Effects of lithium and amphetamine on inositol metabolism in the human brain as measured by 1H and 31P MRS

Psychostimulant drug effects on glutamate, Glx, and creatine in the anterior cingulate cortex and subjective response in healthy humans

Prescription psychostimulants produce rapid changes in mood, energy, and attention. These drugs are widely used and abused. However, their effects in human neocortex on glutamate and glutamine (pooled as Glx), and key neurometabolites such as N-acetylaspartate (tNAA), creatine (tCr), choline (Cho), and myo-inositol (Ins) are poorly understood. Changes in these compounds could inform the mechanism of action of psychostimulant drugs and their abuse potential in humans. We investigated the acute impact of two FDA-approved psychostimulant drugs on neurometabolites using magnetic resonance spectroscopy (¹H MRS). Single clinically relevant doses of d-amphetamine (AMP, 20 mg oral), methamphetamine (MA, 20 mg oral; Desoxyn®), or placebo were administered to healthy participants (n = 26) on three separate test days in a placebo-controlled, double-blinded, within-subjects crossover design. Each participant experienced all three conditions and thus served as his/her own control. ¹H MRS was conducted in the dorsal anterior cingulate cortex (dACC), an integrative neocortical hub, during the peak period of drug responses (140-150 m post ingestion). D-amphetamine increased the level of Glu (p = .0001), Glx (p = .003), and tCr (p = .0067) in the dACC. Methamphetamine increased Glu in females, producing a significant crossover interaction pattern with gender (p = .02). Drug effects on Glu, tCr, and Glx were positively correlated with subjective drug responses, predicting both the duration of AMP liking (Glu: r = +.49, p = .02; tCr: r = +.41, p = .047) and the magnitude of peak drug high to MA (Glu: r = +.52, p = .016; Glx: r = +.42, p = .049). Neither drug affected the levels of tNAA, Cho, or Ins after correction for multiple comparisons. We conclude that d-amphetamine increased the concentration of glutamate, Glx, and tCr in the dACC in male and female volunteers 2¹/₂ hours after drug consumption. There was evidence that methamphetamine differentially affects dACC Glu levels in women and men. These findings provide the first experimental evidence that specific psychostimulants increase the level of glutamatergic compounds in the human brain, and that glutamatergic changes predict the extent and magnitude of subjective responses to psychostimulants.

Lithium and valproate and their possible effects on themyo-inositol second messenger system in healthy volunteers and bipolar patients

Over 25 years ago it was suggested that the mechanism by which lithium was clinically effective may be due to a stabilizing effect on the phosphoinositol second messenger system (PI-cycle), which has multiple effects within cells. It was proposed that lithium, which is an inhibitor of one of the key enzymes in the PI-cycle, acted to lower myo-inositol concentrations; termed the 'inositol-depletion hypothesis'. Initial animal evidence supported this hypothesis, and also suggested that it was possible that sodium valproate could affect the PI-cycle. Since the first magnetic resonance studies in this area in the early 1990s many studies have examined various aspects of this hypothesis in both healthy volunteers and patients utilizing magnetic resonance spectroscopy (MRS). The present review considers research in this area and concludes that, despite initial promise, current evidence suggests that it is unlikely that either lithium or valproate produce clinically relevant changes in myo-inositol concentrations or the PI-cycle. These findings do not suggest that lithium-induced changes in the PI-cycle are the primary mechanism by which lithium or valproate exert their beneficial clinical effects in bipolar disorder. Nonetheless, given the current technical and clinical limitations of the literature to date, this conclusion cannot be considered completely definitive.

Acute dextro-amphetamine administration does not alter brain myo-inositol levels in humans and animals: MRS investigations at 3 and 18.8 T

The pathophysiological underpinnings of bipolar disorder are not fully understood. However, they may be due in part to changes in the phosphatidylinositol second messenger system (PI-cycle) generally, or changes in myo-inositol concentrations more specifically. Dextro-amphetamine has been used as a model for mania in several human studies as it causes similar subjective and physiological symptoms. We wanted to determine if dextro-amphetamine altered myo-inositol concentrations in vivo as it would clearly define a mechanism linking putative changes in the PI-cycle to the subjective psychological changes seen with dextro-amphetamine administration. Fifteen healthy human volunteers received a baseline scan, followed by second scan 75 min after receiving a 25 mg oral dose of dextro-amphetamine. Stimulated echo proton magnetic resonance spectroscopy (MRS) scans were preformed at 3.0 Tesla (T) in the dorsal medial prefrontal cortex (DMPFC). Metabolite data were adjusted for tissue composition and analyzed using LCModel. Twelve adult male rats were treated acutely with a 5-mg/kg intraperitoneal dose of dextro-amphetamine. After 1 h rats were decapitated and the brains were rapidly removed and frozen until dissection. Rat brains were dissected into frontal, temporal, and occipital cortical areas, as well as hippocampus. Tissue was analyzed using a Varian 18.8 T spectrometer. Metabolites were identified and quantified using Chenomx Profiler software. The main finding in the present study was that myo-inositol concentrations in the DMPFC of human volunteers and in the four rat brain regions were not altered by acute dextro-amphetamine. While it remains possible that the PI-cycle may be involved in the pathophysiology of bipolar disorder, it is not likely that the subjective and physiological of dextro-amphetamine are mediated, directly or indirectly, via alternations in myo-inositol concentrations.

Decreased prefrontal Myo-inositol in major depressive disorder

BACKGROUND

Postmortem studies have shown robust prefrontal cortex glial losses and more subtle neuronal changes in major depressive disorder (MDD). Earlier proton magnetic resonance spectroscopy (1H-MRS) studies of the glial marker myo-inositol in MDD were subject to potential confounds. The primary hypothesis of this study was that MDD patients would show reduced prefrontal/anterior cingulate cortex levels of myo-inositol.

METHODS

Thirteen nonmedicated moderate-severe MDD patients and 13 matched control subjects were studied (six male, seven female per group). Proton magnetic resonance spectroscopy stimulated echo acquisition mode spectra (3.0 T; echo time=168 msec; mixing time=28 msec; repetition time=3000 msec) were obtained from prefrontal/anterior cingulate cortex. Metabolite data were adjusted for tissue composition.

RESULTS

Patients with MDD showed significantly lower myo-inositol/creatine ratios (.94+/-.23) than control subjects (1.32+/-.37) [F(1,23)=6.9; p=.016].

CONCLUSIONS

These data suggest a reduction of myo-inositol in prefrontal/anterior cingulate cortex in MDD, which could be a consequence of glial loss or altered glial metabolism. Additional in vivo studies of glial markers could add to the understanding of the pathophysiology of MDD.

Magnetic resonance findings in bipolar disorder

The MR findings reviewed in this article suggest structural, chemical, and functional abnormalities in specific brain regions participating in mood and cognitive regulation, such as the DLPFC, anterior cingulate, amygdala,STG, and corpus callosum in subjects with bipolar disorder. These abnormalities would represent an altered anterior-limbic network disrupting inter- and intrahemispheric communication and underlying the expression of bipolar disorder. Available studies are limited by several confounding variables, such as small and heterogeneous patient samples, differences in clinical and medication status, and cross-sectional design. It is still unclear whether abnormalities in neurodevelopment or neurodegeneration play a major role in the pathophysiology of bipolar disorder. These processes could act together in a unitary model of the disease, with excessive neuronal pruning/apoptosis during childhood and adolescence being responsible for the onset of the disorder and subsequent neurotoxic mechanisms and impaired neuroplasticity and cellular resilience being responsible for further disease progression. Future MR studies should investigate larger samples of first-episode drug-free patients, pediatric patients, subjects at high risk for bipolar disorder, and unaffected family members longitudinally. Such a study population is crucial to examine systematically whether brain changes are present before the appearance of symptoms (eg, maldevelopment) or whether they develop afterwards, as a result of illness course (eg, neurodegeneration). These studies will also be instrumental in minimizing potentially confounding factors commonly found in adult samples, such as the effects of long-term medication, chronicity, and hospitalizations. Juvenile bipolar patients often have a strong family history of bipolar disorder. Future studies could help elucidate the relevance of brain abnormalities as reflections of genetic susceptibility to the disorder. MR studies associated with genetic, post-mortem, and neuropsychologic studies will be valuable in separating state from trait brain abnormalities and in further characterizing the genetic determinants, the neuropathologic underpinnings, and the cognitive disturbances of bipolar disorder.

Lithium and valproate attenuate dextroamphetamine-induced changes in brain activation

BACKGROUND

Previous studies have suggested that both lithium and valproate may decrease phosphoinositol second messenger system (PI-cycle) activity. There is also evidence that dextroamphetamine may increase PI cycle activity. It was previously demonstrated that dextroamphetamine administration in volunteers causes a region and task dependent decrease in brain activation in healthy volunteers. The current study assessed the effect of 14 days pretreatment with lithium and valproate on these dextroamphetamine-induced changes in regional brain activity in healthy volunteers.

METHODS

This was a double-blind, placebo-controlled, study in which volunteers received either 1000 mg sodium valproate (n = 12), 900 mg lithium (n = 9) or placebo (n = 12). Functional images were acquired using functional magnetic resonance imaging (fMRI) while subjects performed three cognitive tasks, a word generation paradigm, a spatial attention task and a working memory task. fMRI was carried out both before and after administration of dextroamphetamine (25 mg). Changes in the number of activated pixels and changes in the magnitude of the blood-oxygen-level-dependent (BOLD) signal after dextroamphetamine administration were then determined.

RESULTS

In keeping with previous findings dextroamphetamine administration decreased regional brain activation in all three tasks. Pretreatment with lithium attenuated changes in the word generation paradigm and the spatial attention task, while pretreatment with valproate attenuated the changes in the working memory task.

CONCLUSIONS

These results suggest that both lithium and valproate can significantly attenuate dextroamphetamine-induced changes in brain activity in a task dependent and region specific manner. This is the first human evidence to suggest that both lithium and valproate may have a similar effect on regional brain activation, conceivably via similar effects on PI-cycle activity.

Bipolar disorder and myo-inositol: a review of the magnetic resonance spectroscopy findings

OBJECTIVES

Myo-inositol is an important component of the phosphatidylinositol second messenger system (PI-cycle). Alterations in PI-cycle activity have been suggested to be involved in the pathophysiology and/or treatment of bipolar disorder. More specifically, lithium has been suggested to act primarily by lowering myo-inositol concentrations, the so-called inositol-depletion hypothesis. myo-Inositol concentrations can be measured in vivo with magnetic resonance spectroscopy (MRS).

METHODS

The current review primarily examines animal and human MRS studies that evaluated the role of myo-inositol in bipolar illness and treatment.

RESULTS

Studies have been carried out in patients who are manic, depressed, and euthymic, both on and off treatment. However, there are several limitations of these studies.

CONCLUSIONS

The preclinical and clinical MRS findings were generally supportive of the involvement of myo-inositol in bipolar disorder and its treatment. Overall, in bipolar patients who are manic or depressed there are abnormalities in brain myo-inositol concentrations, with changes in frontal and temporal lobes, as well as the cingulate gyrus and basal ganglia. These abnormalities are not seen in either euthymic patients or healthy controls, possibly due to a normalizing effect of treatment with either lithium or sodium valproate. There is also increasing evidence that sodium valproate may also act upon the PI-cycle. Nonetheless, it remains uncertain if these changes in myo-inositol concentration are primary or secondary. Findings regarding the specific inositol-depletion hypothesis are also generally supportive in acutely ill patients, although it is not yet possible to definitively confirm or refute this hypothesis based on the current MRS evidence.

Lithium modulation of the human inositol monophosphatase 2 (IMPA2) promoter

The inositol-signaling pathway is a therapeutic target for lithium in the treatment of bipolar disorder. Inositol monophosphatases (IMPases) play a key role in inositol signaling. Lithium's ability to inhibit IMPase 1 is well known, but its effect on IMPase 2 or on the transcriptional regulation of these genes has not been studied. Here, we report the identification and characterization of the minimal promoter of IMPA2 (encoding IMPase 2) in HeLa (epithelial) and SK-N-AS (neuronal) cells. IMPA2 promoter activity appears to be contributed by different elements in the 5' flanking region, suggesting that the gene is differentially regulated in neuronal and non-neuronal cells. Furthermore, IMPA2 promoter activity in both cell lines is downregulated, in a dose-dependent manner, by lithium after treatment for only 24h. This effect is also observed in vivo. Our results suggest a possible role for IMPA2 in bipolar disorder.

1H MRS study of dorsolateral prefrontal cortex in healthy individuals before and after lithium administration

The mechanism of action of lithium is still largely unknown. However, recent animal and human studies suggested the possible neuroprotective effects of this medication. In particular, a recent magnetic resonance spectroscopy (MRS) study showed the increase of cortical brain levels of N-acetyl-aspartate (NAA), a putative marker of neuronal integrity/functioning, in both bipolar patients and normal controls after 4 weeks of lithium administration. We investigated the effects of lithium on NAA levels in a sample of healthy individuals using in vivo 1H MRS in dorsolateral prefrontal cortex (DLPFC), a region likely implicated in the pathophysiology of bipolar disorder. In vivo short echo-time 1H-MRS measurements of 8 cm3 single voxels placed bilaterally in the DLPFC were conducted at baseline and after 4 weeks of lithium administration on 12 healthy individuals (mean age+/-SD = 25.0+/-9.8 years; six males). After lithium administration, no significant differences in NAA, phosphocreatine plus creatine, glycerophosphocholine plus phosphocholine (or choline-containing molecules), and myo-inositol absolute levels or ratios were found in DLPFC (paired t-tests, p > 0.05). Contrary to prior MRS reports in bipolar patients, we found that lithium administration did not significantly increase NAA levels in the DLPFC of healthy individuals. Future longitudinal studies will be needed to further investigate whether chronic lithium treatment increases NAA levels in other brain regions in healthy individuals, and whether it promotes changes in these levels in specific brain regions in bipolar patients.

Lithium and valproic acid treatment effects on brain chemistry in bipolar disorder

BACKGROUND

Prior work reported elevated gray matter (GM) lactate and Glx (glutamate + glutamine + GABA) concentrations in unmedicated patients with bipolar disorder (BP) compared with healthy controls (HC). This study examined whether lithium (Li) and valproic acid (VPA) treatment modulated these chemicals.

METHODS

A subset of previously reported BP patients were treated with Li (n = 12, 3.6 +/- 1.9 months) or VPA (n = 9, 1.4 +/- 1.7 months) and compared untreated HC subjects (n = 12, 2.9 +/- 2.4 months) using proton echo-planar spectroscopic imaging. Regression analyses (voxel gray/white composition by chemistry) were performed at each time point, and change scores computed. Metabolite relaxation and regions of interest (ROI) were also examined.

RESULTS

Across treatment, Li-treated BP subjects demonstrated GM Glx decreases (Li-HC, p =.08; Li-VPA p =.04) and GM myo-inositol increases (Li-HC p =.07; Li-VPA p =.12). Other measures were not significant. Serum Li levels were positively correlated with Glx decreases at the trend level.

CONCLUSIONS

Li treatment of BP was associated with specific GM Glx decreases and myo-inositol increases. Findings are discussed in the context of cellular mechanisms postulated to underlie Li and VPA therapeutic efficacy.

Chronic treatment with lithium, but not sodium valproate, increases cortical N-acetyl-aspartate concentrations in euthymic bipolar patients

Previous studies have found that treatment with lithium over a 4-week period may increase the concentration of N-acetyl-aspartate (NAA) in both bipolar patients and controls. In view of other findings indicating that NAA concentrations may be a good marker for neuronal viability and/or functioning, it has been further suggested that some of the long term benefits of lithium may therefore be due to actions to improve these neuronal properties. The aim of the present study was to utilize H magnetic resonance spectroscopy ( H MRS) to further examine the effects of both lithium and sodium valproate upon NAA concentrations in treated euthymic bipolar patients. In the first part of the study, healthy controls (n =18) were compared with euthymic bipolar patients (type I and type II) who were taking either lithium (n =14) or sodium valproate (n =11), and NAA : creatine ratios were determined. In the second part, we examined a separate group of euthymic bipolar disorder patients taking sodium valproate (n =9) and compared these to age- and sex-matched healthy controls (n =11), and we quantified the exact concentrations of NAA using an external solution. The results from the first part of the study showed that bipolar patients chronically treated with lithium had a significant increase in NAA concentrations but, in contrast, there were no significant increases in the sodium valproate-treated patients compared to controls. The second part of the study also found no effects of sodium valproate on NAA concentrations. These findings are the first to compare NAA concentrations in euthymic bipolar patients being treated with lithium or sodium valproate. The results support suggestions that longer-term administration of lithium to bipolar patients may increase NAA concentrations. However, the study suggests that chronic administration of sodium valproate to patients does not lead to similar changes in NAA concentrations. These findings suggest that sodium valproate and lithium may not share a common mechanism of action in bipolar disorder involving neurotrophic or neuroprotective effects.

Dextro-amphetamine increases phosphoinositol cycle activity in volunteers: an MRS study

AIMS

To help determine the effects of dextro-amphetamine on the phosphoinositol cycle (PI-cycle) in humans, (1)H and (31)P magnetic resonance spectroscopy (MRS) was utilized in 17 healthy volunteers. This was an open-label study carried out before and after administration of 20 mg oral dextro-amphetamine. Subjects also rated the subjective effects of dextro-amphetamine administration using visual analog scales (VAS).

MAJOR FINDINGS

Following dextro-amphetamine administration there was a significant increase in the concentrations of both myo-inositol and phosphomonoesters.

CONCLUSIONS

These findings are in keeping with suggestions that dextro-amphetamine administration increases the activity of the phosphoinositol cycle, probably via an indirect release of dopamine and noradrenaline. These results are the first time that this has been confirmed in humans.

Chronic treatment with both lithium and sodium valproate may normalize phosphoinositol cycle activity in bipolar patients

BACKGROUND

It has been proposed that lithium may be clinically effective due to its actions on the phosphoinositol second messenger system (PI-cycle). Studies have also suggested that untreated manic patients may have raised myo-inositol and phosphomonoester (PME) concentrations and also that unmedicated euthymic bipolar patients may have lowered PME concentrations. The objective of the present study was to test the hypothesis that chronic treatment with either lithium or sodium valproate in patients with bipolar mood disorder leads to a normalization in the activity of the PI-cycle.

METHODS

This study had two parts each with different MRS methodology. The first part compared healthy controls (n = 19) with euthymic bipolar patients who were taking either lithium (n = 16) or sodium valproate (n = 11) using both (1)H-MRS and (31)P-MRS. In the second part we examined a separate group of euthymic bipolar disorder patients taking sodium valproate (n = 9) and compared these with age and sex-matched healthy controls (n = 11) using (1)H-MRS.

RESULTS

Both studies showed that there were no differences in either myo-inositol or phosphomonoester (PME) concentrations between controls and patients taking either medication.

CONCLUSIONS

These findings examine two key components of the PI-cycle in treated euthymic bipolar (myo-inositol and PME concentrations). The results from this study are consistent with the suggestion that chronic treatment with either lithium or sodium valproate in bipolar patients may normalize PI-cycle functioning.

Magnetic resonance spectroscopy: current and future applications in psychiatric research

Magnetic resonance spectroscopy (MRS) provides a useful method for studying a number of psychotropic medications and metabolites in human brain in vivo. New insights regarding the pharmacokinetic and pharmacodynamic properties of psychotropic medications in the target organ (i.e., brain) have been obtained using lithium-7 MRS and fluorine-19 MRS. Both proton and phosphorus-31 MRS have significantly enhanced our knowledge of the pathophysiology of a number of psychiatric disorders by providing estimates of brain concentrations of several important cerebral metabolites. Efforts are also being made to link MRS measures of cerebral metabolism with neurophysiologic and neurocognitive processes. Ongoing improvement and refinement in MRS techniques, including the installation of scanners with increased magnetic field strength and better methods of data processing, will improve both spatial and temporal resolution. In addition, efforts to develop multisite research studies may result in greater standardization of MRS procedures and methods for interpretation of results. In this review, the current status of MRS applications in psychiatric research is reviewed, and new frontiers and possible future developments are discussed.

Defining the neuromolecular action of myo-inositol: application to obsessive-compulsive disorder

Dietary inositol is incorporated into neuronal cell membranes as inositol phospholipids where it serves as a key metabolic precursor in G protein-coupled receptors. In the brain, several subtypes of adrenergic, cholinergic, serotonergic and metabotropic glutamatergic receptors are coupled to the hydrolysis of phosphoinositides (PI) with myo-inositol (MI) crucial to the resynthesis of PI and the maintenance and effectiveness of signalling. Despite a mode of action that remains illusive, MI has demonstrated therapeutic efficacy in obsessive-compulsive disorder (OCD), putative OCD-spectrum disorders, as well as panic and depression. Behavioural and biochemical studies indicate that this efficacy does not involve simply the replenishing of the membrane PI pool. In addition to its precursory role in cell signalling, inositol lipids alter receptor sensitivity, can direct membrane trafficking events, and have been found to modulate an increasing array of signalling proteins. These effects may afford MI an ability to modulate the interaction between neurotransmitters, drugs, receptors and signalling proteins. This paper reviews the neuromolecular and genetic aspects of OCD in terms of the PI-linked 5HT receptor subtypes and relates these to the behavioural and therapeutic effects of MI. Since OCD often is poorly responsive to current drug treatment, understanding the neuropharmacology of MI holds great promise for understanding the neuropathology of this and other MI-responsive disorders.

Effect of lithium on phosphoinositide metabolism in human brain: a proton decoupled (31)P magnetic resonance spectroscopy study

BACKGROUND

The objective of our study was to evaluate whether lithium increases brain phosphomonoester (PME) levels in human subjects.

METHODS

Proton decoupled (31)P magnetic resonance spectra were obtained from eight healthy volunteers before and after the administration of lithium carbonate, 450 mg b.i.d., for 7 and 14 days.

RESULTS

Pairwise comparisons of the mole percent PME revealed a significant increase from baseline at day 7 and day 14 of lithium administration.

CONCLUSIONS

An increase in PME concentration with 7 and 14 days of lithium administration in the human brain in vivo was observed. Because the inositol-1-monophosphate contributes to the PME peak, this result suggests that some of the initial actions of lithium may occur through a reduction of myo-inositol, which in turn may initiate a cascade of secondary changes at different levels of signal transduction process and gene expression in brain, effects that are ultimately responsible for the therapeutic benefits of lithium.

Identification of three polymorphisms in the translated region of PLC-?1 and their investigation in lithium responsive bipolar disorder

Recently, we have found an association between bipolar disorder patients who are excellent responders to lithium prophylaxis and a polymorphic marker located in the first intron of the phospholipase C-gamma1 gene (PLC-gamma1) [Turecki et al., 1998: Mol Psychiatry 3:534-538]. As this variant is not known to be functional, we searched for other markers within the coding region, using single-strand conformational polymorphism (SSCP) analysis. We have identified three polymorphic sites localized in three different exons of the PLC-gamma1 gene (exons 9, 26, 31). Variation studies of these potentially functional sites in a group of 133 bipolar patients with an excellent response to lithium prophylaxis and a comparison group of 99 healthy controls showed no difference in genotype distributions for exon 9 (chi-square = 1.41, df = 2, P = 0.49), exon 26 (chi-square = 2.26, df = 2, P = 0.13), or exon 31 (chi-square = 1.41, df = 2, P = 0.49). Similar results were observed for allele distributions. These results suggest that our previous findings were not the result of linkage disequilibrium with these variants.

Chronic lithium and sodium valproate both decrease the concentration of myo-inositol and increase the concentration of inositol monophosphates in rat brain

One of the mechanisms underlying lithium's efficacy as a mood stabilizer in bipolar disorder has been proposed to be via its effects on the phosphoinositol cycle (PI-cycle), where it is an inhibitor of the enzyme converting inositol monophosphates to myo-inositol. In contrast, sodium valproate, another commonly used mood stabilizer, appears to have no direct effects on this enzyme and was thus believed to have a different mechanism of action. In the present study, high resolution nuclear magnetic resonance (NMR) spectroscopy was used to study the chronic effects of both lithium and sodium valproate on the concentrations of myo-inositol and inositol monophosphates in rat brain. As predicted, lithium-treated rats exhibited a significant increase in the concentration of inositol monophosphates and a significant decrease in myo-inositol concentration compared to saline-treated controls. However, unexpectedly, sodium valproate administration produced exactly the same results as lithium administration. These novel findings suggest that both lithium and sodium valproate may share a common mechanism of action in the treatment of bipolar disorder via actions on the PI-cycle.

Neuroimaging in bipolar disorder: what have we learned?

New technologies are offering increasingly powerful means to obtain structural, chemical, and functional images of the brain during life, often without the use of ionizing radiation. Bipolar disorder, with its clear physiologic features, would appear to be a prime candidate for the application of current brain imaging; however, only a modest number of studies have been reported to date, and most studies have small sample sizes and heterogeneous subject groups. Nonetheless, there are a few consistent findings among these studies, including the following: 1) Structural imaging studies suggest an increased number of white matter hyperintensities in patients with bipolar disorder. These may be lesions unique to bipolar disorder and its treatment, or related to cardiovascular risk factors, which are more common in bipolar patients. Decreased cerebellar size and anomalies of cerebellar blood volume have also been reported. Increased sulcal prominence and enlargement of the lateral and third ventricles are less consistently observed findings. 2) Spectroscopic imaging suggests abnormalities of metabolism of choline-containing compounds in symptomatically ill bipolar patients and, possibly, treatment-induced changes in choline- and myoinositol-containing compounds. Each of these groups of metabolites serves as a component of membrane phospholipids and cellular second-messenger cycles. 3) Metabolic and blood flow studies provide evidence for decreased activity of the prefrontal cortex (PFC) in bipolar patients during depression. It is not clear if these changes are restricted to particular subregions of the PFC, nor if they are reversed with mania. No single pathophysiologic mechanism yet explains these findings, although all might be due to regional alterations in cellular activity and metabolism or changes in cell membrane composition and turnover. The development of imaging technologies has far outpaced their use in bipolar disorder. The promise of future studies is great, with more powerful magnetic resonance scanners, additional ligands for positron emission tomography and single photon emission computed tomography imaging, and improved image generation and processing already available.