Myo-inositol reduces serotonin (5-HT2) receptor induced homologous and heterologous desensitization

Treatment-resistant OCD: Pharmacotherapies in adults

Serotonin reuptake inhibitor (SRI) medications are well established as first-line pharmacotherapeutic treatment for Obsessive-Compulsive Disorder (OCD). However, despite the excellent safety profile and demonstrated efficacy of these medications, a substantial proportion of individuals with OCD fail to attain sufficient benefit from SRIs. In this narrative review, we discuss clinical features of OCD that have been associated with poorer response to SRIs, and we present pharmacotherapeutic interventions that have been explored as augmenting or alternative treatments for treatment-resistant OCD. We additionally highlight non-SRI interventions for OCD that are currently under investigation. Pharmacotherapeutic interventions were identified via expert consensus. To assess the evidence base for individual pharmacotherapies, targeted searches for relevant English-language publications were performed on standard biomedical research databases, including MEDLINE. Information relevant to ongoing registered clinical trials in OCD was obtained by search of ClinicalTrials.gov. Pharmacotherapies are grouped for review in accordance with the general principles of Neuroscience-based Nomenclature (NbN). Clinical features of OCD that may suggest poorer response to SRI treatment include early age of onset, severity of illness, duration of untreated illness, and the presence of symmetry/ordering or hoarding-related symptoms. Based on evolving pathophysiologic models of OCD, diverse agents engaging serotonin, dopamine, norepinephrine, glutamate, and anti-inflammatory pathways have been explored as alternative or adjunctive therapies for treatment-resistant OCD and have at least preliminary evidence of efficacy. Medications with dopamine antagonist activity remain the most robustly evidence-based of augmenting interventions, yet dopamine antagonists benefit only a minority of those who try them and carry elevated risks of adverse effects. Interventions targeting glutamatergic and anti-inflammatory pathways are less well evidenced, but may offer more favorable benefit to risk profiles. Ongoing research should explore whether specific interventions may benefit individuals with particular features of treatment-resistant OCD.

The Biomedical Uses of Inositols: A Nutraceutical Approach to Metabolic Dysfunction in Aging and Neurodegenerative Diseases

Inositols are sugar-like compounds that are widely distributed in nature and are a part of membrane molecules, participating as second messengers in several cell-signaling processes. Isolation and characterization of inositol phosphoglycans containing myo- or d-chiro-inositol have been milestones for understanding the physiological regulation of insulin signaling. Other functions of inositols have been derived from the existence of multiple stereoisomers, which may confer antioxidant properties. In the brain, fluctuation of inositols in extracellular and intracellular compartments regulates neuronal and glial activity. Myo-inositol imbalance is observed in psychiatric diseases and its use shows efficacy for treatment of depression, anxiety, and compulsive disorders. Epi- and scyllo-inositol isomers are capable of stabilizing non-toxic forms of β-amyloid proteins, which are characteristic of Alzheimer’s disease and cognitive dementia in Down’s syndrome, both associated with brain insulin resistance. However, uncertainties of the intrinsic mechanisms of inositols regarding their biology are still unsolved. This work presents a critical review of inositol actions on insulin signaling, oxidative stress, and endothelial dysfunction, and its potential for either preventing or delaying cognitive impairment in aging and neurodegenerative diseases. The biomedical uses of inositols may represent a paradigm in the industrial approach perspective, which has generated growing interest for two decades, accompanied by clinical trials for Alzheimer’s disease.

Integrated analysis of the genetic basis of suicidal behavior: what has been shown by structural genetic studies so far

OBJECTIVE

In recent decades, the role of genetic factors in the predisposition to suicidal behavior has attracted considerable attention. Although each genetic investigation appears to be valuable, no one study on its own can comprehensively explain the etiology of suicidal behavior.

METHODS

In this study, using a broad literature review, we found the suicide-associated gene coexpression network. In addition, cytoband, molecular function, biological process, cellular component, tissue-based expression, and disease/disorder enrichment analyses were carried out to determine the most central cellular and molecular infrastructures involved in suicidal behavior.

RESULTS

The reconstructed network consisted of 104 genes, including 91 previously known genes and 13 novel genes, and 354 interactions. Topological analysis showed that in total, CCK, INPP1, DDC, and NPY genes are the most fundamental hubs in the network. We found that suicide genes are significantly concentrated within chromosomes 11 and 6. Further analysis showed that monoaminergic signal transduction, especially through GPCRs, in the cingulate gyrus, superior prefrontal gyrus, dorsal striatum, and the cerebellum are the main, deficient routes in suicide. Moreover, it turned out that genetically, suicidal behavior is more likely in patients with mood and affective disorders.

CONCLUSION

Like other behavioral disorders, suicide has a complex and multifactorial basis and at present, the only approaches to the integrated study of such disorders are computer-based methods. The results of such studies, although subject to a degree of uncertainty, however, can pave the way for future basic and clinical studies.

The effect of dietary supplements on clinical aspects of autism spectrum disorder: A systematic review of the literature

BACKGROUND

Autism spectrum disorder is associated with significant social and financial burden and no definite treatment for this entity has been identified, yet. In recent years there has been an increasing interest in the use of dietary interventions as a complementary therapeutic option for these patients.

OBJECTIVE

The aim of this systematic review is to provide high evidence level literature data about the effect of dietary supplements on clinical aspects of children with autism.

METHODS

A comprehensive literature search was conducted using Pubmed as the medical database source. Randomized controlled trials conducted in pediatric populations and including measures of clinical outcomes were considered.

RESULTS

A total of 17 eligible prospective studies were selected. Types of dietary supplements evaluated in these studies included amino acids, fatty acids and vitamins/minerals. N-acetylcysteine was shown to exert a beneficial effect on symptoms of irritability. On the other hand, literature data about the efficacy of d-cycloserine and pyridoxine-magnesium supplements was controversial. No significant effect was identified for fatty acids, N,N-dimethylglycine and inositol. Literature data about ascorbic acid and methyl B12 was few, although some encouraging results were found. No serious adverse events were reported in the vast majority of the studies, while the prevalence of adverse reactions was similar between treatment and placebo groups.

CONCLUSIONS

The use of dietary supplements in children with autism seems to be a safe practice with encouraging data about their clinical efficacy. More studies are needed to further investigate this issue.

Relevance of orbitofrontal neurochemistry for the outcome of cognitive-behavioural therapy in patients with obsessive-compulsive disorder

Since the advent of non-invasive methods such as proton magnetic resonance spectroscopy ((1)H-MRS), obsessive-compulsive disorder (OCD) has been increasingly associated with an altered composition of neurometabolites and neurotransmitters in several brain areas. Particularly, Inositol has not only been implicated in OCD pathophysiology, but also shown effective in pilot studies in therapy-refractory OCD patients. However, the relevance of regional brain neurochemistry for therapy outcome has not yet been investigated. Whereas numerous neuroimaging findings support a dysfunction of the orbitofrontal cortex (OFC) in OCD, MR-spectroscopic investigations of this region are missing. (1)H-MRS and psychometric measurements were obtained from twenty unmedicated patients with OCD, subsequently enrolled in a 3-month structured inpatient cognitive-behavioural therapy programme, and from eleven matched control subjects. Multiple regression of symptom score changes (Y-BOCS) on (myo-)inositol concentrations in three areas (right orbitofrontal cortex (OFC), right striatum and anterior cingulate cortex) was performed. The concentration of (myo-)inositol in the OFC only predicted the outcome of subsequent CBT regarding Y-BOCS score reduction (Spearman's r(s) = .81, P < 0.003, corrected). The (myo-)inositol concentration did not differ between OCD patients and healthy controls and did not change during therapy. We provide preliminary evidence for a neurochemical marker that may prove informative about a patient's future benefit from behaviour therapy. Inositol, a metabolite involved in cellular signal transduction and a spectroscopic marker of glial activity, predicted the response to CBT selectively in the OFC, adding to the evidence for OFC involvement in OCD and highlighting neurobiological underpinnings of psychotherapy.

The central role of magnesium deficiency in Tourette's syndrome: causal relationships between magnesium deficiency, altered biochemical pathways and symptoms relating to Tourette's syndrome and several reported comorbid conditions

Prior studies have suggested a common etiology involved in Tourette's syndrome and several comorbid conditions and symptomatology. Reportedly, current medications used in Tourette's syndrome have intolerable side-effects or are ineffective for many patients. After thoroughly researching the literature, I hypothesize that magnesium deficiency may be the central precipitating event and common pathway for the subsequent biochemical effects on substance P, kynurenine, NMDA receptors, and vitamin B6 that may result in the symptomatology of Tourette's syndrome and several reported comorbid conditions. These comorbid conditions and symptomatology include allergy, asthma, autism, attention deficit hyperactivity disorder, obsessive compulsive disorder, coprolalia, copropraxia, anxiety, depression, restless leg syndrome, migraine, self-injurious behavior, autoimmunity, rage, bruxism, seizure, heart arrhythmia, heightened sensitivity to sensory stimuli, and an exaggerated startle response. Common possible environmental and genetic factors are discussed, as well as biochemical mechanisms. Clinical studies to determine the medical efficacy for a comprehensive magnesium treatment option for Tourette's syndrome need to be conducted to make this relatively safe, low side-effect treatment option available to doctors and their patients.

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.

Double-blind, controlled, crossover trial of inositol versus fluvoxamine for the treatment of panic disorder

Only 70% of patients respond to current treatments for panic disorder, and many discontinue drugs because of side effects. myo-Inositol, a natural isomer of glucose and a precursor for the second-messenger phosphatidyl-inositol system, has previously been found superior to placebo in the treatment of depression, panic disorder, and obsessive-compulsive disorder (OCD), but a direct comparison with an established drug has never been performed. A double-blind, controlled, random-order crossover study was undertaken to compare the effect of inositol with that of fluvoxamine in panic disorder. Twenty patients completed 1 month of inositol up to 18 g/day and 1 month of fluvoxamine up to 150 mg/day. Improvements on Hamilton Rating Scale for Anxiety scores, agoraphobia scores, and Clinical Global Impressions Scale scores were similar for both treatments. In the first month, inositol reduced the number of panic attacks per week (mean and SD) by 4.0 (2) compared with a reduction of 2.4 (2) with fluvoxamine (p = 0.049). Nausea and tiredness were more common with fluvoxamine (p = 0.02 and p = 0.01, respectively). Because inositol is a natural compound with few known side effects, it is attractive to patients who are ambivalent about taking psychiatric medication. Continuing reports of inositol's efficacy in the treatment of depression, panic disorder, and OCD should stimulate replication studies.

Chronic inositol increases striatal D(2) receptors but does not modify dexamphetamine-induced motor behavior. Relevance to obsessive-compulsive disorder

A large body of evidence suggests that the neuropathology of obsessive-compulsive disorder (OCD) lies in the complex neurotransmitter network of the cortico-striatal-thalamo-cortical (CSTC) circuit, where dopamine (DA), serotonin (5HT), glutamate (Glu), and gamma-amino butyric acid (GABA) dysfunction have been implicated in the disorder. Chronic inositol has been found to be effective in specific disorders that respond to selective serotonin reuptake inhibitors (SSRIs), including OCD, panic, and depression. This selective mechanism of action is obscure. Since nigro-striatal DA tracts are subject to 5HT(2) heteroreceptor regulation, one possible mechanism of inositol in OCD may involve its effects on inositol-dependent receptors, especially the 5HT(2) receptor, and a resulting effect on DA pathways in the striatum. In order to investigate this possible interaction, we exposed guinea pigs to oral inositol (1.2 g/kg) for 12 weeks. Subsequently, effects on locomotor behavior (LB) and stereotype behavior (SB), together with possible changes to striatal 5HT(2) and D(2) receptor function, were determined. In addition, the effects of chronic inositol on dexamphetamine (DEX)-induced motor behavior were evaluated. Acute DEX (3 mg/kg, ip) induced a significant increase in both SB and LB, while chronic inositol alone did not modify LA or SB. The behavioral response to DEX was also not modified by chronic inositol pretreatment. However, chronic inositol induced a significant increase in striatal D(2) receptor density (B(max)) with a slight, albeit insignificant, increase in 5HT(2) receptor density. This suggests that D(2) receptor upregulation may play an important role in the behavioral effects of inositol although the role of the 5HT(2) receptor in this response is questionable.

Combination of antidepressant drugs: the case of inositol

Inositol is a second messenger precursor that is effective in depression and obsessive-compulsive disorder via a mechanism different from serotonin reuptake inhibitors. However, controlled trials of inositol combined with serotonin reuptake inhibitors in depression or in reuptake inhibitor resistant depressed patients, or in partially responsive obsessive-compulsive patients, did not reveal added benefit. This is comparable to results with combinations of other antidepressant treatments, such as tricyclics plus monoamine oxidase inhibitors. Copyright 2001 John Wiley & Sons, Ltd.

Epi-inositol and inositol depletion: two new treatment approaches in affective disorder

Inositol is a simple polyol precursor in a second messenger system important in brain myo-insitol, the natural isomer, which has been found to be therapeutically effective in depression, panic disorder, and obsessive-compulsive disorder in double-blind controlled trials. Recently, epi-inositol, an unnatural stereoisomer of myo-inositol, was found to have effects similar to those of myo-inositol to reverse lithium-pilocarpine seizures. We measured the behavior of rats in an elevated plus maze model of anxiety after chronic treatment of 11 daily intraperitoneal injections of epi-inositol, myo-inositol, or control solution. Epi-inositol reduced anxiety levels of rats compared with controls, and its effect was stronger than that of myo- inositol. Lithium has been hypothesized to alleviate mania by reducing brain inositol levels. Inositol in brain derives from the second messenger cycle, from new synthesis, or from diet via transport across the blood brain barrier. Because the first two are inhibited by lithium, we propose that an inositol-free diet will augment lithium action in mania by enhancing restriction of inositol.

A pre- and postsynaptic modulatory action of 5-HT and the 5-HT2A, 2C receptor agonist DOB on NMDA-evoked responses in the rat medial prefrontal cortex

Intracellular recordings were made from pyramidal neurons in layers V and VI of the rat medial prefrontal cortex in slice preparations to investigate the effect of the serotonin 5-HT2A,2C receptor agonist (-)-1-2,5-dimethoxy-4-bromophenol-2-aminopropane (DOB) and 5-hydroxytryptamine (5-HT) on N-methyl-D-aspartate (NMDA)-induced responses. Bath application of either DOB or 5-HT [in the presence of antagonists to 5-HT1A, 5-HT3 and gamma-aminobutytric acid (GABA) receptors] produced a concentration-dependent biphasic modulation of the NMDA responses. They facilitated and inhibited NMDA responses at low (</= 1 microM DOB and </= 50 microM 5-HT) and higher concentrations, respectively. Both the facilitating and inhibitory action were blocked by the highly selective 5-HT2A receptor antagonist R-(+)-alpha-(2, 3-dimethoxyphenil)-1-[4-fluorophenylethyl]-4-piperidineme thanol (M100907) and the 5-HT2 receptor antagonist ketanserin, thus indicating that both facilitation and inhibition were mediated by the activation of the 5-HT2A receptor subtype. However, the facilitating, but not inhibitory, action of DOB showed a marked desensitization, suggesting that the facilitation and inhibition of NMDA responses resulted from activation of different 5-HT2A receptor subtypes and/or signal-transduction pathways. Indeed, the selective PKC inhibitor chelerythrine and the Ca2+/CaM-KII inhibitor KN-93 prevented the facilitating and inhibitory action of DOB, respectively. We have generated several lines of evidence to indicate the following scenario. Low concentrations of DOB, at presynaptic nerve terminals, markedly enhance NMDA-induced release of excitatory amino acids (EAAs), which then act upon both NMDA and non-NMDA receptors to elicit inward current. The massive inward current masks the postsynaptic inhibitory action of DOB. At higher concentrations, DOB inhibits the release of EAAs and discloses the postsynaptic inhibitory action.

Acute inositol does not attenuate m-CPP-induced anxiety, mydriasis and endocrine effects in panic disorder

Many anti-panic drugs, administered chronically, can block pharmacologically-induced "panic attacks"; acutely they often exacerbate panic disorder. Theories of action need to account for this biphasic effect. Chronic inositol had previously shown efficacy against panic disorder. The authors investigated the effect of a single dose of 20 g inositol on an m-CPP challenge in a double-blind placebo-controlled crossover trial in panic-disorder patients. Seven patients had robust psychological, physiological and endocrine responses to 0.08 mg m-CPP i.v.; inositol had virtually no effect on these responses, although it had some acute effects during the evening before the challenge. A similar trial involving chronic inositol would be of interest.

Effects of hypomagnesia on histamine H1 receptor-mediated facilitation of NMDA responses

1. The ability of histamine to facilitate the N-methyl-D-aspartate (NMDA) induced depolarization of cortical projection neurones was examined by use of grease-gap recording. 2. Histamine (1 to 15 microM) reversibly facilitated the NMDA-induced depolarization yielding a bellshaped concentration-response relationship. The peak enhancement was 167% above the control at 10 microM histamine. Desensitization was present in 4 out of 5 slices on second exposure 40 min following the first exposure. 3. Histamine did not alter the depolarization induced by 10 microM kainate. 4. The histamine-induced facilitation persisted in the presence of tetrodotoxin, but was reduced in a concentration-dependent manner by diphenhydramine (IC50 = 7.6 nM). Cyproheptadine (10 nM) also reduced the facilitation, whereas ranitidine (200 nM) and thioperamide (10 nM) were ineffective in this regard. 5. Histamine (10 microM) facilitated the NMDA (25 microM)-induced depolarization in nominally Mg(2+)-free medium. The magnitude of the facilitation was smaller than that observed in Mg(2+)-containing medium (17% above the control) and desensitization was not observed. This facilitation was not reduced by cyproheptadine (10 nM) or diphenhydramine (1 microM). 6. We conclude that histamine facilitates the NMDA depolarization at cortical neurones via two distinct mechanisms. One mechanism involves activation of the histamine H1 receptor and is sensitive to Mg2+. The second mechanism is independent of histamine cell surface receptor activation and may reflect a direct action of histamine at the NMDA receptor.

Controlled trials of inositol in psychiatry

Inositol is a simple polyol precursor in a second messenger system important in the brain. Cerebrospinal fluid inositol has been reported as decreased in depression. A double-blind controlled trial of 12 g daily of inositol in 28 depressed patients for four weeks was performed. Significant overall benefit for inositol compared to placebo was found at week 4 on the Hamilton Depression Scale. No changes were noted in hematology, kidney or liver function. Since many antidepressants are effective in panic disorder, twenty-one patients with panic disorder with or without agoraphobia completed a double-blind, placebo-controlled, four week, random-assignment crossover treatment trial of inositol 12 g per day. Frequency and severity of panic attacks and severity of agoraphobia declined significantly with inositol compared to placebo. Side-effects were minimal. Since serotonin re-uptake inhibitors benefit obsessive compulsive disorder (OCD) and inositol is reported to reverse desensitization of serotonin receptors, thirteen patients with OCD completed a double-blind controlled crossover trial of 18 g inositol or placebo for six weeks each. Inositol significantly reduced scores of OCD symptoms compared with placebo. A controlled double-blind crossover trial of 12 g daily of inositol for a month in twelve anergic schizophrenic patients, did not show any beneficial effects. A double-blind controlled crossover trial of 6 g of inositol daily vs. glucose for one month each was carried out in eleven Alzheimer patients, with on clearly significant therapeutic effects. Antidepressant drugs have been reported to improve attention deficit disorder (ADDH) with hyperactivity symptomatology. We studied oral inositol in children with ADDH in a double-blind, crossover, placebo-controlled manner. Eleven children, mean age 8.9 +/- 3.6 years were enrolled in an eight week trial of inositol or placebo at a dose of 200 mg/kg body weight. Results show a trend for aggravation of the syndrome with myo-inositol as compared to placebo. Recent studies suggest that serotonin re-uptake inhibitors are helpful in at least some symptoms of autism. However a controlled double-blind crossover trial of inositol 200 mg/kg per day showed no benefit in nine children with autism. Cholinergic agonists have been reported to ameliorate electroconvulsive therapy (ECT)-induced memory impairment. Inositol metabolism is involved in the second messenger system for several muscarinic cholinergic receptors. Inositol 6 g daily was given in a crossover-double-blind manner for five days before the fifth or sixth ECT to a series of twelve patients, without effect. These results suggest that inositol has therapeutic effects in the spectrum of illness responsive to serotonin selective re-uptake inhibitors, including depression, panic and OCD, and is not beneficial in schizophrenia, Alzheimer's ADDH, autism or ECT-induced cognitive impairment.

Inositol treatment of autism

Recent studies suggest that serotonin reuptake inhibitors are helpful in at least some symptoms of autism. Inositol is a precursor of the second messenger for some serotonin receptors, and has been reported effective in depression, panic disorder and obsessive-compulsive disorder. However a controlled double-blind crossover trial of inositol 200 mg/kg per day showed no benefit on 9 children with autism. Since biochemical studies could evaluate inositol in children already receiving serotonin reuptake inhibitors.

Inositol has behavioral effects with adaptation after chronic administration

Inositol is a simple dietary polyol that serves as a precursor in important second messenger systems. Inositol in pharmacological doses has been reported recently to be therapeutic in depression, panic disorder and obsessive compulsive disorder. We hereby report effects of inositol on the elevated plus maze model of anxiety. These results should allow development of new inositol analogs that could expand psychoactive drug development possibilities via second messenger manipulation.

Action of 5-hydroxytryptamine in facilitating N-methyl-D-aspartate depolarization of cortical neurones mimicked by calcimycin, cyclopiazonic acid and thapsigargin

1. The ability of calcimycin, cyclopiazonic acid and thapsigargin to facilitate the N-methyl-D-aspartate (NMDA)-mediated depolarization of cortical projection neurones was investigated by use of grease-gap recording and the results compared with the facilitation that results from activation of 5-hydroxytryptamine2A receptors. 2. Calcimycin (0.25 to 3 microM), cyclopiazonic acid (5 to 30 microM), and thapsigargin (10 to 300 nM) reversibly facilitated the NMDA (50 microM)-induced depolarization in the presence of tetrodotoxin. The concentration-response relationships were bell-shaped with a mean enhancement of 550% for calcimycin (1 microM) and approximately 400% for cyclopiazonic acid (20 microM) and thapsigargin (100 nM). At the highest concentration of each agent tested, no facilitation was observed. 3. Chlorpromazine (1 microM) partially restored a facilitation at 3 microM calcimycin and 300 nM thapsigargin. Myo-inositol (10 mM) and 100 nM staurosporine were both ineffective in this regard. 4. The depolarization elicited by 10 microM quisqualate or 5 microM kainate was not facilitated by 10 microM cyclopiazonic acid. 5. Calcimycin (0.5 microM), cyclopiazonic acid (20 microM), and thapsigargin (100 nM) elicited a significant facilitation in the presence of an antagonist cocktail consisting of D,L-2-amino-3-phosphonopropionic acid, prazosin, ritanserin, and scopolamine, although the magnitude of the facilitation was reduced. 6. Facilitation of the NMDA depolarization elicited by both 30 microM 5-hydroxytryptamine and 10 microM phenylephrine was eliminated in nominally Mg(2+)-free medium. In contrast, the facilitation induced by 0.5 microM calcimycin remained intact. 7. Bis-(o-aminophenoxy)-ethane-N,N,N,N, tetraacetic acid aminoethoxy (50 microM) or perfusion with nominally Ca(2+)-free medium eliminated facilitation of the NMDA depolarization induced by 30 microM 5-hydroxytryptamine and 100 nM thapsigargin. 8. The facilitation induced by both 30 microM 5-hydroxytryptamine and 1 microM calcimycin was reduced in a concentration-dependent manner by nifedipine (1 to 10 microM). 9. Calcimycin, cyclopiazonic acid and thapsigargin facilitate the NMDA depolarization in a manner which closely mimics the facilitation induced by 5-hydroxytryptamine. It is concluded that enhancement of the NMDA depolarization at cortical projection neurones results from an elevation of Ca2+ in the cytosol and that several sources of Ca2+ contribute to the facilitation.

Differential uptake of myo-inositol in vivo into rat brain areas

Oral inositol has been reported to have antidepressant and antipanic properties in humans. Inositol enters the brain poorly and high doses are required. Natural uptake processes and specific transporters are involved. We here report that intraperitoneally administered inositol is taken up differently by various brain areas and that brain areas have different baseline inositol levels. These effects could be important in understanding the differential effects of lithium-induced lowering of inositol and of behavioral effects of exogenous inositol.

Characterization of metabotropic glutamate receptor-mediated facilitation of N-methyl-D-aspartate depolarization of neocortical neurones

1. Facilitation of the N-methyl-D-aspartate (NMDA) receptor-mediated depolarization of cortical neurones induced by metabotropic glutamate receptor (mGluR) agonists in the presence of tetrodotoxin has been examined by use of grease-gap recording. 2. Quisqualate (1-2 microM) and 10 to 100 microM 1S,3R-I-aminocyclopentane-1,3-dicarboxylic acid (1S,3R-ACPD) facilitated the NMDA-, but not the kainate-induced depolarization with an EC50 of 16 microM for 1S,3R-ACPD. The facilitation induced by quisqualate was reduced, but not blocked, by 4 microM 6-cyano-7-nitroquinoxaline-2,3-dione. 3. D,L-2-Amino-3-phosphonopropionic acid and D,L-2-amino-4-phosphonobutyric acid antagonized the 1S,3R-ACPD facilitation in a non-competitive manner with IC50 values of 0.24 microM and 4.4 microM respectively. 4. Homologous desensitization of the 1S,3R-ACPD induced facilitation was not observed. The facilitation was not altered by 10 nM staurosporine or 3 microM phorbol diacetate. 5. Substitution of 20 microM 8-bromo-cyclic adenosine monophosphate, 20 microM 8-bromo-cyclic guanosine monophosphate, or 10 microM arachidonic acid for 1S,3R-ACPD did not induce facilitation of the NMDA response. However, the 1S,3R-ACPD facilitation was potentiated by 10 mM myo-inositol and exhibited heterologous desensitization following exposure to 100 microM 5-hydroxytryptamine. 6. The 1S,3R-ACPD-induced facilitation persisted in both 10 microM nifedipine and nominally Ca(2+)-free medium and was only gradually eliminated following addition of 100 microM bis-(-o-aminophenoxy)-ethane-N,N,N,N-tetraacetic acid in Ca(2+)-free medium. Facilitation of the NMDA response induced by carbachol, but not phenylephrine, was also observed in nominally Ca(2+)-free medium. Perfusing 50 microM bis-(-aminophenoxy)-ethane-N,N,N,N-tetraacetic acid aminoethoxy eliminated the 1S,3R-ACPD facilitation. 7. These experiments have shown that mGluR agonists selectively facilitate the NMDA depolarization of cortical wedges, most likely by activating one or more mGluR subtypes that couple to phospholipase C. We conclude the facilitation results from a Ca(2+)-sensitive mechanism dependent on activation of phospholipase C and release of internal Ca2+. The facilitation is not contingent on activation of protein kinase C or entry of Ca2+ through nifedipine-sensitive Ca2+ channels.

CSF inositol does not predict antidepressant response to inositol. Short communication

CSF inositol was reported to be reduced in depression and inositol has been reported to be effective in treatment of depression. We studied CSF inositol in 18 drug-free depressed patients and 36 normal controls; the depressed patients then participated in an open trial of 18 gm daily inositol treatment for 4 weeks. There was no difference in pre-treatment CSF inositol between depressed patients and controls. CSF inositol levels did not predict response on the Hamilton Depression Scale to 4 weeks of inositol treatment.

Loss of cortical serotonin2A signal transduction in senescent rats: reversal following inhibition of protein kinase C

Using grease gap recordings, age-related changes in serotonin2A receptors were assessed in sensorimotor regions of the cortex by examining serotonin-induced facilitation of the N-methyl-D-aspartate depolarization in cortical wedges prepared from young adult (3-6 months) and senescent (22-34 months) Fisher 344 rats. Serotonin (10-100 microM) facilitated the N-methyl-D-aspartate depolarization in wedges from young adult rats in a concentration-dependent manner, whereas no facilitation was observed in wedges from senescent rats. Similar results were obtained when +/- 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane, a mixed serotonin2A and serotonin2C receptor agonist, was substituted for serotonin. In contrast, agonists at alpha 1A-adrenoceptors, metabotropic glutamate receptors and muscarinic cholinoceptors facilitated the N-methyl-D-aspartate depolarization in wedges from both young adult and senescent rats. Chelerythrine and staurosporine, inhibitors of protein kinase C, but not concanavalin A, myo-inositol or calmodulin antagonists, restored the serotonin facilitation in wedges from senescent animals. In situ hybridization histochemistry revealed that serotonin2A receptor messenger RNA was present in layers II-VI of the cortex, with the highest density of silver grains located in layers III and V of both young adult and senescent rats. Detailed examination of layer V showed that silver grains were significantly higher than background only over pyramidal cells. We conclude that serotonin2A receptors are expressed by pyramidal cells in both young adult and senescent rats and that serotonin acts directly on these receptors to facilitate the N-methyl-D-aspartate depolarization. Moreover, in senescent rats, signal transduction at cortical serotonin2A receptors involved with facilitation of the N-methyl-D-aspartate response is compromised as a result of protein kinase C activation.