D2 Values Research Articles

Estimation of phenotypic divergence in a collection of Capsicum species for yield-related traits

Phenotypic divergence among the 24 accessions belonging to a collection of six species of Capsicum from different geoclimatic regions available in field gene bank of CIMAP, Lucknow, India, was quantified by multivariate analysis for 12 quantitative and qualitative traits. Based on their values, all 24 accessions were grouped into six clusters such that the genetic stocks within cluster had smaller D2 values among themselves than those belonging to different clusters. The accessions of Capsicum annuum were distributed in different clusters in morphotyping representing different species, suggesting that taxonomic characteristics are not always related to agronomic traits. No parallelism/association was found between geographical and phenotypic diversity. Accessions 15 and 23 (clusters V and VI, respectively) had distinct identity. The three characteristics that played the greatest role in differentiation were fruit diameter, number of fruits per plant, and leaf diameter, which can be utilized as conventional/morphological markers for the improvement of chilli yield and obtaining good segregants in chilli breeding programs.

Fractal analysis of polyferric chloride-humic acid (PFC-HA) flocs in different topological spaces

The fractal dimensions in different topological spaces of polyferric chloride-humic acid (PFC-HA) flocs, formed in flocculating different kinds of humic acids (HA) water at different initial pH (9.0, 7.0, 5.0) and PFC dosages, were calculated by effective density-maximum diameter, image analysis, and N2 absorption-desorption methods, respectively. The mass fractal dimensions (Df) of PFC-HA flocs were calculated by bi-logarithm relation of effective density with maximum diameter and Logan empirical equation. The Df value was more than 2.0 at initial pH of 7.0, which was 11% and 13% higher than those at pH 9.0 and 5.0, respectively, indicating the most compact flocs formed in flocculated HA water at initial pH of 7.0. The image analysis for those flocs indicates that after flocculating the HA water at initial pH greater than 7.0 with PFC flocculant, the fractal dimensions of D2 (logA vs. logdL) and D3 (logVsphere VS. logdL) of PFC-HA flocs decreased with the increase of PFC dosages, and PFC-HA flocs showed a gradually looser structure. At the optimum dosage of PFC, the D2 (logA vs. logdL) values of the flocs show 14%-43% difference with their corresponding Df, and they even had different tendency with the change of initial pH values. However, the D2 values of the flocs formed at three different initial pH in HA solution had a same tendency with the corresponding Dr. Based on fractal Frenkel-Halsey-Hill (FHH) adsorption and desorption equations, the pore surface fractal dimensions (Ds) for dried powders of PFC-HA flocs formed in HA water with initial pH 9.0 and 7.0 were all close to 2.9421, and the Ds values of flocs formed at initial pH 5.0 were less than 2.3746. It indicated that the pore surface fractal dimensions of PFC-HA flocs dried powder mainly show the irregularity from the mesopore-size distribution and marcopore-size distribution.

Phenotypic and RAPD diversity among 80 germplasm accessions of the medicinal plant isabgol (Plantago ovata, Plantaginaceae)

Plantago ovata, popularly known as isabgol, has great commercial and medicinal importance due to thin rosy white membranous seed husk. Isabgol seeds and husks have emollient, demulcent and laxative properties. We used both biometric and molecular techniques to assess the genetic variability and relatedness of 80 germplasm accessions of Plantago spp (P. ovata, P. lanceolata, and P. major) collected both from India and abroad. The range of D2 values (2.01-4890.73) indicated a very high degree of divergence among the accessions. Based on the degree of divergence, 80 accessions/genotypes were grouped into seven clusters. Thirty-six accessions were analyzed through RAPD profiling for similarity and genetic distances, using 20 random primers. Intraspecific differences in all three species were smaller [range for P. ovata (2-17%), P. lanceolata (3-15%), P. major (2-11%)] than interspecific diversity. These highly divergent lines could be used to produce superior hybrids.

Genetic Analysis in Muskmelon (Cucumis melo L.)

Fifty genotypes of muskmelon (Cucumis melo L.) were evaluated for variability, correlation, path analysis and divergence for yield and its contributing characters. Analysis of variance showed significant variation for all the characters, indicating presence of sufficient variability in the material studied. Genotypic correlations were higher than those of their respective phenotypic correlation coefficients in majority of the cases suggesting, that, genotypic correlations were stronger, reliable and free from environmental influences. Path analysis based on genotypic association revealed that number of fruits per plant and moisture percentage was the main yieldattributing characters in fruit yield of muskmelon. Total soluble solids exhibited positive direct effect on fruit yield per plant. Thus, number of fruits per plant, moisture percentage and total soluble solids may be given more weightage for an effective selection to improve fruit yield in muskmelon. On the basis of relative magnitude of D2 values, all the genotypes were grouped in seven clusters. Maximum genetic distance was observed between clusters II and V, while clusters III and VII displayed the lowest degree of divergence. Total soluble sugars followed by total soluble solids and fruit yield per plant contributed the most towards divergence.

Genetic Divergence and Correlations Study in Chlorophytum borivilianum

ABSTRACT Continuous shrinking of natural resources (forest) led to the cultivation of Chlorophytum borivilianum, an ayurvedic crude drug, has necessitated the genetic improvement program of the aforesaid crop. The plant is a member of family liliaceae and naturally occurring populations are open-pollinated, with varying levels of performance. The objective of this study was to assess, characterize, quantify and suitably utilize available genetic variability. Genetic divergence among 31 genotypes was determined using nine characters of C. borivilianum of indigenous origin via Mahalanobis D2 statistic. The genotypes were grouped into eight clusters. Intra-cluster distance was largest for cluster VIII (nine genotypes), followed by cluster I (six genotypes). Inter-cluster D2 values recorded between cluster II and III and those between cluster III and VI indicated the possibility of raising transgressed hybrids from cross hybridization programs using divergent parents of these four clusters. The clustering pat...

Identifying Sites for Elk Restoration in Arkansas

Abstract: We used spatial data to identify potential areas for elk (Cervus elaphus) restoration in Arkansas. To assess habitat, we used locations of 239 elk groups collected from helicopter surveys in the Buffalo National River area of northwestern Arkansas, USA, from 1992 to 2002. We calculated the Mahalanobis distance (D2) statistic based on the relationship between those elk‐group locations and a suite of 9 landscape variables to evaluate winter habitat in Arkansas. We tested model performance in the Buffalo National River area by comparing the D2 values of pixels representing areas with and without elk pellets along 19 fixed‐width transects surveyed in March 2002. Pixels with elk scat had lower D2 values than pixels in which we found no pellets (logistic regression: Wald χ2 = 24.37, P < 0.001), indicating that habitat characteristics were similar to those selected by the aerially surveyed elk. Our D2 model indicated that the best elk habitat primarily occurred in northern and western Arkansas and was associated with areas of high landscape heterogeneity, heavy forest cover, gently sloping ridge tops and valleys, low human population density, and low road densities. To assess the potential for elk‐human conflicts in Arkansas, we used the analytical hierarchy process to rank the importance of 8 criteria based on expert opinion from biologists involved in elk management. The biologists ranked availability of forage on public lands as having the strongest influence on the potential for elk‐human conflict (33%), followed by human population growth rate (22%) and the amount of private land in row crops (18%). We then applied those rankings in a weighted linear summation to map the relative potential for elk‐human conflict. Finally, we used white‐tailed deer (Odocoileus virginianus) densities to identify areas where success of elk restoration may be hampered due to meningeal worm (Parelaphostrongylus tenuis) transmission. By combining results of the 3 spatial data layers (i.e., habitat model, elk‐human conflict model, deer density), our model indicated that restoration sites located in west‐central and north‐central Arkansas were most favorable for reintroduction.

GENETIC DIVERGENCE IN MAIZE (Zea mays L.)

Genetic divergence of 25 genotypes of maize were estimated using D2 and Principal Component Analysis. The genotypes under study fell into five clusters. The inter-cluster distances were higher than intra cluster distances suggesting wider genetic diversity among the genotypes of different groups. The intra-cluster value was maximum in cluster V and minimum in cluster I. The inter cluster D2 values showed the maximum distance between cluster II and III followed by the distance between II and I. The cluster means were higher for days to maturity, plant height and ear height in cluster II; grain yield per plant was higher in cluster IV. Genotypes were much in use having the above mentioned characters in clusters II and IV would offer a good scope for the improvement of this crop through hybridization and rational selection.DOI: http://dx.doi.org/10.3329/bjpbg.v20i1.17027

Precipitation of southwestern Canada: Wavelet, scaling, multifractal analysis, and teleconnection to climate anomalies

Using wavelets, statistically significant interannual and interdecadal oscillations that occurred haphazardly have been detected in southwestern (SW) Canadian seasonal precipitation anomalies. At interannual scales, station precipitation anomalies show unstable relations with large‐scale climate anomalies such as the El Niño–Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), Pacific/North America (PNA), East Pacific (EP) and West Pacific (WP) patterns, and the Central North Pacific (CNP) index. Not all significant precipitation activities could be matched by similar activities in one or more climate anomalies considered. Inconsistent wavelet coherence and phase difference between the leading principal components (PC) of regional precipitation anomalies and climate indices as well as weak Pearson's correlations between band‐passed precipitation PCs and climate indices for the 2–3 year and 3–8 year scales provide supporting evidence for unstable precipitation climate relationships at the interannual scale. On the other hand, interdecadal precipitation variability is mainly associated with low‐frequency variability in CNP, PDO and ENSO. Composite analysis of winter precipitation shows that ENSO, PDO, PNA and WP offer better separation of positive and negative precipitation anomalies than EP and CNP. However, the effect of ENSO is found to be stronger than the others. Precipitation power spectrum plots mostly reveal two linear decay regions of different slopes separated by a breakpoint located approximately at 20 to 30 days, while empirical probability plots reveal power law behavior and hyperbolic intermittency in these data, whose correlation dimensions (D2) are between 8 and 9. Different multifractal behaviors are observed among stations because the amount of different rainfall generating mechanisms vary from station to station, as reflected by the haphazard nature of oscillations detected in most precipitation data. Although the leading PCs of winter regional precipitation show modest correlations at zero‐ to three‐season lead times with ENSO and PDO indices, the high D2 values and absence of consistent interannual precipitation activities suggest that prediction of SW Canadian seasonal precipitation by teleconnection with climate indices is likely limited. Adding other predictor fields such as sea surface temperature and/or sea level pressure may be useful.

AN ALGORITHMIC COMPUTATION OF CORRELATION DIMENSION FROM TIME SERIES

We present an algorithmic scheme to compute the correlation dimension D2 of a time series, without requiring the visual inspection of the scaling region in the correlation sum. It is based on the standard Grassberger–Proccacia [GP] algorithm for computing D2. The scheme is tested using synthetic data sets from several standard chaotic systems as well as by adding noise to low-dimensional chaotic data. We show that the scheme is efficient with a few thousand data points and is most suitable when a nonsubjective comparison of D2 values of two time series is required, such as, in hypothesis testing.

Morphological and chemical variation in 25 collections of the Indian medicinal plant, Withania somnifera (L.) Dunal (Solanaceae)

Six phenotypic characters and three withanolide markers were assessed in 25 accessions of Withania somnifera collected from different states of India for studying genetic variability. The variability ranges observed at phenotypic and chemotypic levels were polymorphic. Based on D2 values and PCA (Principal Component Analysis) of phenotypic traits like plant height, no. of branches/plant, no. of seeds/berry, root length, root diameter and root yield, these 25 accessions were grouped in five clusters. The relative contribution of each character towards genetic divergence was worked out. Five accessions–AGB002 (Rajasthan), AGB003 (J&K), AGB004 (Madhya Pradesh), AGB006 (J&K) and AGB009 (Punjab) representing clusters 2 and 4 exhibited maximum intra and inter-cluster divergence. Cluster 5 representing accession AGB053 (Andhra Pradesh) was having mixed traits. Chemically most of the accessions in cluster 3 showed uniformity in presence of three marker withanolides Withaferin A, Withanone and Withanolide A in the leaves.

Marker-aided genetic divergence analysis inBrassica

Genetic divergence was evaluated in 31 breeding lines from four Brassica species using Mahalanobis' D2. A new method of grouping using D2 values was used to group the 31 lines, based on diagnostic morphological traits (called morphoqts). Isozyme variation of the individual enzymes esterase and glutamate oxaloacetate was quantified by five parameters (called isoqts) developed earlier. Grouping by the same method was also done based on the isoqts, and the grouping by isozymes was compared with that by morphoqts. Overall, there was an agreement of 73% suggesting that isoqts can be used in the choice of parents and also first stage selection of segregants in the laboratory. It was suggested that such an exercise would help to take care of season-bound and field-related problems of breeding. The new isozyme QTs, within lane variance of relative mobility and relative absorption, accounted for about 50% of the total divergence. The utility of the new method and isoqts in cost-effective breeding were highlighted.

Dynamical Heterogeneity of Suprachiasmatic Nucleus Neurons Based on Regularity and Determinism

The suprachiasmatic nucleus (SCN) is known to be the master biological clock in mammals. Despite the periodic mean firing rate, interspike interval (ISI) patterns of SCN neurons are quite complex and irregular. The aim of the present study was to investigate the existence of nonlinear determinism in the complex ISI patterns of SCN neurons. ISI sequences were recorded from 173 neurons in rat hypothalamic slice preparations using a cell-attached patch recording technique. Their correlation dimensions (D2) were estimated, and were then compared with those of the randomly-shuffled surrogate data. We found that only 16 neurons (16/173) exhibited deterministic ISI patterns of spikes. In addition, clustering analysis revealed that SCN neurons could be divided into two subgroups of neurons each having distinct values of coefficient of variation (CV) and skewness (SK). Interestingly, most deterministic SCN neurons (14/16) belonged to the group of irregularly spiking neurons having large CV and SK values. To see if the neuronal coupling mediated by the gamma-aminobutyric acid (GABA), the major neurotransmitter in the SCN, contributed to the deterministic nature, we examined the effect of the GABAA receptor antagonist bicuculline on D2 values of 56 SCN neurons. 8 SCN neurons which were originally stochastic became to exhibit deterministic characteristics after the bicuculline application. This result suggests that the deterministic nature of the SCN neurons arises not from GABAergic synaptic interactions, but likely from properties inherent to neurons themselves.

Using PARTITIONED MAHALANOBIS D2(K) TO FORMULATE A GIS-BASED MODEL OF TIMBER RATTLESNAKE HIBERNACULA

Abstract Mahalanobis Distance (D2) Statistic is a multivariate statistical method that has been used to model habitats occupied by wildlife and plant species. The output, whether standardized squared distance or probability values, represents the similarity of a given set of values with those of an optimum habitat configuration defined exclusively by sites where the species of interest is known to occur. Typically, all principal components with nonzero eigenvalues are used to calculate D2 values. We partitioned D2 into contributions from individual principal components (PCs) and selected PCs corresponding to relatively invariant aspects of the environment across all use sites to formulate D2(k). Partitioned Mahalanobis D2(k) represents the similarity of a given set of values with those of “minimum” habitat requirements of the species as defined by occupied sites using the k subset of principal components. We created a GIS-based model of the habitat surrounding 39 confirmed timber rattlesnake hibernacula o...

Application of Chaos Theory in Analyzing the Cardiac Rhythm in Healthy Subjects at Different Sleep Stages

The changes in the chaotic element of the cardiac rhythm (CR) were quantitated at different sleep stages by calculating the correlation dimension (D2) in 26 healthy subjects of both sexes (mean age 29.2 years), including 7 trained and 19 untrained subjects. Three untrained subjects took part in tests with autonomic nervous system blockers (atropine and propranolol). The study demonstrated a correlation between the changes in D2 at different sleep stages and the level of the autonomic regulation of CR. As the influence of the parasympathetic system on CR increased from one stage of slow wave sleep to another, D2 increased; during rapid eye movement (REM) sleep, this influence weakened and D2 decreased. The character of changes differed in the trained and untrained subjects and depended on the initial level of the autonomic regulation of CR. In the trained subjects, characterized by predominance of the parasympathetic regulation of CR, the initial and subsequent D2 values were higher than in the untrained subjects. Both during wakefulness and at all stages of sleep, D2 increased when the sympathetic regulation of CR was blocked, decreased when the parasympathetic regulation was blocked, and reached the lowest level when both of them were blocked. This showed that the chaotic element of CR, expressed numerically by D2, depends on the regulating effects of the autonomic nervous system.

Correlation dimensions of climate subsystems and their geographic variability

The correlation dimension D2 of precipitation (Canada and Africa), air temperature (Canada, New Zealand, and Southern Hemisphere), geo‐potential height (Canada), and unregulated streamflow (Canada, USA, and Africa) were estimated using the Hill procedure of Mikosch and Wang [1995] and the bias correction of Wang and Gan [1998]. After bias correction, it seems that D2 is distinct between climate subsystems, such that for precipitation, it is between 8 and 9, for streamflow, it is between 7 and 9, for temperature, it is between 10 and 11, and for geo‐potential heights, it is between 12 and 14. The results seem to suggest that climate might be viewed as a loosely coupled set of fairly high‐dimensional subsystems and that different climate variables can yield different D2 values. Further, results also suggest that the D2 values of the climate subsystems studied, generally, have low geographic variability, as found between the precipitation data of Western Canada and Uganda, between the streamflow data of basins representing wide range climate and scales from Canada, USA, and Africa, and among the temperature data of Western Canada, New Zealand, and the southern hemisphere, and that the original D2 values analyzed from Canadian geo‐potential heights are similar to that of Western Europe, eastern North America, and Germany. There is at most a weak relationship among basin physical characteristics, location, basin scale, and streamflow D2, while climatic influence is more obvious, as shown by drier basins having slightly higher D2 values than basins of wetter climate, basins from temperate climate having higher D2 values than those from cold or hot climates, and comparable D2 values between precipitation and streamflow data.

Effect of Ethanol on Human Sleep EEG Using Correlation Dimension Analysis

Our study was designed to investigate the influence of alcohol on sleep using the correlation dimension (D2) analysis. Polysomnography (PSG) was performed in 10 adult human males during a baseline night (BL-N) and an ethanol (0.8 g/kg body weight) night (Et-N). The mean D2 values during the Et-N and BL-N decreased significantly from wakefulness to stages 1, 2, and 3+4 of nonrapid eye movement (non-REM) sleep, and increased during REM sleep. The mean D2 of the sleep electroencephalogram (EEG) during stage 2 during the Et-N was significantly higher than during BL-N. In addition, the mean D2 values of the sleep EEG for the second, third and fourth sleep cycles during the Et-N were significantly higher than during the BL-N. These significant differences between BL-N and Et-N were not recognized by spectral and visual analyses. Our results suggest that D2 is a potentially useful parameter for quantitative analysis of the effect of ethanol on sleep EEGs throughout the entire night.

Hydrophobic modulation of heme properties in heme protein maquettes.

We have investigated the properties of the two hemes bound to histidine in the H10 positions of the uniquely structured apo form of the heme binding four-helix bundle protein maquette [H10H24-L6I,L13F](2), here called [I(6)F(13)H(24)](2) for the amino acids at positions 6 (I), 13 (F) and 24 (H), respectively. The primary structure of each alpha-helix, alpha-SH, in [I(6)F(13)H(24)](2) is Ac-CGGGEI(6)WKL.H(10)EEF(13)LKK.FEELLKL.H(24)EERLKK.L-CONH(2). In our nomenclature, [I(6)F(13)H(24)] represents the disulfide-bridged di-alpha-helical homodimer of this sequence, i.e., (alpha-SS-alpha), and [I(6)F(13)H(24)](2) represents the dimeric four helix bundle composed of two di-alpha-helical subunits, i.e., (alpha-SS-alpha)(2). We replaced the histidines at positions H24 in [I(6)F(13)H(24)](2) with hydrophobic amino acids incompetent for heme ligation. These maquette variants, [I(6)F(13)I(24)](2), [I(6)F(13)A(24)](2), and [I(6)F(13)F(24)](2), are distinguished from the tetraheme binding parent peptide, [I(6)F(13)H(24)](2), by a reduction in the heme:four-helix bundle stoichiometry from 4:1 to 2:1. Iterative redesign has identified phenylalanine as the optimal amino acid replacement for H24 in the context of apo state conformational specificity. Furthermore, the novel second generation diheme [I(6)F(13)F(24)](2) maquette was related to the first generation diheme [H10A24](2) prototype, [L(6)L(13)A(24)](2) in the present nomenclature, via a sequential path in sequence space to evaluate the effects of conservative hydrophobic amino acid changes on heme properties. Each of the disulfide-linked dipeptides studied was highly helical (>77% as determined from circular dichroism spectroscopy), self-associates in solution to form a dimer (as determined by size exclusion chromatography), is thermodynamically stable (-DeltaG(H)2(O) >18 kcal/mol), and possesses conformational specificity that NMR data indicate can vary from multistructured to single structured. Each peptide binds one heme with a dissociation constant, K(d1) value, tighter than 65 nM forming a series of monoheme maquettes. Addition of a second equivalent of heme results in heme binding with a K(d2) in the range of 35-800 nM forming the diheme maquette state. Single conservative amino acid changes between peptide sequences are responsible for up to 10-fold changes in K(d) values. The equilibrium reduction midpoint potential (E(m7.5)) determined in the monoheme state ranges from -156 to -210 mV vs SHE and in the diheme state ranges from -144 to -288 mV. An observed heme-heme electrostatic interaction (>70 mV) in the diheme state indicates a syn global topology of the di-alpha-helical monomers. The heme affinity and electrochemistry of the three H24 variants studied identify the tight binding sites (K(d1) and K(d2) values <200 nM) having the lower reduction midpoint potentials (E(m7.5) values of -155 and -260 mV) with the H10 bound hemes in the parent tetraheme state of [H10H24-L6I,L13F](2), here called [I(6)F(13)H(24)](2). The results of this study illustrate that conservative hydrophobic amino acid changes near the heme binding site can modulate the E(m) by up to +/-50 mV and the K(d) by an order of magnitude. Furthermore, the effects of multiple single amino acid changes on E(m) and K(d) do not appear to be additive.

GENETIC DIVERSITY IN NON-OILSEED SUNFLOWER (Helianthus annuus L.) GENOTYPES / DIVERSIDAD GENETICA DE GENOTIPOS NO OLEAGINOSOS DEL GIRASOL (Helianthus annuus L.) / DIVERSITÉ GÉNÉTIQUE DANS LES GÉNOTYPES DE TOURNESOL NON-OLÉAGINEUX (Helianthus annuus L.)

SUMMARYGenetic diversity was assessed in 46 non-oilseed sunflower genotypes for 14 characters by adopting D2 analysis. Oil content and plant height exhibited maximum contributions towards genetic divergence. The genotypes were grouped into 11 clusters. The inter-cluster D2 values ranged from 288.17 to 3972.34. The contribution of oil content towards genetic divergence in the 46 genotypes was confirmed when D2 analysis was performed for seed characteristics such as test weight, volume weight, hull content, kernel recovery, oil and protein content.

Effect of Total Sleep Deprivation on the Dimensional Complexity of the Waking EEG

Sleep deprivation can affect the waking EEG that may reflect information processing of the brain. We examined the effect of total sleep deprivation (TSD) on nonlinear dynamics of the waking EEG. Paired-group design. A sleep disorders laboratory in a hospital. Twenty healthy male volunteers. Waking EEG data were recorded from subjects with eyes closed after (a) an 8-hour night's sleep and (b) TSD for 24 hours. The dimensional complexity (D2), as a nonlinear measure of complexity, of the EEG after a full night sleep were compared with those of the EEG after TSD. The sleep-deprived states had lower D2 values at three channels (P4, O2, and C3) than normal states. TSD results in the decrease of complexity in the brain, which may imply sub-optimal information processing of the cerebral cortex. We suggest that the investigation of the relation between nonlinear dynamics of the waking EEG induced by TSD and cognitive performance may offer fruitful clues for understanding the role of sleep and the effects of sleep deprivation on brain function.

Brain dopamine and obesity

The cerebral mechanisms underlying the behaviours that lead to pathological overeating and obesity are poorly understood. Dopamine, a neurotransmitter that modulates rewarding properties of food, is likely to be involved. To test the hypothesis that obese individuals have abnormalities in brain dopamine activity we measured the availability of dopamine D2 receptors in brain. Brain dopamine D2 receptor availability was measured with positron emission tomography (PET) and [C-11]raclopride (a radioligand for the dopamine D2 receptor). Bmax/Kd (ratio of the distribution volumes in striatum to that in cerebellum minus 1) was used as a measure of dopamine D2 receptor availability. Brain glucose metabolism was also assessed with 2-deoxy-2[18F]fluoro-D-glucose (FDG). Striatal dopamine D2 receptor availability was significantly lower in the ten obese individuals (2.47 [SD 0.36]) than in controls (2.99 [0.41]; p < or = 0.0075). In the obese individuals body mass index (BMI) correlated negatively with the measures of D2 receptors (r=0.84; p < or = 0.002); the individuals with the lowest D2 values had the largest BMI. By contrast, neither whole brain nor striatal metabolism differed between obese individuals and controls, indicating that striatal reductions in D2 receptors were not due to a systematic reduction in radiotracer delivery. The availability of dopamine D2 receptor was decreased in obese individuals in proportion to their BMI. Dopamine modulates motivation and reward circuits and hence dopamine deficiency in obese individuals may perpetuate pathological eating as a means to compensate for decreased activation of these circuits. Strategies aimed at improving dopamine function may be beneficial in the treatment of obese individuals.