In vitro evaluation of PET radiotracers for imaging synaptic density, the acetylcholine transporter, AMPA-tarp-γ8 and muscarinic M4 receptors in Alzheimer's disease.

Several therapeutics and biomarkers that target Alzheimer's disease (AD) are under development. Our clinical positron emission tomography (PET) research programs are interested in six radiopharmaceuticals to image patients with AD and related dementias, specifically [11C]UCB-J and [18F]SynVesT-1 for synaptic vesicle glycoprotein 2A as a marker of synaptic density, two vesicular acetylcholine transporter PET radiotracers: [18F]FEOBV and [18F]VAT, as well as the transmembrane AMPA receptor regulatory protein (TARP)-γ8 tracer, [18F]JNJ-64511070, and the muscarinic acetylcholine receptor (mAChR) M4 tracer [11C]MK-6884. The goal of this study was to compare all six radiotracers (labeled with tritium or 18F) by measuring their density variability in pathologically diagnosed cases of AD, mild cognitive impairment (MCI) and normal healthy volunteer (NHV) human brains, using thin-section in vitro autoradiography (ARG). Region of interest analysis was used to quantify radioligand binding density and determine whether the radioligands provide a signal-to-noise ratio optimal for showing changes in binding. Our preliminary study confirmed that all six radiotracers show specific binding in MCI and AD. An expected decrease in their respective target density in human AD hippocampus tissues compared to NHV was observed with [3H]UCB-J, [3H]SynVesT-1, [3H]JNJ-64511070, and [3H]MK-6884. This preliminary study will be used to guide human PET imaging of SV2A, TARP-γ8 and the mAChR M4 subtype for imaging in AD and related dementias.

Cell-based serum anticholinergic activity assay and working memory in cognitively healthy older adults before and after scopolamine: An exploratory study.

BACKGROUND: A new cell-based serum anticholinergic activity (cSAA) assay that measures anticholinergic activity specifically at muscarinic M1 receptors and eliminates many of the drawbacks of the existing assay was developed by our team. AIMS: We aimed to study the relationship between changes in working memory and executive function with changes in cSAA using the new assay in cognitively healthy older adults. METHODS: Cognitively healthy participants aged 50 years and above, received a single dose of 0.4 mg of intravenous scopolamine. Cognition and cSAA levels were measured before and 30 min after receiving scopolamine. Cognition was measured using the Cambridge Neuropsychological Test Automated Battery. RESULTS: Ten participants were recruited, and nine (mean age = 69.8, SD = 9.5, range 59-86 years) completed the study. Following scopolamine, participants experienced an increase in cSAA (cSAA pre = 0.90 ± 0.97 vs cSAA post = 12.0 ± 3.70 pmol/L; t-test (df = (8) = -9.5, p < 0.001). In addition, there was an association between change in cSAA and changes in working memory (Spearman's ρ = 0.68, p = 0.042) and executive function (Spearman's ρ = 0.72, p = 0.027). CONCLUSIONS: In our sample of cognitively healthy older adults, the new cSAA assay was able to quantify the scopolamine induced increase in anticholinergic load which correlated significantly with the observed decline in working memory and executive function.

Antidepressant activity of pharmacological and genetic deactivation of the small-conductance calcium-activated potassium channel subtype-3.

RATIONALE: The voltage-insensitive, small-conductance calcium-activated potassium (SK) channel is a key regulator of neuronal depolarization and is implicated in the pathophysiology of depressive disorders. OBJECTIVE: We ascertained whether the SK channel is impaired in the chronic unpredictable stress (CUS) model and whether it can serve as a molecular target of antidepressant action. METHODS: We assessed the depressive-like behavioral phenotype of CUS-exposed rats and performed post-mortem SK channel binding and activity-dependent zif268 mRNA analyses on their brains. To begin an assessment of SK channel subtypes involved, we examined the effects of genetic and pharmacological inhibition of the SK3 channel using conditional knockout mice and selective SK3 channel negative allosteric modulators (NAMs). RESULTS: We found that [125I]apamin binding to SK channels is increased in the prefrontal cortex and decreased in the hippocampus, an effect that was associated with reciprocal levels of zif268 mRNA transcripts indicating abnormal regional cell activity in this model. We found that genetic and pharmacological manipulations significantly decreased immobility in the forced swim test without altering general locomotor activity, a hallmark of antidepressant-like activity. CONCLUSIONS: Taken together, these findings link depression-related neural and behavioral pathophysiology with abnormal SK channel functioning and suggest that this can be reversed by the selective inhibition of SK3 channels.

A calcium fluorescence assay for quantification of cholinergic receptor activity of clinical drugs in serum - comparison with radioactive methods.

A new approach is described for quantifying cholinergic receptor activation status human blood samples, based on M1 receptor-driven mobilization of intracellular calcium stores. The assay identifies anticholinergic as well as agonist cholinergic receptor activity. As a cell-based procedure, the assay shares the high efficiency of recently developed M1 receptor binding protocols, but differs from the latter in relying on fluorescence rather than radioactivity measurements. The assay targets a true functional effect insofar as it reflects a time-dependent process of net changes in activation of cholinergic receptors. Results from experiments with M1-expressing CHO cells exposed to a fluorogenic dye and the standard cholinergic agonist carbachol revealed the assay's ability to isolate pure agonist effects of clinical compounds as well as the net effects of serum containing agonist and antagonist factors. The new protocol thus provides two additional quantitative indices of cholinergic receptor activity in human serum, namely pure agonistic effects and net agonist/antagonist effects. As such, it could constitute a very useful addition to efforts to quantify global cholinergic status in human serum in various clinical conditions. By relying on fluorescence measures it should also prove much more accessible than radioactivity-based protocols.

Relationships Between a New Cultured Cell-Based Serum Anticholinergic Activity Assay and Anticholinergic Burden Scales or Cognitive Performance in Older Adults.

OBJECTIVES: Anticholinergic burden has been associated with deleterious effects on cognition particularly in those with an underlying brain disorder. We developed a new assay based on cultured cells to measure serum anticholinergic activity (cSAA). We report on its relationships with established anticholinergic burden rating scales and cognitive assessments in older patients with mild cognitive impairment (MCI) or major depressive disorder (MDD) in remission or both. DESIGN: The study was cross sectional in nature. SETTING: This was a five-centre study conducted in Toronto, Canada. PARTICIPANTS: Serum samples were collected and cSAA levels were measured in 311 participants aged 60 years or older (154 with MCI, 57 with MDD, and 100 with MCI + MDD). MEASUREMENTS: The cSAA assay uses radio-ligand binding to cultured cells stably expressing the muscarinic M1 receptors, with an added procedure to remove potential confounds associated with serum proteins. Lists of medications were used to calculate Anticholinergic Burden and Anticholinergic Drug Scale total scores. Participants also completed a comprehensive cognitive battery. RESULTS: Higher cSAA levels were associated with higher anticholinergic burden and anticholinergic drug scale scores, and also with lower performance on executive function tests, after adjusting for age, gender, education, and diagnosis. CONCLUSIONS: These results support the use of the cSAA assay as a laboratory measure of anticholinergic burden.

Antidepressant action of transcranial direct current stimulation in olfactory bulbectomised adolescent rats.

BACKGROUND: Antidepressant drugs in adolescent depression are sometimes mired by efficacy issues and paradoxical effects. Transcranial direct current stimulation (tDCS) could represent an alternative. AIMS/METHODS: We tested the antidepressant action of prefrontal tDCS and paroxetine (20 mg/kg, intraperitoneal) in olfactory bulbectomised (OBX) adolescent rats. Using enzyme-linked immunosorbent assays and in situ hybridisation, we examined treatment-induced changes in plasma brain-derived neurotrophic factor (BDNF) and brain serotonin transporter (SERT) and 5-HT-1A mRNA. RESULTS: OBX-induced anhedonia-like reductions in sucrose preference (SP) correlated with open field (OF) hyperactivity. These were accompanied by decreased zif268 mRNA in the piriform/amygdalopiriform transition area, and increased zif268 mRNA in the hypothalamus. Acute paroxetine (2 days) led to a profound SP reduction, an effect blocked by combined tDCS-paroxetine administration. Chronic (14 days) tDCS attenuated hyperlocomotion and its combination with paroxetine blocked OBX-induced SP reduction. Correlations among BDNF, SP and hyperlocomotion scores were altered by OBX but were normalised by tDCS-paroxetine co-treatment. In the brain, paroxetine increased zif268 mRNA in the hippocampal CA1 subregion and decreased it in the claustrum. This effect was blocked by tDCS co-administration, which also increased zif268 in CA2. tDCS-paroxetine co-treatment had variable effects on 5-HT1A receptors and SERT mRNA. 5-HT1A receptor changes were found exclusively within depression-related parahippocampal/hippocampal subregions, and SERT changes within fear/defensive response-modulating brainstem circuits. CONCLUSION: These findings point towards potential synergistic efficacies of tDCS and paroxetine in the OBX model of adolescent depression via mechanisms associated with altered expression of BDNF, 5-HT1A, SERT and zif268 in discrete corticolimbic areas.

Global DNA methylation in suicidal ideation and suicide attempt in schizophrenia.

Suicidal behavior is influenced by many risk factors such as childhood trauma, stressful life events, genetic factors, and severe mental illnesses. Suicidal ideation is present in 50% of schizophrenia patients and is associated with an elevated risk of suicide attempt. Studies have shown that epigenetic mechanisms are associated with suicidal behavior in schizophrenia. Although several studies have suggested the importance of epigenetic factors in suicidal ideation and behavior, no studies have investigated global methylation in association with these two phenotypes. This study investigated global methylation level/change in association with current and emergent suicidal ideation and also with suicide attempt. Forty-seven schizophrenia patients were assessed for the association between global methylation and suicide attempt, and a subsample of these patients (n = 27) was assessed for current suicidal ideation. Afterwards, we performed a longitudinal analysis in which global methylation changes during a 3-month follow-up were compared between patients with and without emergent suicidal ideation. This methylation analysis did not find evidence for a significant association between global methylation and suicidal ideation or suicide attempt. To date, there are no robust biomarkers predicting suicidal ideation or behavior in psychotic patients. This study is the first to investigate global methylation in predicting suicidal ideation and behavior. Although we did not find evidence for an association between global methylation and these phenotypes, our findings may offer novel insights into the molecular mechanisms linked to suicide. Future investigation may measure global methylation in association with suicidal ideation or behavior in larger samples.

A Key Role for Prefrontocortical Small Conductance Calcium-Activated Potassium Channels in Stress Adaptation and Rapid Antidepressant Response.

The muscarinic acetylcholine receptor antagonist scopolamine elicits rapid antidepressant activity, but its underlying mechanism is not fully understood. In a chronic stress model, a single low-dose administration of scopolamine reversed depressive-like reactivity. This antidepressant-like effect was mediated via a muscarinic M1 receptor-SKC pathway because it was mimicked by intra-medial prefrontal cortex (intra-mPFC) infusions of scopolamine, of the M1 antagonist pirenzepine or of the SKC antagonist apamin, but not by the selective serotonin reuptake inhibitor (SSRI) antidepressant fluoxetine. Extracellular and whole-cell recordings revealed that scopolamine and ketamine attenuate the SKC-mediated action potential hyperpolarization current and rapidly enhance mPFC neuronal excitability within the therapeutically relevant time window. The SKC agonist 1-EBIO abrogated scopolamine-induced antidepressant activity at a dose that completely suppressed burst firing activity. Scopolamine also induced a slow-onset activation of raphe serotonergic neurons, which in turn was dependent on mPFC-induced neuroplasticity or excitatory input, since mPFC transection abolished this effect. These early behavioral and mPFC activational effects of scopolamine did not appear to depend on prefrontocortical brain-derived neurotrophic factor and serotonin-1A activity, classically linked to SSRIs, and suggest a novel mechanism associated with antidepressant response onset through SKC-mediated regulation of activity-dependent plasticity.

Rostrocaudal subregions of the ventral tegmental area are differentially impacted by chronic stress.

RATIONALE: The ventral tegmental area (VTA) is implicated in the pathophysiology of depression and addictive disorders and is subject to the detrimental effects of stress. Chronic stress may differentially alter the activity pattern of its different subregions along the rostrocaudal and dorsoventral axes, which may relate to the variable behavioral sensitivity to stress mediated by these subregions. OBJECTIVES: Here, chronic stress-exposed rats were tested for depressive-like reactivity. In situ hybridization for zif268 as a marker of neuronal activation was combined with in vivo single-unit recording of dopaminergic neurons to assess modifications in the activity of the rostral VTA (rVTA) and caudal VTA (cVTA). Changes in the expression of stress-responsive glucocorticoid receptors (GR) and brain-derived neurotrophic factor (BDNF) were also assessed. RESULTS: Stress-induced anhedonia-like, hyper-anxious, and passive-like responding were associated with reductions in dopaminergic burst activity in the cVTA and an increase in local GABAergic activity, particularly in GABAA receptor sensitivity. On the other hand, stress increased single-spiking activity, burst activity, and zif268 mRNA levels in the rVTA, which were associated with increased glutamatergic tonus and enhanced GR and AMPA receptor (AMPAR) expression. rVTA and cVTA activity differentially correlated with sucrose preference and passivity measures. CONCLUSIONS: These data demonstrate that the rVTA and cVTA respond differently to stress and suggest that while cVTA activity may be related to passivity-like states, the activity of both subregions appears to be related to anhedonia and the processing of incentive value. These region-dependent abnormalities indicate the multi-modular composition of the VTA, which could provide multiple substrates for different symptom features.

Deep brain stimulation and fluoxetine exert different long-term changes in the serotonergic system.

Both selective serotonin reuptake inhibitors (SSRIs) and ventromedial prefrontal cortex (vmPFC) deep brain stimulation (DBS) modulate serotonergic activity. We compared the acute (1 day) and long-term (12 days) effects of vmPFC stimulation and fluoxetine on serotonin (5-HT) release and receptor expression in rats. Samples to measure serotonin levels were collected from the hippocampus using microdialysis. Serotonin transporter (SERT), 5-HT1A and 5-HT1B mRNA were measured using in situ hybridization. [3H]8-OH-DPAT and [125I]cyanopindolol autoradiography were used to measure 5-HT1A and 5-HT1B binding. Our results show that after fluoxetine injections serotonin levels were approximately 150% higher than at baseline. Twelve days later, pre-injection 5-HT extracellular concentration was substantially higher than on day 1. In contrast, serotonin levels following DBS were only 50% higher than at baseline. While pre-stimulation 5-HT on day 12 was significantly higher than on treatment day 1, no stimulation-induced 5-HT peak was recorded. SERT expression in the dorsal raphe was increased after acute fluoxetine and decreased following a single day of DBS. Neither fluoxetine nor DBS administered acutely substantially changed 5-HT1A or 5-HT1B binding. Chronic fluoxetine treatment, however, was associated with a decrease in [3H]8-OH-DPAT prefrontal cortex and hippocampus expression. In contrast, chronic DBS induced a significant increase in [125I]cyanopindolol binding in the prefrontal cortex, globus pallidus, substantia nigra and raphe nuclei. mRNA expression of 5-HT1A and 5-HT1B in raphe nuclei was not altered by either treatment. These results suggest that fluoxetine and DBS modulate activity of the serotonergic system but likely exert their effects through different mechanisms.

Deep brain stimulation induces antidepressant-like effects in serotonin transporter knockout mice.

BACKGROUND: Some of the antidepressant-like effects of ventromedial prefrontal cortex (vmPFC) deep brain stimulation (DBS) in rodents have been attributed to the modulation of prefrontal-raphe pathways. This is largely different from selective serotonin reuptake inhibitors (SSRIs), which increase serotonin (5-HT) levels by inhibiting the serotonin transporter (SERT). SSRIs have limited efficacy when given to SERT knockout (KO) mice, or patients with mutations in the serotonin transporter promoter gene (5-HTTLPR). HYPOTHESIS: vmPFC DBS will induce antidepressant-like effects and serotonin release in SERT KOs. RESULTS: DBS-treated wild-type and SERT KO mice had a significant 22-26% decrease in immobility in the forced swim test. DBS delivered to either group was associated with 33-55% increase in 5-HT levels. CONCLUSIONS: DBS induced a significant antidepressant-like effect in KO mice. This suggests that it may be reasonable to consider DBS in states where SERT is not fully operational.

Prefrontal Cortex Deep Brain Stimulation Improves Fear and Anxiety-Like Behavior and Reduces Basolateral Amygdala Activity in a Preclinical Model of Posttraumatic Stress Disorder.

Deep brain stimulation (DBS) is being investigated for a number of psychiatric indications, including posttraumatic stress disorder (PTSD). Preclinical studies continue to be a cornerstone for the development of new DBS applications. We investigate whether DBS delivered to the infralimbic cortex (IL), a region involved in mechanisms of stress resiliency, may counter behavioral abnormalities in rats that present persistent extinction deficits and long-term anxiety after exposure to fear conditioning. Rats undergoing fear conditioning/extinction were segregated into weak and strong extinction groups (WE >70% or SE <30% of freezing during extinction). Following 2 weeks of DBS, animals were exposed to novel recall sessions and tested in the open field, novelty-suppressed feeding, and elevated plus maze. zif268 expression was measured in structures involved in mechanisms of fear and stress. In vivo electrophysiology was used to record activity from the basolateral amygdala (BLA). We found that DBS improved extinction deficits and anxiety-like behavior in WE animals, having no significant effects in SE rats. No major differences in absolute zif268 levels were recorded across groups. However, correlation between zif268 expression in the IL and BLA was disrupted in WE animals, a deficit that was countered by DBS treatment. Electrophysiology experiments have shown that DBS reduced BLA firing of both putative principal cells and interneurons in WE rats, with no significant differences being detected between SE and SE DBS animals. In summary, IL DBS mitigated fear, partially improved anxiety-like behavior, reversed neurocircuitry abnormalities, and reduced BLA cell firing in a preclinical model of PTSD.

Evaluation of a novel radiotracer for positron emission tomography imaging of reactive oxygen species in the central nervous system.

INTRODUCTION: Few, if any, radiotracers are available for the in vivo imaging of reactive oxygen species (ROS) in the central nervous system. ROS play a critical role in normal cell processes such as signaling and homeostasis but overproduction of ROS is implicated in several disorders. We describe here the radiosynthesis and initial ex vivo and in vivo evaluation of [11C]hydromethidine ([11C]HM) as a radiotracer to image ROS using positron emission tomography (PET). METHODS: [11C]HM and its deuterated isotopologue [11C](4) were produced using [11C]methyl triflate in a one-pot, two-step reaction and purified by high performance liquid chromatography. Ex vivo biodistribution studies were performed after tail vein injections of both radiotracers. To demonstrate sensitivity of uptake to ROS, [11C]HM was administered to rats treated systemically with lipopolysaccharide (LPS). In addition, ex vivo autoradiography and in vivo PET imaging were performed using [11C]HM on rats which had been microinjected with sodium nitroprusside (SNP) to induce ROS. RESULTS: [11C]HM and [11C](4) radiosyntheses were reliable and produced the radiotracers at high specific activities and radiochemical purities. Both radiotracers demonstrated good brain uptake and fast washout of radioactivity, but [11C](4) washout was faster. Pretreatment with LPS resulted in a significant increase in brain retention of radioactivity. Ex vivo autoradiography and PET imaging of rats unilaterally treated with microinjections of SNP demonstrated increased retention of radioactivity in the treated side of the brain. CONCLUSIONS: [11C]HM has the attributes of a radiotracer for PET imaging of ROS in the brain including good brain penetration and increased retention of radioactivity in animal models of oxidative stress.

An improved, high-efficiency assay for assessing serum anticholinergic activity using cultured cells stably expressing M1 receptors.

Assessments of total anticholinergic activity (SAA) in serum are of considerable interest for its potential involvement in cognitive impairment associated with polydrug states in the elderly and other populations. Such estimations have been based on the displacement of radioligand binding in rat brain tissues. The validity of such measurements has been questioned, as a potentially distorting effect of large serum proteins was identified. We sought to develop a modified assay that would be more efficient and free of this potential confound. Cultured CHO cells stably expressing M1 receptors M1WT3 were used. Binding of 3H-radioligands was conducted in 96-well plates and tested in serum containing known amounts of anticholinergic medications. Effects of endogenous serum proteins were assessed by pre-assay filtration and also by deproteinization with perchloric acid (PCA). Binding of [3H]quinuclidinyl benzilate ([3H]QNB) or [3H]N-methyl-scopolamine ([3H]NMS) to M1WT3 cells proved reliable and equally sensitive to varying concentrations of anticholinergic agents. In agreement with previous findings (Cox, Kwatra, Shetty, & Kwatra, 2009), filtration of proteins heavier than 50kDa essentially reduced SAA values to zero. In contrast, PCA preserved more than 70% of the binding seen untreated cell membranes. Cell-based assays also showed significant signal increases compared to the conventional rat brain-based protocol. Further advantages of the cell-based protocol described here include increased sensitivity and reliability, smaller amounts of radioligand needed, and higher throughput. PCA pretreatment eliminates potential artifacts attributable to serum proteins. This step, together with improvements in efficiency, should contribute significantly to the usefulness of the assay.

Lower KV7.5 Potassium Channel Subunit Expression in an Animal Model of Paroxysmal Dystonia.

Dystonia is a hyperkinetic disabling movement disorder. In the dt(sz) hamster, a model of paroxysmal dystonia, pronounced antidystonic effects of the KV7.2-5 potassium channel opener retigabine and aggravation of dystonia by a selective KV7.2-5 blocker indicated a pathophysiological role of an abnormal expression of KV7 channels. We therefore investigated the expression of KV7 subunits in brains of dystonic hamsters. While KV7.2 and KV7.3 subunits were unaltered, lower KV7.5 mRNA levels became evident in motor areas and in limbic structures of dystonic hamsters. The KV7.2/3 subunit-preferring channel opener N-(6-chloropyridin-3-yl)-3,4- difluorobenzamide (ICA 27243; 10-30 mg/kg i.p.) failed to reduce the severity of dystonia in mutant hamsters, suggesting that the previously observed antidystonic action of retigabine is mediated by the activation of KV7.5 channels. The experiments indicate a functional relevance for KV7.5 channels in paroxysmal dystonia. We suggest that compounds highly selective for subtypes of KV7 channels, i.e. for KV7.5, may provide new therapeutic approaches.

Acute high frequency stimulation of the prefrontal cortex or nucleus accumbens does not increase hippocampal neurogenesis in rats.

To date, the effects of deep brain stimulation (DBS) on hippocampal neurogenesis have been mainly characterized in the context of memory. Acute stimulation (i.e. for 1 h) of either the entorhinal cortex or the anterior thalamus increases both cell proliferation and survival. We investigate whether stimulation applied to targets being considered for the treatment of depression, namely the ventromedial prefrontal cortex (vmPFC) or nucleus accumbens (Acb), also increases hippocampal neurogenesis in rodents. Rats were treated with vmPFC or Acb DBS for 1 h at different settings. 5'-bromo-2'deoxyuridine (BrdU) was injected three days following stimulation onset and animals were sacrificed 24 h or 28 days later. Overall, we found that neither vmPFC nor Acb DBS increased hippocampal neurogenesis. In summary, the delivery of acute stimulation into targets homologous to those used in human depression trials does not increase hippocampal neurogenesis.

Antidepressant-like Effects of Medial Forebrain Bundle Deep Brain Stimulation in Rats are not Associated With Accumbens Dopamine Release.

BACKGROUND: Medial forebrain bundle (MFB) deep brain stimulation (DBS) is currently being investigated in patients with treatment-resistant depression. Striking features of this therapy are the large number of patients who respond to treatment and the rapid nature of the antidepressant response. OBJECTIVE: To study antidepressant-like behavioral responses, changes in regional brain activity, and monoamine release in rats receiving MFB DBS. METHODS: Antidepressant-like effects of MFB stimulation at 100 µA, 90 µs and either 130 Hz or 20 Hz were characterized in the forced swim test (FST). Changes in the expression of the immediate early gene (IEG) zif268 were measured with in situ hybridization and used as an index of regional brain activity. Microdialysis was used to measure DBS-induced dopamine and serotonin release in the nucleus accumbens. RESULTS: Stimulation at parameters that approximated those used in clinical practice, but not at lower frequencies, induced a significant antidepressant-like response in the FST. In animals receiving MFB DBS at high frequency, increases in zif268 expression were observed in the piriform cortex, prelimbic cortex, nucleus accumbens shell, anterior regions of the caudate/putamen and the ventral tegmental area. These structures are involved in the neurocircuitry of reward and are also connected to other brain areas via the MFB. At settings used during behavioral tests, stimulation did not induce either dopamine or serotonin release in the nucleus accumbens. CONCLUSIONS: These results suggest that MFB DBS induces an antidepressant-like effect in rats and recruits structures involved in the neurocircuitry of reward without affecting dopamine release in the nucleus accumbens.

Development and characterization of a promising fluorine-18 labelled radiopharmaceutical for in vivo imaging of fatty acid amide hydrolase.

Fatty acid amide hydrolase (FAAH), the enzyme responsible for terminating signaling by the endocannabinoid anandamide, plays an important role in the endocannabinoid system, and FAAH inhibitors are attractive drugs for pain, addiction, and neurological disorders. The synthesis, radiosynthesis, and evaluation, in vitro and ex vivo in rat, of an (18)F-radiotracer designed to image FAAH using positron emission tomography (PET) is described. Fluorine-18 labelled 3-(4,5-dihydrooxazol-2-yl)phenyl (5-fluoropentyl)carbamate, [(18)F]5, was synthesized at high specific activity in a one-pot three step reaction using a commercial module with a radiochemical yield of 17-22% (from [(18)F]fluoride). In vitro assay using rat brain homogenates showed that 5 inhibited FAAH in a time-dependent manner, with an IC50 value of 0.82nM after a preincubation of 60min. Ex vivo biodistribution studies and ex vivo autoradiography in rat brain demonstrated that [(18)F]5 had high brain penetration with standard uptake values of up to 4.6 and had a regional distribution which correlated with reported regional FAAH enzyme activity. Specificity of binding to FAAH with [(18)F]5 was high (>90%) as demonstrated by pharmacological challenges with potent and selective FAAH inhibitors and was irreversible as demonstrated by radioactivity measurements on homogenized brain tissue extracts. We infer from these results that [(18)F]5 is a highly promising candidate radiotracer with which to image FAAH in human subjects using PET and clinical studies are proceeding.

Regional brain c-fos activation associated with penile erection and other symptoms induced by the spider toxin Tx2-6.

Brain areas expressing c-fos messenger RNA were mapped by quantitative in situ hybridization after 1-2 h of intoxication with 10 µg/kg Tx2-6, a toxin obtained from the venom of the spider Phoneutria nigriventer. Relative to saline-treated controls, brains from toxin-treated animals showed pronounced c-fos activation in many brain areas, including the supraoptic nucleus, the paraventricular nucleus of the hypothalamus, the motor nucleus of the vagus, area postrema, paraventricular and paratenial nuclei of the thalamus, locus coeruleus, central amydaloid nucleus and the bed nucleus of the stria terminalis. The paraventricular hypothalamus and the bed nucleus of the stria terminalis have been implicated in erectile function in other studies. A possible role for central NO is considered. Acute stress also activates many brain areas activated by Tx2-6 as well as with NOstimulated Fos transcription. Brain areas that appear to be selectively activated by Tx2-6, include the paratenial and paraventricular thalamic nuclei, the bed nucleus of the stria terminalis and the area postrema and the dorsal motor n. of vagus in the medulla. However, direct injections of different doses of the toxin into the paraventricular hypothalamic n. failed to induce penile erection, arguing against CNS involvement in this particular effect.

Aged dogs demonstrate both increased sensitivity to scopolamine impairment and decreased muscarinic receptor density.

Memory deficits associated with aging and Alzheimer's disease have been linked to cholinergic dysfunction. The present study investigated this hypothesis by comparing the effects of the muscarinic cholinergic receptor antagonist scopolamine on recent memory performance and by examining muscarinic receptor density in aged and young dogs. Scopolamine (15 µg/kg; SC) was administered prior to testing young (M=2.8 years) and aged (M=13.0 years) dogs on a delayed-non-matching-to-position task (DNMP). Scopolamine significantly impaired performance of aged, but not young dogs. Muscarinic receptor density was assessed autoradiographically using the non-selective radioligand [(3)H]quinuclidinylbenzilate. Aged dogs (M=14.1 years) showed significantly decreased density of muscarinic receptors in all brain regions examined except the cerebellum compared to young dogs (M=3.7 years). The results are consistent with those seen in aged humans and Alzheimer's patients and support the hypothesis of age-dependent cholinergic dysfunction in the dog, although this was not directly determined in the current study. These findings demonstrate that markers of cholinergic hypofunction, in addition to the natural cognitive decline and amyloid pathology previously noted, are seen in canine aging. Collectively, this supports the use of the aged dog as a model for examining early pathological events in the development of Alzheimer's disease.