Stroke penumbra defined by an MRI-based oxygen challenge technique: 2. Validation based on the consequences of reperfusion

Magnetic resonance imaging (MRI) with oxygen challenge (T₂^* OC) uses oxygen as a metabolic biotracer to define penumbral tissue based on CMRO₂ and oxygen extraction fraction. Penumbra displays a greater T₂^* signal change during OC than surrounding tissue. Since timely restoration of cerebral blood flow (CBF) should salvage penumbra, T₂^* OC was tested by examining the consequences of reperfusion on T₂^* OC-defined penumbra. Transient ischemia (109±20 minutes) was induced in male Sprague-Dawley rats (n=8). Penumbra was identified on T₂^*-weighted MRI during OC. Ischemia and ischemic injury were identified on CBF and apparent diffusion coefficient maps, respectively. Reperfusion was induced and scans repeated. T₂ for final infarct and T₂^* OC were run on day 7. T₂^* signal increase to OC was 3.4% in contralateral cortex and caudate nucleus and was unaffected by reperfusion. In OC-defined penumbra, T₂^* signal increased by 8.4%±4.1% during ischemia and returned to 3.25%±0.8% following reperfusion. Ischemic core T₂^* signal increase was 0.39%±0.47% during ischemia and 0.84%±1.8% on reperfusion. Penumbral CBF increased from 41.94±13 to 116.5±25 mL per 100 g per minute on reperfusion. On day 7, OC-defined penumbra gave a normal OC response and was located outside the infarct. T₂^* OC-defined penumbra recovered when CBF was restored, providing further validation of the utility of T₂^* OC for acute stroke management.     

Responses to odors mapped in snail tentacle and brain by [14C]-2-deoxyglucose autoradiography

The method of 2-deoxyglucose (2-DG) autoradiography has been widely used to map functional neuronal systems in vertebrates, but in invertebrate species, where morphological dimensions favor its use, the applications have been minimal. This study uses [14C]-2-DG to map the olfactory system of a terrestrial snail, Achatina fulica. The olfactory organ in the snail's tentacles bears a striking resemblance to the vertebrate olfactory mucosa. There are also complex neural structures in the tentacle and brain that are devoted to subsequent processing. These facts make the molluscan olfactory system a suitable complement to the traditional vertebrate and insect models in olfaction. The experiments utilized intact snails in which one tentacle was exposed to a controlled odor environment while the contralateral tentacle was held in a retracted position. The dose of [14C]-2-DG (2 microCi/gm) was injected into the hemocele. Tissue processing involved freeze-substitution with acetone, dry sectioning, and the preparation of liquid film autoradiographs. Optical density measurements permitted quantitative comparisons between experimental conditions. The natural odors of conspecific snails and of carrots elicited significantly more uptake of 2-DG in the exposed tentacle than in the unexposed tentacle and, in the exposed tentacle, significantly more label over the axons of the primary sensory neurons than was elicited by exposure to clean air. Amyl acetate and octanol were less effective. A small number of superficially placed sensory neurons were labeled in all stimulus conditions, including clean air, and may represent the mechanosensors. Stimulus-dependent labeling in the brain was limited to the procerebrum and included both neuropilar and cellular parts. In contrast to vertebrate and insect olfactory systems, there was no evidence of spatial coding for odor quality.     

Extrastriatal circuits activated by intrastriatal muscimol: a [14C]2-deoxyglucose investigation

The quantitative autoradiographic [14C]2-deoxyglucose technique has been employed in conscious, lightly restrained rats to investigate the functional consequences (which are reflected as alterations in local rates of glucose utilization) of unilateral intrastriatal administration of the GABAergic agonist, muscimol. Intrastriatal injections of muscimol (500 ng) effect a widespread, homogeneous reduction (by 33%) in glucose utilization throughout the ipsilateral striatum. Increased glucose utilization following intrastriatal muscimol injection was observed in each region to which the principal striatal efferent projections are directed (ipsilateral globus pallidus increased by 29%; ipsilateral entopeduncular nucleus increased by 33%; ipsilateral pars reticulata increased by 46%). Significant focal alterations in glucose utilization occurred in a number of other regions ipsilateral to the injection, including lateral habenular nucleus (increased by 16%), pars compacta of the substantia nigra (increased by 28%), ventrolateral nucleus of the thalamus (decreased by 40%), sensory-motor cortex (decreased by 47%), deep layer of the superior colliculus (decreased by 18%), and subthalamic nucleus (decreased by 18%). In the overwhelming majority of brain regions examined, glucose utilization was unaltered by intrastriatal administration of muscimol. All regions which displayed significant alterations in glucose use with intrastriatal muscimol are known to have direct connections with the striatum (e.g. pallidus and nigra), or to be anatomical components in polysynaptic striatal outflow pathways (e.g. striatal-pallidal-ventral thalamic-neocortical circuit). The present results indicate that activity within striatal efferent circuits can be differentially modified by the effects of the GABAergic agonist, muscimol, within the caudate nucleus.     

[14C] 2-deoxyglucose uptake marks systems activated by rewarding brain stimulation

Autoradiography of sections from the brains of anaesthetized rats injected with [¹⁴C] 2-deoxyglucose revealed neural systems unilaterally activated by rewarding electrical stimulation of the medial forebrain bundle. Since this new technique marks neural systems on the basis of their activity, it has great potential in functional neuroanatomy. The potential is easily realized in brain-stimulation studies, where systems may be driven to exceptionally high levels of activity.     

Selective uptake of [14C]2-deoxyglucose by neurons and astrocytes: high-resolution microautoradiographic imaging by cellular 14C-trajectography combined with immunohistochemistry.

At the moment, there is no direct in vivo evidence of the relative amount of glucose taken up and metabolized by glial cells and neurons, respectively. Therefore, we developed a specific high cellular resolution beta-trajectory approach that allows recording and identification of individual tracks of electrons emitted during disintegrations of 14C. We used [14C]2-deoxyglucose (2DG), which is an analog of glucose and is not metabolized further than the first phosphorylation by hexokinase; this property allows localization of the tracer within the cell type where it is phosphorylated. The present technical approach associated a method of cellular trajectography mainly characterized by the high thickness of the emulsion (15 microm), which permits following of the trajectory of individual electrons. This technique was improved to preserve the in vivo label of diffusible compounds such as 2DG and 2DG-6P and associated with immunohistochemical detection of neurons and astrocytes. beta-Track counting of labeled compounds was performed in 5 microm glial fibrillary acidic protein (GFAP)- and microtubule-associated protein (MAP)2-immunolabeled paraffin adjacent sections. Of 3,075 counted beta-tracks, 53.0% were localized in astrocytes on GFAP-labeled sections and 60.1% in neurons on MAP2-labeled sections. These data represent the first in vivo evidence of the compartmentation of uptake and metabolism of glucose in neurons and astrocytes.     

Metabolic mapping of the rat brain involved in thermoregulatory responses using the [C]2-deoxyglucose technique

The central nervous structures involved in thermoregulatory responses to thermal stimulation of the preoptic/anterior hypothalamic region were investigated in conscious, unrestrained rats by means of the 2-deoxy-d-[¹⁴C]glucose autoradiographic technique. Significant activation in metabolic activity was observed in the medial preoptic area, medial forebrain bundle, anterior part of ventromedial hypothalamus, anteroventral thalamus, dorsomedial thalamus, basal ganglia, pars compacta of substantia nigra, red nucleus and the reticular formation.     

Extrastriatal circuits activated by intrastriatal muscimol: A[C]2-deoxyglucose investigation

The quantitative autoradiographic [¹⁴C]2-deoxyglucose technique has been employed in conscious, lightly restrained rats to investigate the functional consequences (which are reflected as alterations in local rates of glucose utilization) of unilateral intrastriatal administration of the GABAergic agonist, muscimol. Intrastriatal injections of muscimol (500 ng) effect a widespread, homogeneous reduction (by 33%) in glucose utilization throughout the ipsilateral striatum. Increased glucose utilization following intrastriatal muscimol injection was observed in each region to which the principal striatal efferent projections are directed (ipsilateral globus pallidus increased by 29%; ipsilateral entopeduncular nucleus increased by 33%; ipsilateral pars reticulata increased by 46%). Significant focal alterations in glucose utilization occurred in a number of other regions ipsilateral to the injection, including lateral habenular nucleus (increased by 16%), pars compacta of the substantia nigra (increased by 28%), ventrolateral nucleus of the thalamus (decreased by 40%), sensory-motor cortex (decreased by 47%), deep layer of the superior colliculus (decreased by 18%), and subthalamic nucleus (decreased by 18%). In the overwhelming majority of brain regions examined, glucose utilization was unaltered by intrastriatal administration of muscimol. All regions which displayed significant alterations in glucose use with intrastriatal muscimol are known to have direct connections with the striatum (e.g. pallidus and nigra), or to be anatomical components in polysynaptic striatal outflow pathways (e.g. striatal-pallidal-ventral thalamic-neocortical circuit). The present results indicate that activity within striatal efferent circuits can be differentially modified by the effects of the GABAergic agonist, muscimol, within the caudate nucleus.     

Localization of synaptic responses in the in vitro turtle olfactory bulb using the [14C]2-deoxyglucose method

Studies were carried out on the in vitro turtle olfactory bulb preparation with a modification of the [14C]-2-deoxyglucose (2-DG) technique. Electrical stimulation of either the dorsal or ventral division of the olfactory nerve produced broad bands of activity, spreading across laminae, in the corresponding half of the olfactory bulb. Pretreatment of the isolated preparation in a low calcium bath eliminated focal 2-DG uptake induced by electrical stimulation of the nerve. In contrast, pretreatment with the GABAergic antagonist, bicuculline, produced a notable increase in 2-DG accumulation. These findings are discussed in the light of the topographical innervation of the olfactory bulb by the olfactory nerve as well as the known synaptic organization of the olfactory bulb and the putative neurotransmitters operative in local circuits.     

Bilateral [14C]2-deoxyglucose uptake by motor pathways after unilateral neonatal cortex lesions in the rat

The left sensorimotor (SM) cortex was removed in 1-day-old and 30-day-old rats. At 90 days of age [14C]2-deoxyglucose (2DG) was injected and the right motor (MI) cortex was electrically stimulated to produce predominantly left vibrissae movements. Animals were sacrificed and their brains autoradiographed. Right motor cortex (MI) stimulation activated subcortical structures bilaterally in 3 of 5 neonatally lesioned rats. Right MI stimulation activated most subcortical structures unilaterally in 30-day lesioned rats. This implies that a critical period for SM cortex injury may occur between 1 and 30 days of age. We suggest that removal of left SM cortex at 1 day of age occurs before or during the critical period and this induces right MI cortex to form bilateral subcortical connections. The bilateral 2DG uptake increases imply the bilateral connections are functional. The unilateral subcortical activation in 2 of 5 neonatally lesioned animals may have been due to differences in size of the lesion, parameters of stimulation, or perhaps due to the time of the lesion being near the critical period. We also suggest that removal of left SM cortex at 30 days of age occurs after the critical period, but that this does not affect the predominantly ipsilateral subcortical connections from MI cortex which have previously formed during normal development.     

An experimental model of generalized seizures for the measurement of local cerebral glucose utilization in the immature rat. II. Mapping of brain metabolism using the quantitative [14C]2-deoxyglucose technique.

The quantitative autoradiographic [14C]2-deoxyglucose technique (2DG) was applied to measure the effects of pentylenetetrazol (PTZ)-induced status epilepticus (SE) on local cerebral metabolic rates for glucose (LCMRglc) in 10 (P10)-, 14 (P14)-, 17 (P17)- and 21 (P21)-day-old rats. To produce long-lasting SE (55 min), the animals received repetitive, timed intraperitoneal injections of subconvulsive doses of PTZ until SE was reached. At P10 and P14, SE induced a marked increase in LCMRglc which affected 66 of the 76 structures studied. Increases were especially high (200-400%) in limbic and motor cortices at P10 and in some brainstem areas at these 2 ages. At P17 and P21, average brain glucose utilization was similar in seizing and control rats, but in PTZ-treated rats reflected a redistribution in local metabolic rates with increases in brainstem, midbrain, hypothalamus and septum, decreases in cortex, hippocampus, some sensory areas and white matter and no change in many motor and limbic structures. In a few cerebral regions, such as hippocampus, dentate gyrus and mammillary body, LCMRglc did not increase at P10 and P14 and decreased at P17 and P21 in PTZ- vs. saline-treated rats. The results of the present study show that the immature brain responds to sustained seizure activity in a specific way according to its maturational state. Moreover, these data allow the mapping of the vulnerability of cerebral structures to seizures, according to their metabolic response to convulsions.     

Short and long-term changes in cerebral [14C]-2-deoxyglucose uptake in the MPTP-treated marmoset: relationship to locomotor activity

Summary The short-term (0.7 ± 0.1 months post-MPTP) and long-term effects (36.7 ± 4.4 months) of MPTP treatment on motor behaviour and [¹⁴C]-2DG uptake were investigated in the common marmoset. The subcutaneous administration of MPTP greatly reduced locomotor activity (–94% with respect to controls) and induced motor disability in the short-term MPTP-treated marmoset group. In the long-term MPTP group, MPTP treatment did not significantly affect locomotor activity (–27% with respect to controls) and there was partial recovery of motor disability.In the short-term MPTP group, there were increases in [¹⁴C]-2DG uptake in the GP1 (+31 to +37%), SNc (+34 to +42%), VTA (+35%), LC (+23%), PPN (+19%) and in the VA (+19%), VL (+20%) and AM (+17%) thalamic nuclei. [¹⁴C]-2DG uptake was decreased in the STN (–15%). In the long-term MPTP group, [¹⁴C]-2DG uptake was increased in the GP1 (+18%), SNc (+27%), VTA (+25%), PPN (+19%), ventral caudate nucleus (+18 to +23%), NAc (+22%), F.Ctx (+18%) and in the VA (+34%), VL (+28%), AV (+33%) and AM (+24%) thalamic nuclei. [¹⁴C]-2DG uptake was unchanged in the STN.The increase in metabolic activity of the surviving DA neurones and/or the reactive gliosis may account for the initial increase in [¹⁴C]-2DG uptake in the SNc and VTA. On the other hand, in the long-term MPTP-treated animals the increase in [¹⁴C]-2DG uptake in the SNc (though less than in the short-term MPTP group), ventral caudate and NAc may reflect the regenerative changes in the dopaminergic system in these areas. Despite the behavioural recovery, [¹⁴C]-2DG uptake remained elevated in the target areas for medial paludal output (the thalamic nuclei and PPN). However, the attenuation of the changes in [¹⁴C]-2DG uptake in the GP1 and STN of longterm MPTP-treated marmosets suggest that the striato-GPl and GP1-STN outputs closely reflect motor function in this primate model of Parkinson's disease.Anatomical abbreviations AM anteromedial thalamus - AV anteroventral thalamus - CeM centromedian thalamus - d dorsal - F.Ctx frontal cortex - GP1 lateral segment of globus pallidus - GPm medial segment of globus pallidus - HBl lateral habenular - HBm medial habenular - IC inferior colliculus - l lateral - LC locus coeruleus - m medial - MD mediodorsal thalamus - NAc nucleus accumbens - OT olfactory tubercle - PPN pedunculopontine nucleus - Rt reticular thalamus - SNc substantia nigra pars compacta - SNr substantia nigra pars reticulata - STN subthalamic nucleus - v ventral - VA ventral anterior thalamus - VL ventral lateral thalamus - VTA ventral tegmental area Chemical abbreviations DA dopamine - GABA gamma aminobutyric acid - MPP⁺ 1-methyl-4-phenylpyridinium ion - MPTP 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine - [¹⁴C]-2DG [¹⁴C]-2-deoxyglucose     

Isofrequency labelling revealed by a combined [14C]-2-deoxyglucose, electrophysiological, and horseradish peroxidase study of the inferior colliculus of the cat

Tonotopic sequences of single units were recorded in the central nucleus (ICC) of the inferior colliculus of cats. The sites of units with a particular characteristic frequency (CF) were marked histologically. After injection with [14C]-2-deoxyglucose (2-DG), each animal was stimulated with tone bursts, which corresponded to the CFs of the selected units. The position of a selected unit was found to correspond with the position of a band of discrete 2-DG labelling. In some animals, multiple penetrations revealed that more than one unit with the same CF was located on the same band, indicating that the 2-DG bands represent isofrequency contours. Single units were recorded in the pars lateralis (LV) of the medial geniculate body of cats and areas of consistent CF were found, which contained the same frequencies as some of those employed with 2-DG. Horseradish peroxidase (HRP) was ejected into these selected areas and labelled cells were identified in ICC after retrograde transport. The labelled cells were found to lie in a band which had a similar orientation to the 2-DG bands produced by the same frequencies. Both sets of data indicate that ICC is organized into three-dimensional isofrequency sheets, the orientation of which do not match the concentric model of frequency organization inferred from some Golgi studies. The isofrequency sheets slope from medial to lateral throughout ICC with high-frequency contours found more medially and caudally and low-frequency contours more laterally and rostrally. The organization of the isofrequency contours is largely in agreement with a recent Golgi model of the laminations in ICC put forward by Oliver and Morest ('84). The 2-DG contours do not agree with the orientation of laminae in the lateral part of ICC as described by this model. The 2-DG contours also extend further into the dorsal cortex than previous degeneration evidence would suggest. The functional isofrequency contours are often quite narrow and could represent two or three overlapping cellular laminae. The results show clearly that there is only one tonotopic organization extending throughout ICC and the dorsal cortex.     

Functional organization of mustached bat inferior colliculus: I. Representation of FM frequency bands important for target ranging revealed by 14C-2-deoxyglucose autoradiography and single unit mapping

The representation in the inferior colliculus of the frequency modulated (FM) components of the first (25-30 kHz) and second (50-60 kHz) harmonic of the sonar signal of the mustached bat, which may be important for target range processing, was investigated by using the 2-deoxyglucose (2-DG) technique and single-unit mapping. In the 2-DG experiments, bats presented with second harmonic FM stimuli alone showed uptake of label in specific regions of the central nucleus and dorsal cortex of the inferior colliculus, and the nucleus of the brachium. In the central nucleus, a dorsoventrally and mediolaterally elongated slab at the caudal border of the anterolateral division was observed. Labeling in the dorsal cortex was contiguous with this band. Bats stimulated with pairs of first and second harmonic FM stimuli separated by short time delays showed similar patterns of labeling, with the addition of another dorsoventrally elongated region of uptake in the more rostral part of the anterolateral division, associated with label in the dorsal cortex. By comparison to control cases exposed to delayed pairs of first and third harmonic signals, or to a second harmonic constant-frequency tone burst at the bat's reference frequency (ca. 60 kHz), we deduced that this additional region of uptake was attributable to the first harmonic FM component. To elucidate further the details of the tonotopic organization and to correlate the frequency representation with anatomical features of the IC, fine-grained maps of single-unit best frequencies were obtained in the central nucleus. Isofrequency contours were reconstructed by computer from five bats after focal, iontophoretic injection of horseradish peroxidase to locate the penetrations and trace connections of the FM2 area. We found that the tissue volume representing FM2 frequencies (50-60 kHz) showed approximately a sixfold overrepresentation for this frequency band. This region occupied most of the caudal portion of the anterolateral division of the central nucleus. Only a single tonotopic representation was found in the central nucleus, consistent with the pattern seen in other mammals. However, isofrequency contours in the anterolateral division were oriented dorsoventrally, approximately parallel to the coronal plane. The small band of frequencies (ca. 60-62 kHz) associated with the dominant constant-frequency component of the biosonar signal was even more dramatically overrepresented (40x) and was confined to the dorsoposterior division, as previously reported by Zook et al. (1985, 530-456).(ABSTRACT TRUNCATED AT 400 WORDS)     

Beta-oxidation of [1-14C]palmitic acid by mouse astrocytes in primary culture: effects of agents implicated in the encephalopathy of Reye's syndrome.

beta-Oxidation of [1-14C]palmitic acid was examined in homogenates of astrocytes cultured from neonatal mouse brain. Under optimal reaction conditions (< or = 50 micrograms protein, 10 min at 37 degrees C), oxidation increased as a function of palmitate concentration (15 microM to 2 mM) and reached a maximum rate of 1.98 +/- 0.29 nmol/min/mg protein (mean +/- SEM) at 0.2 mM substrate. Eadie-Hofstee analysis of data from four experiments yielded apparent values for Vmax of 1.87 nmol/min/mg protein, and for Km, 35-40 microM. There were no dramatic changes in the oxidation rate in cells between 10 and 36 days in culture. During the 10-min assays, less than 0.05% of the radioactivity was converted to 14CO2 by the astrocytes; water-soluble products accounted for 1-2% of the total substrate added. Studies with KCN indicated that 60-70% of the total activity occurred in the mitochondria. We have been studying the structural and functional changes associated with the cerebral encephalopathy of Reye's syndrome (RS). Three-week-old astrocytes exposed to serum from RS children for the final 7 days of culture exhibited minor mitochondrial pleomorphism and had increased numbers of other intracellular organelles. Examination of the effects of agents implicated in RS indicated that oxidation of [1-14C]palmitate was not altered by Na+ salicylate (1-3 mM), but was inhibited by the industrial surfactant, Toximul MP-8 (> or = 10 micrograms/ml), 4-pentenoic acid (> or = 0.1 microM), or with 4 days' exposure to ammonia (10 nM). The latter treatment also resulted in an increase in protein synthesis, cell volume, and malondialdehyde formation. These results suggest that some of the "toxins" implicated in RS inhibit fatty-acid oxidation in the astrocytes and produce other lipid-related abnormalities that could be related to encephalopathy.     

Neuropeptide FF receptors in rat brain: A quantitative light-microscopic autoradiographic study using [125I][D.Tyr1, (NMe)Phe3]NPFF

The anatomical localization of neuropeptide FF receptors was examined by in vitro autoradiography techniques in rat brain sections by using [¹²⁵I][D.Tyr¹, (NMe)Phe³]NPFF. The specific binding of [¹²⁵I][D.Tyr¹, (NMe)Phe³]NPFF reached 90% of the total binding at 0.05 nM in rat spinal cord sections. Up to 40% of the specific binding of [¹²⁵I][D.Tyr¹, (NMe)Phe³]NPFF to rat spinal cord sections was still detectable following fixation with glutaraldehyde. Afterwards, the distribution of NPFF receptors was studied by light microscopy and their densities by microdensitometry with an image analysis system. In the light microscope, [¹²⁵I][D.Tyr¹, (NMe)Phe³]NPFF labelling appeared more or less uniformly distributed over nerve-cell bodies and surrounding neuropil. High concentrations of binding sites were detected in the presubiculum, parafascicular thalamic nucleus, gracile nucleus, spinal trigeminal tract nucleus, and a number of brainstem nuclei, with virtually no labelling in the cerebellum. In several areas a rostrocaudal gradient of sites concentration was observed. Neuropeptide FF receptors are well-placed to control incoming sensory and autonomic information processing. In contrast, the more recently developed areas of the forebrain possessed low density of sites. The distribution of [¹²⁵I][D.Tyr¹, (NMe)Phe³]NPFF binding sites should suggest anatomical substrates for the actions of neuropeptide FF. © 1996 Wiley-Liss, Inc.     

Brain translocator protein occupancy by ONO‐2952 in healthy adults: A Phase 1 PET study using [11C]PBR28

ONO‐2952, a novel antagonist of translocator protein 18 kDa (TSPO), binds with high affinity to TSPO in rat brain and human tumor cell line membrane preparations. This study used the TSPO‐specific PET radioligand [¹¹ C]PBR28 to confirm binding of ONO‐2952 to brain TSPO in human subjects, and evaluate brain TSPO occupancy and its relationship with ONO‐2952 plasma concentration. Sixteen healthy subjects received a single oral dose of 200, 60, 20, or 6 mg ONO‐2952 (n = 4 per dose). Two PET scans with [¹¹ C]PBR28 were conducted ≤7 days apart: at baseline and 24 h after ONO‐2952 administration. [¹¹ C]PBR28 regional distribution volume (V_T) was derived with kinetic modeling using the arterial input function and a two tissue compartment model. Nonspecific binding (V_ND) was obtained on an individual basis for each subject using linear regression as the x‐intercept of the Lassen plot. The binding potential relative to V_ND (BP_ND) was derived as the difference between V_T in the ROI (V_T ROI) and V_ND, normalized to V_ND; BP_ND = (V_T ROI – V_ND)/V_ND. TSPO occupancy was calculated as the change in BP_ND (ΔBP_ND) from individual's baseline scan to the on‐medication scan to the baseline BP_ND value. TSPO occupancy by ONO‐2952 was dose dependent between 20–200 mg, approaching saturation at 200 mg both in the whole brain and in 15 anatomic regions of interest (ROI). Estimated K_i values ranged from 24.1 to 72.2 nM. This open‐label, single‐center, single‐dose study demonstrated engagement of ONO‐2952 to brain TSPO. The relationship between pharmacokinetics and TSPO occupancy observed in this study support the hypothesis that ONO‐2952 could potentially modulate neurosteroid production by binding to brain TSPO.     

Spinocerebellar ataxia type 1, 2, and 3 and restless legs syndrome: striatal dopamine D2 receptor status investigated by [11C]raclopride positron emission tomography.

In spinocerebellar ataxias (SCAs), up to 30% of patients complain of restless legs syndrome (RLS). In primary RLS, a putative role of the dopaminergic system has been postulated. To assess dopaminergic function in SCA1, 2, and 3, dopamine D(2) receptor binding potential (BP) was assessed by [(11)C]raclopride positron emission tomography in 10 SCA patients, 4 of whom suffered from RLS as demonstrated by polysomnography. BP was compared to 9 age-matched control subjects. In 2 SCA patients, striatal BP was clearly reduced (<2 SD below the mean of controls). However, there were no significant group differences between SCA and controls, largely owing to a significantly higher variance of striatal BP in SCA. BP was negatively correlated with disease duration. The fit suggests an increased BP in early stages, followed by a moderate decline in all quantified regions (caudate, dorsal putamen, ventral striatum) presumably reflecting a progressive loss of D(2) receptors. RLS in SCA was not accompanied by a significant reduction of D(2) receptor availability in the striatum. This missing correlation may point to an extrastriatal origin of RLS.     

Initial detection of [H]clonidine binding to solubilized rat brainα2-adrenergic receptors: regulation by guanine nucleotides

α₂-adrenergic receptors labeled by [³H]clonidine (α₂-antagonist) can be solubilized from the rat brain with a zwitterionic detergent, 3-[(3-cholamidopropyl)-dimethylammonio]-1-propane sulfonate (CHAPS). CHAPS-solubilized receptors have the same characteristics of membrane-boundα₂-receptors in the brain, and the regulation of receptor binding by guanine nucleotides is retained in the soluble state.     

High occupancy of sigma-1 receptors in the human brain after single oral administration of fluvoxamine: a positron emission tomography study using [11C]SA4503.

BACKGROUND: Sigma-1 receptors might be implicated in the pathophysiology of psychiatric diseases, as well as in the mechanisms of action of some selective serotonin reuptake inhibitors (SSRIs). Among the several SSRIs, fluvoxamine has the highest affinity for sigma-1 receptors (Ki = 36 nM), whereas paroxetine shows low affinity (Ki = 1893 nM). The present study was undertaken to examine whether fluvoxamine binds to sigma-1 receptors in living human brain. METHODS: A dynamic positron emission tomography (PET) data acquisition using the selective sigma-1 receptor ligand [(11)C]SA4503 was performed with arterial blood sampling to evaluate quantitatively the binding of [(11)C]SA4503 to sigma-1 receptors in 15 healthy male volunteers. Each subject had two PET scans before and after randomly receiving a single dose of either fluvoxamine (50, 100, 150, or 200 mg) or paroxetine (20 mg). The binding potential of [(11)C]SA4503 in 9 regions of the brain was calculated by a 2-tissue 3-compartment model. In addition, we examined the effects of functional polymorphisms of the sigma-1 receptor (SIGMAR1) gene on the binding potential of [(11)C]SA4503. RESULTS: Fluvoxamine bound to sigma-1 receptors in all brain regions in a dose-dependent manner, whereas paroxetine did not bind to sigma-1 receptors. However, there was no association between the SIGMAR1 gene polymorphism GC-241-240TT and binding potential. CONCLUSIONS: The study demonstrated that fluvoxamine bound to sigma-1 receptors in living human brain at therapeutic doses. These findings suggest that sigma-1 receptors may play an important role in the mechanism of action of fluvoxamine.