Sharon Stone-Elander

Central representation of chronic ongoing neuropathic pain studied by positron emission tomography.

&NA; This study was undertaken to explore whether the neural substrates demonstrated in brain imaging studies on experimentally induced pain are involved in the perception of chronic neuropathic pain. We investigated the cerebral representation of chronic lateralised ongoing pain in patients with painful mononeuropathy (PMN, i.e., pain in the distribution of a nerve, neuralgia) with positron emission tomography (PET), using regional cerebral blood flow (rCBF) as an index for neuronal activity. Eight patients (29–53 years) with PMN in the lower extremity (4 in the right, 4 in the left) were recruited. Paired comparisons of rCBF were made between the patients habitual pain (HP) state and the pain alleviated (PA) state following a successful regional nerve block (RNB) with lidocaine. The ongoing neuropathic pain resulted in activation of bilateral anterior insula, posterior parietal, lateral inferior prefrontal, and posterior cingulate cortices as well as the posterior sector of the right anterior cingulate cortex (ACC), Brodmann area (BA) 24, regardless of the side Of PMN. In addition, a reduction in rCBF was noted in the contralateral posterior thalamus. No significant change of rCBF was detected in the somatosensory areas, i.e., Sl and SII. The cerebral activation pattern, while addressing the differences between the HP and PA states, emphasises the affective‐motivational dimension in chronic ongoing neuropathic pain. The striking preferential activation of the right ACC (BA 24), regardless of the side of the PMN, not only confirms that the ACC participates in the sensorial/affectional aspect of the pain experience but also suggests a possible right hemispheric lateralisation of the ACC for affective processing in chronic ongoing neuropathic pain. Our data suggests that the brain employs different central mechanisms for chronic neuropathic pain and experimentally induced acute pain, respectively.

Pain-related cerebral activation is altered by a distracting cognitive task

Abstract It has previously been suggested that the activity in sensory regions of the brain can be modulated by attentional mechanisms during parallel cognitive processing. To investigate whether such attention‐related modulations are present in the processing of pain, the regional cerebral blood flow was measured using [15O]butanol and positron emission tomography in conditions involving both pain and parallel cognitive demands. The painful stimulus consisted of the standard cold pressor test and the cognitive task was a computerised perceptual maze test. The activations during the maze test reproduced findings in previous studies of the same cognitive task. The cold pressor test evoked significant activity in the contralateral S1, and bilaterally in the somatosensory association areas (including S2), the ACC and the mid‐insula. The activity in the somatosensory association areas and periaqueductal gray/midbrain were significantly modified, i.e. relatively decreased, when the subjects also were performing the maze task. The altered activity was accompanied with significantly lower ratings of pain during the cognitive task. In contrast, lateral orbitofrontal regions showed a relative increase of activity during pain combined with the maze task as compared to only pain, which suggests the possibility of the involvement of frontal cortex in modulation of regions processing pain.

Vascular endothelial growth factor B controls endothelial fatty acid uptake

The vascular endothelial growth factors (VEGFs) are major angiogenic regulators and are involved in several aspects of endothelial cell physiology. However, the detailed role of VEGF-B in blood vessel function has remained unclear. Here we show that VEGF-B has an unexpected role in endothelial targeting of lipids to peripheral tissues. Dietary lipids present in circulation have to be transported through the vascular endothelium to be metabolized by tissue cells, a mechanism that is poorly understood. Bioinformatic analysis showed that Vegfb was tightly co-expressed with nuclear-encoded mitochondrial genes across a large variety of physiological conditions in mice, pointing to a role for VEGF-B in metabolism. VEGF-B specifically controlled endothelial uptake of fatty acids via transcriptional regulation of vascular fatty acid transport proteins. As a consequence, Vegfb-/- mice showed less uptake and accumulation of lipids in muscle, heart and brown adipose tissue, and instead shunted lipids to white adipose tissue. This regulation was mediated by VEGF receptor 1 and neuropilin 1 expressed by the endothelium. The co-expression of VEGF-B and mitochondrial proteins introduces a novel regulatory mechanism, whereby endothelial lipid uptake and mitochondrial lipid use are tightly coordinated. The involvement of VEGF-B in lipid uptake may open up the possibility for novel strategies to modulate pathological lipid accumulation in diabetes, obesity and cardiovascular diseases.

PET analysis of human dopamine receptor subtypes using 11C-SCH 23390 and 11C-raclopride.

Tracer doses of 11C-SCH 23390 and 11C-raclopride, selective D1-dopamine and D2-dopamine receptor antagonists, respectively, were injected intravenously into three healthy male volunteers and two drug-treated schizophrenic patients. Regional radioactivity in brain and plasma was followed during 1 h by positron emission tomography (PET). After injection of both ligands a high accumulation of radioactivity was observed in the dopamine-rich caudate putamen. Experiments with 11C-SCH 23390, but not 11C-raclopride, showed a conspicuous accumulation of radioactivity also in the neocortex. None of the ligands accumulated in the dopamine-poor cerebellum. Specific binding of 11C-raclopride in the putamen was reduced by more than 80% in schizophrenic patients treated with antipsychotic doses of sulpiride or cis(Z)-flupentixol decanoate. 11C-SCH 23390 binding was slightly reduced in both the cortex and the putamen after treatment with cis(Z)-flupentixol decanoate but not after sulpiride. The results indicate that clinical antipsychotic drug treatment with sulpiride and cis(Z)-flupentixol decanoate causes a substantial blockade of D2-dopamine receptors in the basal ganglia but has only a minor effect on D1-dopamine receptors.

Traumatic nociceptive pain activates the hypothalamus and the periaqueductal gray: a positron emission tomography study

&NA; The study was conducted to investigate which areas of the brain respond to a painful encounter of minor dermal injury (a model of clinical pain)_elicited by intracutaneous injection of a minute amount of ethanol. Four healthy volunteers (27–46 years) were subjected to positron emission tomographic (PET) investigation of regional cerebral blood flow (rCBF), using [15O]butanol as tracer. The ethanol (20 &mgr;l, 70%) and saline (20 &mgr;l, 0.9%) were injected intracutaneously 3 times in a single‐blinded, semi‐randomised manner for the pain experiment. All the injections were performed, adjacent to each other, at the lateral aspect of the right upper arm. Subjective sensory intensity of pain, unpleasantness and anxiety were rated with separate 100‐mm visual analogue scales together with the Spielbergers State Anxiety Inventory (Spielberger et al. 1970) and heart rate. Paired‐subtraction (pixel‐by‐pixel) between ethanol and saline was performed. Traumatic pain significantly caused higher ratings of intensity and affect scales, i.e., pain intensity, unpleasantness and increased sympathetic activity (evidenced by tachycardia). In contrast the anxiety rating remained unchanged. Acute traumatic nociceptive pain prominently activated the hypothalamus and periaqueductal gray (PAG). In addition, activations of the prefrontal cortex (PFC), insular, anterior cingulate cortex (ACC), posterior parietal cortex (PPC), primary motor/somatosensory areas (MI/SI: face, upper arm), supplementary motor area (SMA), and cerebellum were also demonstrated. The central processing of the pain‐relevant/anticipatory arousal also engaged the PAG. This study demonstrates the involvement of the human cerebral cortex in perception, arousal, cognitive evaluative processes, and, hence, affective reactions (somatic/ autonomic outflow) associated with pain. The pain stimulus of traumatic character may, by its very nature, evoke the central processing to involve both the hypothalamus and the PAG.

Anticipatory coping of pain expressed in the human anterior cingulate cortex: a positron emission tomography study.

We used positron emission tomography (PET) to monitor the regional cerebral blood flow (rCBF) as an index of brain activity in regions proposed to participate in affective-motivational and cognitive-evaluative dimensions of pain during anticipation of a noxious stimulation. Specifically we were interested in the anterior cingulate cortex (ACC), the ventromedial prefrontal cortex (VMPFC) and the periaqueductal grey (PAG). Anticipating an unpredictable and unlearned pain stimulus activated the right ACC, the VMPFC and the PAG while anticipating a learned pain-stimulus resulted in a decreased activity in the ACC and the VMPFC. These patterns are compatible with two facets of affect-laden cognitive coping: alertness and attention-distraction. The right-preponderant expression of the changes in the ACC supports the hypothesis of a preferential role of the non-dominant hemisphere in negative emotional processing. The data demonstrate an anticipatory coping mechanism and illustrate a neurophysiological process underlying the modulation of attention to pain.

Stereoselective binding of 11C-raclopride in living human brain--a search for extrastriatal central D2-dopamine receptors by PET.

The selective D2-dopamine receptor antagonist raclopride and its pharmacologically inactive (R)-enantiomer FLB472 were labelled with 11C and used in a study with positron emission tomography to examine the stereoselectivity of 11C-raclopride binding to central D2-dopamine receptors in three healthy men. After the injection of 11C-raclopride, there was a high accumulation of radioactivity in the dopamine-rich basal ganglia, whereas after the injection of 11C-FLB472 there was no such accumulation of radioactivity. Thus, the binding of 11C-raclopride is stereoselective. Distribution ratios [radioactivity in a brain region/“free” (not protein-bound) radioactivity in plasma] were calculated for the two enantiomers to study regional differences in the accumulation of radioactivity. The distribution ratios in white matter were similar for the two enantiomers. In the putamen, a three to four-fold higher distribution ratio was found for 11C-raclopride than for 11C-FLB472, reflecting the presence of specific binding of 11C-raclopride binding to D2-dopamine receptors in the basal ganglia. In the temporal and frontal cortices the distribution ratios were, however, only a few per cent higher for 11C-raclopride than for 11C-FLB472, indicating that if D2-dopamine receptors are present in the human neocortex, then their density is indeed very low.

Targeting VEGF-B as a novel treatment for insulin resistance and type 2 diabetes

The prevalence of type 2 diabetes is rapidly increasing, with severe socioeconomic impacts. Excess lipid deposition in peripheral tissues impairs insulin sensitivity and glucose uptake, and has been proposed to contribute to the pathology of type 2 diabetes. However, few treatment options exist that directly target ectopic lipid accumulation. Recently it was found that vascular endothelial growth factor B (VEGF-B) controls endothelial uptake and transport of fatty acids in heart and skeletal muscle. Here we show that decreased VEGF-B signalling in rodent models of type 2 diabetes restores insulin sensitivity and improves glucose tolerance. Genetic deletion of Vegfb in diabetic db/db mice prevented ectopic lipid deposition, increased muscle glucose uptake and maintained normoglycaemia. Pharmacological inhibition of VEGF-B signalling by antibody administration to db/db mice enhanced glucose tolerance, preserved pancreatic islet architecture, improved β-cell function and ameliorated dyslipidaemia, key elements of type 2 diabetes and the metabolic syndrome. The potential use of VEGF-B neutralization in type 2 diabetes was further elucidated in rats fed a high-fat diet, in which it normalized insulin sensitivity and increased glucose uptake in skeletal muscle and heart. Our results demonstrate that the vascular endothelium can function as an efficient barrier to excess muscle lipid uptake even under conditions of severe obesity and type 2 diabetes, and that this barrier can be maintained by inhibition of VEGF-B signalling. We propose VEGF-B antagonism as a novel pharmacological approach for type 2 diabetes, targeting the lipid-transport properties of the endothelium to improve muscle insulin sensitivity and glucose disposal.

A PET activation study of dynamic mechanical allodynia in patients with mononeuropathy

The objective of this study was to investigate the central processing of dynamic mechanical allodynia in patients with mononeuropathy. Regional cerebral blood flow, as an indicator of neuronal activity, was measured with positron emission tomography. Paired comparisons were made between three different states; rest, allodynia during brushing the painful skin area, and brushing of the homologous contralateral area. Bilateral activations were observed in the primary somatosensory cortex (S1) and the secondary somatosensory cortex (S2) during allodynia compared to rest. The S1 activation contralateral to the site of the stimulus was more expressed during allodynia than during innocuous touch. Significant activations of the contralateral posterior parietal cortex, the periaqueductal gray (PAG), the thalamus bilaterally and motor areas were also observed in the allodynic state compared to both non-allodynic states. In the anterior cingulate cortex (ACC) there was only a suggested activation when the allodynic state was compared with the non-allodynic states. In order to account for the individual variability in the intensity of allodynia and ongoing spontaneous pain, rCBF was regressed on the individually reported pain intensity, and significant covariations were observed in the ACC and the right anterior insula. Significantly decreased regional blood flow was observed bilaterally in the medial and lateral temporal lobe as well as in the occipital and posterior cingulate cortices when the allodynic state was compared to the non-painful conditions. This finding is consistent with previous studies suggesting attentional modulation and a central coping strategy for known and expected painful stimuli. Involvement of the medial pain system has previously been reported in patients with mononeuropathy during ongoing spontaneous pain. This study reveals a bilateral activation of the lateral pain system as well as involvement of the medial pain system during dynamic mechanical allodynia in patients with mononeuropathy.

Microwave-enhanced radiochemistry

The application of microwaves to synthetic organic chemistry is currently experiencing considerable growth. Here we show how the area of radiochemistry, with particular reference to the synthesis of 3H- (or T-), 11C- and 18F-labelled compounds, can benefit. Faster, cleaner, more selective reactions are possible with the formation of much reduced levels of radioactive waste.