facing researchers in their drug discovery efforts in developing new anxiolytic drugs, not least the ever-shifting clinical conceptualization of anxiety disorders. In conclusion, to date, although animal models of anxiety have relatively good validity, anxiolytic drugs with novel mechanisms have been slow to emerge. It is clear that a better alignment of the interactions between basic and clinical scientists is needed if this is to change.

Angiotensin IV elevates oxytocin levels in the rat amygdala and produces anxiolytic-like activity through subsequent oxytocin receptor activation

INTRODUCTION

The effects of angiotensin (Ang) IV result from binding to a constitutively active metallopeptidase known as the AT(4) receptor (or oxytocinase/insulin-regulated membrane aminopeptidase). While in vitro evidence indicates that Ang IV inhibits the peptidase activity of AT(4) receptors, leading to increases in the concentrations of several peptides, including oxytocin, the consequence of inhibiting AT(4) peptidase activity in vivo remains unresolved.

DISCUSSION

Microdialysis coupled to immunoassay techniques revealed that systemic and intra-amygdala injection of Nle-Ang IV, a metabolically stable derivative of Ang IV, significantly elevated extracellular levels of oxytocin in the rat amygdala. Based on earlier reports describing the anxiolytic-like effects of oxytocin, we investigated whether disrupting AT(4) peptidase activity would yield similar responses. In the mouse four-plate test, acute treatment with either Nle-Ang IV or LVV-hemorphin-7, a related AT(4) receptor ligand, elicited significant increases in the number of punished crossings. These behavioral responses were comparable to the anxiolytic-like effects of oxytocin and to the standard anxiolytic agent, chlordiazepoxide. Cotreatment with either the AT(4) receptor antagonist, divalinal, or the selective oxytocin receptor antagonist, WAY-162720, reversed the anxiolytic-like effects of Nle-Ang IV, while combining ineffective doses of Nle-Ang IV and oxytocin increased the number of punished crossings in this assay. Conversely, Nle-Ang IV and LVV-hemorphin-7 were inactive in the mouse tail suspension test of antidepressant activity. These findings represent the first in vivo demonstration of the peptidase activity of AT(4) receptors, confirm the anxiolytic-like properties of Ang IV, and reveal a unique and previously uncharacterized relationship between AT(4) and oxytocin receptor systems.

Behavioral effects of neuropeptides in rodent models of depression and anxiety

In recent years, studies have advocated neuropeptide systems as modulators for the behavioral states found in mood disorders such as depression and anxiety disorders. Neuropeptides have been tested in traditional animal models and screening procedures that have been validated by known antidepressants and anxiolytics. However, it has become clear that although these tests are very useful, neuropeptides have distinct behavioral effects and dose-dependent characteristics, and therefore, use of these tests with neuropeptides must be done with an understanding of their unique characteristics. This review will focus on the behavioral actions of neuropeptides and their synthetic analogs, particularly in studies utilizing various preclinical tests of depression and anxiety. Specifically, the following neuropeptide systems will be reviewed: corticotropin-releasing factor (CRF), urocortin (Ucn), teneurin C-terminal associated peptide (TCAP), neuropeptide Y (NPY), arginine vasopressin (AVP), oxytocin, the Tyr-MIF-1 family, cholecystokinin (CCK), galanin, and substance P. These neuropeptide systems each have a unique role in the regulation of stress-like behavior, and therefore provide intriguing therapeutic targets for mood disorder treatment.

Nicotine self-administration diminishes stress-induced norepinephrine secretion but augments adrenergic-responsiveness in the hypothalamic paraventricular nucleus and enhances adrenocorticotropic hormone and corticosterone release

Chronic nicotine self-administration augments the thalamo-pituitary-adrenal (HPA) responses to stress. Altered neuropeptide expression within corticotropin-releasing factor (CRF) neurons in the hypothalamic paraventricular nucleus (PVN) contributes to this enhanced HPA response to stress. Herein, we determined the role of norepinephrine, a primary regulator of CRF neurons, in the responses to footshock during nicotine self-administration. On day 12-15 of self-administration, microdialysis showed nicotine reduced PVN norepinephrine release by footshock (< 50% of saline). Yet, the reduction in footshock-induced adrenocorticotropic hormone and corticosterone secretion because of intra-PVN prazosin (alpha(1) adrenergic antagonist) was significantly greater in rats self-administering nicotine (2-fold) than saline. Additionally, PVN phenylephrine (alpha(1) agonist) stimulated adrenocorticotropic hormone and corticosterone release to a similar extent in unstressed rats self-administering nicotine or saline. Nicotine self-administration also decreased footshock-induced c-Fos expression in the nucleus of the solitary tract-A2/C2 catecholaminergic neurons that project to the PVN. Therefore, footshock-induced nucleus of the solitary tract activation and PVN norepinephrine input are both attenuated by nicotine self-administration, yet PVN CRF neurons are more responsive to alpha(1) stimulation, but only during stress. This plasticity in noradrenergic regulation of PVN CRF neurons provides a new mechanism contributing to the HPA sensitization to stress by nicotine self-administration and smoking.

The supra-additive hyperactivity caused by an amphetamine-chlordiazepoxide mixture exhibits an inverted-U dose response: negative implications for the use of a model in screening for mood stabilizers

One of the few preclinical models used to identify mood stabilizers is an assay in which amphetamine-induced hyperactivity (AMPH) is potentiated by the benzodiazepine chlordiazepoxide (CDP), an effect purportedly blocked by mood stabilizers. Our data here challenge this standard interpretation of the AMPH-CDP model. We show that the potentiating effects of AMPH-CDP are not explained by a pharmacokinetic interaction as both drugs have similar brain and plasma exposures whether administered alone or in combination. Of concern, however, we find that combining CDP (1-12 mg/kg) with AMPH (3 mg/kg) results in an inverted-U dose response in outbred CD-1 as well as inbred C57Bl/6N and 129S6 mice (peak hyperactivity at 3 mg/kg CDP+3 mg/kg AMPH). Such an inverted-U dose response complicates interpreting whether a reduction in hyperactivity produced by a mood stabilizer reflects a "blockade" or a "potentiation" of the mixture. In fact, we show that the prototypical mood stabilizer valproic acid augments the effects of CDP on hypolocomotion and anxiolytic-like behavior (increases punished crossings by Swiss-Webster mice in the four-plate test). We argue that these data, in addition to other practical and theoretical concerns surrounding the model, limit the utility of the AMPH-CDP mixture model in drug discovery.

Acid sensing ion channel (ASIC) inhibitors exhibit anxiolytic-like activity in preclinical pharmacological models

RATIONALE

Acid sensing ion channels (ASICs) are proton-gated ion channels located in the central and peripheral nervous systems. Of particular interest is ASIC1a, which is located in areas associated with fear and anxiety behaviors. Recent reports suggest a role for ASIC1a in preclinical models of fear conditioning and anxiety.

OBJECTIVES

The present experiments evaluated various ASIC inhibitors in preclinical models of autonomic and behavioral parameters of anxiety. In addition, neurochemical studies evaluated the effects of an ASIC inhibitor (A-317567) on neurotransmitter levels in the amygdala.

RESULTS

In electrophysiological studies using hippocampal primary neuronal cultures, three ASIC inhibitors (PcTX-1, A-317567, and amiloride) produced concentration-dependent inhibition of acid-evoked currents. In the stress-induced hyperthermia model, acute administration of psalmotoxin 1 (PcTX-1; 10-56 ng, i.c.v.), A-317567 (0.1-1.0 mg/kg, i.p.), and amiloride (10-100 mg/kg, i.p.) prevented stress-induced elevations in core body temperature. In the four-plate test, acute treatment with PcTX-1 (10-56 ng, i.c.v.) and A-317567 (0.01-0.1 mg/kg, i.p.), but not amiloride (3-100 mg/kg, i.p.), produced dose-dependent and significant increases in the number of punished crossings relative to vehicle-treated animals. Additionally, PcTX-1 (56-178 ng, i.c.v.), A-317567 (0.1-10 mg/kg, i.p.), and amiloride (10-100 mg/kg, i.p.) lacked significant anxiolytic-like activity in the elevated zero maze. In neurochemical studies, an infusion of A-317567 (100 microM) into the amygdala significantly elevated the extracellular levels of GABA, but not glutamate, in this brain region.

CONCLUSIONS

These findings demonstrate that ASIC inhibition produces anxiolytic-like effects in some behavioral models and indicate a potential role for GABAergic mechanisms to underlie these anxiolytic-like effects.

SK3 K+ channel-deficient mice have enhanced dopamine and serotonin release and altered emotional behaviors

SK3 K(+) channels influence neuronal excitability and are present in 5-hydroxytryptamine (5-HT) and dopamine (DA) nuclei in the brain stem. We therefore hypothesized that SK3 channels affect 5-HT and DA neurotransmission and associated behaviors. To explore this, we used doxycycline-induced conditional SK3-deficient (T/T) mice. In microdialysis, T/T mice had elevated baseline levels of striatal extracellular DA and the metabolites dihydroxyphenylacetic acid and homovanillic acid. While baseline hippocampal extracellular 5-HT was unchanged in T/T mice, the 5-HT response to the 5-HT transporter inhibitor citalopram was enhanced. Furthermore, baseline levels of the 5-HT metabolite 5-hydroxyindoleacetic acid were elevated in T/T mice. T/T mice performed equally to wild type (WT) in most sensory and motor tests, indicating that SK3 deficiency does not lead to gross impairments. In the forced swim and tail suspension tests, the T/T mice displayed reduced immobility compared with WT, indicative of an antidepressant-like phenotype. Female T/T mice were more anxious in the zero maze. In contrast, anxiety-like behaviors in the open-field and four-plate tests were unchanged in T/T mice of both sexes. Home cage diurnal activity was also unchanged in T/T mice. However, SK3 deficiency had a complex effect on activity responses to novelty: T/T mice showed decreased, increased or unchanged activity responses to novelty, depending on sex and context. In summary, we report that SK3 deficiency leads to enhanced DA and 5-HT neurotransmission accompanied by distinct alterations in emotional behaviors.

Factors triggering abolishment of benzodiazepines effects in the Four-Plate Test--retest in mice

Abolishment of anxiolytic-like effects of diazepam occurs during re-exposure to some animal tests of anxiety. We investigated the loss of anxiolytic-like effects of diazepam during Trial 2 on previously undrugged mice, namely one-trial tolerance (OTT). Swiss mice were subjected to 1) Four-Plate Test (FPT) without punishments in Trial 1 or 2) FPT without punishments in both Trials or 3) FPT with spatial modifications in Trial 1 or 4) Elevated Plus Maze (EPM), then 24 h later to FPT, with saline, diazepam (1 mg/kg) or DOI (1 mg/kg). Removing punishments in Trial 1 does not counteract the effect reduction of diazepam in Trial 2, but spatial modifications of the aversive environment. Previous exposure to EPM does not trigger a loss of efficacy of diazepam in FPT. Electric punishments do not trigger OTT to benzodiazepines; whilst knowledge of the environment seems to be responsible for this phenomenon. FPT may be useful to study OTT because punishments potentate OTT in this model of anxiety.

Endogenous opiates and behavior: 2006

This paper is the 29th consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning 30 years of research. It summarizes papers published during 2006 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurological disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).

Serotonin transporter density and anxiolytic-like effects of antidepressants in mice

BACKGROUND

Chronic treatment with the dual serotonin/noradrenaline reuptake inhibitor (SNRI) duloxetine reduces the density of serotonin transporter sites in cortex and engenders an anxiolytic-like response. To determine the reproducibility of these effects and their generality to other antidepressants we compared the effects of chronic duloxetine treatment with another SNRI, venlafaxine, and two selective serotonin reuptake inhibitors, paroxetine and fluoxetine.

METHODS

Separate groups of mice were administered vehicle, fluoxetine (15 mg/kg), paroxetine, duloxetine or venlafaxine (10 mg/kg) perorally twice daily for 28 days and tested in the mouse zero-maze and in motility cages on days 21 and 22, respectively, to determine effects on anxiety and motor activity. On day 28 brains were analysed for serotonin transporter (SERT) density in cortex and noradrenaline transporter (NET) density in cortex and hippocampus.

RESULTS

Duloxetine and fluoxetine both reduced SERT density in cortex and induced anxiolytic-like effects. Paroxetine had an identical profile, but it is unclear if this drug down-regulated the SERT since extensive washing of cortical tissue did not remove all drug. Venlafaxine had no effect on behavioural or biochemical parameters. Only duloxetine reduced NET density in cortex, although not hippocampus.

CONCLUSIONS

The reduction in SERT density and anxiolytic-like effects with duloxetine, fluoxetine and, potentially, paroxetine suggest that down-regulation of the SERT may be a relevant mechanism in therapeutic response to these antidepressants.

Effect of GABAergic ligands on the anxiolytic-like activity of DOI (a 5-HT(2A/2C) agonist) in the four-plate test in mice

5-HTergic and GABAergic systems are involved in neurobiology of anxiety. Precedent studies have demonstrated that SSRIs possessed an anxiolytic-like effect in the four-plate test (FPT) at doses that did not modify spontaneous locomotor activity. This effect seems to be mediated through the activation of 5-HT(2A) postsynaptic receptors. The purpose of the present study was to examine the implication of GABA system in the anxiolytic-like activity of DOI in the FPT. To achieve this, the co-administration of DOI (5-HT(2A/2C) receptor agonists) with GABA(A) and GABA(B) receptor ligands was evaluated in the FPT. Alprazolam, diazepam and muscimol (for higher dose) potentiated the anxiolytic-like effect of DOI. Bicuculline, picrotoxin and baclofen inhibited the anxiolytic-like effect of DOI. Flumazenil and CGP 35348 had no effect on the anxiolytic-like activity of DOI. These results suggest that the GABA system seems to be strongly implicated in the anxiolytic-like activity of DOI in the FPT.