Michel Bottlaender

Functional Recovery in a Primate Model of Parkinson's Disease following Motor Cortex Stimulation

A concept in Parkinsons disease postulates that motor cortex may pattern abnormal rhythmic activities in the basal ganglia, underlying the genesis of observed motor symptoms. We conducted a preclinical study of electrical interference in the primary motor cortex using a chronic MPTP primate model in which dopamine depletion was progressive and regularly documented using 18F-DOPA positron tomography. High-frequency motor cortex stimulation significantly reduced akinesia and bradykinesia. This behavioral benefit was associated with an increased metabolic activity in the supplementary motor area as assessed with 18-F-deoxyglucose PET, a normalization of mean firing rate in the internal globus pallidus (GPi) and the subthalamic nucleus (STN), and a reduction of synchronized oscillatory neuronal activities in these two structures. Motor cortex stimulation is a simple and safe procedure to modulate subthalamo-pallido-cortical loop and alleviate parkinsonian symptoms without requiring deep brain stereotactic surgery.

Similar amyloid-β burden in posterior cortical atrophy and Alzheimer's disease

While the clinical presentation of posterior cortical atrophy is clearly distinct from typical Alzheimers disease, neuropathological studies have suggested that most patients with posterior cortical atrophy have Alzheimers disease with an atypical visual presentation. We analysed in vivo pathophysiological markers of Alzheimers disease such as cerebrospinal fluid biomarkers and positron emission tomography imaging with ¹¹C-labelled Pittsburgh compound-B in posterior cortical atrophy to determine whether biochemical profile and fibrillar amyloid-β burden topography are associated with the clinical presentation. Nine patients with posterior cortical atrophy and nine with typical Alzheimers disease individually matched for age, duration and severity of the disease and 10 cognitively normal age-matched controls were included. ¹¹C-labelled Pittsburgh compound-B images were analysed both using volumes of interest and on a voxel-wise basis using statistical parametric mapping, taking into account the individual regional cortical atrophy. Cerebrospinal fluid biomarkers did not differ between posterior cortical atrophy and patients with Alzheimers disease. Compared with normal controls, both posterior cortical atrophy and Alzheimers disease groups showed increased ¹¹C-labelled Pittsburgh compound-B uptake. No significant difference was found in regional or global ¹¹C-labelled Pittsburgh compound-B binding between posterior cortical atrophy and Alzheimers disease groups with both volumes of interest and voxel-wise basis using statistical parametric mapping methods. Our findings demonstrate that cerebrospinal fluid biomarkers and positron emission tomography imaging with ¹¹C-labelled Pittsburgh compound-B may be useful in identifying an atypical visual form of Alzheimers disease. The similar topography of fibrillar amyloid-β deposition between typical Alzheimers disease and posterior cortical atrophy groups suggests that, although amyloid-β accumulation plays a critical role in the pathogenesis of Alzheimers disease, other factors such as neurofibrillary tangles may contribute to the different clinical features observed in posterior cortical atrophy.

Synthesis of 2-[18F]fluoro-3-[2(S)-2-azetidinylmethoxy]pyridine, a highly potent radioligand for in vivo imaging central nicotinic acetylcholine receptors

This paper reports the synthesis of 2-fluoro-3-[2(S)-2-azetidinylmethoxy]pyridine and its radiolabeling with fluorine-18 ([18F]FK-K222) by nucleophilic aromatic nitro-to-fluoro substitution in DMSO by conventional heating at 150°C for 20 min or by microwave activation at 100 Watt for 1 min. This fluoro compound is a closely related analog of the high affinity nicotinic ligand A-85380 (3-[2(S)-2-azetidinylmethoxy]pyridine). This compound is the lead compound of a novel 3-pyridyl ether series of new nAChR ligands recently published, and possesses not only subnanomolar affinity, comparable to that of epibatidine, for the α4β2 subtype, but also a weaker affinity for the other subtypes of nAChRs. 110–140 mCi (4.1–5.2 GBq) of pure 2-[18F]fluoro-3-[2(S)-2-azetidinylmethoxy]pyridine ([18F]fluoro-A-85380) could be obtained in less than 2 hours, with specific radioactivities of 3–5 Ci/μmol (111–185 GBq/μmol) calculated for End of Bombardment (or 1.5–2.5 Ci/μmol (55.5–92.5 GBq/μmol) at End of Synthesis) for a 20 μA, 30 min (36000 μC) irradiation of a 95% enriched [18O]water target with a 16 MeV proton beam [18O(p,n)18F]. Yields (with respect to [18F]fluoride ion): decay-corrected 49–64%; non-decay-corrected 25–33%. Total synthesis time from EOB: 105–110 min (this includes the recovery of the [18F]fluoride ion from the target and the [18F]FK-K222-complex preparation). Preliminary results in rats showed a substantial uptake of the ligand in the thalamus (1% I.D./g tissue at 30 min) while the cerebellar uptake was 2-fold lower. Thalamic uptake was reduced by 75–85% following a pre-treatment with nicotine, cytisine, epibatidine or fluoro-A-85380. The full pharmacological profile and the potential for eventual clinical applications of this ligand as a tracer for PET experiments are currently under investigation.

Modeling Analysis of [11C]Flumazenil Kinetics Studied by PET: Application to a Critical Study of the Equilibrium Approaches

The multi-injection modeling approach was used for the in vivo quantitation of benzodiazepine receptors in baboon brain using positron emission tomography (PET) and [11C]flumazenil (RO 15-1788) as a specific ligand. The model included three compartments (plasma, free, and bound ligand) and five parameters (including the benzodiazepine receptor concentration). The plasma concentration after correction for the metabolites was used as the input function. The experimental protocol consisted of four injections of labeled and/or unlabeled ligand. This protocol allows the evaluation, from a single experiment, of the five model parameters in various regions of interest. For example, in the temporal cortex, the concentration of receptor sites available for binding (B′max) and the equilibrium dissociation constant (Kd) were estimated to be 70 ± 15 pmol/ml and 15.8 ± 2.2 nM, respectively. The validity of the equilibrium approach, which is the most often used quantitation method, has been studied from simulated data calculated using these model parameters. The equilibrium approaches consist of reproducing in PET studies the experimental conditions that permit the use of the usual in vitro methods such as Scatchard analysis. These approaches are often open to criticism because of the difficulty of defining the notion of equilibrium in in vivo studies. However, it appears that the basic relation of Scatchard analysis is valid over a broader range of conditions than those normally used, such as the requirement of a constant bound/free ratio. Simulations showed that the values of the receptor concentration (B′max) and the equilibrium dissociation constant (Kd) found using Scatchard analysis are always underestimated. These simulations also suggest an explanation concerning the dependency of B′max and Kd on the time point employed for the Scatchard analysis, a phenomenon found by several authors. To conclude, we propose new protocols that allow the estimation of the B′max and Kd parameters using a Scatchard analysis but based on a protocol including only one or two injections. These protocols being entirely noninvasive, it thus becomes possible to investigate possible changes in receptor density and/or affinity in patients.

Two distinct amnesic profiles in behavioral variant frontotemporal dementia.

BACKGROUND Whether or not episodic memory deficit is a characteristic of behavioral variant frontotemporal dementia (bvFTD) is a crucial question for its diagnosis and management. METHODS We compared the episodic memory performance profile of bvFTD patients with healthy control subjects and patients with Alzheimers disease (AD) as defined by clinical and biological criteria. Episodic memory was assessed with the Free and Cued Selective Reminding Test, which controls for effective encoding and identifies memory storage ability resulting from consolidation processing. One hundred thirty-four participants were evaluated: 56 patients with typical clinical presentation of AD and pathophysiological evidence as defined by cerebrospinal fluid AD biomarker profile and/or significant amyloid retention on Pittsburgh Compound B positron emission tomography; 56 patients diagnosed with bvFTD with no evidence of AD-cerebrospinal fluid biomarkers when a profile was available (28/56), including 44 progressive (bvFTD) and 12 nonprogressive (phenocopies) patients; and 22 control subjects with negative amyloid imaging. RESULTS Memory scores could not differentiate bvFTD from AD patients (sensitivity and specificity <50%). Taking into account the individual distribution of Free and Cued Selective Reminding Test scores, half of bvFTD patients had a deficit of free recall, total (free + cued) recall, and delayed recall as severe as AD patients. The other half had subnormal scores similar to phenocopies and a delayed recall score similar to control subjects. CONCLUSIONS We observed two distinct amnesic profiles in bvFTD patients that could reflect two types of hippocampal structure and Papez circuit involvement. These findings on episodic memory profiles could contribute to discussions on the recent international consensus criteria for bvFTD.

Is Hippocampal Volume a Good Marker to Differentiate Alzheimer's Disease from Frontotemporal Dementia?

BACKGROUND Previous studies analyzed the ability of hippocampal volumes (HV) to differentiate Alzheimers disease (AD) from frontotemporal dementia (FTD). However, these studies did not include patients selected according to clinico-biological criteria, using pathophysiological biomarkers. OBJECTIVE To analyze the effectiveness of hippocampal volumetric measures to distinguish AD from behavioral variant FTD (bvFTD), using strict inclusion criteria based on clinical and pathophysiological markers. METHODS Seventy-two participants were included: 31 AD patients with predominant and progressive episodic memory deficits associated with typical AD cerebrospinal fluid (CSF) profile and/or positive amyloid imaging (PET with 11C-labeled Pittsburgh Compound B [PiB]), 26 bvFTD patients diagnosed according to consensual clinical criteria and with no AD CSF profile, and 15 healthy controls without amyloid retention on PiB-PET exam. HV were segmented with an automated method and were normalized to total intracranial volume (nHV). RESULTS Significant reductions in HV were found in both AD and bvFTD patients compared with controls, but there were no significant difference between AD and bvFTD patients. Mean nHV distinguished normal controls from either AD or bvFTD with high sensitivity (80.6% and 76.9%, respectively) and specificity (93.3% for both), but it was inefficient in differentiating AD from bvFTD (9.7% specificity). There was no difference in the clinical and neuropsychological profiles according to HV in bvFTD and AD patients. CONCLUSIONS When considered alone, measures of HV are not good markers to differentiate AD from bvFTD. Hippocampal sclerosis associated with FTD may explain the high degree of overlap in nHV between both groups.

Cerebral monoamine oxidase A inhibition in tobacco smokers confirmed with PET and [11C]befloxatone.

The inhibition of cerebral monoamine oxidases (MAOs) by cigarette smoke components could participate to the tobacco addiction. However, the actual extent of this inhibition in vivo in smokers is still poorly known. We investigated cerebral MAO-A availability in 7 tobacco-dependent subjects and 6 healthy nonsmokers, using positron emission tomography (PET) and the MAO-A selective radioligand [11C]befloxatone. In comparison to nonsmokers, smokers showed a significant overall reduction of [11C]befloxatone binding potential (BP) in cortical areas (average reduction, −60%) and a similar trend in caudate and thalamus (−40%). Our findings confirm a widespread inhibition of cerebral MAO-A in smokers. This mechanism may contribute to tobacco addiction and for a possible mood-modulating effect of tobacco.

Decrease of nicotinic receptors in the nigrostriatal system in Parkinson's disease

Smoking is associated with a lower incidence of Parkinsons disease (PD), which might be related to a neuroprotective action of nicotine. Postmortem studies have shown a decrease of cerebral nicotinic acetylcholine receptors (nAChRs) in PD. In this study, we evaluated the decrease of nAChRs in PD in vivo using positron emission tomography (PET), and we explored the relationship between nAChRs density and PD severity using both clinical scores and the measurement of striatal dopaminergic function. Thirteen nondemented patients with PD underwent two PET scans, one with 6-[18F]fluoro-3,4-dihydroxy-l-phenylalanine (6-[18F]fluoro-l-DOPA) to measure the dopaminergic function and another with 2-[18F]fluoro-3-[2(S)-2-azetidinylmethoxy]pyridine (2-[18F]fluoro-A-85380), a radiotracer with high affinity for the nAChRs. Distribution volumes (DVs) of 2-[18F]fluoro-A-85380 measured in the PD group were compared with those obtained from six nonsmoking healthy controls, with regions-of-interest and voxel-based approaches. Both analyses showed a significant (P<0.05) decrease of 2-[18F]fluoro-A-85380 DV in the striatum (10%) and substantia nigra (14.9%) in PD patients. Despite the wide range of PD stages, no correlation was found between DV and the clinical and PET markers of PD severity.

Long-lasting occupancy of central nicotinic acetylcholine receptors after smoking: a PET study in monkeys.

The aim of this study was to compare the degree of occupancy of central nicotinic acetylcholine receptors (nAChR) in isoflurane anaesthetized baboon brain following inhalation of tobacco smoke (one cigarette containing 0.9 mg nicotine) or i.v. nicotine (0.6 mg i.v.). [18F]Fluoro‐A‐85380 and positron emission tomography (PET) were used to assess the distribution volumes (DV) of the radiotracer in selected brain areas using a one‐compartment model. Eighty minutes after nicotine i.v., DV was reduced by 50 and 66% in the thalamus and putamen, respectively. Six hours after nicotine, a reduction in DV (27% in the thalamus) was still observed. Eighty minutes after inhalation of tobacco smoke, DV was decreased by 52 and 65% in the thalamus and putamen, respectively. Previous PET experiments have demonstrated a short‐lasting interaction of [11C]nicotine with nAChRs. Thus, we hypothesized that a metabolite of nicotine with high affinity and long half‐live (several hours) could bind at nAChRs. Eighty minutes after a high dose of nornicotine (0.5 mg i.v.), DV was reduced by 53 and 31% in thalamus and putamen, respectively. No significant effect was observed following 0.15 mg nornicotine. Therefore, nornicotine could contribute to the long‐lasting occupancy of central nAChRs after smoking.

High density of nicotinic receptors in the cingulo-insular network.

The nicotinic system plays an important role in ordinary cognition, particularly in attention. The main nicotinic receptor in the human brain is the heteromeric α4β2 neuronal nicotinic acetylcholine receptor (nAChR), which is distributed throughout the brain, with an especially high density in the thalamus and brainstem. Despite the important role of α4β2 nAChRs in various physiological functions and pathological conditions, their distribution in the human cortex remains poorly characterized. We assessed the in vivo distribution of α4β2 nAChRs in the human cortex in a group of seven non-smoking healthy subjects, using 2-[(18)F]F-A-85380 PET and a volume-of-interest-based analysis. We showed that cortical nAChR density was highest in the insular and anterior cingulate cortices. In functional magnetic resonance imaging studies, these two cortical regions and the thalamus have been shown to be highly correlated during the resting state and various tasks. Here, we also directly assessed nAChR density in this cingulo-insular network as defined in an independent dataset using resting-state functional connectivity, and compared it to other control-related networks, to the default mode network as well as to sensory and motor networks. Receptor density was significantly higher in the cingulo-insular network. This network has been suggested to maintain a variety of foundational capacities fundamental to cognitive function. The demonstration of a high nAChR density in the insular and anterior cingulate cortices reflects a particular neurochemical organization of the cingulo-insular network, and suggests an important role of the nicotinic receptors in its functions.