Discovery and design of novel inhibitors of botulinus neurotoxin A: targeted 'hinge' peptide libraries.

Intoxication by the zinc protease botulinus neurotoxin A (BoNT-A) results from cleavage of a single Q-R bond in the neuronal protein SNAP-25, which disables the docking mechanism required for neurotransmitter release. In the present study, potential inhibitors of BoNT-A were assessed from their effects on the BoNT-A cleavage of a synthetic 17-mer peptide (SNAP-25, residues 187-203) spanning the Q-R cleavage site. Compounds that inhibited BoNT-A included thiols (zinc chelators) such as dithiothreitol, dimercaptopropanesulfonic acid, mercaptosuccinic acid and captopril. In addition, compounds containing multiple acidic functions, such as the SNARE motif V2 (ELDDRADALQ), the tripeptide Glu-Glu-Glu and the steroid glycoside glycyrrhizic acid, were effective inhibitors. 'Hinge' peptide mini-libraries (PMLs) having the structure acetyl-X(1)-X(2)-linker-X(3)-X(4)-NH(2) or X(1)-X(2)-linker-X(3), where X(1)-X(4) were mixtures of selected amino acids and the flexible linker was 4-aminobutyric acid, also provided effective inhibition. Targeted PMLs containing the acidic amino acids Asp and Glu, the scissile-bond amino acids Gln and Arg and the zinc chelators His and Cys produced pronounced inhibition of BoNT-A. Deconvolution of these libraries will provide novel ligands with improved inhibitory potency as leads in the design of peptide mimetics to treat BoNT poisoning.

Increased medial thalamic choline in pediatric obsessive-compulsive disorder as detected by quantitative in vivo spectroscopic imaging.

The thalamus has been implicated in the pathophysiology of obsessive-compulsive disorder. Using a multislice spectroscopic imaging sequence, we reported reductions in right and left medial thalamic N-acetylaspartate/cytosolic choline + creatine/phosphocreatine and N-acetylaspartate/cytosolic choline levels in 11 pediatric patients with obsessive-compulsive disorder, 8 to 15 years, versus 11 case-matched healthy controls. These changes may reflect a change in N-acetylaspartate, cytosolic choline, or creatine concentrations. Therefore, using a validated phantom replacement methodology, we obtained absolute measures (mmol/L) of N-acetylaspartate, a putative marker of neuronal viability, cytosolic choline, and creatine in these subjects. A significant increase in cytosolic choline was observed in right and left medial but not lateral thalami in patients with obsessive-compulsive disorder versus controls. N-acetylaspartate and creatine did not differ significantly between case-control pairs in the medial or lateral thalamus. These findings provide new evidence of cytosolic choline abnormalities in the thalamus in pediatric obsessive-compulsive disorder.

Case study: caudate glutamatergic changes with paroxetine persist after medication discontinuation in pediatric OCD.

Proton magnetic resonance spectroscopy (1H-MRS) was used to examine glutamatergic (Glx) abnormalities in the caudate nucleus in pediatric obsessive-compulsive disorder (OCD), associated with severity of illness and response to acute (12 weeks) treatment with paroxetine. In this report, OCD symptoms improved markedly in an 8-year-old girl treated for 14 months with the selective serotonin reuptake inhibitor paroxetine (titrated from 10 to 40 mg/day). Paroxetine dose was then decreased in 10-mg decrements and discontinued without symptom recurrence. Serial 1H-MRS examinations were acquired before and after 12 weeks of paroxetine treatment (40 mg/day) and 3 months after medication discontinuation. A striking decrease in caudate Glx was observed after 12 weeks of treatment which persisted after medication discontinuation. These data provide further support for a reversible glutamatergically mediated dysfunction of the caudate nucleus in OCD that may serve as a pathophysiological and treatment response marker.

Bipolar disorder: leads from the molecular and cellular mechanisms of action of mood stabilizers.

BACKGROUND: New research is dramatically altering our understanding of the molecular mechanisms underlying neuronal communication. AIM: To elucidate the molecular mechanisms underlying the therapeutic effects of mood stabilizers. METHOD: Results from integrated clinical and laboratory studies are reviewed. RESULTS: Chronic administration of lithium and valproate produced a striking reduction in protein kinase C (PKC) isozymes in rat frontal cortex and hippocampus. In a small study, tamoxifen (also a PKC inhibitor) had marked antimanic efficacy. Both lithium and valproate regulate the DNA binding activity of the activator protein I family of transcription factors. Using mRNA differential display, it was also shown that chronic administration of lithium and valproate modulates expression of several genes. An exciting finding is that of a robust elevation in the levels of the cytoprotective protein, bcl-2. CONCLUSIONS: The results suggest that regulation of signalling pathways may play a major part in the long-term actions of mood stabilizers. Additionally, mood stabilizers may exert underappreciated neuroprotective effects.

Brain anatomy and chemistry may predict treatment response in paediatric obsessive--compulsive disorder.

Obsessive--compulsive disorder (OCD) is a severe, highly prevalent and often chronically disabling illness with frequent onset in childhood and adolescence. This underscores the importance of studying the illness during childhood near the onset of illness to minimize potential confounds of long-term illness duration and treatment intervention as well as to examine the developmental underpinnings of the illness. In this review, the authors focus on an integrated series of brain-imaging studies in paediatric OCD suggesting a reversible glutamatergically mediated thalamo-cortical--striatal dysfunction in OCD and their relevance for improved diagnosis and treatment of the condition. Developmental neurobiological models for OCD are presented and particular attention is devoted to evaluating neuroimaging studies designed to test these models and how they may help predict treatment response in paediatric OCD.

Bipolar disorder: leads from the molecular and cellular mechanisms of action of mood stabilisers.

Background New research is dramatically altering our understanding of the molecular mechanisms underlying neuronal communication. Aim To elucidate the molecular mechanisms underlying the therapeutic effects of mood stabilisers. Method Results from integrated clinical and laboratory studies are reviewed. Results Chronic administration of lithium and valproate produced a striking reduction in protein kinase C (PKC) isozymes in rat frontal cortex and hippocampus. In a small study, tamoxifen (also a PKC inhibitor) had marked antimanic efficacy. Both lithium and valproate regulate the DNA binding activity of the activator protein 1 family of transcription factors. Using mRNA differential display, it was also shown that chronic administration of lithium and valproate modulates expression of several genes. An exciting finding is that of a robust elevation in the levels of the cytoprotective protein, bcl-2. Conclusions The results suggest that regulation of signalling pathways may play a major part in the long-term actions of mood stabilisers. Additionally, mood stabilisers may exert underappreciated neuroprotective effects.

Prefrontal cortex as the site of estrogen's effect on cognition.

The hippocampus has long been presumed the primary site of action of estrogens on cognition; and explicit memory is considered the cognitive function most vulnerable to menopausal loss of estrogen. We hypothesize instead that the prefrontal cortex and its neural circuitry are prime mediators of estrogen's role in cognition. We also propose that previously reported menopausal cognitive decline, presumed to be hippocampally mediated, may be secondary to executive dysfunction. We used a cross sectional design to compare the performance of nine menopausal women on hormone replacement therapy (HRT) and 10 menopausal women with no prior exposure to HRT on a battery of neuropsychological tests. The battery was comprised primarily of tests of memory and executive functioning. Executive functioning is mediated by the frontal lobes and encompasses working memory, directed attention, the inhibition of inappropriate responses, cognitive set switching, and behavioral monitoring. Unlike most previous studies, we used a memory measure that yields multiple scores reflecting various problem-solving strategies and error types, thus isolating spared and impaired cognitive processes. Results yielded both qualitative and quantitative evidence for disruption of cognitive processes subserved by the frontal lobes rather than the hippocampus: 1) despite intact free recall on a list-learning task (CVLT), untreated menopausal women were relatively impaired in correctly recognizing words previously learned and distinguishing them from items not on the list (discriminability), 2) untreated women also had difficulty inhibiting inappropriate responses in the form of perseverative errors, and 3) the non-HRT group consistently performed worse on the N-back test of working memory. The prefrontal cortex is critical for intact working memory and estrogen enhances performance on working memory tasks. In conclusion, this study provides preliminary evidence for executive dysfunction in untreated menopausal women as women with HRT outperformed women without HRT on tests requiring directed attention, inhibition of inappropriate responses, and cognitive set switching.

Neuroplasticity and cellular resilience in mood disorders.

Although mood disorders have traditionally been regarded as good prognosis diseases, a growing body of data suggests that the long-term outcome for many patients is often much less favorable than previously thought. Recent morphometric studies have been investigating potential structural brain changes in mood disorders, and there is now evidence from a variety of sources demonstrating significant reductions in regional CNS volume, as well as regional reductions in the numbers and/or sizes of glia and neurons. Furthermore, results from recent clinical and preclinical studies investigating the molecular and cellular targets of mood stabilizers and antidepressants suggest that a reconceptualization about the pathophysiology and optimal long-term treatment of recurrent mood disorders may be warranted. It is proposed that impairments of neuroplasticity and cellular resilience may underlie the pathophysiology of mood disorders, and further that optimal long-term treatment for these severe illnesses may only be achieved by the early and aggressive use of agents with neurotrophic/neuroprotective effects. It is noteworthy that lithium, valproate and antidepressants indirectly regulate a number of factors involved in cell survival pathways including CREB, BDNF, bcl-2 and MAP kinases, and may thus bring about some of their delayed long-term beneficial effects via underappreciated neurotrophic effects. The development of novel treatments which more directly target molecules involved in critical CNS cell survival and cell death pathways have the potential to enhance neuroplasticity and cellular resilience, and thereby modulate the long-term course and trajectory of these devastating illnesses.

Lithium-induced increase in human brain grey matter.

Rodent studies have shown that lithium exerts neurotrophic or neuroprotective effects. We used three-dimensional magnetic resonance imaging and brain segmentation to study pharmacologically-induced increases in grey matter volume with chronic lithium use in patients with bipolar mood disorder. Grey-matter volume increased after 4 weeks of treatment. The increases in grey matter probably occurred because of neurotrophic effects.

Clinical and preclinical evidence for the neurotrophic effects of mood stabilizers: implications for the pathophysiology and treatment of manic-depressive illness.

Recent neuroimaging studies have demonstrated regional central nervous system volume reductions in mood disorders, findings that are complemented by postmortem observations of cell atrophy and loss. It is thus noteworthy that lithium and valproate have recently been demonstrated to robustly increase the expression of the cytoprotective protein bcl-2 in the central nervous system. Chronic lithium not only exerts neuroprotective effects in several preclinical paradigms but also enhances hippocampal neurogenesis. Valproate robustly promotes neurite outgrowth and activates the ERK mitogen-activated protein kinase pathway, a signaling pathway utilized by many endogenous neurotrophic factors. Consistent with its preclinical neurotrophic/neuroprotective effects, chronic lithium treatment of patients with manic-depressive illness increases brain N-acetylaspartate (a putative marker of neuronal viability and function) levels, an effect that is localized almost exclusively to gray matter. To determine if lithium was producing neuropil increases, quantitative three-dimensional magnetic resonance imaging studies were undertaken, which revealed that chronic lithium significantly increases total gray matter volume in the human brain of patients with manic-depressive illness. Together, these results suggest that a reconceptualization about the optimal long-term treatment of recurrent mood disorders is warranted. Optimal long-term treatment for these severe illnesses may only be achieved by the early use of agents with neurotrophic/neuroprotective effects, irrespective of the primary, symptomatic treatment.

Decrease in caudate glutamatergic concentrations in pediatric obsessive-compulsive disorder patients taking paroxetine.

OBJECTIVE: To measure in vivo neurochemical changes in the caudate nucleus in pediatric obsessive-compulsive disorder (OCD) before and after treatment. METHOD: Single-voxel proton magnetic resonance spectroscopic (1H-MRS) examinations of the left caudate were conducted in 11 psychotropic drug-naive children, aged 8 to 17 years, with OCD before and after 12 weeks of monotherapy with the selective serotonin reuptake inhibitor paroxetine (10-60 mg/day) and 11 healthy children aged 8 to 17 years. A different sample of 8 pediatric OCD patients and 8 healthy children had a 1H-MRS examination of occipital cortex. RESULTS: Caudate glutamatergic concentrations (Glx) were significantly greater in treatment-naive OCD patients than in controls but declined significantly after paroxetine treatment to levels comparable with those of controls. Decrease in caudate Glx was associated with decrease in OCD symptom severity. Occipital Glx did not differ between OCD patients and controls. CONCLUSIONS: These preliminary findings provide new evidence of Glx abnormalities in the caudate nucleus in pediatric OCD and suggest that paroxetine treatment may be mediated by a serotonergically modulated reduction in caudate Glx.

The design and synthesis of a potent Angiotensin II cyclic analogue confirms the ring cluster receptor conformation of the hormone Angiotensin II.

The novel amide linked Angiotensin II potent cyclic analogue, c-[Sar1,Lys3,Glu5] ANG II 19 has been designed and synthesized in an attempt to test the aromatic ring clustering and the charge relay bioactive conformation we have recently suggested for ANG II. This constrained cyclic analogue was synthesized by connecting the Lys3 amino and Glu5 carboxyl side chain groups, and it was found to be potent in the rat uterus assay and in anesthetized rabbits. The central part of the molecule is fixed covalently in the conformation predicted according to the backbone bend conformational model proposed for Angiotensin II. The obtained results using a combination of 2D NMR, 1D NOE spectroscopy and molecular modeling revealed a similar Tyr4-Ile5-His6 bend, a His6-Pro7 trans configuration and a side chain aromatic ring cluster of the key aminoacids Tyr4, His6, Phe8 for c-[Sar1,Lys3,Glu5] ANG II as it has been found for ANG II (Matsoukas, J. H.; Hondrelis, J.; Keramida, M.; Mavromoustakos, T.; Markriyannis, A.; Yamdagni, R.; Wu, Q.; Moore, G. J. J. Biol. Chem. 1994, 269, 5303). Previous study of the conformational properties of the Angiotensin II type I antagonist [Hser(gamma-OMe)8] ANG II (Matsoukas, J. M.; Agelis, G.; Wahhab, A.; Hondrelis, J.; Panagiotopoulos. D.; Yamdagni, R.; Wu, Q.; Mavromoustakos, T.; Maia, H.; Ganter, R.; Moore, G. J. J. Med. Chem. 1995, 38, 4660) using 1-D NOE spectroscopy coupled with the present study of the same type of lead antagonist Sarilesin revealed that the Tyr4-Ile5-His6 bend, a conformational property found in Angiotensin II is not present in type I antagonists. The obtained results provide an important conformational difference between Angiotensin II agonists and type I antagonists. It appears that our synthetic attempt to further support our proposed model was successful and points out that the charge relay system and aromatic ring cluster are essential stereoelectronic features for Angiotensin II to exert its biological activity.

Thalamic volume in pediatric obsessive-compulsive disorder patients before and after cognitive behavioral therapy.

BACKGROUND: Neurobiologic abnormalities in the thalamus have been implicated in the pathophysiology of obsessive-compulsive disorder. We recently reported increased thalamic volume in treatment-naive pediatric obsessive-compulsive disorder patients versus case-matched healthy comparison subjects that decreased to levels comparable to control subjects after effective paroxetine therapy. To our knowledge, no prior study has measured neuroanatomic changes in the thalamus of obsessive-compulsive disorder patients near illness onset before and after cognitive behavioral therapy. METHODS: Volumetric magnetic resonance imaging studies were conducted in 11 psychotropic drug-naive 8-17-year-old children with obsessive-compulsive disorder before and after 12 weeks of effective cognitive behavioral therapy monotherapy (> or =30% reduction in obsessive-compulsive disorder symptom severity). RESULTS: No significant change in thalamic volume was observed in obsessive-compulsive disorder patients before and after cognitive behavioral therapy. CONCLUSIONS: Our findings suggest that reduction in thalamic volume after paroxetine therapy may be specific to paroxetine treatment and not the result of a general treatment response or spontaneous improvement. These results are preliminary in view of the small sample studied.

Lithium increases N-acetyl-aspartate in the human brain: in vivo evidence in support of bcl-2's neurotrophic effects?

BACKGROUND: Recent preclinical studies have shown that lithium (Li) robustly increases the levels of the major neuroprotective protein, bcl-2, in rat brain and in cells of human neuronal origin. These effects are accompanied by striking neuroprotective effects in vitro and in the rodent central nervous system in vivo. We have undertaken the present study to determine if lithium exerts neurotrophic/ neuroprotective effects in the human brain in vivo. METHODS: Using quantitative proton magnetic resonance spectroscopy, N-acetyl-aspartate (NAA) levels (a putative marker of neuronal viability and function) were investigated longitudinally in 21 adult subjects (12 medication-free bipolar affective disorder patients and 9 healthy volunteers). Regional brain NAA levels were measured at baseline and following 4 weeks of lithium (administered in a blinded manner). RESULTS: A significant increase in total brain NAA concentration was documented (p < .0217). NAA concentration increased in all brain regions investigated, including the frontal, temporal, parietal, and occipital lobes. CONCLUSIONS: This study demonstrates for the first time that Li administration at therapeutic doses increases brain NAA concentration. These findings provide intriguing indirect support for the contention that chronic lithium increases neuronal viability/function in the human brain, and suggests that some of Li's long-term beneficial effects may be mediated by neurotrophic/neuroprotective events.

Evidence for coupling between glucose metabolism and glutamate cycling using FDG PET and 1H magnetic resonance spectroscopy in patients with epilepsy.

The purpose of this study was to examine the relation between glucose metabolism and glutamate concentration in the human brain, in both the normal and diseased state. Regional values of glucose metabolism measured with 2-deoxy-2[F-18]fluoro-D-glucose positron emission tomography (FDG PET) studies and single-voxel proton magnetic resonance spectroscopy (1H MRS) measurements of the glutamate/ glutamine/gamma-aminobutyric acid (Glx) tissue concentration were determined in multiple brain regions in 11 patients (5 girls and 6 boys, mean age 7.5 years) with medically intractable partial epilepsy. FDG PET and 1H MRS studies were performed in the interictal state in seven patients and in the ictal/periictal state in four patients. Regions of interest were identified in epileptic cortex (determined by intracranial and/or scalp electroencephalography) and in contralateral normal brain regions. Lower glucose metabolism and lower Glx concentrations were found in the epileptic focus than in the contralateral normal cortex in all seven patients examined in the interictal state, whereas higher glucose metabolism and higher Glx concentrations were observed in the epileptic focus in the four patients who had ictal/periictal studies. Significant correlations were found between the values of cerebral glucose utilization and Glx concentration in epileptic brain region, in nonepileptic brain regions, and in epileptic and nonepileptic regions combined. These results demonstrate a significant relation between glucose metabolism and glutamate/glutamine concentration in normal and epileptic cerebral cortex. This relation is maintained in both the interictal and ictal states.

Decrease in thalamic volumes of pediatric patients with obsessive-compulsive disorder who are taking paroxetine.

BACKGROUND: Thalamic dysfunction has been implicated in obsessive-compulsive disorder (OCD). While OCD frequently has its onset during childhood, to our knowledge, no prior study has measured neuroanatomical changes in the thalamus of patients with OCD near the onset of illness, and before and after treatment. METHODS: Volumetric magnetic resonance imaging studies were conducted in 21 psychotropic drug-naive children, aged 8 to 17 years, with OCD and 21 case-matched healthy comparison subjects. Magnetic resonance imaging studies were also conducted in 10 of the 21 patients with OCD after 12 weeks of monotherapy with the selective serotonin reuptake inhibitor, paroxetine hydrochloride. RESULTS: Thalamic volumes were significantly greater in treatment-naive patients with OCD than in controls but declined significantly after paroxetine monotherapy to levels comparable with those of controls. Decrease in thalamic volume in patients with OCD was associated with reduction in OCD symptom severity. CONCLUSIONS: Our findings provide new evidence of thalamic abnormalities in pediatric OCD and further suggest that paroxetine treatment may be paralleled by a reduction in thalamic volume. These reductions may, however, not be specific to paroxetine treatment and could be due to a more general treatment response, and/or spontaneous improvement in symptoms. Our findings are preliminary given the small sample size and our inability to measure discrete thalamic nuclei.

Lithium up-regulates the cytoprotective protein Bcl-2 in the CNS in vivo: a role for neurotrophic and neuroprotective effects in manic depressive illness.

Although mood disorders have traditionally been conceptualized as "neurochemical disorders," considerable literature from a variety of sources demonstrates significant reductions in regional central nervous system (CNS) volume and cell numbers (both neurons and glia) in persons with mood disorders. It is noteworthy that recent advances in cellular and molecular biology have resulted in the identification of 2 novel, hitherto completely unexpected targets of lithium's actions, discoveries that may have a major impact on the future use of this unique cation in biology and medicine. Chronic lithium treatment has been demonstrated to markedly increase the levels of the major neuroprotective protein bc1-2 in rat frontal cortex, hippocampus, and striatum. Similar lithium-induced increases in bc1-2 are also observed in cells of human neuronal origin and are observed in rat frontal cortex at lithium levels as low as approximately 0.3 mM. Bc1-2 is widely regarded as a major neuroprotective protein, and genetic strategies that increase bc1-2 levels have demonstrated not only robust protection of neurons against diverse insults, but have also demonstrated an increase in the regeneration of mammalian CNS axons. Lithium has also been demonstrated to inhibit glycogen synthase kinase 3beta (GSK-3beta), an enzyme known to regulate the levels of phosphorylated tau and beta-catenin (both of which may play a role in the neurodegeneration observed in certain forms of Alzheimer's disease). Consistent with the increases in bc1-2 levels and inhibition of GSK-3beta, lithium has been demonstrated to exert robust protective effects against diverse insults both in vitro and in vivo. These findings suggest that lithium may exert some of its long-term beneficial effects in the treatment of mood disorders via underappreciated neurotrophic and neuroprotective effects. To date, lithium remains the only medication demonstrated to markedly increase bc1-2 levels in several brain areas; in the absence of other adequate treatments, an investigation of the potential efficacy of lithium in the long-term treatment of several neurodegenerative disorders is warranted. Additionally, we suggest that a reconceptualization of the use of lithium in mood disorders may be warranted-namely, that the use of lithium as a neurotrophic/neuroprotective agent should be considered in the long-term treatment of mood disorders, irrespective of the "primary" treatment modality being used for the condition.

Structural comparison between type I and type II antagonists: possible implications in the drug design of AT1 antagonists.

Analogues of sarilesin (type I AT1 antagonists), and sarmesin (type II AT1 antagonists) with homoserine (hSer) at position 8 were prepared and bioassayed. The presence of a Tyr4-Ile5-His6 bend found in sarmesin but not in sarilesin was identified. The obtained results coupled with conformational analysis studies, using a combination of NMR spectroscopy and computational chemistry, propose important conformational and stereoelectronic properties for agonist and antagonist activity at AT1 receptors.

Proton spectroscopic imaging of the thalamus in treatment-naive pediatric obsessive-compulsive disorder.

BACKGROUND: Neurobiological abnormalities in the thalamus, particularly the dorsomedial nucleus of the thalamus, are believed to be involved in the pathophysiology of obsessive-compulsive disorder. Although obsessive-compulsive disorder commonly arises in childhood and adolescence, no prior study has examined the thalamus in pediatric obsessive-compulsive disorder patients. METHODS: In this study, N-acetyl-aspartate, a putative marker of neuronal viability, creatine/phosphocreatine, and choline levels were measured in the lateral and medical subregions of the left and right thalami using a multislice proton magnetic resonance spectroscopic imaging sequence in 11 treatment-naive, nondepressed obsessive-compulsive disorder outpatients, 8-15 years old, and 11 case-matched control subjects. RESULTS: A significant reduction in N-acetyl-aspartate/choline and N-acetyl-aspartate/(creatine/phosphocreatine + choline) was observed in both the right and left medial thalami in obsessive-compulsive disorder patients compared with control subjects. The N-acetyl-aspartate/choline and N-acetyl-aspartate/(creatine/phosphocreatine + choline) levels did not differ significantly between case-control pairs in either the left or the right lateral thalamus. Reduction in N-acetyl-aspartate levels in the left medial thalamus was inversely correlated with increased obsessive-compulsive disorder symptom severity. CONCLUSIONS: These findings provide new evidence of localized functional neurochemical marker abnormalities in the thalamus in pediatric obsessive-compulsive disorder. Our results must be considered preliminary, however, given the small sample size.

Temporal dissociation between lithium-induced changes in frontal lobe myo-inositol and clinical response in manic-depressive illness.

OBJECTIVE: The most widely accepted hypothesis regarding the mechanism underlying lithium's therapeutic efficacy in manic-depressive illness (bipolar affective disorder) is the inositol depletion hypothesis, which posits that lithium produces a lowering of myo-inositol in critical areas of the brain and the effect is therapeutic. Lithium's effects on in vivo brain myo-inositol levels were investigated longitudinally in 12 adult depressed patients with manic-depressive illness. METHOD: Medication washout (minimum 2 weeks) and lithium administration were conducted in a blinded manner. Regional brain myo-inositol levels were measured by means of quantitative proton magnetic resonance spectroscopy at three time points: at baseline and after acute (5-7 days) and chronic (3-4 weeks) lithium administration. RESULTS: Significant decreases (approximately 30%) in myoinositol levels were observed in the right frontal lobe after short-term administration, and these decreases persisted with chronic treatment. The severity of depression measured by the Hamilton Depression Rating Scale also decreased significantly over the study. CONCLUSIONS: This study demonstrates that lithium administration does reduce myo-inositol levels in the right frontal lobe of patients with manic-depressive illness. However, the acute myo-inositol reduction occurs at a time when the patient's clinical state is clearly unchanged. Thus, the short-term reduction of myo-inositol per se is not associated with therapeutic response and does not support the inositol depletion hypothesis as originally posited. The hypothesis that a short-term lowering of myo inositol results in a cascade of secondary signaling and gene expression changes in the CNS that are ultimately associated with lithium's therapeutic efficacy is under investigation.