Yohimbine is a 5-HT1A agonist in rats in doses exceeding 1 mg/kg

Antagonism of the antinociceptive effects of fentanyl and the veterinary anesthetic xylazine in mice

A recent twist to the ongoing tragedy of the opioid epidemic is the adulteration of fentanyl with the veterinary tranquilizer xylazine, an α2-adrenoreceptor agonist. Unfortunately, our knowledge of how fentanyl and xylazine interact pharmacologically in different behavioral assays is limited. We examined fentanyl and xylazine alone, with 4 antagonists, and in multiple dose ratio combinations using a 52.5 °C hot-plate antinociception assay in Swiss-Webster male and female mice. Both fentanyl and xylazine produced full, dose-dependent increases in antinociception. In antagonism studies, naltrexone blocked fentanyl whereas yohimbine and the selective α2-adrenoreceptor antagonist, idazoxan, blocked the antinociceptive effects of xylazine. Naltrexone failed to inhibit xylazine antinociception and yohimbine increased or decreased the potency of fentanyl depending on the dose. Haloperidol, a D2/σ1 antagonist, significantly shifted the potency of fentanyl and xylazine to the left. Overall, combining xylazine with fentanyl failed to significantly alter the potency of fentanyl although when xylazine proportion was higher, fentanyl was significantly less potent than fentanyl alone. Either naltrexone or yohimbine alone failed to block the 2.5X xylazine to fentanyl combination. However, naltrexone with either yohimbine or idazoxan blocked the antinociceptive effects of the 2.5X xylazine to fentanyl combination suggesting that both opioid and noradrenergic receptors appear involved in the antinociceptive effects of this combination. In conclusion, the antinociceptive effects of fentanyl combined with xylazine are dependent on the proportions coadministered and multiple antagonists may be required to block the effects of fentanyl adulterated with xylazine. SIGNIFICANCE STATEMENT: Combinations of the opioid agonist fentanyl and the veterinary tranquilizer xylazine currently appear on the illicit drug market. The experiments described here examine the pharmacology of these drugs alone and in combination using a model of antinociception in mice to better understand the underlying receptor mechanisms for fentanyl alone, xylazine alone, and fentanyl and xylazine in combination. The antinociceptive effects were predominantly a simple combination of opioid and α2-adrenoreceptor agonism.

The anxiogenic drug yohimbine is a reinforcer in male and female rats

The indole alkaloid yohimbine is an anxiogenic drug that activates stress-responsive systems in the brain. However, because yohimbine also elicits approach behaviors, this study employed male and female Sprague-Dawley rats to explore its potential reinforcing effects. Thus, it was first determined if intravenous (IV) infusions of yohimbine (0.25 mg/kg/infusion) could maintain lever pressing, whether intake could be modulated by dose/infusion, and if lever pressing would persist in the absence of yohimbine or yohimbine-paired cues. Next, to assess yohimbine's effect on memory consolidation, 0.3, 1.25 or 3 mg/kg yohimbine was administered post-training using an object recognition memory task. Finally, place conditioning assessed whether doses of yohimbine that elevate blood serum corticosterone levels (1.25 or 3 mg/kg) could elicit a conditioned place preference. It was found that both sexes acquired yohimbine IV self-administration, that intake was modulated by dose/infusion, and that lever pressing persisted during extinction and in the absence of the yohimbine-paired cue. As well, post-training injections of 1.25 mg/kg yohimbine enhanced consolidation of object memory, and 1.25 and 3 mg/kg elevated corticosterone levels and elicited a place preference in both sexes. Finally, in behavioral tests of psychomotor functions, acute yohimbine increased lever pressing for a visual cue and elevated locomotor activity. These findings reveal a profile of yohimbine's behavioral effects that is consistent with that of psychostimulant reinforcing drugs.

Multifaced Nature of Yohimbine-A Promising Therapeutic Potential or a Risk?

A natural compound derived from the Pausinystalia yohimbe tree-yohimbine, has a rich history of use in traditional medicine and is currently being explored for its potential therapeutic applications. This indole alkaloid primarily acts as an antagonist of α2-adrenergic receptors. Initially recognized for its purported aphrodisiac properties, yohimbine has been investigated for a wide range of applications, including sports or the treatment of erectile dysfunction and metabolic disorders. However, toxicological concerns exist, particularly at higher doses. Ongoing researches help to fully assess yohimbine's efficacy and safety profile and to explore strategies for enhancing its bioavailability and reducing toxicity. This review examines the multifaceted nature of yohimbine, delving into both its promising therapeutic potential and the associated risks.

Exploring the therapeutic effect of core components in Xuanshen Yishen mixture on hypertension through network pharmacology

OBJECTIVE

This study aims to elucidate the mechanism of action and impact of the "Xuanshen Yishen Mixture" (XYM) on hypertension.

METHODS

Active components were identified and potential targets were predicted using the Traditional Chinese Medicine Systems Pharmacology database. Hypertension-related targets were collected from GeneCards, DRUGBANK, OMIM, TTD, and PharmaGKB databases. Intersections of disease and drug targets were visualized using the R package "VennDiagram". A protein-protein interaction network was established via the STRING database. GO function enrichment and KEGG pathway analyses were conducted using "clusterProfiler", while "Cytoscape" was used to construct a "drug-component-target" network. Additionally, data from 60 patients with essential hypertension from the Affiliated Hospital of Shandong University of Traditional Chinese Medicine were retrospectively analyzed. Patients were divided into a control group (n = 30) and an XYM group (n = 30) based on treatment regimen.

RESULTS

Sixty active ingredients and 98 related targets were identified from Uncaria, Radix Scrophulariae, and Epimedium in hypertension treatment. Key active components such as quercetin, kaempferol, yohimbine, and beta-sitosterol were pinpointed, with PTGS2, PTGS1, AR, DPP4, and F2 as crucial targets. KEGG pathway analysis highlighted significant pathways including IL-17 signaling, TNF signaling, Relaxin signaling, and HIF-1 signaling. Clinical data indicated that XYM's therapeutic effects are comparable to those of valsartan, which significantly reduced diastolic and systolic blood pressure and demonstrated good biosafety.

CONCLUSIONS

Uncaria, Radix Scrophulariae, and Epimedium effectively mitigate hypertension through multiple components, targets, and pathways. Additionally, DPP4, IL-17, and TNF-α are identified as potential therapeutic targets for traditional Chinese medicine preparations in hypertension treatment. This study provides a foundation for further investigation into XYM's mechanisms in hypertension management.

Yeast Platforms for Production and Screening of Bioactive Derivatives of Rauwolscine

Monoterpene indole alkaloids (MIAs) make up a highly bioactive class of metabolites produced by a range of tropical and subtropical plants. The corynanthe-type MIAs are a stereochemically complex subclass with therapeutic potential against a large number of indications including cancer, psychotic disorders, and erectile dysfunction. Here, we report yeast-based cell factories capable of de novo production of corynanthe-type MIAs rauwolscine, yohimbine, tetrahydroalstonine, and corynanthine. From this, we demonstrate regioselective biosynthesis of 4 fluorinated derivatives of these compounds and de novo biosynthesis of 7-chlororauwolscine by coexpression of a halogenase with the biosynthetic pathway. Finally, we capitalize on the ability of these cell factories to produce derivatives of these bioactive scaffolds to establish a proof-of-principle drug discovery pipeline in which the corynanthe-type MIAs are screened for bioactivity on human drug targets, expressed in yeast. In doing so, we identify antagonistic and agonistic behavior against the human adrenergic G protein-coupled receptors ADRA2A and ADRA2B, and the serotonergic receptor 5HT4b, respectively. This study thus demonstrates a proto-drug discovery pipeline for bioactive plant-inspired small molecules based on one-pot biocatalysis of natural and new-to-nature corynanthe-type MIAs in yeast.

Effects of atipamezole on selected physiologic parameters in cynomolgus macaques (Macaca fascicularis)

BACKGROUND

Atipamezole, an α-2 adrenergic receptor antagonist, reverses the α-2 agonist anesthetic effects. There is a dearth of information on the physiological effects of these drugs in cynomolgus macaques (Macaca fascicularis). We assessed atipamezole's physiologic effects. We hypothesized atipamezole administration would alter anesthetic parameters.

METHODS

Five cynomolgus macaques were sedated with ketamine/dexmedetomidine intramuscularly, followed 45 min later with atipamezole (0.5 mg/kg). Anesthetic parameters (heart rate, blood pressure [systolic (SAP), diastolic (DAP), and mean (MAP) blood pressure], body temperature, respiratory rate, and %SpO2) were monitored prior to and every 10 min (through 60 min) post atipamezole injection.

RESULTS

While heart rate was significantly increased for 60 min; SAP, DAP, MAP, and temperature were significantly decreased at 10 min.

CONCLUSIONS

This study indicates subcutaneous atipamezole results in increased heart rate and transient blood pressure decrease. These findings are clinically important to ensure anesthetist awareness to properly support and treat patients as needed.

Activation of transient receptor potential channels is involved in reactive oxygen species (ROS)-dependent regulation of blood flow by (-)-epicatechin tetramer cinnamtannin A2

Intervention trials confirmed that blood flow-mediated dilatation increases significantly after intake of astringent (-)-epicatechin (EC) oligomers (procyanidins)-rich foods, but the mechanism remains unclear. We have previously found that procyanidins can activate the sympathetic nervous and subsequently increase blood flow. Here, we examined whether procyanidin-derived reactive oxygen species (ROS) activate transient receptor potential (TRP) channels in gastrointestinal sensory nerves and consequently induce sympathoexcitation. We evaluated the redox properties of EC and its tetramer cinntamtannin A2 (A2) at pH 5 or 7, mimicking plant vacuole or oral cavity/small intestine using a luminescent probe. At pH 5, A2 or EC showed O₂^･- scavenging ability, but they promoted O₂^･- generation at pH 7. We observed blood flow in rat cremaster arterioles using laser Doppler, a single oral dose of 10 µg/kg A2 markedly increased blood flow, while EC showed little activity. This change with A2 was significantly dampened by co-administration of adrenaline blocker, ROS scavenger N-acetyl-L-cysteine (NAC), TRP vanilloid 1, or ankyrin 1 antagonist. We also performed a docking simulation of EC or A2 with the binding site of a typical ligand for each TRP channel and calculated the respective binding affinities. The binding energies were notably higher for A2 than typical ligands, suggesting that A2 is less likely to bind to these sites. ROS produced at neutral pH following the orally administered A2 to the gastrointestinal tract could activate TRP channels, triggering sympathetic hyperactivation and causing hemodynamic changes.

Acute glucagon-like peptide-1 receptor agonist liraglutide prevents cue-, stress-, and drug-induced heroin-seeking in rats

Substance use disorder is challenging to treat due to its relapsing nature. In the last decade, opioid use disorder has been a threat to public health, being declared an epidemic by the Centers for Disease Control and Prevention. This is a tragic situation, considering there currently are only three effective, yet not ideal, treatments to prevent relapse to opioids. Recent research has shown that hormones that modulate hunger and satiety also can modulate motivated behavior for drugs of abuse. For example, the short-acting analog of glucagon-like peptide-1 (GLP-1), an incretin hormone that regulates homeostatic feeding, has been shown to reduce responding for rewarding stimuli such as food, cocaine, heroin, and nicotine when administered over several days or weeks. This may serve as an effective adjuvant during treatment; however, whether it would be effective when used acutely to bridge a patient between cessation of use and onset of medication for the treatment of an opioid addiction is unknown. Here, we tested the acute effects of the longer acting GLP-1 analog, liraglutide, on heroin-seeking. In rats with heroin self-administration experience, we found that subcutaneous administration of an acute dose of 0.3-mg/kg liraglutide was effective in preventing drug-seeking after exposure to three major precipitators: drug-associated cues, stress (yohimbine-induced), and the drug itself. Finally, we confirmed that the reduction in drug-seeking is not due to a locomotor impairment, as liraglutide did not significantly alter performance in a rotarod test. As such, acute use of GLP-1 analogs may serve as a new and effective nonopioid bridge to treatment.

Dexmedetomidine attenuates lipopolysaccharide-induced inflammation through macrophageal IL-10 expression following α7 nAchR activation

Dexmedetomidine, a highly selective α₂-adrenoceptor agonist, has been recently reported to alleviate systemic inflammatory response induced by lipopolysaccharide (LPS), in addition to its sedative, analgesic, bradycardic and hypotensive properties. This study aimed to illustrate the molecular mechanisms underlying dexmedetomidine-induced anti-inflammation. In the LPS-pretreated mice, subcutaneous injection of dexmedetomidine reduced the spleen weight as well as serum and spleen expression of proinflammatory cytokines, tumor necrosis factor-α (TNF-α), interleukin (IL)-6 and IL-1β, and increased serum and spleen expression of IL-10, a known anti-inflammatory cytokine. In addition, dexmedetomidine-attenuated proinflammatory cytokine reduction was entirely inhibited by selective α7 nicotinic acetylcholine receptor (nAChR) antagonist methyllycaconitine but not α₂-adrenoceptor antagonist yohimbine. Dexmedetomidine also increased macrophageal IL-10 expression in the presence and absence of LPS, which was also attenuated by methyllycaconitine but not yohimbine. Furthermore, the stimulatory effect of dexmedetomidine on the expression of IL-10 was also reduced by the α7 nAChR gene silencer siRNA/α7 nAChR. Lastly, pretreatment with the IL-10 neutralizing antibody reversed dexmedetomidine-supressed expression of proinflammatory cytokines. Our findings illustrate that dexmedetomidine-induced anti-inflammation is through macrophageal expression of IL-10 following activation of α7 nAchRs but not α₂-adrenoceptors.

Blockade of alpha2-adrenergic receptors in the caudal raphe region enhances the renal sympathetic nerve activity response to acute intermittent hypercapnia in rats

The study investigated the role of alpha2-adrenergic receptors of the caudal raphe region in the sympathetic and cardiovascular responses to the acute intermittent hypercapnia (AIHc). Urethane-anesthetized, vagotomized, mechanically ventilated Sprague-Dawley rats (n=38) were exposed to the AIHc protocol (5×3 min, 15 % CO2+50 % O2) in hyperoxic background (50 % O2). alpha2-adrenergic receptor antagonist-yohimbine was applied intravenously (1 mg/kg, n=9) or microinjected into the caudal raphe region (2 mM, n=12) prior to exposure to AIHc. Control groups of animals received saline intravenously (n=7) or into the caudal raphe region (n=10) prior to exposure to AIHc. Renal sympathetic nerve activity (RSNA), mean arterial pressure (MAP) and heart rate (HR) were monitored before exposure to the AIHc protocol (T0), during five hypercapnic episodes (THc1-5) and at 15 min following the end of the last hypercapnic episode (T15). Following intravenous administration of yohimbine, RSNA was significantly greater during THc1-5 and at T15 than in the control group (P<0.05). When yohimbine was microinjected into the caudal raphe region, AIHc elicited greater increases in RSNA during THc1-5 when compared to the controls (THc1: 138.0+/-4.0 % vs. 123.7+/-4.8 %, P=0.032; THc2: 137.1+/-5.0 % vs. 124.1+/-4.5 %, P=0.071; THc3: 143.1+/-6.4 % vs. 122.0±4.8 %, P=0.020; THc4: 146.1+/-6.2 % vs. 120.7+/-5.7 %, P=0.007 and THc5: 143.2+/-7.7 % vs. 119.2+/-7.2 %, P=0.038). During THc1-5, significant decreases in HR from T0 were observed in all groups, while changes in MAP were observed in the group that received yohimbine intravenously. These findings suggest that blockade of the alpha2-adrenegic receptors in the caudal raphe region might have an important role in sympathetic responses to AIHc.

Modulation of Spatial Memory Deficit and Hyperactivity in Dopamine Transporter Knockout Rats via α2A-Adrenoceptors

Attention deficit hyperactivity disorder (ADHD) is manifested by a specific set of behavioral deficits such as hyperactivity, impulsivity, and inattention. The dopamine neurotransmitter system is postulated to be involved in the pathogenesis of ADHD. Guanfacine, a selective α2A-adrenoceptor agonist, is prescribed for ADHD treatment. ADHD also is known to be associated with impairment of multiple aspects of cognition, including spatial memory, however, it remains unclear how modulation of the norepinephrine system can affect these deficits. Hyperdopaminergic dopamine transporter knockout (DAT-KO) rats are a valuable model for investigating ADHD. The DAT-KO rats are hyperactive and deficient in spatial working memory. This work aimed to evaluate the effects of noradrenergic drugs on the fulfillment of spatial cognitive tasks by DAT-KO rats. The rats were tested in the Hebb - Williams maze during training and following noradrenergic drugs administration. The efficiency of spatial orientation was assessed as to how fast the animal finds an optimal way to the goal box. Testing in a new maze configuration allowed us to evaluate the effects of drug administration after the acquisition of the task rules. The behavioral variables such as the distance traveled, the time to reach the goal box, and the time spent in the error zones were analyzed. It has been observed that α2A-adrenoceptor agonist Guanfacine (0.25 mg/kg) had only a minimal inhibitory effect on hyperactivity of DAT-KO rats in the maze but significantly ameliorated their perseverative pattern of activity and reduced the time spent in the error zones. In contrast, α2A-adrenoceptor antagonist Yohimbine, at the dose of 1 mg/kg, increased the distance traveled by DAT-KO rats and elevated the number of perseverative reactions and the time spent in the error zones. Guanfacine caused minimal effects in wild-type rats, while Yohimbine altered several parameters reflecting a detrimental effect on the performance in the maze. These data indicate that modulation of α2A-adrenoceptor activity potently affects both dopamine-dependent hyperactivity and cognitive dysfunctions. Similar mechanisms may be involved in the beneficial effects of Guanfacine on cognitive deficits in ADHD patients. This study further supports the translational potential of DAT-KO rats for testing new pharmacological drugs.

Physiological and transcriptomic changes of zebrafish (Danio rerio) embryos-larvae in response to 2-MIB exposure

2-Methylisoborneol (2-MIB), a natural odorous substance, is widely distributed in water environment, but there is a paucity of information concerning its systemic toxicity. Herein, we investigated the effects of 2-MIB exposure on developmental parameters, locomotive behavior, oxidative stress, apoptosis and transcriptome of zebrafish. Zebrafish embryos exposed to different concentrations (0, 0.5, 5 and 42.8 μg/L) of 2-MIB showed no changes in mortality, hatchability, and malformation rate, but the body length of zebrafish larvae was significantly increased in a dose-dependent manner, and accompanied by the changes of growth hormone/insulin-like growth factor (GH/IGF) axis and the hypothalamic-pituitary-thyroid (HPT) axis genes. Moreover, the swimming activity of zebrafish larvae increased, which may be due to the increase of acetylcholinesterase (AChE) activity. Meanwhile, 2-MIB caused oxidative stress and apoptosis in zebrafish larvae by altering the NF-E2-related factor 2 (Nrf2) and mitochondrial signaling pathways, respectively. Transcriptome sequencing assay showed that the phototransduction signaling pathway was significantly enriched, and most of the genes in this pathway exhibited enhanced expression after exposure to 2-MIB. These findings provide an important reference for risk assessment and early warning to 2-MIB exposure.

The effects of clonidine and yohimbine in the tail flick and hot plate tests in the naked mole rat (Heterocephalus glaber)

Objective

The naked mole rat (NMR) (Heterocephalus glaber) is increasingly considered an important biomedical research model for various conditions like hypoxic brain injury, cancer and nociception. This study was designed to investigate the effects of clonidine and yohimbine, an alpha-2 (α₂) adrenoceptor agonist and antagonist respectively in the tail flick and hot plate tests.

Results

A significant difference in tail flick latency was noted between saline control and 30 µg/kg clonidine, which was reduced after administration of 30 µg/kg yohimbine. A significant difference in hot plate latency was also noted between saline control and 30 µg/kg clodinine during the periods 30, 45, 60, 75 and 90 min after administration, and between saline control and 10 µg/kg clonidine during 30 min after administration. The hot plate latency by 30 µg/kg clonidine was also reduced by 30 µg/kg yohimbine during 30 min after administration. Since the tail-flick and hot plate tests mediate the effects at spinal and supraspinal levels respectively, the present study indicates the presence and involvement of noradrenergic receptors in thermal antinociception at spinal and supraspinal levels of the NMR, similar to what has been found in other mammals.

Investigation of noradrenergic receptor system in anti-nociception using formalin test in the naked mole rat (Heterocephalus glaber)

The naked mole rat (NMR) is a rodent that has gained importance as a biomedical research model for various conditions like hypoxic brain injury, cancer and nociception. This study was designed to investigate possible involvement of the noadrenergic receptor system in antinoception in the NMR, using the alpha-2 adrenergic receptor specific ligands clonidine (agonist) and yohimbine (antagonist) in the formalin test. Formalin test followed 30 min after intraperitoneal administration of ligands or control. A total of 96 naked mole rats were used. A significant reduction in nociceptive behaviours was demonstrated after administration of clonidine in the doses 1,3,10 and 30 μg/kg (n = 8 per group). Doses of clonidine above 30 μg/kg caused loss of motor and proprietion skills exhibited by prostration and failure to turn over when placed on their backs. The antinociception by 3 μg/kg clonidine was reversed by administration of 30 μg/kg of yohimbine. The present study demonstrates that the noradrenergic receptor system is present and involved in formalin test-related antinociceptive mechanisms in the NMR, similar to other mammals. Given the increasing importance of the NMR as a model for pain and nociception, the species may prove useful as an animal model for noradrenergic mechanisms in pain modulation.

Norepinephrine released by intestinal Paneth cells exacerbates ischemic AKI

Small intestinal Paneth cells play a critical role in acute kidney injury (AKI) and remote organ dysfunction by synthesizing and releasing IL-17A. In addition, intestine-derived norepinephrine is a major mediator of hepatic injury and systemic inflammation in sepsis. We tested the hypothesis that small intestinal Paneth cells synthesize and release norepinephrine to exacerbate ischemic AKI. After ischemic AKI, we demonstrated larger increases in portal venous norepinephrine levels compared with plasma norepinephrine in mice, consistent with an intestinal source of norepinephrine release after renal ischemia and reperfusion. We demonstrated that murine small intestinal Paneth cells express tyrosine hydroxylase mRNA and protein, a critical rate-limiting enzyme for the synthesis of norepinephrine. We also demonstrated mRNA expression for tyrosine hydroxylase in human small intestinal Paneth cells. Moreover, freshly isolated small intestinal crypts expressed significantly higher norepinephrine levels after ischemic AKI compared with sham-operated mice. Suggesting a critical role of IL-17A in Paneth cell-mediated release of norepinephrine, recombinant IL-17A induced norepinephrine release in the small intestine of mice. Furthermore, mice deficient in Paneth cells (SOX9 villin Cre mice) have reduced plasma norepinephrine levels after ischemic AKI. Finally, supporting a critical role for norepinephrine in generating ischemic AKI, treatment with the selective α-adrenergic antagonists yohimbine and phentolamine protected against murine ischemic AKI with significantly reduced renal tubular necrosis, inflammation, and apoptosis and less hepatic dysfunction. Taken together, we identify Paneth cells as a critical source of norepinephrine release that may lead to intestinal and liver injury and systemic inflammation after AKI.

Select panicogenic drugs and stimuli induce consistent increases in tail skin flushes and decreases in core body temperature

Panic attacks (PAs) are episodes of intense fear or discomfort that are accompanied by a variety of both psychological and somatic symptoms. Panic induction in preclinical models (e.g. rats) has largely been assayed through flight and avoidance behavioral tests and cardiorespiratory activity. Yet, the literature pertaining to PAs shows that thermal sensations (hot flushes/heat sensations and chills) are also a common symptom during PAs in humans. Considering that temperature alterations are objectively measurable in rodents, we hypothesized that select panicogenic drugs and stimuli induce consistent changes in thermoregulation related to hot flushes and chills. Specifically, we challenged male rats with intraperitoneal injections of the GABAergic inverse agonist FG-7142; the α2 adrenoceptor antagonist yohimbine; the serotonin agonist D-fenfluramine, and 20% CO2 (an interoceptive homeostatic challenge). We assayed core body temperature and tail skin temperature using implanted radiotelemetry probes and tail thermistors/thermal imaging camera, respectively, and found that all challenges elicited rapid, high-amplitude (~7-9°C) increase in tail skin temperature and delayed decreases (~1-3°C) in core body temperature. We propose that thermal sensations such as these may be an additional indicator of a panic response in rodents and humans, as these panicogenic compounds or stimuli are known to precipitate PAs in persons with panic disorder.

Faster emergence behavior from ketamine/xylazine anesthesia with atipamezole versus yohimbine

Recent interest in reversal of the hypnotic effects of anesthesia has mainly focused on overcoming a surge in GABA-mediated inhibitory signaling through activation of subcortical arousal circuits or antagonizing GABA receptors. Here we examine the reversal of anesthesia produced from non-GABA agents ketamine/xylazine and the effects of antagonists of adrenoreceptors. These antagonists vary in selectivity and produce temporally unique waking behavior post-anesthesia. We compared two antagonists with differential selectivity for α₁- vs. α₂-receptors, yohimbine (YOH, 1:40 selectivity) and atipamezole (ATI, 1:8500). Adult mice received intraperitoneal injections of either YOH (4.3 mg/kg), ATI (0.4 mg/kg), or saline after achieving sustained loss of righting following injection of ketamine/xylazine (ketamine: 65.0 mg/kg; xylazine: 9.9 mg/kg). Behaviors indicative of the post-anesthesia, re-animation sequence were carefully monitored and the timing of each behavior relative to anesthesia induction was compared. Both YOH and ATI hastened behaviors indicative of emergence, but ATI was faster than YOH to produce certain behaviors, including whisker movement (YOH: 21.9±1.5 min, ATI: 17.5±0.5 min, p = 0.004) and return of righting reflex (RORR) (YOH: 40.6±8.8 min, ATI: 26.0±1.2 min, p<0.001). Interestingly, although YOH administration hastened early behavioral markers of emergence relative to saline (whisking), the completion of the emergence sequence (time from first marker to appearance of RORR) was delayed with YOH. We attribute this effect to antagonism of α₁ receptors by yohimbine. Also notable was the failure of either antagonist to hasten the re-establishment of coordinated motor behavior (e.g., attempts to remove adhesive tape on the forepaw placed during anesthesia) relative to the end of emergence (RORR). In total, our work suggests that in addition to pharmacokinetic effects, re-establishment of normal waking behaviors after anesthesia involves neuronal circuits dependent on time and/or activity.

Impact of obesity on the toxicity of a multi-ingredient dietary supplement, OxyELITE Pro™ (New Formula), using the novel NZO/HILtJ obese mouse model: Physiological and mechanistic assessments

Herbal dietary supplement (HDS)-induced hepato- and cardiotoxicity is an emerging clinical problem. In this study, we investigated the liver and heart toxicity of HDS OxyELITE-PRO™ New Formula (OEP-NF), a dietary supplement marketed for weight loss and performance enhancement that was recently withdrawn from the market. Using a novel NZO/HlLtJ obese mouse model, we demonstrated that administration of clinically relevant mouse equivalent doses (MED) of OEP-NF produced cardio- and hepatotoxic risks following both short- and long-term administration schedules. Specifically, gavaging female NZO/HlLtJ with up to 2X MED of OEP-NF resulted in 40% mortality within two weeks. Feeding mice with either 1X or 3X MED of OEP-NF for eight weeks, while not exhibiting significant effects on body weights, significantly altered hepatic gene expression, increased the number of apoptotic and mast cells in the heart and affected cardiac function. The degree of toxicity in NZO/HlLtJ mice was higher than that observed previously in non-obese CD-1 and B6C3F1 strains, suggesting that an overweight/obese condition can sensitize mice to OEP-NF. Adverse health effects linked to OEP-NF, together with a number of other hepato- and cardiotoxicity cases associated with HDS ingestion, argue strongly for introduction of quality standards and pre-marketing safety assessments for multi-ingredient HDS.

Inflammatory and neuropathic pain conditions do not primarily evoke anxiety-like behaviours in C57BL/6 mice

BACKGROUND

Chronic pain is often accompanied by comorbidities like anxiety and depression. The temporal correlations, as well as the underlying mechanisms of these reciprocal correlations, are unclear. Moreover, preclinical studies examining emotional behaviour are very controversial, and a chronological analysis of anxiety-like behaviour in mouse pain models considering both genders has not been performed so far.

METHODS

We used several behavioural tests to assess and validate anxiety-like behaviour in complete Freund's adjuvant (CFA) and spared nerve injury (SNI) pain models in C57BL/6 mice. Among these were the elevated plus maze test, open field test, hole-board test and light-dark test. Additionally, we included a late stage analysis of depression-like behaviour using the forced swim test. All tests were applied once for each cohort of mice. Importantly, we used C57BL/6N mice of both genders; we investigated the effect of social isolation, the impact of pain induction to either the right or left hind limb and also investigated C57BL/6J mice.

RESULTS

The validity of test conditions was confirmed using the anxiogenic drugs Yohimbine and Pentylenetetrazol. Anxiety-like behaviour was analysed throughout the time period when mice exhibited hypersensitivity to mechanical stimuli. We did not observe any consistent alteration in anxiety-like behaviour at any of the investigated time points between 1 and 14 days following CFA-induced inflammation or 3 and 84 days following SNI surgery using different behavioural tests.

CONCLUSIONS

Inflammatory and neuropathic pain conditions do not primarily evoke anxiety- and depression-like behavioural alterations within the herein investigated time period.

SIGNIFICANCE

Anxiety-like behaviour is not primarily altered following CFA and SNI in C57BL6 mice, irrespective of the gender, mouse sub-strain, housing conditions or affected body side within the herein investigated time period.

Monoaminergic Involvement in Decreased Locomotor Activity of Mice Treated with α and β-amyrin from Protium heptaphyllum

A triterpenic mixture of α and β-amyrin (AMY) extracted from Protium heptaphyllum has demonstrated several pharmacological effects, including activity in the central nervous system. The aim of this study was to evaluate the effect of AMY administration on locomotor activity of mice by the open field test using some monoaminergic agonists and antagonists and the cerebral cortex levels of monoamines and their major metabolites by high-performance liquid chromatography. Mice were treated acutely with AMY at doses of 1, 2.5 and 5 mg/kg given intraperitoneally and with the pharmacological agents and placed in open field test, then the animals were sacrificed and the cerebral cortex extracted, and monoamines were assayed in tissue homogenates. AMY at 1, 2.5 and 5 mg/kg decreased locomotor activity of animals by 25, 31 and 39%, respectively in the open field test. Ondasentron, doxazosin, oxymetazoline and clonidine did not reverse the inhibitory effect of 5 mg/kg AMY. Venlafaxine and yohimbine reversed the inhibitory effect of 5 mg AMY. In the cortex, the 5-HT and 5-HIAA were significantly reduced by the administration of AMY. NE and HVA were also reduced with 2.5 and 5 mg/kg AMY, while Dopamine and DOPAC were not increased with AMY. In conclusion, AMY decreased locomotor activity of animals accompanied by a decrease in 5-HT and NE levels in the cerebral cortex, this locomotor effect is reversed by drug that blocker the α-2-adrenoreceptor.

Characterization of the locomotor activities of zebrafish larvae under the influence of various neuroactive drugs

Background

Behavioral changes in animals reflect functional changes in their central nervous system. Neuroactive drugs that act on different neural pathways can induce specific behavioral responses; therefore, it is possible to infer the activities of neuroactive drugs by studying the behavioral changes induced by drugs of interest in animals.

Methods

In this study, AB strain zebrafish larvae at 7 days post fertilization (dpf) were treated with different concentrations of drugs that act on different neural pathways. Changes in the swimming distances of zebrafish larvae under different illumination conditions and the differences in locomotor activities between light and dark conditions (lighting motor index) were analyzed.

Results

Among the drugs studied, different concentrations of sulpiride had no effect on larval locomotor activity either under light or dark conditions. Progressively decreased spontaneous movements were observed in zebrafish larvae treated with increasing doses of MK-801 and valproic acid. With increasing concentrations of pentylenetetrazole and yohimbine, the spontaneous movement of larval zebrafish presented a bell-shaped response. When the illumination changed from light to dark, zebrafish larvae not treated with drugs demonstrated increased locomotor activities. However, high levels of yohimbine, pentylenetetrazole decreased the degree of change in the lighting motor index.

Conclusions

In conclusion, drugs that affect different neural pathways exert different influences on the locomotor activities of zebrafish larvae. This study presents an initial effort to establish a framework that correlates the drug activities and the behavioral responses of zebrafish larvae under drug treatments, which may provide a potential identification of the pathways of novel drugs with neurological activities through their behavioral influences.

Novel effect of α-lactalbumin on the yohimbine-induced hot flush increase of the tail skin temperature in ovariectomized rats

5-Hydroxytryptamine (5-HT) and noradrenaline have been thought to play important roles in the mechanism of hot flush. Then, to clarify the relation between serotonergic and adrenergic nervous systems on the mechanism of hot flush, the effect of paroxetine, 5-HT reuptake inhibitor (SSRI) was evaluated on the yohimbine-induced hot flush increase of tail skin temperature in ovariectomized female rats. Yohimbine (adrenaline α₂ antagonist) significantly increased the tail skin temperature in course of time. Clonidine (adrenaline α₂ agonist) significantly attenuated this effect. Paroxetine also significantly inhibited the increase of tail skin temperature by yohimbine. α-Lactalbumin having SSRI activity in vitro study also significantly inhibited the increase of tail skin temperature, but not significantly decreased the initial temperature. This difference may explain the different mechanism between paroxetine (SSRI) and α-lactalbumin, suggesting new mechanism of hot flush.

Radioligand binding analysis of α 2 adrenoceptors with [11C]yohimbine in brain in vivo: Extended Inhibition Plot correction for plasma protein binding

We describe a novel method of kinetic analysis of radioligand binding to neuroreceptors in brain in vivo, here applied to noradrenaline receptors in rat brain. The method uses positron emission tomography (PET) of [¹¹C]yohimbine binding in brain to quantify the density and affinity of α₂ adrenoceptors under condition of changing radioligand binding to plasma proteins. We obtained dynamic PET recordings from brain of Spraque Dawley rats at baseline, followed by pharmacological challenge with unlabeled yohimbine (0.3 mg/kg). The challenge with unlabeled ligand failed to diminish radioligand accumulation in brain tissue, due to the blocking of radioligand binding to plasma proteins that elevated the free fractions of the radioligand in plasma. We devised a method that graphically resolved the masking of unlabeled ligand binding by the increase of radioligand free fractions in plasma. The Extended Inhibition Plot introduced here yielded an estimate of the volume of distribution of non-displaceable ligand in brain tissue that increased with the increase of the free fraction of the radioligand in plasma. The resulting binding potentials of the radioligand declined by 50–60% in the presence of unlabeled ligand. The kinetic unmasking of inhibited binding reflected in the increase of the reference volume of distribution yielded estimates of receptor saturation consistent with the binding of unlabeled ligand.

Tetrandrine, an alkaloid from S. tetrandra exhibits anti-hypertensive and sleep-enhancing effects in SHR via different mechanisms

BACKGROUND

Sleep disorders have been found to be associated with hypertension in both cross-sectional and longitudinal epidemiological studies. Tetrandrine, a major component of Stephania tetrandra, is well known as an antihypertensive agent. The anti-hypertension mechanism mainly relies on its L-type calcium channel blocking property. In the previous study, tetrandrine revealed both anti-hypertension and hypnotic effects in spontaneously hypertensive rats (SHRs).

PURPOSE

This study aims to elucidate whether the antihypertensive mechanism of tetrandrine in SHRs is relevant to its hypnotic effect.

DESIGN/METHODS

Sleep-wake behavior of the SHRs was detected by electroencephalography (EEG) and electromyography (EMG) recordings. Blood pressure was measured by noninvasive blood pressure tail cuff test. Immunohistochemistry was performed to evaluate the noradrenergic neuronal activity. The level of norepinephrine (NE) was detected by HPLC-ECD.

RESULTS

Amlodipine (100mg/kg, i.g.), the well-known L-type Ca²⁺ channel blockers (CCBs) exhibited remarkable antihypertensive activities in SHRs, but did not show effects on sleep of SHRs. Tetrandrine (30 and 60mg/kg/day, i.g.) significantly suppressed blood pressure of SHRs. Meanwhile, tetrandrine (60mg/kg/day, i.g.) remarkably increased non-rapid eye movement sleep (NREMS) time, bouts and mean duration. The hypnotic effect of tetrandrine was potentiated by prazosin (0.5mg/kg, i.p.) but attenuated by yohimbine (2mg/kg, i.p.). Administration of tetrandrine (60mg/kg/day, i.g.) not only significantly decreased c-Fos positive ratio of noradrenergic neurons in the locus coeruleus (LC), but also significantly decrease NE in the endogenous sleep-wake regulating pathways including LC, hypothalamus and ventrolateral preoptic nucleus (VLPO).

CONCLUSION

In spite of a good potency in blocking L-type Ca²⁺ channel, the hypnotic effects of tetrandrine may be related to its suppressing effects on the noradrenergic system other than to block calcium channels. As a multi-targets drug, tetrandrine might be favorable to the hypertension patients who suffered poor sleep.

New 2-Aminothiazoline derivatives lower blood pressure of spontaneously hypertensive rats (SHR) via I1-imidazoline and alpha-2 adrenergic receptors activation

2-Aminothiazolines share an isosteric relationship with imidazolines and oxazolines with antihypertensive activity mainly mediated by the imidazoline I₁-receptor. In the present work, we have prepared five aminothiazolines, following a previously described synthetic pathway. Aminothiazolines derived from dicyclopropylmethylamine (ATZ1) and cyclohexylamine (3) are unprecedented in the literature. Competitive radioligand assay was carried out with all synthetic compounds, and the I₁ receptor affinity in comparison to rilmenidine in PC12 cells was determined. Surprisingly, the rilmenidine isoster (ATZ1) showed no I₁-receptor interaction. Diethyl (ATZ4) and 2-ethyl-hexylamine (ATZ5) derivatives bind to the receptor with 11.98 and 10.94nmol/l, respectively. These compounds were selected for in vivo experiments. Both compounds reduced the blood pressure of spontaneously hypertensive rats (SHR). The hypotensive effect of these compounds was abrogated in the presence of α₂ adrenergic (yohimbine) and I₁ (efaroxan) receptor antagonists suggesting that both aminothiazolines bind to the adrenergic and imidazoline receptors. Lipinski's descriptors of the synthesized aminothiazolines were calculated and are similar to the known imidazoline I₁ receptor ligands. 3D-Similarity between ATZ5 and agmatine, the natural imidazoline receptor ligand, was also observed.

Baclofen blocks yohimbine-induced increases in ethanol-reinforced responding in rats

Chronic or repeated stress increases alcohol consumption. The GABA-B agonist baclofen decreases alcohol consumption and may be most effective for individuals with comorbid anxiety/stress disorders. The present study sought to determine if baclofen blocks stress-induced increases in ethanol self-administration as modeled by repeated yohimbine injections in rats. Rats were trained to respond for 15% w/v ethanol in operant chambers using a method that applies neither water deprivation nor saccharin/sucrose fading. Following training, the rats received 6 injections of 1.25mg/kg yohimbine were given immediately prior to the operant sessions during a 2-week time period. Subsequently, some rats were pair-matched to receive either 1.25mg/kg yohimbine or saline in the presence of 0.3, 1, and 3mg/kg baclofen prior to sessions. Acquisition of ethanol self-administration was poor. Pretreatment with yohimbine consistently increased responding across repeated injections. Yohimbine's effect on ethanol intake unexpectedly diverged from the effect on responding as the rats failed to consume all reinforcers earned. Smaller doses of baclofen paired with saline injections had no effect on ethanol responding; only 3mg/kg baclofen reduced ethanol self-administration. The smallest baclofen dose of 0.3mg/kg failed to block the yohimbine-induced increase in self-administration. The large baclofen dose of 3mg/kg continued to suppress ethanol self-administration when given with yohimbine. Baclofen 1mg/kg blocked the effect of yohimbine even though it had no effect when given in the absence of yohimbine. Exposure to high ethanol concentrations may induce self-administration only in certain conditions. The dissociation between responding and intake suggests that repeated yohimbine injections may initiate other behavioral or physiological mechanisms that confound its effects as a pharmacological stressor. Furthermore, an optimal baclofen dose range may specifically protect against stress-induced alcohol self-administration, highlighting a specific contribution of GABA-B receptors and a potential therapeutic efficacy of GABA-B agonists at a non-sedating dose.