Yohimbine Inhibits PDGF-Induced Vascular Smooth Muscle Cell Proliferation and Migration via FOXO3a Factor.

Yohimbine (YHB) has been reported to possess anti-inflammatory, anticancer, and cardiac function-enhancing properties. Additionally, it has been reported to inhibit the proliferation, migration, and neointimal formation of vascular smooth muscle cells (VSMCs) induced by platelet-derived growth factor (PDGF) stimulation by suppressing the phospholipase C-gamma 1 pathway. However, the transcriptional regulatory mechanism of YHB controlling the behavior of VSMCs is not fully understood. In this study, YHB downregulated the expression of cell cycle regulatory proteins, such as proliferating cell nuclear antigen (PCNA), cyclin D1, cyclin-dependent kinase 4 (CDK4), and cyclin E, by modulating the transcription factor FOXO3a in VSMCs induced by PDGF. Furthermore, YHB decreased p-38 and mTOR phosphorylation in a dose-dependent manner. Notably, YHB significantly reduced the phosphorylation at Y397 and Y925 sites of focal adhesion kinase (FAK), and this effect was greater at the Y925 site than Y397. In addition, the expression of paxillin, a FAK-associated protein known to bind to the Y925 site of FAK, was significantly reduced by YHB treatment in a dose-dependent manner. A pronounced reduction in the migration and proliferation of VSMCs was observed following co-treatment of YHB with mTOR or p38 inhibitors. In conclusion, this study shows that YHB inhibits the PDGF-induced proliferation and migration of VSMCs by regulating the transcription factor FOXO3a and the mTOR/p38/FAK signaling pathway. Therefore, YHB may be a potential therapeutic candidate for preventing and treating cardiovascular diseases such as atherosclerosis and vascular restenosis.

Effects of stress-related neuromodulators on amygdala and hippocampus resting state functional connectivity.

BACKGROUND: The human stress response is characterized by increases in neuromodulators, including norepinephrine (NE) and cortisol. Both neuromodulators can enter the brain and affect neurofunctional responses. Two brain areas associated with stress are the amygdala and the hippocampus. The precise influence of NE and cortisol on the amygdala and hippocampal resting state functional connectivity (RSFC) is poorly understood. AIMS: To investigate the influence of NE and cortisol on the amygdala and hippocampal RSFC. METHODS: We recruited 165 participants who received 10 mg yohimbine and/or 10 mg hydrocortisone in a randomized, placebo-controlled design. With seed-based analyses, we compared RSFC of the hippocampus and amygdala separately between the three groups that received medication versus placebo. RESULTS: We found no differences between yohimbine and placebo condition or between hydrocortisone and placebo condition regarding amygdala or hippocampal FC. Compared with placebo, the yohimbine/hydrocortisone condition showed increased amygdala and hippocampal RSFC with the cerebellum. Also, they had increased hippocampal RSFC with the amygdala and cerebral white matter. DISCUSSION: The group with elevated NE and cortisol showed significantly increased RSFC between the amygdala, hippocampus, and cerebellum compared to placebo. These three brain areas are involved in associative learning and emotional memory, suggesting a critical role for this network in the human stress response. Our results show that NE and cortisol together may influence the strength of this association. Compared to placebo, we found no differences in the groups receiving only one medication, suggesting that increasing one neuromodulator alone may not induce differences in neurofunctional responses. The study procedure has been registered at clinicaltrials.gov (ID: NCT04359147).

Effect of thymoquinone on acetic acid-induced visceral nociception in rats: role of central cannabinoid and α2-adrenergic receptors.

Thymoquinone (TQ) is the main biologically active substance of Nigella sativa (black seeds). It has anti-cancer, anti-inflammatory, anti-diabetic, anti-oxidative and anti-nociceptive properties. This study was aimed to explore the effect of TQ on acetic acid-induced visceral nociception. The central mechanisms of the effect of TQ were investigated using cannabinergic (AM251) and α2-adrenergic (yohimbine [Yoh]) antagonists. The lateral ventricle of the brain was cannulated for intracerebroventricular (ICV) injections. Visceral nociception was induced by intra-peritoneal (IP) injection of acetic acid (1.00% in a volume of 1.00 mL). Measuring the latency time to the first writhing appearance and counting the number of writhing in 5-min intervals for a period of 60 min were performed. Locomotor activity was determined using an open-field test. Oral administration (PO) of 2.50 and 10.00 mg kg-1 TQ increased the latency time to the first writhing appearance and decreased the number of writhing. The AM251 (5.00 µg per rat; ICV) and Yoh (5.00 µg per rat; ICV) partially prevented TQ (10.00 mg kg-1; PO)-induced anti-nociception. Locomotor activity was not altered by these treatments. The results of the present study showed that TQ had the ability to reduce visceral nociception caused by IP injection of acetic acid. The central mechanisms of this action of TQ might be partially mediated by cannabinergic and α2-adrenegic receptors.

Beyond the Buzz: The Fatal Consequences of Caffeine Overconsumption.

Caffeine is a naturally occurring stimulant present in dozens of plant species including Coffea arabica and Camellia sinensis, from which we obtain coffee and tea, respectively. It is one of the world's most widely consumed psychoactive substances frequently used to increase alertness, elevate mood, and ward off fatigue. In traditional preparations, caffeine is generally well-tolerated by the consumer. However, complications can arise with the addition of caffeine to products like energy drinks, medications, and supplements. Furthermore, with pure caffeine accessible online, a consumer may unknowingly or inadvertently consume caffeine in dangerous amounts. Symptoms of caffeine toxicity include classic CNS stimulation side effects such as agitation, insomnia, gastrointestinal distress, tachycardia, seizures, and death in extreme cases. To evaluate concentrations of toxicological significance, caffeine cases were assessed at a large reference laboratory (NMS Labs). From 2019-2023, 406 blood cases underwent confirmation testing via LC-MS-MS; the mean and median caffeine concentrations were 35 µg/mL and 4.8 µg/mL, respectively. While most caffeine-containing cases indicate traditional use in the general population with concentrations below 25 µg/mL (62%, N = 254), 10% (N=42) of the cases were greater than 100 µg/mL, indicating levels which may contribute to a fatal outcome. To gain insight into the significance of caffeine in determining the cause and manner of death, cases with various manners of death are presented. Despite being one of the most common toxicological findings in medicolegal death investigations, caffeine is often overlooked. Screening results should undergo scrutiny, and confirmation testing should be considered in cases where caffeine intoxication prominently features in the case history or scene investigation.

A Comparative Study of the Antiemetic Effects of α2-Adrenergic Receptor Agonists Clonidine and Dexmedetomidine against Diverse Emetogens in the Least Shrew (Cryptotis parva) Model of Emesis.

In contrast to cats and dogs, here we report that the α2-adrenergic receptor antagonist yohimbine is emetic and corresponding agonists clonidine and dexmedetomidine behave as antiemetics in the least shrew model of vomiting. Yohimbine (0, 0.5, 0.75, 1, 1.5, 2, and 3 mg/kg, i.p.) caused vomiting in shrews in a bell-shaped and dose-dependent manner, with a maximum frequency (0.85 ± 0.22) at 1 mg/kg, which was accompanied by a key central contribution as indicated by increased expression of c-fos, serotonin and substance P release in the shrew brainstem emetic nuclei. Our comparative study in shrews demonstrates that clonidine (0, 0.1, 1, 5, and 10 mg/kg, i.p.) and dexmedetomidine (0, 0.01, 0.05, and 0.1 mg/kg, i.p.) not only suppress yohimbine (1 mg/kg, i.p.)-evoked vomiting in a dose-dependent manner, but also display broad-spectrum antiemetic effects against diverse well-known emetogens, including 2-Methyl-5-HT, GR73632, McN-A-343, quinpirole, FPL64176, SR141716A, thapsigargin, rolipram, and ZD7288. The antiemetic inhibitory ID50 values of dexmedetomidine against the evoked emetogens are much lower than those of clonidine. At its antiemetic doses, clonidine decreased shrews' locomotor activity parameters (distance moved and rearing), whereas dexmedetomidine did not do so. The results suggest that dexmedetomidine represents a better candidate for antiemetic potential with advantages over clonidine.

Enterococcus-derived tyramine hijacks α2A-adrenergic receptor in intestinal stem cells to exacerbate colitis.

Inflammatory bowel disease (IBD) is characterized by dysbiosis of the gut microbiota and dysfunction of intestinal stem cells (ISCs). However, the direct interactions between IBD microbial factors and ISCs are undescribed. Here, we identify α2A-adrenergic receptor (ADRA2A) as a highly expressed GPCR in ISCs. Through PRESTO-Tango screening, we demonstrate that tyramine, primarily produced by Enterococcus via tyrosine decarboxylase (tyrDC), serves as a microbial ligand for ADRA2A. Using an engineered tyrDC-deficient Enterococcus faecalis strain and intestinal epithelial cell-specific Adra2a knockout mice, we show that Enterococcus-derived tyramine suppresses ISC proliferation, thereby impairing epithelial regeneration and exacerbating DSS-induced colitis through ADRA2A. Importantly, blocking the axis with an ADRA2A antagonist, yohimbine, disrupts tyramine-mediated suppression on ISCs and alleviates colitis. Our findings highlight a microbial ligand-GPCR pair in ISCs, revealing a causal link between microbial regulation of ISCs and colitis exacerbation and yielding a targeted therapeutic approach to restore ISC function in colitis.

Dexmedetomidine, an alpha-2 adrenoceptors agonist, provides a neuroprotective effect for dopaminergic neurons in the substantia nigra and attenuates glucose imbalance in the 6-hydroxydopamine animal model of Parkinson's disease.

INTRODUCTION: Studies have shown that dexmedetomidine (DEX, an a2-adrenoceptors agonist) provides a neuroprotective effect and influences blood glucose levels. Here, we evaluated the effect of prolonged treatment with low doses of DEX on the survival rate of dopaminergic (DAergic) neurons in the substantia nigra and also serum glucose levels in 6-hydroxydopamine (6-OHDA) - induced Parkinson's disease (PD) in the rat. MATERIAL AND METHODS: The neurotoxin of 6-OHDA was injected into the medial forebrain bundle by stereotaxic surgery. DEX (25 and 50 µg/kg, i.p) and yohimbine, an a2-adrenoceptor antagonist (1 mg/kg, i.p) were administered before the surgery to the 13 weeks afterward. Apomorphine-induced rotational tests and blood sampling were carried out before the surgery and multiple weeks after that. Thirteen weeks after the surgery, the rats' brain was transcardially perfused to assess the survival rate of DAergic neurons using the tyrosine hydroxylase (TH) immunohistochemistry. RESULTS: DEX remarkably attenuated the severity of rotational behavior and reversed the progress of the PD. It also increased the number of TH-labeled neurons by up to 60%. The serum glucose levels in 6-OHDA-received rats did not change in the third and seventh weeks after the surgery but decreased significantly in the thirteenth week. Treatment with DEX prevented this decrement in glucose levels. On the other hand, Treatment with yohimbine did not affect PD symptoms and glucose levels. CONCLUSION: Our data indicate that DEX through neuroprotective activity attenuates the severity of 6-OHDA-induced PD in rats. DEX might also prevent hypoglycemia during the progress of the PD.

The effects of yohimbine and hydrocortisone on selective attention to fearful faces: An fMRI study.

INTRODUCTION: Selective attention to salient emotional information can enable an advantage in the face of danger. The present study aims to investigate the influence of the stress neuromodulators, norepinephrine and cortisol, on selective attention processes to fearful faces and its neuronal activation. METHODS AND MATERIALS: We used a randomized, double-blind, placebo-controlled design. 167 healthy men between 18 and 35 years (mean [SD] age: 25.23 [4.24] years) participated in the study. Participants received either: (A) yohimbine (n= 41), (B) hydrocortisone (n = 41), (C) yohimbine and hydrocortisone (n = 42) or (D) placebo only (n= 43) and participated in a dot-probe task with fearful and neutral faces in an fMRI scanner. RESULTS: We found an attentional bias toward fearful faces across all groups and related neuronal activation in the left cuneus. We did not find any differences between experimental treatment groups in selective attention and its neuronal activation. DISCUSSION: Our results provide evidence that fearful faces lead to an attentional bias with related neuronal activation in the left cuneus. We did not replicate formerly reported activation in the amygdala, intraparietal sulcus, dorsal anterior cingulate cortex, and thalamus. Suitability of the dot-probe task for fMRI studies and insignificant treatment effects are discussed.

Extinction and reinstatement of methamphetamine-induced conditioned place preference in zebrafish.

Conditioned place preference (CPP) paradigm in zebrafish has been used to measure drug reward, but there is limited research on CPP reinstatement to determine relapse vulnerability. The present study aimed to investigate extinction and reinstatement of methamphetamine (MA)-induced CPP in zebrafish and evaluate the model's predictive validity. Zebrafish received different doses of MA (0-60 mg/kg) during CPP training. The preferred dose of MA at 40 mg/kg was used for extinction via either confined or nonconfined procedures. The extinguished CPP was reinstated by administering a priming dose of MA (20 mg/kg) or various stressors. To assess persistent susceptibility to reinstatement, MA CPP and reinstatement were retested following 14 days of abstinence. In addition, the effects of SCH23390, naltrexone, and clonidine on MA CPP during acquisition, expression, or reinstatement phases were monitored. MA induced CPP in a dose-dependent manner. Both nonconfined and confined extinction procedures time-dependently reduced the time spent on the MA-paired side. A priming dose of MA, chasing stress, or yohimbine reinstated the extinguished CPP. After 14 days of abstinence, the MA CPP remained extinguished and was significantly reinstated by MA priming or chasing stress. Similar to the observations in rodents, SCH23390 suppressed the acquisition of MA CPP, naltrexone reduced the expression and MA priming-induced reinstatement, while clonidine prevented stress-induced reinstatement of MA CPP. This work expanded the zebrafish CPP paradigm to include extinction and reinstatement phases, demonstrating predictive validity and highlighting its potential as a valuable tool for exploring drug relapse.

Measuring neuron-regulated immune cell physiology via the alpha-2 adrenergic receptor in an ex vivo murine spleen model.

The communication between the nervous and immune systems plays a crucial role in regulating immune cell function and inflammatory responses. Sympathetic neurons, which innervate the spleen, have been implicated in modulating immune cell activity. The neurotransmitter norepinephrine (NE), released by sympathetic neurons, influences immune cell responses by binding to adrenergic receptors on their surface. The alpha-2 adrenergic receptor (α2AR), expressed predominantly on sympathetic neurons, has received attention due to its autoreceptor function and ability to modulate NE release. In this study, we used fast-scan cyclic voltammetry (FSCV) to provide the first subsecond measurements of NE released in the white pulp region of the spleen and validated it with yohimbine, a known antagonist of α2AR. For further application of FSCV in neuroimmunology, we investigated the extent to which subsecond NE from sympathetic neurons is important for immune cell physiology and cytokine production, focusing on tumor necrosis factor-alpha (TNF-α), interleukin-10 (IL-10), and interleukin-6 (IL-6). Our findings provide insights into the regulatory mechanisms underlying sympathetic-immune interactions and show the significance of using FSCV, a traditional neurochemistry technique, to study these neuroimmune mechanisms.

Xylazine potentiates the lethal but not the rewarding effects of fentanyl in mice.

BACKGROUND: Fentanyl is commonly laced with xylazine. People who use this combination report heightened effects, but it also increases death risk. Although no medication has been approved to counteract overdoses produced by fentanyl and xylazine, naloxone is frequently used. This paper studies the preclinical rewarding and lethal effects of fentanyl combined with xylazine and the efficacy of yohimbine or naloxone to prevent death. METHODS: Male Swiss Webster mice were treated with (in mg/kg, i.p.) xylazine (0.3, 1, 3, or 5.6), fentanyl (0.01, 0.3, or 0.1), or 1 xylazine plus 0.01 (non-effective) or 0.1 (effective) fentanyl doses during the conditioned-place preference (CPP) test. In addition, independent groups received (in mg/kg, i.p.): xylazine (31.6, 60, 74.2, or 100), fentanyl (3.1 or 10), or both substances at two doses: 31.6 xylazine + 3.1 fentanyl, or 60 xylazine + 10 fentanyl to analyze lethal effects. We determined whether yohimbine or naloxone (each medication tested at 10 or 30mg/kg) could prevent the lethality produced by fentanyl/xylazine combinations. Female mice were also tested in key experiments. RESULTS: Xylazine neither induced CPP nor altered fentanyl's rewarding effects. In contrast, lethality was potentiated when fentanyl was combined with xylazine. Naloxone, but not yohimbine, effectively prevented the lethality of the fentanyl/xylazine combinations. CONCLUSIONS: At the doses tested, xylazine does not increase the rewarding effect of fentanyl on the CPP in male mice but potentiates the risk of fatal overdose in male and female mice. A high naloxone dose prevents death induced by coadministration of fentanyl and xylazine in both sexes.

Chemical Reactions of Indole Alkaloids That Enable Rapid Access to New Scaffolds for Discovery.

This graphical review provides a concise overview of indole alkaloids and chemical reactions that have been reported to transform both these natural products and derivatives to rapidly access new molecular scaffolds. Select biologically active compounds from these synthetic efforts are reported herein.

Locus coeruleus inhibition of vibrissal responses in the trigeminal subnucleus caudalis are reduced in a diabetic mouse model.

Diabetic neuropathy is the loss of sensory function beginning distally in the lower extremities, which is also characterized by pain and substantial morbidity. Furthermore, the locus coeruleus (LC) nucleus has been proposed to play an important role in descending pain control through the activation of α2-noradrenergic (NA) receptors in the spinal dorsal horn. We studied, on control and diabetic mice, the effect of electrical stimulation of the LC nucleus on the tactile responses in the caudalis division of the spinal trigeminal nucleus (Sp5C), which is involved in the relay of orofacial nociceptive information. Diabetes was induced in young adult C57BL/6J mice with one intraperitoneal injection of streptozotocin (50 mg/kg) daily for 5 days. The diabetic animals showed pain in the orofacial area because they had a decrease in the withdrawal threshold to the mechanical stimulation in the vibrissal pad. LC electrical stimulation induced the inhibition of vibrissal responses in the Sp5C neurons when applied at 50 and 100 ms before vibrissal stimulation in the control mice; however, the inhibition was reduced in the diabetic mice. These effects may be due to a reduction in the tyrosine hydroxylase positive (TH+) fibers in the Sp5C, as was observed in diabetic mice. LC-evoked inhibition was decreased by an intraperitoneal injection of the antagonist of the α2-NA receptors, yohimbine, indicating that it was due to the activation of α2-NA receptors. The decrease in the LC-evoked inhibition in the diabetic mice was partially recovered when clonidine, a non-selective α2-agonist, was injected intraperitoneally. These findings suggest that in diabetes, there is a reduction in the NA inputs from the LC in the Sp5C that may favor the development of chronic pain.

Oxytocin Attenuates Yohimbine-Induced Reinstatement of Alcohol-Seeking in Female Rats via the Central Amygdala.

Alcohol use disorder is a significant public health concern, further exacerbated by an increased risk of relapse due to stress. In addition, factors such as biological sex may contribute to the progression of addiction, as females are especially susceptible to stress-induced relapse. While there have been many studies surrounding potential pharmacological interventions for male stress-induced ethanol reinstatement, research regarding females is scarce. Recently, the neuropeptide oxytocin has gained interest as a possible pharmacological intervention for relapse. The present study examines how oxytocin affects yohimbine-induced reinstatement of ethanol-seeking in female rats using a self-administration paradigm. Adult female rats were trained to press a lever to access ethanol in daily self-administration sessions. Rats then underwent extinction training before a yohimbine-induced reinstatement test. Rats administered with yohimbine demonstrated significantly higher lever response indicating a reinstatement of ethanol-seeking behavior. Oxytocin administration, both systemically and directly into the central amygdala, attenuated the effect of yohimbine-induced reinstatement of ethanol-seeking behavior. The findings from this study establish that oxytocin is effective at attenuating alcohol-relapse behavior mediated by the pharmacological stressor yohimbine and that this effect is modulated by the central amygdala in females. This provides valuable insight regarding oxytocin's potential therapeutic effect in female stress-induced alcohol relapse.

The effects of hydrocortisone and yohimbine on human behavior in approach-avoidance conflicts.

RATIONALE: Balancing approach of positive and avoidance of negative stimuli is essential when faced with approach-avoidance conflicts, e.g., situations with both positive and negative outcomes. This balance is disturbed in several mental disorders, e.g., excessive avoidance in anxiety disorders, and heightened approach in substance use disorders. Since stress is assumed to impact these disorders' etiology and maintenance, it seems crucial to understand how stress influences behavior in approach-avoidance conflicts. Indeed, some studies suggested altered approach-avoidance behavior under acute stress, but the mechanism underlying these effects is unknown. OBJECTIVES: Investigate how the pharmacological manipulation of major stress mediators (cortisol and noradrenaline) influences task-based approach-avoidance conflict behavior in healthy individuals. METHODS: Ninety-six participants (48 women, 48 men) received either 20mg hydrocortisone, 20mg yohimbine, both, or placebo before performing a task targeting foraging under predation in a fully crossed double-blind between-subject design. Moreover, we investigated effects of gender and endogenous testosterone and estradiol levels on approach-avoidance behavior. RESULTS: While biological stress markers (cortisol concentration, alpha amylase activity) indicated successful pharmacological manipulation, behavior in approach-avoidance conflicts was not affected as expected. Although yohimbine administration affected risky foraging latency under predation, we found no main effect of hydrocortisone or their interaction on behavior. In contrast, we found gender differences for almost all behavioral outcome measures, which might be explained by differences in endogenous testosterone levels. CONCLUSIONS: The investigated major stress mediators were not sufficient to imitate previously shown stress effects on approach-avoidance conflict behavior. We discuss potential reasons for our findings and implications for future research.

Mifepristone as a pharmacological intervention for stress-induced alcohol craving: A human laboratory study.

Preclinical and clinical work suggests that mifepristone may be a viable treatment for alcohol use disorder (AUD). This was a Phase 1/2, outpatient, cross-over, randomized, double-blind, placebo-controlled trial with non-treatment-seeking individuals with AUD (N = 32). We assessed safety, alcohol craving and consumption, after 1-week mifepristone 600 mg/day administration, in a human laboratory study comprised of a single oral yohimbine administration (32.4 mg), a cue-reactivity procedure and alcohol self-administration. Safety was monitored by adverse events and hemodynamic parameters, alcohol craving by alcohol craving questionnaire and cue-induced saliva output. During the alcohol self-administration, we assessed alcohol pharmacokinetics, subjective effects and consumption. Outcomes were assessed using Generalized Estimating Equations and mediation analysis. Mild-moderate adverse events were reported in both conditions. There was no statistically significant difference between mifepristone and placebo in alcohol pharmacokinetics and subjective effects. Furthermore, blood pressure increased only in the placebo condition after the stress-induced laboratory procedures. Mifepristone, compared to placebo, significantly reduced alcohol craving and increased cortisol levels. Mifepristone-induced cortisol increase was not a mediator of alcohol craving. Mifepristone, compared to placebo, did not reduce alcohol consumption in the laboratory or in a naturalistic setting. This study successfully translated a developed preclinical procedure to a human laboratory study, confirming the safety of mifepristone in people with AUD and providing evidence to its role in reducing alcohol craving under stress procedures. The lack of effects on alcohol drinking may be related to the selection of non-treatment seekers and suggests future treatment-oriented trials should investigate mifepristone in people with AUD.

Emotion-related impulsivity moderates the role of arousal on reflection impulsivity.

Emotion-related impulsivity is an important behavioural phenotype in clinical psychology and public health. Here, we test the hypothesis that emotion-related impulsivity moderates the effects of arousal on cognition using pharmacological manipulation. Participants completed a measure of emotion-related impulsivity, four cognitive tasks tapping onto different facets of impulsive behaviours, and a blinded arousal manipulation using yohimbine hydrochloride, which acts on noradrenergic receptors. Our findings suggest that emotion-related impulsivity moderates the role of arousal on impulsive performance on the Information Sampling Task. As expected, more severe emotion-related impulsivity was related to more impulsive decisions in the yohimbine but not in the placebo group. Results provide some of the first experimental evidence that emotion-related impulsivity is related to differential behavioural responses in the face of high arousal. Despite this preliminary support, we discuss findings for one task that did not fit hypotheses, and provide suggestions for replication and extension.

Combined In Vivo Microdialysis and PET Studies to Validate [11C]Yohimbine Binding as a Marker of Noradrenaline Release.

The noradrenaline system attracts attention for its role in mood disorders and neurodegenerative diseases but the lack of well-validated methods impairs our understanding when assessing its function and release in vivo. This study combines simultaneous positron emission tomography (PET) and microdialysis to explore if [11C]yohimbine, a selective antagonist radioligand of the α2 adrenoceptors, may be used to assess in vivo changes in synaptic noradrenaline during acute pharmacological challenges. Anesthetised Göttingen minipigs were positioned in a head holder in a PET/CT device. Microdialysis probes were placed in the thalamus, striatum and cortex and dialysis samples were collected every 10 min. Three 90 min [11C]yohimbine scans were acquired: at baseline and at two timepoints after the administration of amphetamine (1-10 mg/kg), a non-specific releaser of dopamine and noradrenaline, or nisoxetine (1 mg/kg), a specific noradrenaline transporter inhibitor. [11C]yohimbine volumes of distribution (VT) were obtained using the Logan kinetic model. Both challenges induced a significant decrease in yohimbine VT, with time courses reflecting their different mechanisms of action. Dialysis samples revealed a significant increase in noradrenaline extracellular concentrations after challenge and an inverse correlation with changes in yohimbine VT. These data suggest that [11C]yohimbine can be used to evaluate acute variations in synaptic noradrenaline concentrations after pharmacological challenges.

Distribution of α2-Adrenergic Receptors in the Living Human Brain Using [11C]yohimbine PET.

The neurofunctional basis of the noradrenergic (NA) system and its associated disorders is still very incomplete because in vivo imaging tools in humans have been missing up to now. Here, for the first time, we use [11C]yohimbine in a large sample of subjects (46 healthy volunteers, 23 females, 23 males; aged 20-50) to perform direct quantification of regional alpha 2 adrenergic receptors' (α2-ARs) availability in the living human brain. The global map shows the highest [11C]yohimbine binding in the hippocampus, the occipital lobe, the cingulate gyrus, and the frontal lobe. Moderate binding was found in the parietal lobe, thalamus, parahippocampus, insula, and temporal lobe. Low levels of binding were found in the basal ganglia, the amygdala, the cerebellum, and the raphe nucleus. Parcellation of the brain into anatomical subregions revealed important variations in [11C]yohimbine binding within most structures. Strong heterogeneity was found in the occipital lobe, the frontal lobe, and the basal ganglia, with substantial gender effects. Mapping the distribution of α2-ARs in the living human brain may prove useful not only for understanding the role of the NA system in many brain functions, but also for understanding neurodegenerative diseases in which altered NA transmission with specific loss of α2-ARs is suspected.

Tyraminergic control of vitellogenin production and release in the blood-feeding insect, Rhodnius prolixus.

In insects, the biogenic amine tyramine (TA) has been shown to control several physiological processes. Recently, the involvement of the type 1 tyramine receptor (TAR1) in reproductive processes has been demonstrated in different insects. Here, we investigate the putative role of Rhodnius prolixus TAR1 (RpTAR1) in reproduction in female R. prolixus. RpTAR1 transcript was highly expressed in tissues associated with egg development. Moreover, after a blood meal, which is the stimulus for full egg development, RpTAR1 transcript was upregulated in the ovaries and in the fat body. After RNAi-mediated RpTAR1 knockdown, an ovarian phenotype characterized by the absence or reduction of egg production was observed. Furthermore, protein and Vg accumulation in the fat body was observed, suggesting an impairment in protein release from the fat body into the hemolymph. However, even though fewer eggs were produced and laid, there was no difference in hatching ratio of those laid, in comparison to the controls, indicating that the overall low protein uptake by the ovaries did not influence the viability of individual eggs produced. Interestingly, the eggs from dsTAR1-treated insects appeared more red, indicating a higher content of RHBP compared to the control. A higher colocalization between Vg and Rab11, a marker for the recycling endosome pathway, was observed after dsTAR1 injection, suggesting that a more active lysosome degradation pathway in response to the Vg accumulation may occur. In addition to the Vg accumulation in the fat body, dsTAR1 treatment altered JH pathway. However, it remains to be elucidated whether this event is either directly related to the RpTAR1 downregulation or for a consequence to the Vg accumulation. Lastly, the RpTAR1 action on Vg synthesis and release in the fat body was monitored in the presence or absence of yohimbine, the antagonist of TAR1, in an ex-vivo experiment. Yohimbine antagonises the TAR1 stimulated release of Vg. These results provide critical information concerning the role of TAR1 in Vg synthesis and release in R. prolixus. Furthermore, this work opens the way for further investigation into innovative methods for controlling R. prolixus.