Effects Of Yohimbine Research Articles

Alterations in ethanol seeking and self-administration following yohimbine in selectively bred alcohol-preferring (P) and high alcohol drinking (HAD-2) rats

Evidence suggests that stress increases alcohol drinking and promotes relapse in humans. Animal models that assess related behaviors include the sipper tube ethanol self-administration and the stress-induced reinstatement paradigms. While selectively bred for the same high-ethanol-drinking behavior, alcohol-preferring P rats appear to show greater sensitivity to ethanol reinforcement than high-alcohol-drinking HAD rats. The present experiment tested the effects of the pharmacological stressor, yohimbine, on the motivation to seek and consume ethanol implementing a combined sipper tube/reinstatement model using male P and HAD-2 rats. Following training to self-administer ethanol using the sipper tube procedure, rats were tested for the effects of yohimbine (0.625–2.5mg/kg) on ethanol drinking. Subsequently, rats were tested for the effects of 1.25mg/kg yohimbine on reinstatement of ethanol seeking. Yohimbine (0.625 and 1.25mg/kg) increased ethanol self-administration, and the latter dose also decreased latency to complete the response requirement. Yohimbine elicited reinstatement of ethanol seeking in both lines. HAD-2 rats drank more ethanol, but showed similar responding on the ethanol-associated lever compared to P rats. These findings extend both the reinstatement and sipper tube models and justify further exploration of this unique combined paradigm. Despite prior evidence suggesting that P rats are more motivated to seek and consume ethanol, differences in these behaviors between P and HAD-2 rats were not systematic in the present experiment. Further investigation may elucidate whether either selected line may be more sensitive than other selectively bred or outbred rats to stress-related changes in ethanol's reinforcing effects.

Alpha2-adrenergic receptors in spiral ganglion neurons may mediate protective effects of brimonidine and yohimbine against glutamate and hydrogen peroxide toxicity

Brimonidine, an alpha2-adrenergic receptor (α2-AR) agonist, is thought to be neuroprotective in some types of neurons via the activation of α2-AR. However, it is still unknown whether the α2-ARs exist in cochlear spiral ganglion neurons (SGNs). The authors aimed to demonstrate the presence and localization of α2-ARs in rat-cultured SGNs and to investigate the effect of brimonidine on glutamate- and hydrogen peroxide (H2O2)-induced damage in the primary-cultured rat SGNs. The expression of α2-ARs was determined by reverse transcription-polymerase chain reaction, Western blot analysis and immunofluorescence. Then SGNs were exposed to glutamate or H2O2 respectively with or without brimonidine. Cell viability was measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay. Apoptosis was determined by acridine orange and Hoechst 33342/propidium iodide double staining. The protein expressions of α2-ARs, Bax, Bcl-2, Caspase-9, Caspase-3, p-ERK1/2, iNOS, and artemin were determined by Western blot respectively. The cell viability was markedly reduced after exposure of glutamate (1mM) or H2O2 (300μM) to SGNs. Treatment with brimonidine protected SGNs against glutamate- or H2O2-induced cell damage, enhanced SGNs survival, decreased the elevation of Bax, Caspase-9, Caspase-3, p-ERK1/2, and artemin triggered by glutamate or H2O2, and altered the expressions of Bcl-2 and iNOS. These protective effects of brimonidine can be reversed by yohimbine. Overall, the study describes the localization of α2-ARs in rat-cultured SGNs and indicates that brimonidine, which may work directly via interaction with α2-ARs, attenuates glutamate- and H2O2-induced damage in SGNs by Caspase-dependent modes as well as Caspase-independent modes.

Meranzin hydrate exhibits anti-depressive and prokinetic-like effects through regulation of the shared alpha 2-adrenoceptor in the brain–gut axis of rats in the forced swimming test

BackgroundIn recent years, the brain–gut axis theory has received increasing attention in studies of depression. However, most studies separately address potential antidepressant and prokinetic treatments. Investigations of drugs that could potentially treat comorbid depression and gastrointestinal (GI) dysfunction via a common mechanism of action have not yet been performed in detail. AimTo find a common mechanism of action of our patented drug, meranzin hydrate (MH), in the antidepressant and prokinetic treatment. MethodsThe forced swimming test (FST) model of depression, plasma ghrelin measurement, and in vivo and in vitro measurements of GI motility were used. Results1. Administration of MH (9 mg/kg) decreased the immobility time during the FST after acute treatment; this effect was inhibited by the alpha 2-adrenoceptor antagonist, yohimbine, but not by the alpha 1-adrenoceptor antagonist, prazosin. 2. After chronic treatment, the immobility time of rats during the FST was decreased significantly by MH (2.25 mg/kg). 3. MH (9 mg/kg) increased plasma ghrelin levels in rats subjected to the FST; this increase was enhanced by the ghrelin receptor agonist, GHRP-6. 4. MH (9 mg/kg) also promoted gastric emptying and intestinal transit in rats with or without FST. 5. In vitro, MH (10 μM) increased jejunal contractions in rats subjected to the FST; this effect was inhibited by yohimbine. Furthermore, the inhibitory effect of yohimbine was partly reversed by the ghrelin receptor agonist, GHRP-6. ConclusionOur study revealed that MH from natural resources exhibits antidepressive and prokinetic-like effects through the regulation of the common mediator, the alpha 2-adrenoceptor.

Effects of noradrenergic stimulation on memory in patients with major depressive disorder

Major depressive disorder (MDD) has been associated with alterations in the noradrenergic system and impaired memory function. In turn, enhanced memory function has been associated with noradrenergic stimulation. In this study, we examined whether noradrenergic stimulation would differentially improve memory function in patients with MDD and healthy controls. In a placebo-controlled crossover study, 20 patients with MDD and 18 age- and sex-matched healthy controls received either placebo or 5 mg of yohimbine, an alpha-2-adrenoceptor antagonist that causes increased noradrenergic activity, orally before memory testing. A word list paradigm was used to test memory consolidation. Furthermore, the autobiographical memory test assessing memory retrieval and a working memory test were administered. Salivary alpha-amylase and blood pressure were measured. Yohimbine improved memory consolidation (word list learning) across groups (main effect of yohimbine: p = 0.05). This effect was more prominent in depressed patients compared with controls (post hoc t-test: MDD p = 0.01, controls p = 0.77). Memory retrieval (autobiographical memory specificity) and working memory were not affected by yohimbine. Across groups, yohimbine administration resulted in an increase in blood pressure and alpha-amylase. In sum, these results further support the hypothesis that noradrenergic stimulation enhances memory consolidation. The mechanism by which yohimbine leads to stronger memory consolidation in depressed patients compared with healthy controls remains to be elucidated.

Winter Day Lengths Counteract Stimulatory Effects of Apomorphine and Yohimbine on Sexual Behavior of Male Syrian Hamsters

Yohimbine and apomorphine selectively act on noradrenergic and dopaminergic neural substrates to augment male sexual behavior (MSB) in several rodent species. The present study assessed whether these drugs can overcome the suppressive effects of short winter-like day lengths on MSB. Yohimbine treatments that markedly increase copulatory behavior of male hamsters in long days were completely ineffective in facilitating MSB when injected after gonadal regression induced by 16 wks of short day lengths and after complete gonadal recrudescence after 32 wks of short days; apomorphine was similarly ineffective. The brain circuit that mediates MSB either may be less responsive to yohimbine and apomorphine in short than long days, or these drugs may not produce equivalent neurotransmitter changes in the two day lengths. After 32 wks of short-day treatment, all males had undergone testicular recrudescence and successfully ejaculated on initial tests with sexually receptive females after a hiatus of at least 4 mo during which they were denied mating opportunities. This suggests that overwintering males in the field are in a state of reproductive readiness at the outset of spring conditions favorable for survival of offspring. (Author correspondence: piekarski@berkeley.edu)

Effect of yohimbine, naloxone and their combination on analepsia from ketamine-induced anesthesia in mice

Effect of yohimbine, naloxone and their combination on analepsia from ketamine-induced anesthesia in mice

Reinstatement of cocaine seeking in rats by the pharmacological stressors, corticotropin-releasing factor and yohimbine: role for D1/5 dopamine receptors

Two pharmacological stressors commonly used in the study of stress-induced reinstatement of drug seeking are central injections of the stress peptide, corticotropin-releasing factor (CRF), and systemic administration of the α(2)-adrenoceptor antagonist, yohimbine. Despite the widespread use of these stressors, the neurochemical systems mediating their ability to reinstate cocaine-seeking behaviour have not been fully characterized. The present study was designed to characterize the role, specifically, of dopamine transmission in the reinstating effects of CRF and yohimbine on cocaine seeking. Male Long-Evans rats were trained to self-administer cocaine (0.23 mg/kg/infusion) for 8-10 days. Subsequently, responding for drug was extinguished, and tests for CRF- (0.5 μg; i.c.v.) and yohimbine-induced (1.25 mg/kg; i.p.) reinstatement were conducted following pretreatment with the dopamine D1/5 receptor antagonists, SCH23390 (0.05, 0.1 mg/kg; i.p.) and/or SCH31966 (0.2 mg/kg; i.p.), and the D2/3 receptor antagonist, raclopride (0.25, 0.5 mg/kg; i.p.). Pretreatment with SCH23390, but not raclopride, blocked CRF-induced reinstatement of cocaine seeking. Pretreatment with SCH23390 and SCH31966, but not raclopride, blocked yohimbine-induced reinstatement of cocaine seeking. These findings demonstrate that transmission at D1/5, but not D2/3, receptors mediates the reinstatement of cocaine seeking induced by CRF and yohimbine.

Immobilization of white‐tailed deer with telazol, ketamine, and xylazine, and evaluation of antagonists

AbstractTelazol–xylazine and ketamine–xylazine are versatile and safe drug combinations that are used frequently for chemical immobilization of cervids. Although neither combination consistently offers rapid induction and recovery, we hypothesized that a combination of Telazol, ketamine, and xylazine (TKX) would provide a safe and effective alternative for immobilization of white‐tailed deer (Odocoileus virginianus). During a 2‐stage study, we evaluated the effectiveness of yohimbine and tolazoline as alpha2‐adrenergic antagonists (2005–2006), and characterized the factors that affected chemical immobilization of male deer with a targeted dose of telazol (2.20 mg/kg), ketamine (1.76 mg/kg), and xylazine (0.44 mg/kg), using explosive‐charged darts (2007–2010). During the first stage, we randomly assigned deer to antagonist treatments, including a control group that did not receive an antagonist (n = 8), a tolazoline (4 mg/kg) treatment (n = 16), and a yohimbine (0.11 mg/kg) treatment (n = 15). Recovery times $({\bar {x}}\pm {\rm SE)}$ were longer (P = 0.0013) for control (150.6 ± 21.7 min) and yohimbine (74.5 ± 13.1 min), compared with tolazoline (12.5 ± 12.3 min). Tolazoline resulted in faster and more complete recovery compared with the frequent incomplete antagonism and ataxia observed with yohimbine. During the second stage, 56 immobilization events (2007–2010) with TKX yielded a mean induction time of 7.8 minutes (SE = 0.44). Repeated‐measures analyses indicated that induction and recovery were affected by body weight, with larger males taking longer to become recumbent (P = 0.08), but they recovered more rapidly (P = 0.003) following administration of tolazoline. Physiological parameters we measured under anesthesia were within normal ranges for white‐tailed deer; however, initial temperature was higher (β = −0.86) for younger males (P = 0.014). Final physiological parameters were closely related to initial measurements, with rectal temperature being the most preserved (β = 0.90); heart and respiration rate declined (β < 0.60) during anesthesia. Our results indicate that TKX may be useful for chemically immobilizing white‐tailed deer, and we recommend tolazoline as an antagonist for xylazine. © 2012 The Wildlife Society.

Effect of yohimbine stress on reacquisition of oxycodone seeking in rats

Stress, a powerful precipitant of drug seeking during abstinence, may also accelerate the return to pathological patterns of intake after initial instances of drug reuse. To explore the effect of stress on a learning process underlying relapse, this study assessed the effect of yohimbine on reacquisition of oxycodone seeking. One hundred thirty-two male Sprague-Dawley rats underwent place conditioning with oxycodone (2 mg/kg, SC; ×6 days), extinction (vehicle × 6 days), and reconditioning with 0, 0.25, 2, or 5 mg/kg oxycodone (2 days). Yohimbine (0, 2.5, or 5 mg/kg, IP) was administered 30 min prior to reconditioning. Pretreatment with 2.5 mg/kg yohimbine increased, while 5 mg/kg yohimbine decreased, reacquisition of oxycodone-induced place preference. A follow-up study (n = 30) further indicated that the effect of yohimbine was specific to reacquisition. The observation that yohimbine can enhance reacquisition of oxycodone seeking supports the hypothesis that stress can facilitate learning processes involved in the unfolding of relapse.

Yohimbine does not affect opioid receptor activation but prevents adenylate cyclase regulation by morphine in NG108-15 cells

Aims Yohimbine has been shown to modulate the pharmacological actions of opioid drugs in a way that could be of potential therapeutic interest. This work tries to study if this interaction involves the impairment of opioid receptor activation at the cellular level by studying the effects of morphine and yohimbine on NG108-15 neuroblastoma x glioma hybrid cells. Main methods [ 35S]GTPγS binding assays were performed to study δ-opioid and α 2B-adrenoceptor activation by opioid and adrenoceptor agonists in the presence and absence of yohimbine. The effect of morphine was also studied after 6 h pre-incubations with morphine, yohimbine and combinations of these drugs taking into account previous results showing an interaction between both drugs in these conditions. Forskolin-induced cAMP accumulation was also studied by immunoassay in cells incubated with morphine for 6 h in the presence and absence of naloxone and yohimbine. Key findings Yohimbine behaved as a competitive antagonist/inverse agonist on α 2B-adrenoceptors but did not modify G-protein activation by morphine, either in acute conditions or after 6 h of incubation. However, morphine-induced inhibition of cAMP accumulation was prevented both by naloxone and yohimbine when these drugs were present in the incubation medium. Significance Yohimbine seems to desensitise adenylate cyclase to the inhibitory effect of opioid-activated G proteins. This cellular effect could underlie the antagonistic actions of yohimbine on many pharmacological effects of the opioid both in vitro and in vivo.

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 50mg/kg daily for 7days 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.

Effect of Tizanidine, Rilmenidine, and Yohimbine on Naloxon-Induced Morphine Withdrawal Syndrome in Mice

In this study using clonidine (a mixed α 2 /I 1 receptors agonist), tizanidine (pure α 2 -receptor agonist), rilmenidine (I 1 receptor agonist) and yohimbine (α 2 -receptor antagonist), we tried to clarify the role of imidazoline and α 2 -receptors in morphine withdrawal syndrome. Morphine-dependence was induced by administration of increasing doses of morphine in mice. After the last administration of morphine, clonidine (0.3 mg/kg, i.p.), tizanidine (1 and 2 mg/kg, i.p.) and rilmenidine (1.5 and 3 mg/kg, i.p.), with / without pretreatment with yohimbine (1 mg/kg, i.p.) were administered 30 min before naloxone (5 mg/kg, i.p.) challenge. Withdrawal symptoms including: jumping, ptosis, piloerection, tremor and diarrhea were recorded. Rilmenidine (3 mg/kg) decreased naloxone-induced jumping and this effect was partially inhibited by yohimbine. Rilmenidine (1.5 mg/kg), tizanidine and clonidine had no significant effect on jumping. None of drugs influenced ptosis. All drugs increased piloerection and decreased diarrhea. Clonidine and tizanidine decreased tremor. We conclude that Imidazoline receptors as well as α 2 receptors are involved in morphine withdrawal symptoms and yohimbine as an α 2 -antagonist can suppress at least some effects of imidazoline agonists. It is suggested that α 2 -receptors are located down-stream to imidazoline receptors and their blockade can inhibit imidazoline effects.

Role of dorsal medial prefrontal cortex dopamine D1-family receptors in relapse to high-fat food seeking induced by the anxiogenic drug yohimbine.

In humans, relapse to maladaptive eating habits during dieting is often provoked by stress. In rats, the anxiogenic drug yohimbine, which causes stress-like responses in both humans and nonhumans, reinstates food seeking in a relapse model. In this study, we examined the role of medial prefrontal cortex (mPFC) dopamine D1-family receptors, previously implicated in stress-induced reinstatement of drug seeking, in yohimbine-induced reinstatement of food seeking. We trained food-restricted rats to lever press for 35% high-fat pellets every other day (9-15 sessions, 3 h each); pellet delivery was accompanied by a discrete tone-light cue. We then extinguished operant responding for 10-16 days by removing the pellets. Subsequently, we examined the effect of yohimbine (2 mg/kg, i.p.) on reinstatement of food seeking and Fos (a neuronal activity marker) induction in mPFC. We then examined the effect of systemic injections of the D1-family receptor antagonist SCH23390 (10 μg/kg, s.c.) on yohimbine-induced reinstatement and Fos induction, and that of mPFC SCH23390 (0.5 and 1.0 μg/side) injections on this reinstatement. Yohimbine-induced reinstatement was associated with strong Fos induction in the dorsal mPFC and with weaker Fos induction in the ventral mPFC. Systemic SCH23390 injections blocked both yohimbine-induced reinstatement and mPFC Fos induction. Dorsal, but not ventral, mPFC injections of SCH23390 decreased yohimbine-induced reinstatement of food seeking. In addition, dorsal mPFC SCH23390 injections decreased pellet-priming-induced reinstatement, but had no effect on ongoing high-fat pellet self-administration or discrete-cue-induced reinstatement. Results indicate a critical role of dorsal mPFC dopamine D1-family receptors in stress-induced relapse to palatable food seeking, as well as relapse induced by acute re-exposure to food taste, texture, and smell.

Yohimbine Increases Impulsivity Through Activation of cAMP Response Element Binding in the Orbitofrontal Cortex

Stress can increase impulsivity and has a negative impact on psychiatric outcome. Norepinephrine is heavily implicated in responses to stress, and the alpha(2) antagonist yohimbine is used clinically to study this aspect of the stress response. Yohimbine induces mild anxiety and increases impulsivity in healthy volunteers but has more detrimental effects in some psychiatric populations, triggering mania in bipolar patients and drug craving in substance-dependent individuals. Understanding the mechanism by which yohimbine affects brain function could provide insight into the heightened reaction to stress in these patients. Yohimbine's effects were assessed in rats using the five-choice serial reaction time test of attention and impulse control. We then examined whether yohimbine altered activity of cyclic adenosine monophosphate response element binding (CREB) protein-a transcription factor implicated in the stress response-in brain areas that regulate impulsivity. The behavioral consequences of any changes in CREB activity were subsequently assessed using viral-mediated gene transfer to regionally overexpress CREB or the dominant negative antagonist mCREB. Yohimbine increased impulsive responding in rats and selectively increased CREB phosphorylation within the orbitofrontal cortex but not medial prefrontal cortex or nucleus accumbens. Overexpressing mCREB within the orbitofrontal cortex blocked yohimbine's effects on impulsivity, whereas overexpressing CREB in this region increased impulsive responding and potentiated the proimpulsive actions of yohimbine. These data suggest a novel molecular mechanism contributing to impulsivity that may be sensitive to stress. Such findings may improve our understanding of the neurobiological pathways linking the response to stress and impulsivity in both healthy and psychiatric populations.

Pharmacological facilitation of fear extinction and the search for adjunct treatments for anxiety disorders - the case of yohimbine

There is current interest in identifying drugs that facilitate fear extinction, as this form of learning is the basis of certain cognitive therapies for anxiety disorders. Following an initial report several years ago that the alpha2-adrenoreceptor antagonist yohimbine facilitated extinction in mice, more recent studies have shown mixed effects or even impairment. It has become clear that the effect of yohimbine on extinction depends on a number of factors, including genetic background, contextual variables and the presence of competing behaviors. To what extent theses effects of yohimbine are mediated through the alpha2-adrenoreceptor, as opposed to other sites of action, is also uncertain. More work is needed before this drug can be approved as a pharmacological adjunct for extinction-based therapies. More generally, the case of yohimbine may serve as a model for the development of other extinction facilitators.

Yohimbin, ein Alpha-2-Antagonist: Literaturübersicht zu psychiatrisch relevanten Wirkungen und Nebenwirkungen mit aktuellem Fallbericht

We describe a 21-year old female patient who had taken the alpha-2-antagonist yohimbine for weight-loss. The patient reported alterations in alcohol- and cocaine-seeking along with changes in defensive behaviour, including suicidal tendencies. Pre-clinical and clinical studies are discussed, which support the hypothesis of a causal relationship. We added an overview of relevant psychiatric effects and side effects of yohimbine.

Yohimbine relaxes the human corpus cavernosum through a non-adrenergic mechanism involving the activation of K+ATP-dependent channels

The mechanism by which yohimbine relaxes the human corpus cavernosum remains unclear. Using the human corpus cavernosum strips immersed in isometric baths containing Krebs-Henseleit solution, this study investigates the effect of yohimbine on the relaxation of the human corpus cavernosum through nitrergic pathways involving the activation of ATP-dependent potassium channels (K(ATP)). The maximal relaxation induced by yohimbine in the human corpus cavernosum strips pre-contracted with phenylephrine was 100+/-0% and only 30.5+/-5.0% when they were pre-contracted with 60-mM potassium (K(+)) solution. The maximal relaxation induced by yohimbine in phenylephrine pre-contracted tissues was significantly inhibited by tetrodotoxin, 1H-[1,2,4] oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) or 7-nitroindazole (43.6, 36.1 and 42.6%, respectively). Neither the combination charybdotoxin-apamin nor tetraethylammonium altered the response of the human corpora cavernosa strips to yohimbine. Nevertheless, glibenclamide decreased the maximum relaxant response to yohimbine by 29.8% (P<0.05; n=12). The results suggest that yohimbine relaxes the human corpus cavernosum by a non-adrenergic, non-cholinergic mechanism, probably activating the nitrergic-soluble guanylate cyclase (NO-sGc) pathway and K(ATP).

Interacting noradrenergic and corticosteroid systems shift human brain activation patterns during encoding

Emotionally arousing experiences are usually well retained, an effect that depends on the release of adrenal stress hormones. Animal studies have shown that corticosterone and noradrenaline – representing the two main stress hormone systems – act in concert to enhance memory formation by actions involving the amygdala, hippocampus and prefrontal cortex (PFC). Here we test whether interactions between these two stress hormone systems also affect human memory formation as well as the associated pattern of brain activation. To this end, forty-eight male human subjects received hydrocortisone, yohimbine or both before presentation of emotional and neutral pictures. Activity in the amygdala, hippocampus and PFC was monitored with functional Magnetic Resonance Imaging (fMRI) during encoding of these stimuli, when hormonal levels were elevated. Memory performance was tested 1 week later. We investigated whether an increased level of one of the two hormone systems would lead to differential effects compared to the combined application of the drugs on brain activation and memory performance. We report that the application of cortisol led to an overall enhancing effect on recognition memory, with no significant additional effect of yohimbine. However, during encoding the brain switched from amygdala/hippocampus activation with either hormone alone, to a strong deactivation of prefrontal areas under the influence of the combination of both exogenous hormones. Although we did not find evidence that exogenous stimulation of the noradrenergic and corticosteroid systems led to significant interaction effects on memory performance in this experiment, we conclude that stress hormone levels during encoding did differentially determine the activation pattern of the brain circuits here involved.

Yohimbine prevents the effect of morphine on the redox status of neuroblastoma×glioma NG108-15 cells

The alpha(2)-adrenoceptor antagonist yohimbine is known to interact with the effects of opioid receptor agonists in vivo, and thus could modulate the action of morphine-like analgesics. The focus of the present work was to further study these interactions in a cell culture endowed with opioid and alpha(2)-adrenoceptors in order to know if they could happen at the cellular level. In a first step, incubation with morphine (10microM) or the delta opioid agonist DPDPE (1microM) for 6h was shown to decrease the reduction of (4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium (MTT) by NG108-15 neuroblastomaxglioma hybrid cells in a naloxone-sensitive manner, thus showing that the opioids affect the redox status of the cells in a delta receptor-mediated way. Further experiments with 2-24h incubation periods were subsequently performed with morphine 0.1microM, 10microM and 1mM and several tests to confirm the effects on metabolism (MTT, Alamar Blue tests) to examine the potential toxic consequences (neutral red test, trypan blue exclusion assay, LDH test, caspase 3/7 activity) and to study the potential effect of yohimbine on morphine toxicity. These studies confirmed that incubation with morphine (0.1microM and 10microM) affected to a similar extent the redox status of the cells, an effect that did not translated into significant cell death and was transient since completely disappeared after 24h of incubation. Morphine 1mM was much more toxic than the lower concentrations. Yohimbine effectively prevented the effects of the lower concentrations of morphine when added to the incubation medium at 10microM, a concentration devoid of significant toxicity. It seems that the exposure to pharmacologically relevant concentrations of morphine gives rise to short-term metabolic alterations of NG108-15 cells mediated by delta receptors and also sensitive to alpha(2)-adrenoceptor blockade; therefore, the interactions previously described in vivo between opioid and alpha(2)-adrenoceptor ligands do not necessarily require the presence of functional neuronal networks and they could happen at the cellular level.

Diminution of ejaculatory capacity induced by frequent ejaculation in dogs: prevention and reversal by yohimbine.

The effect of yohimbine, an alpha-2 adrenoceptor antagonist, on diminished ejaculatory capacity induced by frequent ejaculation was investigated in dogs. Ejaculation was elicited by manual penile stimulation (for 5 min) 5-8 times every 30 min. The amount of ejaculate produced by the stimulation was drastically reduced during a period of frequent ejaculation in a frequency-dependent manner. When administered immediately after the first ejaculation, yohimbine (0.1 mg kg-1, i.p.) completely prevented the decrease in the amount of ejaculate produced in the succeeding ejaculation. Moreover, similar treatment with yohimbine immediately after the fifth ejaculation when the dogs displayed a greatly reduced ejaculatory capacity restored the capacity to the initial level. In addition, yohimbine increased the total number of sperm produced during a period of frequent ejaculation. These data corroborate our previous finding that yohimbine at a low dose has a stimulatory effect on ejaculatory function in dogs. The present study also indicates that an alpha-2 adrenergic mechanism may be involved in the diminution of ejaculatory capacity induced by frequent ejaculation.