Role of noradrenergic and dopaminergic systems in the antinociceptive effect of N-(3-(phenylselanyl)prop-2-yn-1-yl)benzamide in mice.

Pain has a negative impact on public health, reducing quality of life. Unfortunately, current treatments are not fully effective and have adverse effects. Therefore, there is a need to develop new analgesic compounds. Due to promising results regarding the antinociceptive effect of N-(3-(phenylselanyl)prop-2-in-1-yl)benzamide (SePB), this study aimed to evaluate the participation of the dopaminergic and noradrenergic systems in this effect in mice, as well as its toxicity. To this, the antagonists sulpiride (D2/D3 receptor antagonist, 5 mg/kg), SCH-23390 (D1 receptor antagonist, 0.05 mg/kg), prazosin (α1 adrenergic receptor antagonist, 0.15 mg/kg), yohimbine (α2-adrenergic receptors, 0.15 mg/kg) and propranolol (non-selective ß-adrenergic antagonist, 10 mg/kg) were administered intraperitoneally to mice 15 min before SePB (10 mg/kg, intragastrically), except for propranolol (20 min). After 26 min of SePB administration, the open field test was performed for 4 min to assess locomotor activity, followed by the tail immersion test to measure the nociceptive response. For the toxicity test, animals received a high dose of 300 mg/kg of SePB. SePB showed an increase in the latency for nociceptive response in the tail immersion test, and this effect was prevented by SCH-23390, yohimbine and propranolol, indicating the involvement of D1, α2 and ß-adrenergic receptors in the antinociceptive mechanism of the SePB effect. No changes were observed in the open field test, and the toxicity assessment suggested that SePB has low potential to induce toxicity. These findings contribute to understanding SePB's mechanism of action, with a focus on the development of new alternatives for pain treatment.

Yohimbine Directly Induces Cardiotoxicity on Human-Induced Pluripotent Stem Cell-Derived Cardiomyocytes.

Yohimbine is a highly selective and potent α2-adrenoceptor antagonist, which is usually treated as an adjunction for impotence, as well for weight loss and natural bodybuilding aids. However, it was recently reported that Yohimbine causes myocardial injury and controversial results were reported in the setting of cardiac diseases. Here, we used human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) as a model system to explore electrophysiologic characterization after exposure to Yohimbine. HiPSC-CMs were differentiated by employment of inhibitory Wnt compounds. For analysis of electrophysiological properties, conventional whole-cell patch-clamp recording was used. Specifically, spontaneous action potentials, pacemaker currents (If), sodium (Na+) channel (INa), and calcium (Ca++) channel currents (ICa) were assessed in hiPSC-CMs after exposure to Yohimbine. HiPSC-CMs expressed sarcomeric-α-actinin and MLC2V proteins, as well as exhibited ventricular-like spontaneous action potential waveform. Yohimbine inhibited frequency of hiPSC-CMs spontaneous action potentials and significantly prolonged action potential duration in a dose-dependent manner. In addition, rest potential, threshold potential, amplitude, and maximal diastolic potential were decreased, whereas APD50/APD90 was prolonged. Yohimbine inhibited the amplitude of INa in low doses (IC50 = 14.2 µM, n = 5) and inhibited ICa in high doses (IC50 = 139.7 µM, n = 5). Whereas Yohimbine did not affect the activation curves, treatment resulted in left shifts in inactivation curves of both Na+ and Ca++ channels. Here, we show that Yohimbine induces direct cardiotoxic effects on spontaneous action potentials of INa and ICa in hiPSC-CMs. Importantly, these effects were not mediated by α2-adrenoceptor signaling. Our results strongly suggest that Yohimbine directly and negatively affects electrophysiological properties of human cardiomyocytes. These findings are highly relevant for potential application of Yohimbine in patients with atrioventricular conduction disorder.

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

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

Effects of 071031B, a novel serotonin and norepinephrine reuptake inhibitor, on monoamine system in mice and rats.

Our previous study indicated that 071031B, a novel potential serotonin and norepinephrine reuptake inhibitor, showed robust antidepressant activity in multiple depression models, and could simultaneously inhibit 5-HT and NE reuptake in vitro. The present study was to evaluate the effects of 071031B on monoamine system in vivo, by using pharmacological models, including 5-HTP induced head-twitch test, yohimbine toxicity potentiation test, and reserpine induced hypothermia test, and determining monoamine transmitter levels in reserpine induced monoamine depletion model or chronic unpredictable stress (CUS) model. Results in pharmacological models indicated that acute administration of 071031B at 5-20 mg/kg significantly enhanced 5-HTP induced head-twitch behavior, potentiated yohimbine induced lethal rate, and reversed reserpine induced hypothermia. Further monoamine assays demonstrated that acute or chronic administration of 071031B at 10 or 20 mg/kg increased 5-HT and/or NE levels in various brain regions in reserpine or CUS induced monoamine depletion models, respectively, without effect on DA and its metabolites. Our results revealed that 071031B produces potent inhibition of 5-HT and NE reuptake in vivo.

Role of the kappa-opioid receptor system in stress-induced reinstatement of nicotine seeking in rats.

RATIONALE: The correlation between stress and smoking is well established. The mechanisms that underlie this relationship are, however, unclear. Recent data suggest that the kappa-opioid system is involved in the mediation of negative affective states associated with stress thereby promoting drug addiction and relapse. Pharmacological treatments targeting the kappa-opioid system and this mechanism may prove to be useful therapeutics for nicotine addiction in the future. OBJECTIVES: We sought to determine whether there was a stress-specific role of the kappa-opioid system in nicotine seeking behavior. METHOD: Groups of male Long Evans rats were trained to self-administer nicotine intravenously; their operant responding for nicotine was extinguished prior to tests of reinstatement. Pretreatment with systemic injections of the kappa-opioid receptor (KOR) antagonist nor-binaltorphimine (nor-BNI) was given prior to tests of stress (systemic injections of yohimbine (YOH)) or cue-induced reinstatement of nicotine seeking. Systemic injections of the KOR agonist U50,488 were also given in a test for reinstatement of nicotine seeking. RESULTS: Nor-BNI pretreatment at 1h and 24h prior to testing was able to block YOH-induced, but not cue-induced reinstatement of nicotine seeking. U50,488 reinstated nicotine seeking behavior in a dose-dependent manner. CONCLUSIONS: These findings support the hypothesis that the kappa-opioid system is involved in relapse to nicotine seeking induced by stress, but not by conditioned cues. KOR antagonists such as nor-BNI may therefore be useful novel therapeutic agents for decreasing the risk of stress-induced drug relapse.

Antidepressant-like property of Jobelyn®, an African unique herbal formulation, in mice.

OBJECTIVES: The purpose of this investigation was to evaluate whether Jobelyn® (JB) possesses anti-depressant-like property in the mouse forced swimming test (FST), tail suspension test (TST) and yohimbine-induced lethality test (YLT) in aggregated mice. METHODS: Mice were given JB (10-100 mg/kg, p.o.) daily for 7 days and then subjected to FST, TST, YLT and open field test. The parameters assessed in both FST and TST were the time (s) spent in active movement (struggling time), first occurrence of immobility (s) and the duration of immobility (s). In the YLT, the mortality rate was recorded 24 h after yohimbine (35 mg/kg, i.p.) administration. In the open field test, the number of line crosses and total distance travelled (m) were measured for 10 min in the open field chamber. RESULTS: JB significantly (p<0.05) decrease the duration of immobility both in the FST and TST, which suggests antidepressant-like property. JB significantly (p<0.05) prolonged the time spent in active swimming and delayed the first occurrence of immobility, indicating endurance promoting effect. It potentiated the toxic effect of yohimbine, which further suggests antidepressant-like activity and facilitation of both serotonergic and noradrenergic neurotransmissions. However, JB did not significantly increase the locomotor activity in the open-field test. CONCLUSIONS: Jobelyn® has antidepressant-like activity, which may be related to the stimulation of serotonergic and noradrenergic pathways. The ability of Jobelyn® to delay the onset of immobility and to prolong the struggling time support its use as energizer in general body weakness or exhaustion.

FG7142, yohimbine, and ßCCE produce anxiogenic-like effects in the elevated plus-maze but do not affect brainstem activated hippocampal theta.

The neurobiological underpinnings of anxiety are of paramount importance to selective and efficacious pharmaceutical intervention. Hippocampal theta frequency in urethane anaesthetized rats is suppressed by all known (and some previously unknown) anti-anxiety (anxiolytic) drugs. Although these findings support the predictive validity of this assay, its construct validity (i.e., whether theta frequency actually indexes anxiety per se) has not been a subject of systematic investigation. We reasoned that if anxiolytic drugs suppress hippocampal theta frequency, then drugs that increase anxiety (i.e., anxiogenic agents) should increase theta frequency, thus providing evidence of construct validity. We used three proven anxiogenic drugs--two benzodiazepine receptor inverse agonists, N-methyl-ß-carboline-3-carboxamide (FG7142) and ß-carboline-3-carboxylate ethyl ester (ßCCE), and one α2 noradrenergic receptor antagonist, 17α-hydroxy-yohimban-16α-carboxylic acid methyl ester (yohimbine) as pharmacological probes to assess the construct validity of the theta model. Although all three anxiogenic drugs significantly increased behavioural measures of anxiety in the elevated plus-maze, none of the three increased the frequency of hippocampal theta oscillations in the neurophysiological model. As a positive control, we demonstrated that diazepam, a proven anxiolytic drug, decreased the frequency of hippocampal theta, as in all other studies using this model. Given this discrepancy between the significant effects of anxiogenic drugs in the behavioural model and the null effects of these drugs in the neurophysiological model, we conclude that the construct validity of the hippocampal theta model of anxiety is questionable.

Case study: two fatal case reports of acute yohimbine intoxication.

Yohimbine is an alkaloid that has been encountered on the streets as an aphrodisiac, hallucinogen, dietary supplement and erectile dysfunction drug. Yohimbine hydrochloride is an alpha 2-adrenoreceptor antagonist, blocking the pre- and postsynaptic alpha-2 adrenoreceptors and causing an increased release of noradrenaline and dopamine. An average oral dose of 5-15 mg produces a therapeutic whole blood level range of 40-400 ng/mL. Overdoses leading to neurotoxic effects have been seen with blood concentrations up to 5,000 ng/mL. The laboratories from the Maricopa County Medical Examiner and the Los Angeles County Department of Coroner each encountered a case in which yohimbine was identified in whole blood by means of a liquid-liquid basic drug extraction with detection on a GC-MS. Because validated quantitative methods for yohimbine did not exist at either facility, both agencies referred the blood specimens to NMS Labs, Inc. The reference laboratory analyzed the blood specimens with an LC-MS-MS and determined the quantitative values of yohimbine to be 7,400 and 5,400 ng/mL. Given the absence of other significant positive findings and the substantial yohimbine blood concentrations cited, the respective Medical Examiners determined the cause of death to be acute yohimbine intoxication with the mode being an accident. Yohimbine is a rarely encountered drug in medical examiner casework, and interpretation of the results is difficult to assess toward the cause and manner of death without such case studies being described.

Behavioral profile of Hypericum perforatum (St. John's Wort) extract. A comparison with standard antidepressants in animal models of depression.

BACKGROUND AND OBJECTIVES: Hypericum (H.) perforatum, popularly called St. John's Wort has been used traditionally for the treatment of anxiety, depression and as a nerve tonic. Large amount of clinical and animal experimental data demonstrate that H. perforatum acts by biochemical mechanisms similar to the tricyclic antidepressants or serotonin reuptake inhibitors. However, its efficacy in comparison to standard antidepressant drugs is not well studied. The present study evaluated H. perfortum extract in animal models of depression compared to clinically used antidepressants. MATERIALS AND METHODS: The effects of standardized extract of H. perforatum was compared with standard antidepressants using animal models of depression such as forced swim test (FST), yohimbine induced lethality test, pnetylenetetrazole (PTZ) induced convulsion and locomotor activity tests. Different doses of the plant extract and standard drugs were administered to rats or mice intraperitoneally (i.p). RESULTS: In the FST, H. perforatum extract (30-90 mg/kg i.p.) caused a dose dependent reduction in immobility time in rats with maximal effect being 53% at 90 mg/kg. This effect was reversed at higher doses (100 mg/kg) showing a U-shaped dose response curve. Fluoxetine and imipramine (30-70 mg/kg i.p.) produced similar reduction in the immobility time in rats. Venlafaxine exhibited weak antidepressant effect. H. perforatum extract (30-100 mg/kg i.p.), dothiepin (10-50 mg/kg i.p.), fluoxetine (30-60 mg/kg i.p.) and venlafaxine (20-40 mg/kg i.p.) potentiated yohimbine induced lethality. PTZ induced toxicity was also enhanced with these agents. In the locomotor activity test H. perforatum decreased the locomotor counts of mice similar to standard antidepressants. CONCLUSIONS: H. perforatum has antidepressant properties similar to standard antidepressants. The antidepressant profile of H. perforatum is closely related to the selective serotonin reuptake inhibitors class of antidepressants.

Antidepressant-like effects of the extract from Cimicifuga foetida L.

ETHNOPHARMACOLOGICAL RELEVANCE: Cimicifuga foetida L., a traditional Chinese medicine, has been developed for the treatment of perimenopausal symptoms including depression in China (Brand name: XIMINGTING(®), XMT). The primary active constituents are believed to be the triterpene glycosides. Nevertheless, there are no studies about the antidepressant-like effects of XMT in rodents. AIMS OF THE STUDY: The present study aimed to evaluate antidepressant-like effects of XMT. MATERIALS AND METHODS: Antidepressant-like activity of XMT was studied using forced swimming test (FST) and tail suspension test (TST) in female mice, as well as chronic mild stress (CMS) procedure in female rats. In addition, 5-hydroxytryptophan (5-HTP)-induced head-twitch test and yohimbine toxicity potentiation test in female mice were conducted to propose the possible serotonergic or noradrenergic mechanisms in the antidepressant-like effects of XMT. In mice, XMT was administrated acutely and for 7 consecutive days (20, 40 and 80 mg/kg/day, p.o.); and in rats for 28 consecutive days (10, 20 and 40 mg/kg/day, p.o.). RESULTS: XMT significantly reduced immobility duration in FST and TST without affecting locomotor activity, increased swimming and climbing durations in FST, and enhanced 5-HTP-induced head-twitch response while did not affect yohimbine-induced lethality in female mice. XMT also normalized the inhibition of sucrose intake and decreased the levels of plasma adrenocorticotropic hormone and serum corticosterone and adrenal gland weight in CMS-treated female rats. CONCLUSIONS: These data indicate XMT processes antidepressant-like properties in rodents, which could be related to its serotonergic and noradrenergic activation and normalization of the hypothalamic-pituitary-adrenal axis.

Antidepressant activity of methyl jasmonate, a plant stress hormone in mice.

Methyl jasmonate (MJ) is a hormone released by plants in response to external stress, injury or pathogenic invasions. This present investigation evaluated the antidepressant effect of intraperitoneal doses of MJ in mice. Mice were given MJ in the doses of 10, 25 and 50 mg/kg daily for 7 days and then subjected to forced swim test (FST), tail suspension test (TST) and yohimbine lethality test (YLT). The results showed that MJ produced a significant decrease in the period of immobility in the FST and TST, indicating antidepressant activity. MJ potentiated the toxic effect of yohimbine in the YLT, which further suggests antidepressant property and also indicates facilitatory effect on both serotonergic and noradrenergic systems respectively. However, MJ did not significantly alter the spontaneous motor activity of the animals, which indicates a lack of central nervous system stimulant effect. Taken together, these findings suggest that MJ has antidepressant activity and the mechanisms underlying this effect may involve serotonergic and noradrenergic systems.

Synthesis and antidepressant-like action of 9-alkoxy-7H-furo[3,2-g] chromen-7-ones in mice.

The present study describes the chemical synthesis and pharmacological evaluation of a series of 9-alkoxy-7H-furo[3,2-g]-chromen-7-ones. The pharmacological results of these compounds show that nine of them, given orally, reduced the immobility time in the forced swimming test. The results of the open-field test further confirmed that these compounds possessed an antidepressant-like effect. In the 5-hydroxytryptophan induced head-twitch test, 9-(3-chlorobenzyloxy)-7H-furo[3,2-g]chromen-7-one (3 m, 40 mg/kg p. o.) significantly increased the cumulative numberof head twitches. This finding suggested that the antidepressant-like profile seems to involve the serotonergic system as underlying mechanism.

Role for serotonin in the antidepressant-like effect of a flavonoid extract of Xiaobuxin-Tang.

Xiaobuxin-Tang (XBXT), a traditional Chinese herbal decoction, has been used for the treatment of depressive disorders for centuries in China. Herein, we explored the antidepressant-like effect and its monoaminergic mechanism of the total flavonoids (XBXT-2) isolated from the extract of XBXT. In present study, single XBXT-2 (25, 50, 100 mg/kg, p.o.) administration significantly potentiated the mouse head-twitch response induced by 5-hydroxytryptophan (5-HTP, a metabolic precursor to serotonin), and also, decreased the immobility time in mouse tail suspension test, which was completely prevented by p-chlorophenylalanine (PCPA, an inhibitor of serotonin synthesis) pretreatment. However, single treatment with XBXT-2 had no effect on yohimbine toxicity and high dose of apomorphine-induced hypothermia in mice. These results indicated that acute treatment with XBXT-2 produced serotonergic, but not noradrenergic activation. In addition, chronic XBXT-2 (25, 50 mg/kg, p.o., 28 days) treatments significantly reversed the depressive-like behaviors in chronically mildly stressed (CMS) rats, including the reduced sucrose preference, deficient locomotor activity and prolonged latency to novelty-suppressed feeding. Furthermore, XBXT-2 normalized the neurotransmitter changes, including the decreased serotonin (5-HT) and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) levels in hippocampus and prefrontal cortex in CMS rats. These findings confirm the antidepressant-like effect of XBXT-2 in CMS model of rats, which may be primarily based on its serotonergic activation.

Synthesis of some tropane derivatives of anticipated activity on the reuptake of norepinephrine and/or serotonin.

A variety of tropane derivatives 14a-g were prepared via the reaction of the alcohol analogs 12a and 12b with substituted fluorobenzenes 13a-f. The prepared compounds were tested for their activity and selectivity toward the norepinephrine transporter (NET) and serotonin transporter (SERT) using yohimbine-induced mortality and 5-hydroxytryptophan-induced neurotoxicity in mice, respectively. All the tested compounds were found to be NE and 5-HT reuptake inhibitors except 14d which exhibited selective 5-HT reuptake inhibition activity.

Influence of pharmacologically-induced experimental anxiety on nociception and antinociception in rats.

Animal studies reveal that diverse environmental stimuli that generate anxiety-like behaviors also induce antinociception; conversely, clinical data show that pain perception is reduced under anxiolysis. This study was conducted to investigate the influence of pharmacologically induced-anxiety on nociception and antinociception. Experimental anxiety levels were measured using the rat burying behavior test. Diazepam (0, 0.5, 1.0 and 2.0 mg/kg, i.p.) or yohimbine (0, 0.5 and 1.0 mg/kg, i.p.) were used as anxiolytic or anxiogenic drugs, respectively. To evaluate the influence of different experimental anxiety levels on nociception, the pain-induced functional impairment in the rat (PIFIR model) was used. Nociception was induced by an intra-articular injection of 15% uric acid into the knee joint of the right hind limb. Diazepam or yohimbine were administered 15 min before uric acid and the ability of the rat to use the injured hind limb was recorded. To analyze the influence of different levels of anxiety on the antinociceptive effects produced by acetylsalicylic acid (0, 31, 100 and 310 mg/kg, p.o.); this analgesic was administered 3.5 h after uric acid. Fifteen min before diazepam (2.0 mg/kg) or yohimbine (1.0 mg/kg) were administered. We found that, in the burying behavior test, diazepam and yohimbine produced a dose-dependent decrease or augment in the cumulative time of burying, effects denoting reduced or increased experimental anxiety, respectively. Diazepam or yohimbine, administered alone, was unable to produce nociception. The results showed an influence of anxiety on nociception since a decreased (by diazepam) or increased (by yohimbine) experimental anxiety prevented nociception. Control experiments showed that acetylsalicylic acid did not modify experimental anxiety in the burying behavior test, but effectively reversed the nociception induced by uric acid (15%) in the PIFIR model. Such antinociceptive effect was unmodified by the anxiolytic or anxiogenic actions of diazepam or yohimbine. Data are discussed on the bases of clinical- and animal-studies revealing interactions between anxiety and nociception.

Molecular and pharmacological analysis of an octopamine receptor from American cockroach and fruit fly in response to plant essential oils.

Octopamine receptors from American cockroach, Periplaneta americana (Pa oa1), and fruit fly, Drosophila melanogaster (OAMB), were cloned and permanently expressed in HEK-293 cells, and found to activate adenylate cyclase activity and increase [Ca2+]i levels through G-protein coupled receptor signaling pathways. Sequencing information (GenBank accession number AY333178) and functional data of Pa oa1 were recently published. Saturation binding analysis with 3H-yohimbine was performed with Pa oa(1) and OAMB expressed in COS-7 cells. The K(d) values were determined to be 28.4 and 43.0 nM, respectively. B(max) was determined to be 11.8 and 8.04 pmol receptor/mg protein, respectively. Competitive binding data using cell membranes expressing either OAMB or Pa oa1 demonstrated significantly decreased binding activity in binding assays performed in the presence of plant essential oils, eugenol, cinnamic alcohol, and trans-anethole. Eugenol decreased cAMP level in HEK-293 cells expressing Pa oa1, but trans-anethole increased cAMP in HEK-293 cells expressing OAMB. All three chemicals increased [Ca2+]i level in both cell models. Toxicity data against fruit flies and American cockroaches demonstrated species differences in response to treatment with tested plant essential oils. The toxicity of tested chemicals against wild type and octopamine mutant (iav) fly strains suggested that an octopamine receptor mediates the toxicity of cinnamic alcohol, eugenol, trans-antehole, and 2-phenethyl propionate against fruit flies. Collectively, the data suggest a correlation between cellular changes induced by tested plant essential oils and their toxicity against fruit fly and American cockroach.

The anxiogenic drug yohimbine reinstates methamphetamine seeking in a rat model of drug relapse.

BACKGROUND: Brain noradrenaline is involved in footshock stress-induced reinstatement of drug seeking in a rat relapse model. We studied whether yohimbine, an alpha-2 adrenoceptor antagonist that increases noradrenaline release and induces anxiety-like responses in human and nonhuman subjects, would reinstate methamphetamine seeking in rats. METHODS: In experiment 1, the effect of yohimbine (1.25-2.5 mg/kg) on reinstatement was compared with that of intermittent footshock (5 min;.2-.6 mA) in rats that were trained to lever press for intravenous methamphetamine (9-11 days) and subsequently underwent 7 days of extinction training. In experiment 2, the effect of yohimbine on reinstatement of drug seeking was determined during early (1 day) and late (21 or 51 days) withdrawal periods. On the test days, rats were first given 3-hour extinction sessions and were then tested for reinstatement induced by yohimbine. RESULTS: In experiment 1, both yohimbine and footshock stress reinstated methamphetamine seeking after extinction. In experiment 2, extinction responding was higher after 21 or 51 withdrawal days than after 1 withdrawal day. In contrast, no significant time-dependent changes in yohimbine-induced reinstatement were observed. CONCLUSIONS: Results indicate that yohimbine is a potent stimulus for reinstatement of methamphetamine seeking in a rat relapse model.

Pharmacological blockade of alpha2-adrenoceptors induces reinstatement of cocaine-seeking behavior in squirrel monkeys.

Converging evidence suggests a role for noradrenergic mechanisms in stress-induced reinstatement of cocaine seeking in animals. Yohimbine, an alpha(2)-adrenoceptor antagonist, is known to be anxiogenic and induce stress-related responses in humans and animals. Here, we tested the ability of yohimbine to reinstate cocaine-seeking behavior and induce behavioral and physiological signs characteristic of stress in squirrel monkeys. Monkeys were trained to self-administer cocaine under a second-order schedule of i.v. drug injection. Drug seeking subsequently was extinguished by substituting saline for cocaine injections and omitting the cocaine-paired stimulus. The ability of yohimbine and the structurally distinct alpha(2)-adrenoceptor antagonist RS-79948 to reinstate cocaine-seeking behavior was assessed by administering priming injections immediately before test sessions in which the cocaine-paired stimulus was either present or absent. Priming injections of yohimbine (0.1-0.56 mg/kg, i.m.) or RS-79948 (0.01-0.1 mg/kg, i.m.) induced dose-related reinstatement of cocaine-seeking behavior. The magnitude of yohimbine-induced reinstatement was similar regardless of the presence or absence of the cocaine-paired stimulus. Yohimbine also significantly increased salivary cortisol levels, a physiological marker of stress, as well as scratching and self-grooming, behavioral markers of stress in nonhuman primates. In drug interaction experiments, pretreatment with the alpha(2)-adrenoceptor agonist clonidine (0.1-0.3 mg/kg, i.m.) dose-dependently inhibited yohimbine-induced reinstatement of cocaine seeking. In contrast, pretreatment with the dopamine receptor antagonist flupenthixol failed to inhibit yohimbine-induced reinstatement of cocaine seeking. The results show that pharmacological blockade of alpha(2)-adrenoceptors can induce reinstatement of cocaine-seeking behavior and characteristic stress responses in squirrel monkeys, providing a potentially useful model of stress-induced relapse to drug seeking.

High prevalence of potentially hepatotoxic herbal supplement use in patients with fulminant hepatic failure.

HYPOTHESIS: The use of potentially hepatotoxic herbal and dietary supplements is highly prevalent in the fulminant hepatic failure (FHF) patient population at our institution, and this subgroup of patients has a worse prognosis. DESIGN: Retrospective case series. Settings An adult tertiary care university hospital and a Veterans Affairs hospital in Oregon. PATIENTS: All patients referred to the liver transplantation service for FHF from January 2001 through October 2002 (N = 20). We defined FHF as onset of encephalopathy within 8 weeks of onset of jaundice in the absence of preexisting liver disease. All patients underwent investigation for potential causes of liver injury. Potentially hepatotoxic supplements were defined as those with previously published reports of hepatic injury related to their use. RESULTS: Ten patients (50%) were recent or active users of potentially hepatotoxic supplements or herbs; 10 had no history of supplement use. In the supplement group, 7 patients (35%) had no other identified cause for hepatic failure. Six patients in the supplement group and 2 patients in the nonsupplement group underwent orthotopic liver transplantation. Five patients in each group died. There were no significant differences in transplantation rate (P =.07) or survival (P>.99) between groups. Supplement use alone accounted for the most cases of FHF during this period, exceeding acetaminophen toxicity and viral hepatitis. CONCLUSIONS: Herbal and dietary supplements were potential hepatotoxins in a high proportion of patients with FHF at our institution. Enhanced public awareness of the potential hepatotoxicity of these commonly used agents and increased regulatory oversight of their use is strongly urged.

Corneal toxicity of xylazine and clonidine, in combination with ketamine, in the rat.

PURPOSE: To compare the corneal toxicity of xylazine (XYL)/ketamine (KET) with that of clonidine (CLO)/KET in the rat, in the presence or not of the alpha(2)-adrenergic antagonist yohimbine (YOH). METHODS: XYL (10 mg/kg) and CLO (0.15 mg/kg) were administered subcutaneously in the rat in combination with KET (50 mg/kg), in the presence or not of YOH (2 mg/kg). RESULTS: The corneas immediately lost transparency and luster, but recovered within 120 min. By both light and electron microscopy, a marked stromal edema and alterations of all layers were observed. In addition, XYL/KET altered the permeability of the cornea as indicated by the augmented levels of (14)C-indomethacin, topically administered 30 min after the anesthetic combination. CONCLUSIONS: The mechanism of the corneal toxicity of XYL and CLO in the rat is unclear but we speculate that: (a) proptosis and inhibition of normal blinking did not play a major role because topical application of hyaluronic acid did not protect against it; corneal decompensation, edema and opacification could be due to (b) osmotic or (c) mechanical endothelial stress: the first resulting from the sudden increase of the glucose concentration in the aqueous humor due to the well-known inhibition of insulin release by alpha(2)-adrenergic agonists, and the second from the acute elevation of intraocular pressure caused by these alpha(2)-adrenergic mydriatics in the rat; (d) addition, XYL and CLO could act by directly interacting with local alpha(2)- or, possibly, alpha(1)-adrenergic receptors, whose function is still not clear but probably essential for corneal homeostasis.