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

BACKGROUND: The clinical effectiveness of lithium may be due to its decreasing the intracellular concentration of myo-inositol and increasing that of its inositol monophosphate precursors, which is known as the inositol depletion hypothesis. METHODS: Magnetic resonance spectroscopy (MRS) was used to measure the concentration of both myo-inositol (1H MRS) and phosphomonoesters (PME) [31P MRS], in healthy volunteers in a double-blind placebo-controlled study. MRS measurements were made at baseline, again on the 7th day of lithium (1200 mg, n = 10) or placebo (n = 6) administration, and again on day 8, 2 hours following oral administration of 20 mg dextroamphetamine to stimulate the phosphoinositol (PI) cycle. RESULTS: Subjects who received lithium showed a greater increase in PME ratios in response to amphetamine administration than did placebo-treated subjects. CONCLUSIONS: The present results support the hypothesis that lithium administration blocks the conversion of inositol monophosphates to myo-inositol, and that this effect is especially apparent following PI cycle stimulation. The effects of lithium treatment on myo-inositol in healthy volunteers in vivo are uncertain, and may have to await improvements in the ability to measure myo-inositol in the brain.     

High-dose dietary myo-inositol supplementation does not alter the ischaemia phenomenon in human diabetics

Five diabetic patients and 3 non-diabetics were subjected to a dietary supplement of 20 g per day of myo-inositol (40 X the normal ingestion) for 14 days. This amount neither produced toxic side-effects nor changed the peripheral nervefunction expressed by motor conduction velocity or resistance to ischaemia.     

Unlike lithium, anticonvulsants and antidepressants do not alter rat brain myo-inositol

Lithium is the first-line in bipolar disorder treatment. Lithium's clinical efficacy might be due to its inhibition of myo-inositol turnover in the phosphatidylinositol second messenger system. This study aimed to determine whether this action can extend to antidepressants and anticonvulsants also used to treat bipolar symptoms. Male rats were treated for 2 weeks with an intraperitoneal injection of phenelzine, fluoxetine, desipramine, carbamazepine, lamotrigine, sodium valproate or vehicle. Brains were dissected and myo-inositol concentrations were analyzed using high-field nuclear magnetic resonance spectroscopy at 18.8 T and quantified using Chenomx Profiler software. Brain regions assessed included the prefrontal, temporal and occipital cortical areas as well as the hippocampus. The main finding is that contrary to lithium, the anticonvulsants and antidepressants do not alter brain myo-inositol concentration. This suggests that these agents might work via a mechanism that is not centered on changes in myo-inositol concentration.     

Substance P does not alter interleukin-1 expression by splenic or granuloma macrophages in murine schistosomiasis.

Substance P (SP) is an undecapeptide with neurotransmitter and immunoregulatory properties. In murine schistosomiasis, ova naturally induce liver and intestinal granulomas. These granulomas contain macrophages, and eosinophils that produce SP. A report showed that human blood monocytes isolated by adherence release interleukin-1 (IL-1) in response to SP (Lotz et al. (1989) Science 241, 1218). IL-1 is important for initiation of hypersensitivity granulomas. Therefore, it was determined whether SP modulates granuloma macrophage IL-1 production in murine schistosomiasis. Macrophages were obtained from lung and liver granulomas, and from spleens of infected mice. A thymocyte proliferation assay measured IL-1 activity in culture supernatants. Total RNA, extracted from macrophages, was assayed for IL-1 alpha and beta mRNA by Northern blotting using cDNA probes. In response to lipopolysaccharide (LPS), splenic macrophages and macrophages from young lung granulomas released appreciable IL-1. Macrophages from liver granulomas, that were lesions older than the lung granulomas, were unresponsive to LPS with regard to IL-1 secretion. Yet, granuloma macrophages spontaneously expressed IL-1 alpha and beta mRNA. LPS enhanced IL-1 mRNA expression in both splenic and granuloma macrophages. Exposure of macrophages from all sources to SP did not alter IL-1 secretion or gene expression. Similarly, the responsiveness of macrophages to LPS was not affected by concomitant exposure to SP. It is concluded that, in the murine system, SP does not directly influence splenic or granuloma macrophage IL-1 secretion or gene expression. Also, it appears that macrophage secretion of IL-1 is rapidly down-regulated following granuloma elicitation.     

Lithium does not alter the choline/creatine ratio in the temporal lobe of human volunteers as measured by proton magnetic resonance spectroscopy.

OBJECTIVE: To study the effect of lithium administration on brain choline/creatine (Cho/Cr) ratios in healthy volunteers. DESIGN: Double-blind, placebo-controlled, prospective study. SETTING: The Nuclear Magnetic Resonance Research Unit at the University of Alberta. PARTICIPANTS: Sixteen healthy volunteers, recruited through advertisements. Subjects were excluded if they had a physical illness, or a personal or family history of psychiatric illness. The study period was from Feb. 6, 1996, to Mar. 21, 1996. INTERVENTIONS: Subjects received a baseline proton magnetic resonance spectroscopy (1H MRS) scan, and then were instructed to take either lithium (1,200 mg) or placebo at night for 7 days. On Day 8, the subjects returned for a second 1H MRS scan. Study participants were seen by a physician at the beginning and at the end of the experiment, and had access to the physician throughout the study period. OUTCOME MEASURES: Ratios of Cho/Cr measured in the temporal lobes by 1H MRS. RESULTS: There were no significant differences in the Cho/Cr ratios between the 2 groups on the test day (placebo 0.748 [standard deviation 0.29] versus lithium 0.811 [SD 0.25]; F = 0.147, p = 0.72), and there was no significant change from baseline in either group (0.003 above baseline for placebo; 0.056 above baseline for lithium; F = 1.21, p = 0.32). CONCLUSIONS: Lithium administration to healthy volunteers does not alter the Cho/Cr ratio in temporal lobe as measured by 1H MRS. The result concurs with reports that differences in Cho/Cr ratios observed in patients with bipolar disorder are likely specific to the illness, and are not the result of lithium therapy. Hence, alterations in choline function are not involved in the clinical effectiveness of lithium.     

Recombinant human interferon-alpha does not alter reward behavior, or neuroimmune and neuroendocrine activation in rats

Recombinant human interferon-alpha (IFN-alpha) induces depression, and neuroendocrine and neuroimmune activation, in a significant number of patients undergoing treatment for viral illnesses (e.g., hepatitis C), yet these effects have not been consistently reproduced in rodents. As such, we sought to determine the effects of acute or chronic IFN-alpha treatment on basic reward and immobility in the forced swim test (FST), neuroendocrine and neuroimmune activation, and monoamine turnover in brain. In the first experiment, male Wistar rats (N = 7/group) treated with human recombinant IFN-alpha (100,000 IU/kg, i.p.), as compared to saline, did not exhibit alterations to rate of sucrose pellet self-administration or total reinforcers obtained, corticosterone release, plasma IL-6 release, IL-1beta or IL-6 mRNA expression in hippocampus, or monoamine turnover in prefrontal cortex, striatum, nucleus accumbens, or amygdala. However, acute IFN-alpha decreased body weight and produced a trend toward reduced food consumption in the home cage 2 h after injection. In the second experiment, Wistar rats (N=4/group) were subjected to a chronic treatment regimen of saline or IFN-alpha (100,000 IU/kg, i.p.) once daily for 14 consecutive days. The data reveal that animals exposed to chronic IFN-alpha exhibited similar amounts of time immobile and similar latencies to primary immobility in the FST as compared to saline-treated controls. Chronic IFN-alpha did not induce corticosterone release, plasma TNF-alpha, or IL-6 release. Tissue monoamine analysis revealed that chronic IFN-alpha reduced DA levels in prefrontal cortex, and decreased 5-HT levels and increased 5-HT turnover in amygdala. In the third experiment, Wistar rats (N = 4/group) were exposed to either acute or chronic pegylated IFN-alpha (pegIFN-alpha: 3.25, 10 or 75 mg/kg, i.p.) at one of several time points from 1 h to 23 days. The data reveal that neither acute nor chronic pegIFN-alpha induced corticosterone release. Overall, the current report demonstrates that neither acute nor chronic IFN-alpha induced depressive-like behavior and neither IFN-alpha nor peg-IFN-alpha was capable of inducing neuroendocrine or neuroimmune activation. Despite the neurochemical alterations observed in the chronic treatment regimen, the data indicate that recombinant human IFN-alpha does not produce a robust model of depressive-like behavior in rodents.     

N-Acetylaspartate and creatine levels measured by (1)H MRS relate to recognition memory

OBJECTIVES: To investigate the relationship between recognition memory and metabolite levels in medial structures of the temporal lobes in the living human brain. METHODS: Proton MRS ((1)H MRS) and the intracarotid amobarbital test were performed in 16 epileptic patients found suitable for temporal lobectomy. All patients had mesial temporal sclerosis. Metabolite ratios between N:-acetylaspartate (NAA), creatine and phosphocreatine (Cr + PCr), and choline-containing compounds (Cho) [NAA/(Cr + PCr), NAA/Cho, and NAA/(Cr + PCr + Cho)] were calculated for (1)H MRS voxels that included the amygdala, anterior half of the hippocampus, and underlying subiculum. Metabolite ratios were correlated with unilateral memory scores estimated by the intracarotid amobarbital test for words, objects, faces, and total score. RESULTS: The total memory score, memory for objects and faces, and NAA/(Cr + PCr) were significantly lower for the hemisphere ipsilateral to the resection. The asymmetry indexes for NAA/(Cr + PCr) correlated with asymmetry indexes for words (rho = 0.82, p = 0.0001) and total memory (rho = 0. 72, p = 0.002). Analysis of memory scores and metabolite ratios from all 32 hemispheres revealed a correlation between NAA/(Cr + PCr) and memory for words (rho = 0.45, p = 0.009). A correlation between memory for words and NAA/(Cr + PCr) existed in the contralateral (rho = 0.58, p = 0.019) and in the right (rho = 0.51, p = 0.045) hemispheres, and a trend was found in the left hemispheres (rho = 0. 48, p = 0.06). CONCLUSION: There is a correlation between memory for words and the NAA/(Cr + PCr) ratio from medial temporal structures in patients with mesial temporal sclerosis. The findings suggest that medial temporal structures and adjacent neocortex play a significant role in recognition memory in humans, particularly for words.     

Traumatic spinal cord injury in rabbits decreases intracellular free magnesium concentration as measured by P MRS

The mechanisms by which traumatic injury to the central nervous system cause irreversible tissue damage remain speculative. Recent reports suggest that a decrease in tissue total and free Mg²⁺ concentration may be an important factor in the development of such injury after experimental brain trauma. Although total Mg changes have been reproted following spinal cord trauma, no studies have examined spinal cord-free Mg²⁺. In the present study, we have used phosphorus magnetic resonance spectroscopy to determine intracellular free Mg²⁺ concentration and atomic absorption spectrophotometry to measure total tissue Mg concentration in rabbit spinal cord prior to and following impact trauma. We report that intracellular free Mg²⁺ concentration decreases from a pre-injury value of 0.80 ± 0.12mM (mean ±S.E.M.) to 0.31 ± 0.05mM at 2 h post-trauma. Following injury there was a associated decrease in total tissue Mg and K concentration, but no alterations in tissue Na or water content.     

Traumatic spinal cord injury in rabbits decreases intracellular free magnesium concentration as measured by 31P MRS

The mechanisms by which traumatic injury to the central nervous system cause irreversible tissue damage remain speculative. Recent reports suggest that a decrease in tissue total and free Mg2+ concentration may be an important factor in the development of such injury after experimental brain trauma. Although total Mg changes have been reported following spinal cord trauma, no studies have examined spinal cord-free Mg2+. In the present study, we have used phosphorus magnetic resonance spectroscopy to determine intracellular free Mg2+ concentration and atomic absorption spectrophotometry to measure total tissue Mg concentration in rabbit spinal cord prior to and following impact trauma. We report that intracellular free Mg2+ concentration decreases from a pre-injury value of 0.80 +/- 0.12 mM (mean +/- S.E.M.) to 0.31 +/- 0.05 mM at 2 h post-trauma. Following injury there was an associated decrease in total tissue Mg and K concentration, but no alterations in tissue Na or water content.     

Temporal lobectomy for epilepsy: recovery of the contralateral hippocampus measured by (1)H MRS

(1)H MRS imaging was obtained from 10 patients with mesial temporal lobe epilepsy before and after surgery. After surgery, metabolic recovery in the contralateral hippocampus was detected. Preoperatively, reduced N-acetylaspartate (p < 0.04) increased after surgery nonsignificantly to equal control values. Cholines increased after surgery (p < 0.02) and creatine-phosphocreatine showed a trend to higher values. The results suggest that the contralateral hippocampus is affected by repeated seizure activity in the ipsilateral hippocampus, rather than presence of bilateral mesial temporal sclerosis.     

Inositol-1-phosphatase of human erythrocytes is inhibited by therapeutic lithium concentrations

Lithium is widely used in psychiatric chemotherapy and is especially effective in the treatment of manic-depressive illness (MDI), but the mechanism for its therapeutic properties and side effects remains to be elucidated. One of the possibilities relates to the inhibitory effect of Li+ on inositol-1-phosphatase (I-1-P'ase) activity. Indeed, the concentration of inositol-1-phosphate (I-1-P) after treatment with Li+ was shown to be increased in various mammalian cells. Yet, no direct study of I-1-P'ase activity in human cells has been reported. Erythrocytes are readily accessible for routine studies and could facilitate the investigation of I-1-P'ase as affected by Li+ in relation to MDI. It is now shown that I-1-P'ase can be measured in lysate of human erythrocytes, using a small blood sample. The enzymatic activity is localized in the soluble fraction. The Km for I-1-P is 0.14 mM. Intriguingly, the Ki for Li+ is 0.86 mM, within the range of therapeutic concentrations in MDI patients.     

Inhibition of multidrug transporters by verapamil or probenecid does not alter blood-brain barrier penetration of levetiracetam in rats

Overexpression of multidrug efflux transporters such as P-glycoprotein (Pgp; ABCB1) or multidrug resistance proteins (MRPs; ABCC) in the blood-brain barrier has recently been suggested to explain, at least in part, pharmacoresistance in epilepsy, which affects about 30% of all patients with this common brain disorder. The novel antiepileptic drug (AED) levetiracetam (LEV) is an effective and well tolerated drug in many patients with otherwise AED-refractory epilepsy. One explanation for the favorable efficacy of LEV in pharmacoresistant patients would be that LEV is not a substrate for Pgp or MRPs in the BBB. In the present study, we used in vivo microdialysis in rats to study whether the concentration of LEV in the extracellular fluid of the cerebral cortex can be modulated by inhibition of Pgp or MRPs, using the Pgp inhibitor verapamil and the MRP1/2 inhibitor probenecid. Local perfusion with verapamil or probenecid via the microdialysis probe did not increase the extracellular brain concentration of LEV, which is in contrast to various other AEDs which have been studied previously by the same experimental protocol in this model. The data indicate that brain uptake of LEV is not affected by Pgp or MRP1/2 which may be an important reason for its antiepileptic efficacy in patients whose seizures are poorly controlled by other AEDs.     

Deletion of the adenosine A1 receptor gene does not alter neuronal damage following ischaemia in vivo or in vitro

Extracellular adenosine is dramatically increased during cerebral ischaemia and is considered to be neuroprotective due to its inhibitory effect on synaptic transmission mediated by the adenosine A1 receptor (A1R). We investigated the importance of the A1R in a mouse model of global ischaemia and in a murine hippocampal slice culture model of in vitro ischaemia, using mice with the A1R gene deleted. In brains from mice lacking the A1R, damage induced by global ischaemia was similar to that in wild-type animals. In contrast, treatment with a selective A1R antagonist [8-cyclo-pentyl theophylline (8-CPT)], administered before the ischaemic insult in naive wild-type mice, exacerbated the neuronal damage following global ischaemia. Although the inhibitory action of adenosine on excitatory neurotransmission in hippocampal slices was lost in A1R knockout mice, there was no difference in damage between slices from wild-type and knockout mice after in vitro ischaemia. The results suggest that some effects of the A1R are compensated for in knockout animals.     

Blockade of GPIIb/IIIa by eptifibatide and tirofiban does not alter tissue factor induced thrombin generation in human endotoxemia

Activated platelets facilitate thrombin generation by providing a catalytic surface on which coagulation activation occurs. The glycoprotein (GP) IIb/IIIa receptor might play a major role in this process as shown by in vitro and animal experiments. However, it is controversial whether the GPIIb/IIIa receptor facilitates tissue factor-induced thrombin generation in humans as well. We therefore investigated whether two clinically used GPIIb/IIIa antagonists (tirofiban and eptifibatide) may blunt TF-induced coagulation in humans. Thirty male volunteers received 2 ng/kg endotoxin and standard doses of eptifibatide, tirofiban or placebo over 5 hours in a randomized, double-blind, placebo-controlled, double-dummy parallel-group trial. Markers of thrombin generation (prothrombin fragment 1+2, thrombin-antithrombin complexes), fibrinolysis (D-dimer, plasmin-antiplasmin complexes) as well as inflammatory markers (interleukin-6, tumor necrosis factor-alpha) were measured by enzyme linked immunoasssays, TF-mRNA expression was quantified by RT-PCR. Neither eptifibatide nor tirofiban influenced LPS-induced coagulation activation or fibrinolytic activity. Additionally, the increase of TNF-alpha and IL-6 was similar in all groups. In conclusion, GPIIb/IIIa blockade with eptifibatide or tirofiban did not influence TF-induced coagulation activation in human low grade endotoxemia.     

A point mutation in the human connexin32 promoter P2 does not correlate with X-linked dominant Charcot-Marie-Tooth neuropathy in Germany

The sensorimotor neuropathy Charcot-Marie-Tooth disease (CMT) is the most common hereditary disorder of the peripheral nervous system. The X-linked dominant form of CMT (CMTX) is associated with mutations in the connexin32 gene (Cx32). The majority of CMTX cases harbour mutations in the coding region while a few cases have been reported to result from mutations in the promoter region. We found a G-713A transition of the nerve specific Cx32 promoter P2 in the Caucasian German population. The allele frequency reached 50%, both in CMT patients and in healthy control individuals. In contrast, in an earlier contribution to this journal [Brain Res. Mol. Brain Res.78 (2000) 146], the same base transition was reported to cause CMTX in a Taiwanese family. These divergent results are important for genetic counselling and require careful consideration of ethnic backgrounds and of diagnostic and experimental pitfalls.     

The common inositol-reversible effect of mood stabilizers on neurons does not involve GSK3 inhibition, myo-inositol-1-phosphate synthase or the sodium-dependent myo-inositol transporters

We previously showed that the mood stabilizers lithium, valproate (VPA), and carbamazepine (CBZ) have a common, inositol-reversible effect on the dynamic behavior of sensory neurons, suggesting that they all inhibit phosphoinositide (PIns) synthesis. We now report similar effects of the drugs in cortical neurons and show by mRNA analysis that these neurons do not express myo-inositol-1-phosphate synthase (MIP-synthase) or the sodium-dependent myo-inositol transporters (SMIT1 and SMIT2), but they do express the H+/myo-inositol transporter (HMIT) mRNA and protein. We used glycogen synthase kinase-3 (GSK3) inhibitors and Western blotting of GSK3 targets to confirm that the common effects of the drugs on both sensory and cortical neuron growth cones are inositol-dependent and GSK3-independent. Moreover, the anti-convulsant drugs gabapentin and phenytoin do not mimic the mood stabilizers. These results confirm that the common inositol-reversible effect of mood stabilizers on neurons does not involve GSK3 and further show that the effects are independent of MIP-synthase and SMIT transporters.     

Chronic high dose l-dopa treatment does not alter the levels of dopamine D-1, D-2 or D-3 receptor in the striatum of normal monkeys: an autoradiographic study

Summary. To assess the role of dopamine receptors in the genesis of dyskinesia, we have used quantitative autoradiography to determine the effect of chronic l-dopa administration on dopamine D-1 (using [³H]SCH 23390), D-2 (using [³H]spiperone) and D-3 (using [³H]7-OH-DPAT) receptor binding levels in the striatum of dyskinetic or non-dyskinetic monkeys. Total and subregional striatal analysis showed no difference in D-1, D-2 or D-3 receptor binding in the caudate and putamen between monkeys receiving high dose l-dopa treatment with marked dyskinesia and those without dyskinesia compared to untreated animals. It thus appears unlikely that changes in dopamine receptor expression are a primary cause of l-dopa induced dyskinesia. Rather, a functional dissociation of D-2 receptor coupling to co-expressed enkephalin/adenosine-2a receptor activity in the striato-GPe indirect pathway may be more important in the development or expression of l-dopa-induced involuntary movements. Received July 3, 2000; accepted March 13, 2001     

At therapeutic concentrations, olanzapine does not affect basal or insulin-stimulated glucose transport in 3T3-L1 adipocytes

The newer, atypical antipsychotic drugs have improved the treatment of schizophrenia and are widely used. A disadvantage is that they increase food intake, promote weight gain and may facilitate development of diabetes. The mechanism of the latter effect is controversial. A possible interaction of these drugs with glucose transporters has been proposed: peripheral insulin resistance may develop if these drugs inhibited glucose transport in cells which express the insulin responsive glucose transporter, GLUT4, i.e., muscle and adipocytes. To test this hypothesis, we incubated 3T3-L1 adipocytes, which express GLUT1 and GLUT4, with the atypical antipsychotic drug olanzapine for 1 or 20 h and then measured basal and insulin-stimulated glucose transport. The doses of olanzapine tested (70 nM and 350 nM) encompass and exceed maximal steady-state concentrations of the drug in plasma of patients maintained on maximal recommended doses (20 mg QD) of olanzapine. A maximally stimulating insulin concentration (100 nM) accelerated glucose transport 10- to 15-fold in 3T3-L1 adipocytes, and the half-maximally stimulating insulin dose was 0.4 nM. Olanzapine (70 or 350 nM) did not affect basal or insulin-stimulated glucose transport following 1 or 20 h drug treatment at any insulin concentration tested. The data do not support the hypothesis that olanzapine at therapeutically relevant concentrations may cause peripheral insulin resistance by direct interaction with the insulin responsive glucose transport system.     

Brain N-acetyl aspartate concentrations measured by H MRS are reduced in adult male rats subjected to perinatal stress: preliminary observations and hypothetical implications for neurodevelopmental disorders

The present study was undertaken to determine if the concentration of brain N-acetyl-aspartate (NAA), a putative neuronal marker, is reduced in adult rats subjected to stress during the perinatal period. As the prenatal stressor, pregnant rats were subjected to restraint stress for one hour twice daily from days 14-21 of gestation; stressed offspring were reared by normal dams and studied as adults. As the postnatal stressor, normal pups were reared by prenatally 'stressed' dams and studied as adults. As compared to non-stressed controls (n=6), NAA concentrations were significantly reduced 21 and 25% in left frontal cortex from the prenatal (n=4) and postnatal (n=6) stress groups. respectively. The data suggest that in perinatally stressed adult offspring permanent neuronal damage or loss has occurred. While no direct causal associations between perinatal stress and the developmental of particular disorders can be inferred from these limited data, the effects of perinatal stress on subsequent brain neuropathology are reviewed. particularly in relation to NAA. For hypothesis-generating purposes, the possible relevance of stress and NAA to the neurodevelopmental hypothesis of schizophrenia is discussed in greater detail.