Surgical treatment of spinal cord compression due to Hirayama disease: illustrative case

BACKGROUND

Hirayama disease (HD), also known as juvenile spinal muscular atrophy, is a rare condition in which flexion of the cervical neck causes compression and ischemic changes to the anterior horns of the spinal cord. Here the authors presented the first reported case of HD in North America that was successfully treated via surgical intervention.

OBSERVATIONS

The patient was a 15-year boy with insidious onset upper limb weakness and atrophy. His findings were a classic presentation of HD although his complex history and relative rarity of the disease caused him to remain undiagnosed for months. After conservative management via cervical collar failed, the patient was successfully treated via C5-C7 anterior cervical discectomy and fusion. The patient’s symptoms stabilized by the 3-month follow-up.

LESSONS

The diagnosis of HD is easy to miss because of the lack of reporting and widespread knowledge of this condition in North America. Thus, when presented with a case of insidious onset limb weakness in a juvenile patient, HD should be placed on the differential list and verified with cervical flexion magnetic resonance imaging. Additionally, surgical intervention should be considered a safe and effective option for HD when conservative methods have failed.

Focused versus conventional radiotherapy in spinal oncology: is there any difference in fusion rates and pseudoarthrosis?

INTRODUCTION

Radiotherapy is considered standard of care for adjuvant peri-operative treatment of many spinal tumors, including those with instrumented fusion. Unfortunately, radiation treatment has been linked to increased risk of pseudoarthrosis. Newer focused radiotherapy strategies with enhanced conformality could offer improved fusion rates for these patients, but this has not been confirmed.

METHODS

We performed a retrospective analysis of patients at three tertiary care academic institutions with primary and secondary spinal malignancies that underwent resection, instrumented fusion, and peri-operative radiotherapy. Two board certified neuro-radiologists used the Lenke fusion score to grade fusion status at 6 and 12-months after surgery. Secondary outcomes included clinical pseudoarthrosis, wound complications, the effect of radiation timing and radiobiological dose delivered, the use of photons versus protons, tumor type, tumor location, and use of autograft on fusion outcomes.

RESULTS

After review of 1252 spinal tumor patients, there were 60 patients with at least 6 months follow-up that were included in our analyses. Twenty-five of these patients received focused radiotherapy, 20 patients received conventional radiotherapy, and 15 patients were treated with protons. There was no significant difference between the groups for covariates such as smoking status, obesity, diabetes, intraoperative use of autograft, and use of peri-operative chemotherapy. There was a significantly higher rate of fusion for patients treated with focused radiotherapy compared to those treated with conventional radiotherapy at 6-months (64.0% versus 30.0%, Odds ratio: 4.15, p = 0.036) and 12-months (80.0% versus 42.1%, OR: 5.50, p = 0.022). There was a significantly higher rate of clinical pseudoarthrosis in the conventional radiotherapy cohort compared to patients in the focused radiotherapy cohort (19.1% versus 0%, p = 0.037). There was no difference in fusion outcomes for any of the secondary outcomes except for use of autograft. The use of intra-operative autograft was associated with an improved fusion at 12-months (66.7% versus 37.5%, OR: 3.33, p = 0.043).

CONCLUSION

Focused radiotherapy may be associated with an improved rate of fusion and clinical pseudoarthrosis when compared to conventional radiation delivery strategies in patients with spinal tumors. Use of autograft at the time of surgery may be associated with improved 12-month fusion rates. Further large-scale prospective and randomized controlled studies are needed to better stratify the effects of radiation delivery modality in these patients.

Tools for optimising pharmacotherapy in psychiatry (therapeutic drug monitoring, molecular brain imaging and pharmacogenetic tests): focus on antidepressants

Objectives: More than 40 drugs are available to treat affective disorders. Individual selection of the optimal drug and dose is required to attain the highest possible efficacy and acceptable tolerability for every patient.Methods: This review, which includes more than 500 articles selected by 30 experts, combines relevant knowledge on studies investigating the pharmacokinetics, pharmacodynamics and pharmacogenetics of 33 antidepressant drugs and of 4 drugs approved for augmentation in cases of insufficient response to antidepressant monotherapy. Such studies typically measure drug concentrations in blood (i.e. therapeutic drug monitoring) and genotype relevant genetic polymorphisms of enzymes, transporters or receptors involved in drug metabolism or mechanism of action. Imaging studies, primarily positron emission tomography that relates drug concentrations in blood and radioligand binding, are considered to quantify target structure occupancy by the antidepressant drugs in vivo. Results: Evidence is given that in vivo imaging, therapeutic drug monitoring and genotyping and/or phenotyping of drug metabolising enzymes should be an integral part in the development of any new antidepressant drug.Conclusions: To guide antidepressant drug therapy in everyday practice, there are multiple indications such as uncertain adherence, polypharmacy, nonresponse and/or adverse reactions under therapeutically recommended doses, where therapeutic drug monitoring and cytochrome P450 genotyping and/or phenotyping should be applied as valid tools of precision medicine.

Is the Blind Spot Enlarged in Early Glaucoma?

Purpose

We investigated whether the blind spot is larger in early “preperimetric” glaucoma with already deeply excavated optic discs than in normal persons.

Methods

We examined eight eyes of five patients with definite glaucomatous optic disc cupping but normal visual fields. Ten eyes of five normal healthy volunteers, with normal central excavation, served as controls. With SLO-perimetry we measured the differential light sensitivity 0.5-1.0° outside the disc margins, “within” the center (Goldmann V stimulus) and along the horizontal meridian of the optic discs. Optic disc topography was documented with the Heidelberg Retina Tomograph (HRT).

Results

Differential light sensitivities adjacent to the optic discs did not differ in the two groups (normal 8.3dB, early glaucoma 8.4dB). Goldmann IV stimuli presented on the horizontal meridian of optic discs with glaucomatous cupping were seen up to 0.7° centrally (i.e., towards the center) of the disc margin. In the control group this distance was significantly greater (1.3°). The light differential thresholds with stimulus presentation in the disc center (Goldmann V) were significantly higher in the glaucoma group (0±2.8dB) than in the normal controls (6.6±1.3dB), though disc size was the same in both groups.

Conclusions

Blind spots of normal discs seem to be smaller than those of deeply excavated discs in eyes with early glaucoma, possibly because there is more light scattering by the normal disc surface towards the adjacent functioning retina.

Serotonin transporter binding is reduced in seasonal affective disorder following light therapy

OBJECTIVE

To investigate the effects of light therapy on serotonin transporter binding (5-HTT BP_ND ), an index of 5-HTT levels, in the anterior cingulate and prefrontal cortices (ACC and PFC) during winter in seasonal affective disorder (SAD). 5-HTT BP_ND fluctuates seasonally to a greater extent in SAD relative to health. We hypothesized that in SAD, 5-HTT BP_ND would be reduced in the ACC and PFC following light therapy.

METHODS

Eleven SAD participants underwent [¹¹ C] DASB positron emission tomography (PET) scans to measure 5-HTT BP_ND before and after 2 weeks of daily morning light therapy.

RESULTS

The primary finding was a main effect of treatment on 5-HTT BP_ND in the ACC and PFC (repeated-measures manova, F_(2,9) = 6.82, P = 0.016). This effect was significant in the ACC (F_(1,10) = 15.11 and P = 0.003, magnitude of decrease, 11.94%) and PFC (F_(1,10) = 8.33, P = 0.016, magnitude of decrease, 9.13%). 5-HTT BP_ND also decreased in other regions assayed following light therapy (repeated-measures manova, F_(4,7) = 8.54, P = 0.028) including the hippocampus, ventral striatum, dorsal putamen, thalamus and midbrain (F_(1,10) = 8.02-36.94, P < 0.0001-0.018; magnitude -8.83% to -16.74%).

CONCLUSIONS

These results demonstrate that light therapy reaches an important therapeutic target in the treatment of SAD and provide a basis for improvement of this treatment via application of [¹¹ C]DASB PET.

Light therapy and serotonin transporter binding in the anterior cingulate and prefrontal cortex

OBJECTIVE

To investigate the effects of light therapy on serotonin transporter binding (5-HTT BPND ), an index of 5-HTT levels, in the anterior cingulate and prefrontal cortices (ACC and PFC) of healthy individuals during the fall and winter. Twenty-five per cent of healthy individuals experience seasonal mood changes that affect functioning. 5-HTT BPND has been found to be higher across multiple brain regions in the fall and winter relative to spring and summer, and elevated 5-HTT BPND may lead to extracellular serotonin loss and low mood. We hypothesized that, during the fall and winter, light therapy would reduce 5-HTT BPND in the ACC and PFC, which sample brain regions involved in mood regulation.

METHOD

In a single-blind, placebo-controlled, counterbalanced, crossover design, [(11) C]DASB positron emission tomography was used measure 5-HTT BPND following light therapy and placebo conditions during fall and winter.

RESULTS

In winter, light therapy significantly decreased 5-HTT BPND by 12% in the ACC relative to placebo (F1,9 = 18.04, P = 0.002). In the fall, no significant change in 5-HTT BPND was found in any region across conditions.

CONCLUSION

These results identify, for the first time, a central biomarker associated with the intervention of light therapy in humans which may be applied to further develop this treatment for prevention of seasonal depression.

Neuroinflammation in healthy aging: a PET study using a novel Translocator Protein 18kDa (TSPO) radioligand, [(18)F]-FEPPA

One of the cellular markers of neuroinflammation is increased microglia activation, characterized by overexpression of mitochondrial 18kDa Translocator Protein (TSPO). TSPO expression can be quantified in-vivo using the positron emission tomography (PET) radioligand [(18)F]-FEPPA. This study examined microglial activation as measured with [(18)F]-FEPPA PET across the adult lifespan in a group of healthy volunteers. We performed genotyping for the rs6971 TS.PO gene polymorphism to control for the known variability in binding affinity. Thirty-three healthy volunteers (age range: 19-82years; 22 high affinity binders (HAB), 11 mixed affinity binders (MAB)) underwent [(18)F]-FEPPA PET scans, acquired on the High Resolution Research Tomograph (HRRT) and analyzed using a 2-tissue compartment model. Regression analyses were performed to examine the effect of age adjusting for genetic status on [(18)F]-FEPPA total distribution volumes (VT) in the hippocampus, temporal, and prefrontal cortex. We found no significant effect of age on [(18)F]-FEPPA VT (F (1,30)=0.918; p=0.346), and a significant effect of genetic polymorphism (F (1,30)=8.767; p=0.006). This is the first in-vivo study to evaluate age-related changes in TSPO binding, using the new generation TSPO radioligands. Increased neuroinflammation, as measured with [(18)F]-FEPPA PET was not associated with normal aging, suggesting that healthy elderly individuals may serve as useful benchmark against patients with neurodegenerative disorders where neuroinflammation may be present.

A randomised trial of enteric-coated nutrient pellets to stimulate gastrointestinal peptide release and lower glycaemia in type 2 diabetes

AIMS/HYPOTHESES

Glucagon-like peptide-1 (GLP-1), an important mediator of postprandial glycaemia, could potentially be stimulated by delivering small quantities of nutrient to a long length of distal gut. We aimed to determine whether enteric-coated pellets, releasing small amounts of lauric acid throughout the ileum and colon, could reduce glycaemic responses to meals in type 2 diabetes, associated with stimulation of GLP-1.

METHODS

Eligible patients, who had type 2 diabetes controlled by diet or metformin, were each studied on two occasions in a hospital setting. After an overnight fast, patients consumed 5 g active pellets (47% lauric acid by weight) or placebo with breakfast (T = 0 min) and lunch (T = 240 min), in a crossover design with order randomised by the hospital pharmacy and allocation concealed by numbered containers. Patients and investigators making measurements were blinded to the intervention. Blood was sampled frequently for blood glucose (the primary outcome) and hormone assays.

RESULTS

Eight patients were randomised (four to receive either intervention first), and all completed the study without adverse effects. Blood glucose was lower after breakfast (T = 0-240 min, area under the curve (AUC) 2,075 ± 368 vs 2,216 ± 163 mmol/l × min) and lunch (T = 240-480 min, AUC 1,916 ± 115 vs 2,088 ± 151 mmol/l × min) (p = 0.02 for each) after active pellets than after placebo. Plasma GLP-1 concentrations were higher after breakfast (p = 0.08) and lunch (p = 0.04) for active pellets. While there were no differences in insulin or glucose-dependent insulinotropic polypeptide concentrations, glucagon concentrations were higher after breakfast and lunch (p = 0.002 for each) for active pellets.

CONCLUSIONS/INTERPRETATION

Delivering small amounts of nutrient to the ileum and colon can stimulate substantial endogenous GLP-1 release and attenuate postprandial glycaemia. This novel approach has therapeutic potential in type 2 diabetes.

TRIAL REGISTRATION

Australian New Zealand Clinical Trials Registry ACTRN12612000600842.

FUNDING

The study was funded by Meyer Nutriceuticals.

Relationship of monoamine oxidase A binding to adaptive and maladaptive personality traits

BACKGROUND

Monoamine oxidase A (MAOA) is an important enzyme that metabolizes monoamines such as serotonin, norepinephrine and dopamine in the brain. In prefrontal cortex, low MAOA binding is associated with aggression and high binding is associated with major depressive disorder (MDD) and also risk for recurrence of depressive episodes. In rodent models, low MAOA levels are associated with increased aggression and fear conditioning, and decreased social and exploratory investigative behaviors. Our objective was to measure MAOA binding in prefrontal cortex and concurrently evaluate a broad range of validated personality traits. We hypothesized that prefrontal MAOA binding would correlate negatively with angry-hostility, a trait related to aggression/anger, and positively with traits intuitively related to adaptive investigative behavior.

METHOD

Participants were aged 19-49 years, healthy and non-smoking. MAOA binding was measured with [11C]harmine positron emission tomography (PET) in prefrontal brain regions and personality traits were measured with the NEO Personality Inventory Revised (NEO PI-R).

RESULTS

Prefrontal MAOA binding correlated negatively with angry-hostility (r=-0.515, p=0.001) and positively with deliberation (r=0.514, p=0.001). In a two-factor regression model, these facets explained 38% of variance in prefrontal MAOA binding. A similar relationship was found in prefrontal cortex subregions.

CONCLUSIONS

We propose a new continuum describing the relationship between personality and MAOA: deliberate/thoughtful contrasting aggressive/impulsive. Additionally, the association between high MAOA binding and greater deliberation may explain why some people have moderately high levels of MAOA, although very high levels occur during MDD. In health, higher MAOA binding is associated with an adaptive personality facet.

Effect of lipase inhibition on gastric emptying of, and the glycemic and incretin responses to, an oil/aqueous drink in type 2 diabetes mellitus

This study examined the effects of the lipase inhibitor, orlistat, on gastric emptying of, and the glycemic and incretin hormone responses to, a drink containing oil and glucose components in patients with type 2 diabetes. Seven patients (aged 58 +/- 5 yr), managed by diet alone, consumed 60 ml olive oil (labeled with 20 MBq (99m)Tc-V-thiocyanate) and 300 ml water containing 75 g glucose (labeled with 6 MBq (67)Ga-EDTA), on two occasions, with and without 120 mg orlistat, positioned in the left lateral decubitus position with their back against a gamma camera. Venous blood samples, for measurement of blood glucose and plasma insulin, glucagon-like peptide-1 and glucose-dependent insulintropic polypeptide were obtained immediately before, and after, the drink. Gastric emptying of both oil (P < 0.001) and glucose (P < 0.0005) was faster after orlistat compared with control. Postprandial blood glucose (P < 0.001) and plasma insulin (P < 0.05) were substantially greater after orlistat compared with control. In contrast, plasma glucagon-like peptide-1 (P < 0.005) and glucose-dependent insulintropic polypeptide (P < 0.05) were less after orlistat. In conclusion, inhibition of fat digestion, by orlistat, may exacerbate postprandial glycemia, as a result of more rapid gastric emptying and a diminished incretin response.

Lower dopamine transporter binding potential in striatum during depression

Previous studies suggest that there is a dopamine lowering process during major depressive episodes (MDE). To investigate this, we measured the dopamine transporter binding potential (DAT BP) in the striatum of depressed and healthy subjects using [(11)C]RTI-32 PET. The DAT, a predominantly presynaptic receptor, decreases in density after chronic dopamine depletion and the BP is proportional to receptor density. In all striatal regions, subjects with MDE had significantly lower DAT BP. Low striatal DAT BP in MDE is consistent with a downregulation of DAT in response to a dopamine lowering process. There was also a strong, highly significant, inverse correlation between striatal DAT BP and neuropsychological tests of dopamine-implicated symptoms in patients (i.e. patients with lower DAT BP performed better). Lower DAT BP itself reduces extracellular clearance of dopamine. Patients who did not decrease their striatal DAT BP failed to compensate for low dopamine and showed greater impairment on dopamine related tests.

Occupancy of serotonin transporters by paroxetine and citalopram during treatment of depression: a [(11)C]DASB PET imaging study

OBJECTIVE

Selective serotonin reuptake inhibitors are commonly used to treat major depression; however, the percentage of serotonin (5-HT) transporter (5-HTT) sites occupied during clinical dosing is unknown. This study measured the proportion of 5-HTT sites blocked during paroxetine and citalopram treatment of depression and assessed the relationship between serum paroxetine levels and the proportion of 5-HTT sites blocked.

METHOD

Twelve medication-free depressed patients completed a 6-week trial of either paroxetine (N=8) or citalopram (N=4). Striatal 5-HTT binding potential was measured with [(11)C]DASB and positron emission tomography, before and after 4 weeks of treatment. The binding potential is proportional to receptor density. Striatal 5-HTT binding potential was measured twice in six healthy subjects and once in 11 healthy subjects.

RESULTS

A significant decrease in striatal 5-HTT binding potential was found after either treatment, compared to changes found over a 4-week period in healthy subjects. For patients treated with 20 mg/day of paroxetine (N=7), the mean proportion of 5-HTT sites occupied was 83%. For patients treated with 20 mg/day of citalopram (N=4), the mean 5-HTT occupancy was 77%. 5-HTT occupancy increased in a nonlinear relationship with serum levels of paroxetine such that a plateau of occupancy around 85% occurred for serum paroxetine levels greater than 28 microg/liter.

CONCLUSIONS

During treatment with clinical doses of paroxetine or citalopram, approximately 80% of 5-HTT receptors are occupied. This change in 5-HTT binding potential is greater than the known physiological range of changes in 5-HTT binding potential but may be necessary for some therapeutic effects.

Positron emission tomography quantification of [(11)C]-DASB binding to the human serotonin transporter: modeling strategies

[(11) C]-DASB, namely [(11) C]-3-amino-4-(2-dimethylaminomethyl-phenylsulfanyl)-benzonitrile, is a new highly selective radioligand for the in vivo visualization of the serotonin transporter (SERT) using positron emission tomography (PET). The current study evaluates different kinetic modeling strategies for quantification of [(11)C]-DASB binding in five healthy humans. Kinetic analyses of tissue data were performed with a one-tissue (1CM) and a two-tissue (2CM) compartment model. Time-activity curves were well described by a 1CM for all regions. A 2CM model with four parameters failed to converge reliably. Reliable fits of the data were obtained only if no more than three parameters were allowed to vary. However, even then, the rate constants k(3) and k(4) were estimated with poor precision. Only the ratio k(3)/k(4) was stable. Goodness of fit was not improved by using a 2CM as compared with a 1CM. The minimal study duration required to obtain stable k(3)/k(4) estimates was 80 minutes. For routine use of [(11)C]-DASB, several simplified methods using the cerebellum as a reference region to estimate nonspecific binding were also evaluated. The transient equilibrium, the linear graphical analysis, the ratio of target to reference region, and the simplified reference tissue methods all gave binding potential values consistent with those obtained with the 2CM. The suitability of [(11)C]-DASB for research on the SERT using PET is thus supported by the observations that tissue data can be described using a kinetic analysis and that simplified quantitative methods, using the cerebellum as reference, provide reliable estimates of SERT binding parameters.

Duodenal fat intensifies the perception of heartburn

BACKGROUND

Patients with gastro-oesophageal reflux disease (GORD) frequently report that meals high in fat worsen heartburn. Nevertheless, studies to determine whether high fat meals promote gastro-oesophageal reflux have produced conflicting and equivocal conclusions.

PATIENTS AND METHODS

To determine, alternatively, whether fat in the small intestinal lumen intensifies the perception of heartburn, we studied 11 patients with typical heartburn from GORD. After being placed on omeprazole to suppress endogenous acid, these fasting subjects underwent oesophageal perfusions with graded doses of HCl at pH values of 1.0, 1.5, 2.0, and 2.5. Oesophageal perfusions were conducted while the duodenum was perfused with saline (control) and again with fat at 8 g/h.

RESULTS

Time to onset, intensity, and severity of heartburn varied with dose of oesophageal acid (p<0.01). Time to onset was significantly (p<0.01) shorter, and intensity and severity of heartburn significantly (p<0.05) greater, during duodenal perfusion with fat.

CONCLUSION

We conclude that duodenal fat intensifies the perception of heartburn.

Postcibal gastric emptying of pancreatin pellets: effects of dose and meal oil

To treat pancreatic exocrine insufficiency, physicians often prescribe enterically coated pellets of pancreatin to be taken with meals. The pellets are only partially effective in correcting the digestion and absorption of fat. We sought to determine in normal subjects whether emptying of pellets from the postcibal stomach was dose-related and whether the gastric emptying of lipophilic Creon-20 or Pancrease was altered by the presence or the absence of oil in a meal. Gastric emptying of pellets surface-labeled with 113mIn or 99mTc was followed with a gamma camera for 300 min after isocaloric meals. From our observations, we concluded that gastric emptying of 0.28-1.12 g of 1-mm or 2-mm pellets was dose-related (P < 0.01) and emptying of neither Creon-20 nor Pancrease was much affected by oil in the meal.

Changes in regional brain glucose metabolism measured with positron emission tomography after paroxetine treatment of major depression

OBJECTIVE

Depression is commonly associated with frontal hypometabolic activity accompanied by hypermetabolism in certain limbic regions. It is unclear whether successful antidepressant treatments reverse these abnormalities or create new resting levels of metabolism. The aim of the present study was to assess the effects of successful paroxetine treatment on regional glucose metabolism in patients with major depression.

METHOD

Positron emission tomography with [(18)F]fluorodeoxyglucose was performed on 13 male patients before and after 6 weeks of paroxetine therapy. Resting state scans were also acquired under similar conditions in 24 healthy male subjects for comparison.

RESULTS

After successful paroxetine therapy, increased glucose metabolism occurred in dorsolateral, ventrolateral, and medial aspects of the prefrontal cortex (left greater than right), parietal cortex, and dorsal anterior cingulate. Areas of decreased metabolism were noted in both anterior and posterior insular regions (left) as well as right hippocampal and parahippocampal regions. In comparison to metabolism levels in a group of healthy volunteers, the increase in prefrontal metabolic activity represented a normalization of previously reduced metabolic activity, whereas the reduction in pregenual anterior cingulate activity represented a decrease from previously elevated metabolic levels.

CONCLUSIONS

These results provide further support for a dysfunction in cortical-limbic circuitry in depression, which is at least partly reversed after successful paroxetine treatment.

Serotonin 5-HT1A receptor binding potential declines with age as measured by [11C]WAY-100635 and PET

Positron emission tomography (PET) and [11C]WAY-100635 were used to examine the effect of age on serotonin-1A (5-HT1A) receptor binding potential (BP) in 19 healthy subjects. Regions of interest (ROI) were drawn on the co-registered magnetic resonance imaging (MRI) in orbitofrontal (OFC), dorsolateral prefrontal (DLPFC), anterior cingulate (ACC), lateral (LTC), and mediotemporal (MTC), parietal, occipital and cerebellar cortex, and the raphe nuclei. BP values were calculated using a simplified reference tissue method. In addition, a voxelwise analysis was performed using SPM99. Voxelwise analysis revealed a significant global decrease of 5-HT(1A) BP with age (set level <.001). ROI analysis revealed significant age-related 5-HT(1A) BP decreases in DLPFC (r = -0.56), ACC (r = -0.44), OFC (r = -0.42), LTC (r = -0.40), parietal (r = -0.65), and occipital cortex (r = -0.43), but not in MTC or raphe nuclei. Overall, cortical 5-HT(1A) BP declined by approximately 10% per decade, except for the MTC, where we did not find a significant age effect. Hence, careful age matching may be recommended for future studies using PET and [11C]WAY-100635 to examine 5-HT1A receptors.

An introduction to PET and SPECT neuroreceptor quantification models

PET and SPECT using appropriate radioligands allow imaging of certain critical components of neurotransmission such as presynaptic transporters and postsynaptic receptors in living human brains. PET and SPECT data are commonly analyzed by applying tracer kinetic models. These modeling approaches assume a compartmental system and derive the outcome measure called the binding potential, which reflects the densities of transporters or receptors in a brain region of interest. New models are often noninvasive in that they do not require arterial blood sampling. In this review, the concept and principles of tracer kinetic modeling are introduced and commonly used PET and SPECT neuroreceptor quantification models are discussed.

Noradrenergic dysfunction in the prefrontal cortex in depression: an [15O] H2O PET study of the neuromodulatory effects of clonidine

BACKGROUND

Noradrenergic dysfunction has been consistently implicated in depression. Much of the evidence, though, has been indirect, such as an attenuated growth hormone response to the alpha2-adrenoceptor agonist clonidine. To more directly examine central functioning of the noradrenergic system in depression, we have used [15O] H2O positron emission tomography (PET) to measure cerebral blood flow (rCBF) in combination with clonidine as a neuromodulatory probe.

METHODS

Subjects were six depressed and six healthy women, medication free and matched for age and phase of menstrual cycle. Two PET scans were acquired at baseline and two scans at 20 and 35 min following an intravenous clonidine infusion of 1.4 microg/kg while subjects performed a sustained attention task.

RESULTS

The growth hormone response did not show a significant difference between groups. However, PET results revealed a difference in the right superior prefrontal cortex that was resolved as an interaction from decreased rCBF in healthy control subjects but increased rCBF in the depressed group, which was not accounted for by differences in task performance.

CONCLUSIONS

This differential effect of clonidine in the right prefrontal cortex provides in vivo evidence of noradrenergic dysfunction in depression, which we postulate arises from functionally impaired presynaptic alpha2-adrenoceptors as well as regionally "supersensitive" postsynaptic cortical alpha2-adrenoceptors.

Dilutions of low- vs. high-fat diets on intakes and gastric volumes in rats

Rats adapt to changes in dietary energy to maintain nearly constant energy intakes. This regulation indicates that animals sense and respond to nutrient content. We sought to determine whether this response was affected by the fat content of the diet. Our second goal was to determine how energy dilution affected intragastric volumes. Rats were randomized to high (18% w/w) and low fat (4.5% w/w) as the energy density of the diet was altered from 2.0 to 3.5 kcal/g. Average energy intake during 7-h feeds rose steeply (P<.01) when density was increased from 2.0 to 3.0 kcal/g, but modestly as density increased from 3.0 to 3.5 kcal/g. In other rats on 18% vs. 32% fat diets, energy intakes increased significantly (P<.01) as density of the diet was raised from 3.5 to 4.5 kcal/g. During diets at 2.0 and 2.5 kcal/g, animals on 18% fat ate fewer kilocalories than those on 4.5% fat; but over 3.0-4.5 kcal/g, energy intake was similar regardless of fat concentration (4.5-32%). Gastric contents after 7-h feeds increased with grams of food ingested similarly for high- and low-fat diets. We concluded that in rats: (a) compensation to energy dilution or concentration was inexact but (b) was about equal for high- vs. low-fat diets; thus, high fat was as well sensed as high carbohydrate; (c) compensations for energy densities were made despite varied gastric volumes; thus, rats learned to override the stimulus of gastric stretch and to sense energy via extra gastric mechanisms.

The effect of paroxetine on 5-HT(2A) receptors in depression: an [(18)F]setoperone PET imaging study

OBJECTIVE

In the cortex of animals, serotonin (5-HT) levels increase after several weeks of treatment with selective serotonin reuptake inhibitors (SSRIs). Studies using an intrasubject design to examine the effects of SSRI treatment on 5-HT(2A) receptors in the cortex of drug-free depressed patients are needed. In theory, agonist stimulation of 5-HT(2A) receptors could be relevant to SSRI treatment by promoting neuronal growth and survival as well as direct elevation of mood. The objective of this study was to evaluate the effect of 6 weeks of paroxetine treatment on 5-HT(2A) receptors in depressed patients.

METHOD

After a medication-free period of at least 3 months, 19 depressed patients were treated for 6 weeks with paroxetine, 20 mg/day. The authors used [(18)F]setoperone and positron emission tomography to assess 5-HT(2A) receptor binding potential in the patients before and after treatment and in 19 age-matched healthy subjects.

RESULTS

5-HT(2A) binding potential declined with age in all cortical regions in the depressed and healthy subjects. There was a significant interaction between age and treatment effect on 5-HT(2A) binding potential in all cortical regions. Subjects aged 20 to 30 years had a 10% decrease in 5-HT(2A) binding potential after treatment, whereas subjects aged 30 to 40 had no change. No regional differences in 5-HT(2A) binding potential between depressed and healthy subjects were found.

CONCLUSIONS

5-HT(2A) receptors down-regulate in young depressed subjects after treatment with paroxetine, but this down-regulation attenuates with age. This suggests that over 6 weeks paroxetine treatment increases 5-HT agonism on 5-HT(2A) receptors in the cortex of young patients with depression.

Modeling of receptor ligand data in PET and SPECT imaging: a review of major approaches

Over the past decade, a number of new kinetic modeling techniques have been developed for PET and SPECT ligands. This article will review commonly used modeling solutions for reversible positron-emission tomography (PET) and single photon emission computed tomography (SPECT) radioligands, with an emphasis on noninvasive methods. All of the modeling approaches in PET and SPECT assume a compartmental system and derive parameters that describe the compartmental system. These parameters will be defined, and their relationship to analogous parameters in pharmacology will be discussed. Then the major approaches are presented under the categories of graphical or mathematical as well as invasive or noninvasive.

Imaging the serotonin transporter with positron emission tomography: initial human studies with [11C]DAPP and [11C]DASB

Two novel radioligands, N,N-dimethyl-2-(2-amino-4-methoxyphenylthio) b enzylamine (DAPP) and (N,N-dimethyl-2-(2-amino-4-cyanophenylthio) benzylamine (D ASB), were radiolabeled with carbon-11 and evaluated as in vivo probes of the serotonin transporter (SERT) using positron emission tomography (PET). Both compounds are highly selective, with nanomolar affinity for the serotonin transporter and micromolar affinity for the dopamine and norepinephrine transporters. Six volunteers were imaged twice, once with each of the two radioligands. Both ligands displayed very good brain penetration and selective retention in regions rich in serotonin reuptake sites. Both had similar brain uptake and kinetics, but the cyano analogue, [11C]DASB, had a slightly higher brain penetration in all subjects. Plasma analysis revealed that both radiotracers were rapidly metabolized to give mainly hydrophilic species as determined by reverse-phase high-performance liquid chromatography. Inhibition of specific binding to the SERT was demonstrated in three additional subjects imaged with [11C]DASB following an oral dose of the selective serotonin reuptake blocker citalopram. These preliminary studies indicate that both these substituted phenylthiobenzylamines have highly suitable characteristics for probing the serotonin reuptake system with PET in humans.

A voxel-by-voxel analysis of [18F]setoperone PET data shows no substantial serotonin 5-HT(2A) receptor changes in schizophrenia

Several postmortem studies have reported regionally localized decreases in serotonin(2A) receptors (5-HT(2A)R) in schizophrenia. This was not confirmed by two recent [18F]setoperone positron emission tomography (PET) studies. In these two studies relatively large regions of interest (ROIs) were used; hence, 5-HT(2A)R changes may have been missed in some brain areas. Therefore, data from one study were analyzed on a voxel-by-voxel basis using Statistical Parametric Mapping (SPM). We also used this method to examine the relationship between 5-HT(2A)R binding potential (BP) and five PANSS-derived factors: negative, positive, activation, dysphoric and autistic preoccupation. Thirteen schizophrenic patients (10 antipsychotic-naïve, 3 antipsychotic-free; 11 M, 2 F; age 31+/-7 years) and 35 age-matched control subjects (15 M, 20 F; age 30+/-7 years) were scanned. The 5-HT(2A)R BP was determined for each voxel using the pseudoequilibrium ratio method on PET data obtained between 65 and 90 min after [18F]setoperone bolus injection. The resulting parametric 5-HT(2A)R BP images were spatially normalized using a ligand specific template. Analyses of covariance were done using SPM99 with age as covariate. In tests for the effect of schizophrenia and for partial correlations between 5-HT(2A)R BP and the five factors, corrected P values <0.05 at cluster or voxel level were considered significant. No significant differences were detected between patients and control subjects, and no significant correlations were observed between 5-HT(2A)R BP and any of the five factors. Thus, in agreement with the previous ROI studies, voxel-by-voxel analysis confirmed the lack of substantial 5-HT(2A)R BP differences between schizophrenic patients and control subjects.

beta-blocker binding to human 5-HT(1A) receptors in vivo and in vitro: implications for antidepressant therapy

A novel strategy for improving the treatment of depressive illness is augmentation of antidepressants with a 5-HT1(1A) autoreceptor antagonist. However, trials using the 5-HT1(1A)/beta-blocker pindolol are proving inconsistent. We report how positron emission tomography (PET) and in vitro autoradiography can inform trials of antidepressant augmentation. We show that in healthy volunteers, in vivo, pindolol (n = 10) and penbutolol (n = 4), but not tertatolol (n = 4) occupy the human 5-HT(1A) receptors, at clinical doses. Pindolol, as well as the beta-blockers penbutolol and tertatolol, has high affinity for human 5-HT(1A) receptors in post-mortem brain slices (n = 4). Pindolol shows preference for 5-HT(1A) autoreceptors versus the post-synaptic receptors both in vitro and in vivo. Our data reveal that pindolol doses used in antidepressant trials so far are suboptimal for significant occupancy at the 5-HT(1A) autoreceptor. Penbutolol or higher doses of pindolol are candidates for testing as antidepressant augmenting regimes in future clinical trials.

Novel radiotracers for imaging the serotonin transporter by positron emission tomography: synthesis, radiosynthesis, and in vitro and ex vivo evaluation of (11)C-labeled 2-(phenylthio)araalkylamines

A series of four 2-(phenylthio)araalkylamines have been radiolabeled with (11)C and evaluated as potential radiotracers for imaging the serotonin transporter (SERT) by positron emission tomography (PET). All four candidates display high affinity for SERT and low affinity for the dopamine or norepinephrine transporters using in vitro binding assays. Biodistribution studies in rats demonstrated that tail-vein injection of the (11)C-labeled radiotracers resulted in high brain uptake of radioactivity with a preferential distribution in brain regions known to be rich in SERT such as hypothalamus and thalamus. The most promising candidate, 16, had hypothalamus-to-cerebellum ratios of 9:1, 1 h postinjection, an indication of high specific to nonspecific binding. Ex vivo pharmacological studies demonstrated that uptake in SERT-rich brain regions was both saturable and selective for SERT. Two of the tested radiotracers, 15 and 16, have highly favorable properties for imaging SERT and will be used in pilot human PET imaging studies.

Variation in contrasting forms of 'memorising' and associated observables

BACKGROUND

There is a posited conceptual distinction in the student learning literature in higher education between contrasting forms of 'memorising': as a process of rehearsal which is usually equated with rote learning, and as a process of committing to memory material that in two separate senses is temporally either 'understood' before or after the event.

AIMS

The present study reports on the operationalisation of these contrasting forms of 'memorising' and investigates their empirical association with one another, their gender sensitivity, and their joint association with other modelling sources of explanatory variation in student learning.

SAMPLES

Two samples of entering first-year economics students at the Universities of South Australia (N = 896) and Adelaide (N = 448) which are combined in the present study (N = 1344). The combined sample is further distinguishable by gender (females, N = 662, males, N = 682).

METHOD

Students were surveyed prior to the commencement of lectures and reported retrospectively on their most recent school-based learning experiences. Resultant data in the form of inventory responses were subjected to exploratory and confirmatory factor analyses, multivariate analysis of variance, and correlation analysis.

RESULTS

Empirically the three forms of 'memorising' are independent of one another and they are furthermore sensitive to gender-based response differences in terms of both location and structure. Forms of 'memorising' are respectively associated in a theoretically congruent manner with 'deep'-level processes, learning pathologies, and contrasting conceptions of learning.

CONCLUSIONS

The unqualified use of 'memorising' in studies of student learning is contra indicated. Contrasting forms of 'memorising' represent discrete sources of explanatory variation that can be used to construct finer grained models of student learning in process terms.

Increased left posterior parietal-temporal cortex activation after D-fenfluramine in women with panic disorder

It is unclear whether the functional changes found in panic disorder reflect disturbed physiology of particular neurotransmitters. One method of investigating altered neurotransmission is to assess regional brain activations in response to agonist challenges. D-Fenfluramine is a medication that induces neuronal release of serotonin. Using ¿15OH(2)O and positron emission tomography (PET), measurements of regional cerebral blood flow (rCBF) were done at t=-20, -5, +20 and +35 relative to the IV D-fenfluramine injection (t=0) in nine panic-disordered and 18 healthy subjects. Subjects were otherwise healthy, right-handed, non-smoking and not taking psychotropic medication. ¿15OH(2)O PET scans were assessed with Statistical Parametric Mapping using individual global cerebral blood flow as a covariate. Comparisons of the (baseline) first two scans between healthy and panic-disordered subjects showed a decreased rCBF in the left posterior parietal-superior temporal cortex in the patient group. Fenfluramine-induced increases as defined by the last two scans minus the first two scans were compared between groups and a significantly greater increase in the same left posterior parietal-superior temporal region was found in panic-disordered subjects. Consistent with this finding, differences between the last two scans (post-fenfluramine) of the healthy and panic-disordered subjects showed an increased rCBF in the left superior temporal cortex in panic-disordered subjects. Functional pathology in the left parietal-superior temporal cortex in panic disorder may be related to abnormal modulation by serotonin.

Prefrontal cortex 5-HT2 receptors in depression: an [18F]setoperone PET imaging study

OBJECTIVE

Widespread disturbances of serotonin (5-HT) are implicated in the pathophysiology of depression. Of 5-HT receptor abnormalities reported, the most replicated finding is increased 5-HT2 receptor binding in the postmortem prefrontal cortex of depressed suicide victims. The extent to which these findings exist in depressed persons without recent suicide attempts is uncertain. The objective of this study was to evaluate 5-HT2 receptors in depressed patients who were medication-free and who had not made recent suicide attempts.

METHOD

With the use of [18F]setoperone and positron emission tomography (PET), 5-HT2 receptor binding potential was assessed in 14 depressed and 19 healthy subjects. Exclusion criteria for depressed patients included use of antidepressant medication within the past 6 months, a history of suicide attempts within the past 5 years, other current axis I disorders including bipolar disorder, and the presence of psychotic symptoms. The 5-HT2 (setoperone) binding potential in the two groups of subjects was compared by analysis of covariance with age as the covariate.

RESULTS

Age had a significant effect on 5-HT2 binding potential, but depression did not. The interaction of age and depression was not significant.

CONCLUSIONS

The 5-HT2 binding potential is not increased in untreated depressed subjects who have not made recent suicide attempts. This negative finding does not rule out the possibility that there is a role for 5-HT2 receptors in treatment or that 5-HT2 receptors are increased in highly suicidal states.

Gastric emptying of indigestible versus digestible oils and solid fats in normal humans

Recent scintigraphic studies indicate that lipolytic products in the small intestine do not inhibit gastric emptying of fat as potently as previously suggested by studies that compared a liquid indigestible oil with a solid digestible fat. The older studies left open the confounding possibility that solid fats emptied differently than liquid oil. We studied eight normal subjects who ingested four meals in which fat was (1) liquid, digestible Crisco oil, (2) liquid, indigestible sucrose polyester oil, (3) digestible, solid Crisco, and (4) indigestible, solid olestra. Fats were labeled with iodine-123, and their gastric emptying was followed with a gamma camera. Indigestible fats (whether liquid or solid) emptied consistently faster than digestible fats (P < 0.005), although differences were small. Solid fats emptied about as rapidly as oils in the first hour; but more slowly thereafter (P < 0.01). A comparison of present scintigraphic with older studies suggested that solid fats were not well tracked by duodenal, marker-perfusion techniques, which misled previous investigators.

The effects of single dose nefazodone and paroxetine upon 5-HT2A binding potential in humans using [18F]-setoperone PET

RATIONALE

Alterations in 5-HT2A receptor binding are implicated in suicidality and depression. 5-HT2A receptors may also be involved in the therapeutic effects of antidepressants.

OBJECTIVES

The purpose of this study was to assess the effect of paroxetine and nefazodone on 5-HT2A receptors after a single dose.

METHODS

Seven subjects received a single dose of nefazodone 200 mg and five subjects received a single dose of paroxetine 20 mg. Before and after the dose, 5-HT2A binding potentials (Bmax/Kd) were determined in each subject using [18F]-setoperone PET.

RESULTS

Nefazodone induced a significant change in 5-HT2A binding potential (-39+/-17%,, P = 0.003) while paroxetine showed no significant alteration of 5-HT2A binding potential (+3+/-13%, P = 0.73).

CONCLUSIONS

The change in 5-HT2A binding potential seen with nefazodone represents blockade of 5-HT2A receptors by the drug. We do not find evidence for acute downregulation of 5-HT2A receptors with paroxetine within 9 h.

Neurosteroid regulation of inhibitory synaptic transmission in the rat hippocampus in vitro

The effect of the neurosteroid dehydroepiandrosterone sulfate on inhibitory synaptic transmission was studied in area CA1 of the rat hippocampus using an in vitro hippocampal slice preparation. Synaptic responses elicited by stimulation of Schaffer collateral fibers were recorded extracellularly as population spikes in the somatic region and as synaptic field potentials in the dendritic region. Bath application of dehydroepiandrosterone sulfate (10 microM) enhanced the synaptically evoked somatic population spike with no effect on the dendritic synaptic potential. Isolation of the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate receptor-mediated component of the synaptic response by addition of antagonists of N-methyl-D-aspartate and GABA receptors to the perfusion saline demonstrated that dehydroepiandrosterone sulfate had no effect on this component of the dendritic synaptic potential. In contrast, dehydroepiandrosterone sulfate antagonized GABA receptor-mediated inhibitory effects in the somatic region, resulting in an augmentation of the somatic population spike amplitude. Paired-pulse facilitation was unaltered by dehydroepiandrosterone sulfate, thus arguing against possible presynaptic sites of dehydroepiandrosterone sulfate's actions. These results indicate that dehydroepiandrosterone sulfate can alter synaptic transmission in the hippocampus through selective postsynaptic actions on inhibitory synaptic transmission. A synaptic effect of dehydroepiandrosterone sulfate is consistent with a neuromodulatory role for this neurosteroid in the central nervous system, and may contribute to the reported effects of dehydroepiandrosterone sulfate on cognitive processes such as learning and memory.

Variation in medical students' approaches to diagnosis: a basis for initiating conceptual change among teachers and students

OBJECTIVES

This study examines Finnish medical students' approaches to diagnosis and investigates further how medical teachers can use information about variation in their students' approaches to diagnosis to foster teaching in medical school.

DESIGN

The medical students responded to the Conceptions and Experiences of Diagnosis Inventory (CEDI).

SETTING

Faculty of Medicine, University of Helsinki.

SUBJECTS

Ninety medical students in their clinical years and eight clinical teachers from the same Faculty of Medicine.

RESULTS

The 11 subscales of the CEDI formed two contrasting factors: the first reflecting variation in 'non-virtuously' labelled, and the second in 'virtuously' labelled, aspects of diagnosis.

CONCLUSIONS

Cluster analyses revealed subgroup characteristics of students' diagnostic processes that are of potential benefit to both students and teachers. Teacher interviews indicated that, for students, the CEDI may act as a self-assessment tool to help develop their diagnostic and metacognitive skills. For teachers, the CEDI was seen to offer important information about their students' conceptions of diagnosis and diagnostic skills.

Assessment of spatial normalization of PET ligand images using ligand-specific templates

Recent advances allow robust computation of parametric maps of ligand-receptor binding from PET data sets. Parametric maps may be statistically analyzed at the voxel level, given suitable techniques for both the spatial normalization of image data into a standard space and the application of appropriate statistical tests. The purpose of this study was to spatially normalize parametric maps of [carbonyl-11C]WAY-100635 and [11C]raclopride binding using SPM 96 and ligand-specific templates. Ligand-specific templates were created from integral images taken from healthy subjects. For this, a MRI-based spatial normalization was used: T1-weighted MRI scans were coregistered to the PET integral images, and the spatial normalization of the MRI to the SPM 96 T1 MRI template was applied to the integral images. These integral images were meaned and smoothed to form [carbonyl-11C]WAY-100635 and [11C]raclopride templates. Reliability of spatial normalization using the ligand template method and the previous MRI-based spatial normalization was investigated by using a second set of integral images taken from a different cohort: Landmark coordinates were defined on all spatially normalized integral images. Mean coordinates were found in order to produce an overall (average) landmark for each location. For each image, at each location, the distance from the landmark coordinates to the overall landmark were found. A multivariate analysis of variance was used to examine the effects of observer variance, landmark location, and the method used. Visually acceptable templates were created. While observer variance was not significant, the landmark x method interaction was significant. The ligand template method had significantly smaller distances: Among the landmark locations with this method, the mean distances between individual image landmarks and overall image landmarks ranged from 1. 1 to 4.9 mm. The ligand template method provides a reliable approach for spatial normalization of PET ligand images.

PYY immunoneutralization does not alter lipid-induced inhibition of gastric emptying in rats

PYY is released from the distal ileum by fat and may be involved in mediating lipid-induced inhibition of gastric acid secretion and intestinal motility. The role of PYY in intestinal lipid-induced inhibition of gastric emptying in awake rats was investigated using a specific polyclonal antibody raised against PYY.

METHODS

Gastric emptying of liquids was measured in awake rats fitted with a Thomas gastric cannula. Intralipid (total dose 50 or 100 mg) was perfused for 10 min (0.05 ml/min) into a duodenal (n = 11) or mid-intestinal cannula (60 cm from Ligament of Treitz; n = 8), and gastric emptying was measured over the 5-10 min period. Gastric emptying was measured 15 min after IP injection of PYY (1 nmol/rat). PYY antibody (20 mg) or a control antibody (anti-KLH; keyhole limpet hemocyanin) was injected ip 8-12 h before experiments.

RESULTS

Exogenous PYY (1 nmol) inhibited gastric emptying and administration of PYY antibody blocked this response. Perfusion of lipid (50 and 100 mg) into the proximal intestine produced a 46% and 66% inhibition of gastric emptying respectively. Inhibition of gastric emptying in response to 50 mg lipid in the proximal small intestine was unaffected by administration of PYY antibody but was abolished by administration of the CCK A receptor antagonist devazepide (0.1 mg/kg ip). Perfusion of lipid into the distal intestine (50 and 100 mg) inhibited gastric emptying by 10% and 32% respectively. Inhibition of gastric emptying in response to 100 mg lipid in the distal intestine was unaffected by PYY antibody.

CONCLUSIONS

Lipid perfused into either the proximal or distal intestine inhibits gastric emptying via a PYY-independent mechanism. CCK is involved in proximal lipid induced inhibition of gastric emptying.

An exploratory student learning model of clinical diagnosis

This paper investigates how students vary in their conception and engagement of the diagnostic process. The research question is whether it is possible to isolate appropriate sources of variation that are sufficiently psychometrically and conceptually robust for modelling purposes. Eleven such sources of variation are reported, together with an associated common-factor empirical model that is readily interpretable in conceptual terms.

Length of intestinal contact on nutrient-driven satiety

Chemosensors throughout small bowel and colon inhibit food intakes when contacted by monomeric nutrients. We postulated that calorie-dependent inhibition of food intakes depended on additions of feedbacks from sensors in proximal and distal bowel contacted after high intakes of nutrients. Therefore, we determined how feedback from sensors in proximal gut interacted with feedback from simultaneously contacted sensors in distal bowel and whether suppression of nutrient intakes by intestinally perfused nutrients depended on length of gut contacted. Suppression of food intakes by maltose simply added to that from dodecanoate when both were present together either in proximal or distal small bowel. When dodecanoate was infused into proximal gut while maltose was infused distally, suppression of intake was threefold higher and was thus potentiated. Limiting contact of slowly absorbed lactose or oleate to 35 cm of jejunum nearly abolished the satiating potencies each exhibited during access to whole gut. The observations were consistent with our hypothesis.

Chemical specificities and intestinal distributions of nutrient-driven satiety

We measured intakes of sham- and naturally feeding rats during gut perfusions of nutrients. Our objectives were to determine 1) which nutrient products in gut lumen suppressed intakes; 2) how suppression by various nutrients is distributed along gut; and 3) whether time courses of suppression were similar among different nutrients. We found that satiating nutrients consisted of fatty acids only longer than 10 carbons, of monomeric carbohydrates only with affinity for the glucose transporter, and, among several amino acids, of only phenylalanine and tryptophan. Dimeric maltose had about the same potency as an isocaloric mixture of longer glucose polymers; since responses to either were blocked by a glucosidase inhibitor, each probably acted after hydrolysis to free glucose. Effective nutrients suppressed intakes about equally on infusion into duodenum vs. midgut, and the same nutrients also suppressed intakes when infused into colon. Food intakes were suppressed only while maltose was infused, not after it was stopped, but suppression persisted for 2 h after stopping perfusions with fatty or amino acids.

Role of small intestine in caloric compensations to oil premeals in rats

We postulated that dose-responsive satiety after oil premeals varies with the number of gut sensors stimulated by lipolytic products along intestine. These experiments in fasted rats on satiety after oil premeals were performed to 1) determine whether satiety was induced by lipolytic products but not triglycerides; 2) confirm that oil empties from the stomach at rates that vary with oil loads; 3) ascertain that increasing rates of oil entry into duodenum extend the length of gut contacted by lipolytic products; and 4) judge whether length of gut contacted correlated with dose-responsive satieties to dietary oils. 5) Using specific antagonists, we attempted to define how satiety was signalled by gut sensors. Timing and degrees of satiety did not correlate with timing and extent of gastric distensions but, rather, with the timing and extent of spread of lipolytic products along small bowel. Satiety after the highest premeal load of oil was blocked by Pluronic L-81, an inhibitor of intestinal secretion of apolipoprotein A-IV, but was unaffected by MK-329 (a specific antagonist of cholecystokinin) or by capsaicin blockade of chemosensory nerves.

No effect of depression on [(15)O]H2O PET response to intravenous d-fenfluramine

OBJECTIVE

Subnormal prolactin responses to the serotonin-releasing agonist fenfluramine occur in depression. Since many measures of serotonin pathology occur in depression, abnormal responses to fenfluramine may occur in brain structures other than the hypothalamic-pituitary axis. One study compared six depressed and six healthy subjects' responses to oral d,l-fenfluramine by assessing [18F]fluorodeoxyglucose uptake as detected by positron emission tomography (PET). That study showed several abnormalities within the cortex, and the authors concluded that low responsivity to d,l-fenfluramine is widespread in depression. In this study abnormalities in regional neuromodulation by serotonin in major depression were assessed with intravenous d-fenfluramine and [(15)O]H2O PET.

METHOD

Changes in regional cerebral blood flow (CBF) were detected by using [(15)O]H2O PET after administration of intravenous d-fenfluramine to 13 depressed and 18 healthy women. The PET scans were done 20 and 5 minutes before and 20 and 35 minutes after d-fenfluramine administration. Differences between the depressed and healthy groups in change in regional CBF (mean postfenfluramine minus mean prefenfluramine) were analyzed by using statistical parametric mapping.

RESULTS

There were no significant differences between depressed and healthy subjects; in fact, changes in regional CBF after intravenous d-fenfluramine were remarkably similar.

CONCLUSIONS

Degrees of neuronal responsivity to d-fenfluramine are similar in depressed and healthy subjects. Differences between the previous and current findings may be accounted for by greater specificity of intravenous d-fenfluramine to serotonin release, timing of scans, paucity of suicidal subjects in the current study, or greater variance in regional CBF from direct vascular effects of serotonin.

Inhibition of gastric emptying in response to intestinal lipid is dependent on chylomicron formation

Lipid in the intestine initiates feedback inhibition of proximal gastrointestinal function and food intake. In rats and humans, inhibition of gastric emptying is mediated, at least in part, by cholecystokinin (CCK)-A receptors, and in rats there is evidence for involvement of an intestinal vagal afferent pathway. The mechanism by which luminal lipid acts to release CCK or activate vagal afferent nerve terminals is unclear. The role of chylomicron formation in this sensory transduction pathway has been investigated using the hydrophobic surfactant Pluronic L-81 that inhibits chylomicron formation. Gastric emptying of liquids was measured in awake rats fitted with a Thomas gastric fistula and a duodenal cannula. Intestinal perfusion of lipid induced a dose-dependent inhibition of gastric emptying (6, 12, and 39% inhibition for 25, 50, and 100 mg lipid, respectively). Perfusion of lipid with Pluronic L-81 (2.8% wt/vol) reversed the lipid-induced inhibition of gastric emptying. Pluronic L-63, a chemically similar surfactant that has no effect on chylomicron formation, had no effect on lipid-induced inhibition of gastric emptying. Perfusion of the intestine with lipid (100 mg) increased plasma levels of CCK from 1.9 +/- 0.8 to 6. 5 +/- 1 pM. This increase was blocked by Pluronic L-81 but unaffected by L-63. These results provide evidence that chylomicron formation is important in the signaling of lipid in the intestinal lumen to CCK endocrine cells and to producing feedback inhibition of gastric emptying.