Regional brain responses to serotonin in major depressive disorder

BACKGROUND

Positron Emission Tomography (PET) studies have reported altered resting regional brain glucose metabolism in mood disorders. This study examines the relationship of such changes to serotonin system abnormalities associated with depression.

METHODS

Thirteen male medication free subjects who were inpatients with a DSM-IIIR major depressive disorder and seven healthy male subjects underwent an [18F]-fluorodeoxyglucose (18FDG) PET scan on consecutive days. Three hours prior to 18FDG subjects received single blind placebo or fenfluramine. Comparisons of voxel level regional glucose metabolic rate responses (rCMRglu) between groups in the two states were performed with SPM99.

RESULTS

Unlike healthy male subjects who have significant increases in rCMRglu in prefrontal and parietal cortical regions after receiving fenfluramine, depressed male subjects have no significant increases in rCMRglu.

CONCLUSIONS

Blunted increases in rCMRglu in response to fenfluramine in prefrontal and parietal cortex are consistent with our previous pilot study and the indoleamine hypothesis of depression. Differences in specific brain regions affected between this study and previous studies may be attributable to gender differences.

Regional brain gray matter volume differences in patients with bipolar disorder as assessed by optimized voxel-based morphometry

BACKGROUND

Structural magnetic resonance imaging (MRI) studies of regions of interest in brain have been inconsistent in demonstrating volumetric differences in subjects with bipolar disorder (BD). Voxel-based morphometry (VBM) provides an unbiased survey of the brain, can identify novel brain areas, and validates previously hypothesized regions. We conducted both optimized VBM, comparing MRI gray matter volume, and traditional VBM, comparing MRI gray matter density, in 11 BD subjects and 31 healthy volunteers. To our knowledge, these are the first VBM analyses of BD.

METHODS

Segmented MRI gray matter images were normalized into standardized stereotactic space, modulated to allow volumetric analysis (optimized only), smoothed, and compared at the voxel level with statistical parametric mapping.

RESULTS

Optimized VBM showed that BD subjects had smaller volume in left ventromedial temporal cortex and bilateral cingulate cortex and larger volume in left insular/frontoparietal operculum cortex and left ventral occipitotemporal cortex. Traditional VBM showed that BD subjects had less gray matter density in left ventromedial temporal cortex and greater gray matter density in left insular/frontoparietal operculum cortex and bilateral thalamic cortex. Exploratory analyses suggest that these abnormalities might differ according to gender.

CONCLUSIONS

Bipolar disorder is associated with volumetric and gray matter density changes that involve brain regions hypothesized to influence mood.

Synthesis of [O-methyl-11C]1-(2-chlorophenyl)-5-(4-methoxyphenyl)-4-methyl-1H-pyrazole-3-carboxylic acid piperidin-1-ylamide: a potential PET ligand for CB1 receptors

Synthesis and in vitro evaluation of [O-methyl-(11)C]1-(2-chlorophenyl)-5-(4-methoxyphenyl)-4-methyl-1H-pyrazole-3-carboxylic acid piperidin-1-ylamide ([(11)C]-1), a potential imaging agent for CB(1) receptors using PET is described. 1-(2-Chlorophenyl)-5-(4-hydroxyphenyl)-4-methyl-1H-pyrazole-3-carboxylic acid piperidin-1-ylamide (5), the precursor for radiolabeling, was synthesized from 4-OTBDPS-propiophenone (2) in five steps with 30% overall yield. The reaction of alcohol 5 with [(11)C]MeOTf at 60 degrees C afforded [(11)C]-1 with an average radiochemical yield of 14.5% (EOS) and >2000 Ci/mmol specific activity. The radiotracer was found to selectively label CB(1) receptors in slide-mounted sections of postmortem human brain containing prefrontal cortex as demonstrated by in vitro autoradiography using phosphor imaging.

Volumetric analysis of the prefrontal cortex, amygdala, and hippocampus in major depression

Magnetic resonance imaging (MRI) studies in depressed subjects report smaller volumes of amygdala, hippocampus, inferior anterior cingulate, and the orbital prefrontal cortex (OPFC), components of the limbic-cortico-thalamic circuit. Major depression occurs more commonly in women, raising the possibility of an additional psychopathological process affecting women and not men. We sought to determine whether volumetric differences related to mood disorders are dependent on sex. Eight male and 10 female depressed subjects, meeting DSM III R criteria for a major depressive episode, and eight male and 10 female healthy volunteers had MRI scans on a 1.5 T GE Signa Advantage scanner. The regions of interest included amygdala, hippocampus, inferior anterior cingulate, and OPFC. In all analyses, regional volumes were normalized for total cerebral volume. Volumetric changes in the ROIs showed a significant sex by diagnosis interaction, indicating a different pattern of volumetric changes in depressed males compared with females relative to controls. Relative to sex-matched controls, the left inferior anterior cingulate was smaller in depressed males (23%) compared with depressed females (11%). Depressed females but not depressed males had smaller amygdala compared with controls (F-value = 4.946, p = 0.033). No significant volumetric differences were noted in the hippocampus or OPFC. No volumetric correlations were noted with clinical variables, depression subtypes, or a reported history of sexual or physical abuse. Sex may affect volumetric deficits in amygdala and anterior cingulate cortex in mood disorders, but no effects were found in the hippocampus or OPFC. The biology of mood disorders in females may differ in some aspects from males, and may contribute to the higher rate of depression in women.

OS-EM and FBP reconstructions at low count rates: effect on 3D PET studies of [11C] WAY-100635

11C-labeled neuroreceptor ligands frequently require long scan durations to quantify ligand-receptor binding. In this paper, we compare the accuracy of two three-dimensional (3D) positron emission tomography (PET) reconstructions: ordered-subset expectation-maximization (OS-EM) versus filtered backprojection (FBP) under low count rate conditions exhibited by 11C neuroreceptor studies. Data were obtained from a dynamic 11C phantom acquisition as well as six dynamic human [11C] WAY-100635 studies, all acquired in 3D mode using the EXACT HR+ PET scanner. Model-based scatter correction of the phantom datum was found to overcorrect in low count rate situations producing a negative bias in FBP reconstruction and a positive bias in OS-EM reconstruction, the OS-EM bias attributed to the non-negativity constraint of sinogram values. In the phantom OS-EM and FBP, reconstruction bias occurred at activities less than 25 Bq/cm3. In the human cerebellum, OS-EM deviated from FBP at activities less than 50 Bq/cm3. The total volume of distribution (VT), as determined from the metabolite corrected arterial input function and a two-tissue compartment kinetic model, was more sensitive to the positive bias of OS-EM than the negative bias of FBP at low count rates. To avoid reconstruction bias with 3D PET studies using the HR+, the scan duration should be limited so as to yield a final non-decay-corrected activity concentration of no less than 50 Bq/cm3. In neuroreceptor studies, if such a low count rate cannot be avoided, FBP reconstruction is preferable to OS-EM to estimate VT.

Determination of volume of distribution using likelihood estimation in graphical analysis: elimination of estimation bias

The graphical analysis uses an ordinary least squares (OLS) fitting of transformed data to determine the total volume of distribution (VT) and is not dependent upon a compartmental model configuration. This method, however, suffers from a noise-dependent bias. Approaches for reducing this bias include incorporating a presmoothing step, minimizing the squared perpendicular distance to the regression line, and conducting multilinear analysis. The solution proposed by Ogden, likelihood estimation in graphical analysis (LEGA), is an estimation technique in the original (nontransformed) domain based upon standard likelihood theory that incorporates the specific assumptions made on the noise inherent in the measurements. To determine the impact of this new method upon the noise-dependent bias, we compared VT determinations by compartmental modeling, graphical analysis (GA), and LEGA in 36 regions of interest in dynamic PET data from 25 healthy volunteers injected with [11C]-WAY-100635 and [11C]-McN-5652, which are agents used to image the serotonin 1A receptor and serotonin transporter, respectively. As predicted by simulations, LEGA eliminates the noise-dependent bias associated with GA using OLS. This method is a valuable addition to the tools available for the quantification of radioligand binding data in PET and SPECT.

Applications of positron emission tomography in psychiatry

Blood flow, metabolism, and structural imaging studies suggest altered neural circuits in major psychiatric disorders including mood disorders, schizophrenia, and obsessive compulsive disorder. Neuroreceptor mapping studies have identified serotonergic abnormalities in mood disorders and dopaminergic abnormalities in schizophrenia. Further imaging applications have involved development of new positron emission tomography (PET) tracers that may identify abnormalities in peptide neurotransmitter systems such as corticotrophin releasing factor or substance P. Finally, PET can play an important role in quantifying the relationship between receptor occupancy, drug blood levels, oral dose and therapeutic outcome. In that way PET scanning can contribute to both therapeutics and to drug development by more rapid identification of the likely therapeutic dose range compared with conventional parallel group dose comparisons or dose ranging studies.

Positron emission tomography of regional brain metabolic responses to a serotonergic challenge and lethality of suicide attempts in major depression

BACKGROUND

Lower serotonergic activity correlates with high-lethality suicide attempts in major depression. Postmortem studies of serotonin receptors in suicides localize changes to the ventral prefrontal cortex (PFC). We studied serotonergic response in ventral PFC in depressed patients surviving a high-lethality suicide attempt.

METHODS

Depressed patients with a history of a high-lethality suicide attempt (n = 16) were compared with those with low-lethality attempts (n = 9) for level of depression, suicidal intent and ideation, impulsivity, aggression, and neuropsychological test performance. Subjects were scanned while medication free after a single-blind placebo and after fenfluramine hydrochloride administration on a second day. Brain responses were measured by positron emission tomography imaging of fludeoxyglucose F 18 and serial prolactin levels. Scans were compared by means of statistical parametric mapping. Correlations of changes in relative regional cerebral uptake (rCMRglu) with clinical and neuropsychological measures were assessed.

RESULTS

Depressed high-lethality suicide attempters had lower rCMRglu in ventral, medial, and lateral PFC compared with low-lethality attempters. This difference was more pronounced after fenfluramine administration. Lower ventromedial PFC activity was associated with lower lifetime impulsivity, higher suicidal intent (planning), and higher-lethality suicide attempts. Higher verbal fluency was positively correlated with rCMRglu in the same regions.

CONCLUSIONS

Prefrontal localized hypofunction and impaired serotonergic responsivity are proportional to the lethality of the suicide attempt and may mediate the effects of suicide intent and impulsivity on lethality. Positron emission tomographic neuroreceptor studies are needed to determine whether postmortem serotonin receptor findings are also present in vivo and contribute to the abnormal rCMRglu responses.

Effects of sex, age, and aggressive traits in man on brain serotonin 5-HT1A receptor binding potential measured by PET using [C-11]WAY-100635

Serotonin (5-HT) 1A receptors have been implicated in a variety of conditions including, depression, suicidal behavior, and aggression. Post-mortem brain studies and in vivo imaging studies report a variety of age and sex effects on brain 5-HT(1A) binding. Behavioral data from 5-HT(1A) specific pharmacological challenges suggest a role for 5-HT(1A) receptors in aggression. The goal of the present study was to determine age, sex, and severity of life-time aggression effects on 5-HT(1A) binding potential (BP) in vivo using positron emission tomography (PET) and the high affinity 5-HT(1A) antagonist, [carbonyl-C-11]WAY-100635 in 12 healthy females (ages 41.0+/-15.7 years) and 13 healthy males (ages 39.6+/-15.5 years). Regions of interest included the dorsal raphe, anterior cingulate cortex, cingulate body, hippocampus, amygdala, medial prefrontal cortex (PFC), and orbital PFC. No significant correlation between age and BP was detected in any brain region. MANOVA of the first three principle components demonstrated a significantly higher BP in females compared with males (P=0.0127). Post-hoc tests confirmed sex differences (P<0.05) in the following regions: dorsal raphe, amygdala, anterior cingulate, cingulate body, medial PFC, and orbital PFC. The cerebellar volume of distribution was also significantly higher in females. There is a significant negative correlation between binding in several regions and lifetime aggression. We have replicated our post-mortem finding of higher 5-HT(1A) binding in females compared to males. We did not detect an age dependent decrease in binding in males or females. Lower 5-HT(1A) binding in more aggressive individuals is consistent with pharmacological challenge studies. Future studies should determine whether the binding is a state or trait effect.

Dopamine D(2) receptor availability and amphetamine-induced dopamine release in unipolar depression

BACKGROUND

Reduced dopaminergic transmission has been implicated in the pathophysiology of major depression. The aim of the present study was to measure striatal D(2) receptor availability and amphetamine-induced dopamine release in nonpsychotic, unmedicated, unipolar patients during an episode of major depression.

METHODS

The striatal equilibrium specific to nonspecific partition coefficient (V(3)") of the D(2) receptor antagonist [(123)I]IBZM was measured with single photon emission computerized tomography before and after amphetamine administration in 9 depressed subjects and 10 matched healthy control subjects.

RESULTS

No significant differences were observed in preamphetamine D(2) receptor availability between depressed patients (0.73 +/- 0.08) and control subjects (0.78 +/- 0.10, p =.23). Amphetamine-induced reduction in [(123)I]IBZM V(3)" (DeltaV(3)") was similar in depressed patients (-9.8 +/- 5.5%) and control subjects (-7.8 +/- 2.5%, p =.32). Amphetamine induced a transient improvement in symptomatology in depressed patients, but this improvement did not correlate with [(123)I]IBZM DeltaV(3)".

CONCLUSIONS

This study did not replicate previously reported alterations in striatal D(2) receptor density in depressed patients and suggests that stimulant-induced dopamine release is not altered in major depression.

Differential occupancy of somatodendritic and postsynaptic 5HT(1A) receptors by pindolol: a dose-occupancy study with [11C]WAY 100635 and positron emission tomography in humans

Augmentation of selective serotonin reuptake inhibitors (SSRIs) therapy by the 5-HT(1A) receptor agent pindolol may reduce the delay between initiation of antidepressant treatment and clinical response. This hypothesis is based on the ability of pindolol to block 5-HT(1A) autoreceptors in the dorsal raphe nuclei (DRN) and to potentiate the increase in 5-HT transmission induced by SSRIs. However, placebo-controlled clinical studies of pindolol augmentation of antidepressant therapy have reported inconsistent results. Here, we evaluated the occupancy of 5-HT(1A) receptors during treatment with pindolol controlled release (CR) in nine healthy volunteers with Positron Emission Tomography and [11C]WAY 100635. Subjects were studied four times: at baseline, following one week of pindolol CR 7.5 mg/day (4 and 10 hrs post dose), and following one dose of pindolol CR 30 mg(4 hrs post dose). Occupancy of the DRN was 40 +/- 29% on scan 2, 38 +/- 26% on scan 3, and 64 +/- 15% on scan 4. The average occupancy in all other regions was significantly lower at each doses (18 +/- 5% on scan 2, 12 +/- 3% on scan 3, and 42 +/- 4% on scan 4). These results suggest that the blockade in the DRN reached in clinical studies (7.5 mg/day) might be too low and variable to consistently augment the therapeutic effect of SSRIs. However, these data indicate that pindolol exhibits in vivo selectivity for the DRN 5-HT(1A) autoreceptors. As DRN selectivity is desirable for potentiation of 5-HT function, this observation represents an important proof of concept for the development of 5-HT(1A) agents in this application.

In vivo quantification of brain serotonin transporters in humans using [11C]McN 5652

Abnormal brain regional densities of serotonin (5-hydroxytryptamine [5-HT]) transporters have been reported in postmortem studies in several neuropsychiatric conditions, such as major depression and schizophrenia. trans-1,2,3,5,6,10-beta-Hexahydro-6-[4-(methylthio)phenyl]pyrrolo-[2,1-a]-isoquinoline ([11C]McN 5652) is the first PET radioligand successfully developed to label 5-HT transporters in the living human brain. The purpose of this study was to develop an imaging protocol and analytic method to measure regional 5-HT transporter binding potential (BP) with [11C]McN 5652 in humans.

METHODS

The arterial input function and brain uptake of (+)-[11C]McN 5652 and (-)-[11C]McN 5652, the active and inactive enantiomers, respectively, were measured in 6 healthy volunteers.

RESULTS

(+)-[11C]McN 5652 concentrated in brain regions rich in 5-HT transporters (midbrain, thalamus, basal ganglia, and medial temporal lobe structures), whereas the uptake of (-)-[11C]McN 5652 was more uniformly distributed. Total distribution volumes (V(T)) were derived using kinetic 2-compartment analysis and graphic analysis. V(T) derived by both methods were highly correlated. (+)-[11C]McN 5652 regional V(T) ranged from 18 +/- 2 mL/g in the cerebellum to 46 +/- 13 mL/g in the midbrain. (-)-[11C]McN 5652 regional VT ranged from 10 +/- 2 mL/g in the cerebellum to 14 +/- 3 mL/g in the thalamus. (+)-[11C]McN 5652 V(T) were higher than (-)-[11C]McN 5652 V(T) in all regions, including the cerebellum, a region devoid of 5-HT transporters. Blocking experiments were also performed in baboons with saturating doses of citalopram and in humans with nonsaturating doses of paroxetine. Cerebellar and neocortical (+)-[11C]McN 5652 V(T) were unaffected by pretreatment with 5-HT transporter blockers. In areas of high receptor concentration (midbrain, caudate, and thalamus) 5-HT transporter blockers decreased (+)-[11C]McN 5652 V(T) to the level of cerebellum (+)-[11C]McN 5652 V(T).

CONCLUSION

These experiments indicate that the use of the difference between (+)- and (-)-[11C]McN 5652 V(T) to define specific binding to 5-HT transporters leads to an overestimation of specific binding. 5-HT transporter BP was derived as the difference between the regional and cerebellar (+)-[11C]McN 5652 V(T). BP values were in good agreement with the distribution of 5-HT transporters in the human brain, except for regions of relatively low 5-HT transporter concentration, such as the prefrontal cortex, where no specific binding was detected using (+)-[11C]McN 5652. (+)-[11C]McN 5652 is an appropriate radiotracer to quantify 5-HT transporters in regions with relatively high concentration of 5-HT transporters, such as the midbrain, thalamus, and basal ganglia, and should prove useful in elucidating abnormalities of 5-HT transmission in neuropsychiatric conditions.

Derivation of [(11)C]WAY-100635 binding parameters with reference tissue models: effect of violations of model assumptions

In several positron-emission tomography studies of human subjects, analyses of data from the 5-hydroxytryptamine(1A) (5-HT(1A)) receptor radioligand, [(11)C]WAY-100635 ¿[carbonyl-(11)C]N-(2-(4-methoxy-phenyl)-1-piperazin-1-yl)ethyl)-N -(2 -pyridyl)cyclohexanecarboxamide¿ have shown a discrepancy between the outcome measure k(3)/k(4) (binding potential normalized to cerebellum) as estimated by the simplified reference region method and results obtained by conventional kinetic modeling with an arterial input function. The reference region method has yielded results that are lower than the conventional approach, with the relative underestimation appearing to be an increasing function of k(3)/k(4). We performed simulations on idealized data to identify the source of the discrepancy. Both the simplified reference tissue model (SRTM) and the original full reference tissue model (FRTM) were tested to determine (a) if the error in estimated k(3)/k(4) is dependent on the blood flow in the region of interest relative to the blood flow in the region of reference (R(1)) and on the receptor density in the region of interest (true k(3)/k(4)), and (b) which violation of the reference model assumptions were responsible for this effect. FRTM returned parameter estimates that were independent and accurate if the reference region was constructed precisely as a one-tissue compartment model. SRTM overestimated k(3)/k(4) when the reference region was constructed as a one-tissue compartment model and underestimated k(3)/k(4) when the reference region was constructed as a two-tissue compartment model (which is the case for [(11)C]WAY-100635). In both cases, the magnitude of the error in k(3)/k(4) returned by SRTM was dependent on true R(1) and true k(3)/k(4). In conclusion, the SRTM is associated with a bias in the derivation of k(3)/k(4) that is not a simple scaling factor. This magnitude of these errors should be carefully evaluated for each new radioligand.

Validation and reproducibility of measurement of 5-HT1A receptor parameters with [carbonyl-11C]WAY-100635 in humans: comparison of arterial and reference tisssue input functions

Serotonin 5-HT(1A) receptors are implicated in the pathophysiology of neuropsychiatric conditions. The goal of this study was to evaluate methods to derive 5-HT(1A) receptor parameters in the human brain with positron emission tomography (PET) and [carbonyl-(11)C]WAY 100635. Five healthy volunteer subjects were studied twice. Three methods of analysis were used to derive the binding potential (BP), and the specific to nonspecific equilibrium partition coefficient (k3/k4). Two methods, kinetic analysis based on a three compartment model and graphical analysis, used the arterial plasma time-activity curves as the input function to derive BP and k3/k4. A third method, the simplified reference tissue model (SRTM), derived the input function from uptake data of a region of reference, the cerebellum, and provided only k3/k4. All methods provided estimates of regional 5-HT(1A) receptor parameters that were highly correlated. Results were consistent with the known distribution of 5-HT(1A) receptors in the human brain. Compared with kinetic BP, graphical analysis slightly underestimated BP, and this phenomenon was mostly apparent in small size-high noise regions. Compared with kinetic k3/k4, the reference tissue method underestimated k3/k4 and the underestimation was apparent primarily in regions with high receptor density. Derivation of BP by both kinetic and graphical analysis was highly reliable, with an intraclass correlation coefficient (ICC) of 0.84 +/- 0.14 (mean +/- SD of 15 regions) and 0.84 +/- 0.19, respectively. In contrast, the reliability of k3/k4 was lower, with ICC of 0.53 +/- 0.28, 0.47 +/- 0.28, and 0.55 +/- 0.29 for kinetic, graphical, and reference tissue methods, respectively. In conclusion, derivation of BP by kinetic analysis using the arterial plasma input function appeared as the method of choice because of its higher test-retest reproducibility, lower vulnerability to experimental noise, and absence of bias.

Positron emission tomography study of pindolol occupancy of 5-HT(1A) receptors in humans: preliminary analyses

Preclinical studies in rodents suggest that augmentation of serotonin reuptake inhibitors (SSRIs) therapy by the 5-hydroxytryptamine(1A) (5-HT(1A)) receptor agent pindolol might reduce the delay between initiation of treatment and antidepressant response. This hypothesis is based on the ability of pindolol to potentiate the increase in serotonin (5-HT) transmission induced by SSRIs, an effect achieved by blockade of the 5-HT(1A) autoreceptors in the dorsal raphe nuclei (DRN). However, placebo-controlled clinical studies of pindolol augmentation of antidepressant therapy have reported inconsistent results. Here, we evaluated the occupancy of 5-HT(1A) receptors following treatment with controlled release pindolol in nine healthy volunteers with positron-emission tomography (PET). Each subject was studied four times: at baseline (scan 1), following 1 week of oral administration of pindolol CR (7.5 mg/day) at peak level, 4 h after the dose (scan 2), and at 10 h following the dose (scan 3), and following one dose of pindolol CR (30 mg) (at peak level, 4 h) (scan 4). Pindolol occupancy of 5-HT(1A) receptors was evaluated in the DRN and cortical regions as the decrease in binding potential (BP) of the radiolabelled selective 5-HT(1A) antagonist [carbonyl-(11)C]WAY-100635 or [carbonyl-(11)C] N-(2-(4-(2-methoxyphenyl)-1-piperazinyl)ethyl)-N-(2-pyridyl)cyclohexa necarboxamide abbreviated as [(11)C]WAY-100635. Pindolol dose-dependently decreased [(11)C]WAY-100635 BP. Combining all the regions, occupancy was 20 +/- 8% at scan 2, 14 +/- 8% at scan 3, and 44 +/- 8% at scan 4. The results of this study suggest that at doses used in clinical studies of augmentation of the SSRI effect by pindolol (2.5 mg t.i.d.), the occupancy of 5-HT(1A) receptors is moderate and highly variable between subjects. This factor might explain the variable results obtained in clinical studies. On the other hand, at each dose tested, pindolol occupancy of 5-HT(1A) receptors was higher in the DRN compared to cortical regions, demonstrating a significant in vivo selectivity for DRN 5-HT(1A) autoreceptors relative to cortico-limbic postsynaptic receptors. This selectivity is necessary for the potentiation of 5-HT transmission, and this finding represents an important proof of concept in the development of 5-HT(1A) agents for this application. Early evaluation of new drugs with PET imaging will enable rapid screening of compounds based on DRN selectivity and more appropriate determination of doses for clinical trials.

Quantitative analysis of T2 signal intensities in Alzheimer's disease

Hypointensities (focal areas of decreased signal intensity) have been reported on T2 weighted magnetic resonance images (MRI) in normal aging and in some neurological disease processes. Increased concentrations of iron have been suggested as one cause of these hypointensities. In Alzheimer's Disease, data suggests that there is both a disruption in iron metabolism as well as the presence of T2 hypointensities. We endeavored to determine if the decreased signal intensities could be quantitatively determined and, if so, in what regions, in an effort to establish a non-invasive biological marker and diagnostic aide. We performed a quantitative analysis of the T2 signal intensities in 13 MRIs from AD patients and 16 age- and sex-matched control subjects. We found that while there were statistically significant differences in the intensities of the putamen and red nucleus, these differences were small. We were unable to detect differences in intensities in a whole slice or the frontal lobe. To our knowledge this is the first quantitative comparison of MRI signal intensities in Alzheimer's Disease.

A new MRI ratio method for in-vivo estimation of signal hypointensity in aging and Alzheimer's disease

1. Alzheimer's Disease (AD) is accompanied by a disruption in iron metabolism. There is no universally accepted method for detecting brain iron. 2. The authors have developed a novel "ratio" method which uses the red nucleus as an internal reference. We postulated that this method would improve our sensitivity in detecting differences in MRI signal intensities and that it would allow us to measure brain iron deposition. 3. The ratio method reasonably reproduced previous reports of the normal deposition of iron in brain that occurs with aging. It failed to distinguish any differences in three brain areas: putamen, left frontal lobe and whole slice in AD patients versus age and sex matched controls. 4. It also failed to detect differences with AD progression or severity. 5. The ratio method itself warrants further investigation.

Ascorbic acid modulation of calcium channels in pancreatic beta cells

We have studied the effect of ascorbic acid on voltage-dependent calcium channels in pancreatic beta cells. Using the whole-cell and perforated-patch variants of the patch clamp technique to record calcium tail currents, we have shown that the slowly deactivating (SD) calcium channel, which is similar to the T-type channel in other cells, is inhibited in a voltage-dependent manner by ascorbic acid (AA). The other channels that carry inward current in beta cells, FD calcium channels and sodium channels, are unaffected by AA. Ascorbic acid causes a voltage-dependent decrease in the magnitude of the SD channel conductance which can be explained by the hypothesis that approximately 50-60% of the channels have their voltage dependence shifted by approximately 62 mV in the depolarizing direction. Thus, ascorbate appears to modify only a fraction of the SD channels. The activation kinetics of the ascorbate-modified channels are slower than control channels in a manner that is consistent with this hypothesis. Deactivation and inactivation kinetics are unaffected by ascorbate. These effects of ascorbate require metal ions, and it appears that some of the activity of ascorbate is due to a product of its metal catalyzed oxidation, perhaps dehydroascorbate.

Analysis and use of the perforated patch technique for recording ionic currents in pancreatic beta-cells

We have used the nystatin perforated patch technique to study ionic currents in rat pancreatic beta-cells. The access resistance (Ra) between the pipette and the cell cytoplasm, measured by analyzing capacitive currents, decreased with a slow exponential time course (tau = 5.4 +/- 2.7 min) after seal formation. As Ra decreased, the magnitude of voltage-dependent K and Ca currents increased with a similar time course, and their activation kinetics became faster. After Ra stabilized, the macroscopic currents remained stable for up to an hour or more. When the final Ra was sufficiently low, Ca tail currents could be resolved which had properties similar to those recorded with the classical whole-cell technique. Two types of K channels could be characterized with perforated patch recordings of macroscopic K currents: (i) ATP-blockable K (KATP) channels which generate a time and voltage independent current that is blocked by glyburide and enhanced by pinacidil and (ii) voltage-dependent K (Kv) channels. Whole-cell recordings of KATP currents in the absence of ATP in the pipette showed that the maximum KATP conductance of the beta-cell was 83.8 +/- 40 nS. Perforated patch recordings show that the resting KATP conductance is 3.57 +/- 2.09 nS, which corresponds to about 4% of the channels being open in the intact beta-cell. In classical whole-cell recordings. Kv activation kinetics become faster during the first 10-15 min of recording, probably due to a dissipating Donnan potential. In perforated patch recordings where the Donnan potential is very small, Kv activation kinetics were nearly identical to the steady-state whole cell measurements.