Mania: not the opposite of depression, but an extension? Neuronal plasticity and polarity.

What underlies bipolar disorder? What pathophysiologic process can produce symptoms that are apparently polar opposites? Recent studies of neuronal plasticity suggest a mechanism. Both zinc deficiency and social isolation impair neuronal plasticity; both are associated with major depression. Yet when zinc deficiency and social isolation occur together, they are associated with aggression, not with depression. On that basis, and according to additional findings in rats reported herein, it was inferred that moderate impairment of neuronal plasticity induces a depressive state, but that further impairment of neuronal plasticity induces not more depression, but a manic state. However, not only neuronal plasticity, but also some kind of load toward neuronal function can influence polarity or symptoms of mood disorder. Our hypothesis is that mania is an extension of depression from the perspective of neuronal plasticity, and that multiaxial evaluation by neuronal plasticity and neuronal load is useful to elucidate the pathophysiology of mood disorder. Using this hypothesis, many clinical aspects that have been heretofore difficult to interpret can be understood. A mood stabilizer or electric convulsive therapy is often used for the treatment of mood disorder, but it has remained unclear why such therapies are useful for both mania and depression. This hypothesis can explain how mood stabilizers or electric convulsive therapy can improve both mania and depression through the recovery of neuronal plasticity. It is difficult to explain the pathophysiology of manic switching by antidepressants solely from the perspective of the impairment of neuronal plasticity. To interpret this phenomenon, the action of antidepressants to neuronal load should be regarded as the other axis from neuronal plasticity. Based on this hypothesis, it is expected that the pathophysiology of mood disorder and clinical mechanism of mood stabilizers and antidepressants can be understood in an integrated manner.

Region-specific causal mechanism in the effects of ammonia on cerebral glucose metabolism in the rat brain.

Ammonia, which is considered to be the main agent responsible for hepatic encephalopathy, inhibits oxidative glucose metabolism in the brain. However, the effects of ammonia on cerebral glucose metabolism in different brain regions remains unclear. To clarify this issue, we added ammonia directly to fresh rat brain slices and measured its effects on glucose metabolism. Dynamic positron autoradiography with [(18)F]2-fluoro-2-deoxy-D-glucose and 2-(4-iodophenyl)-3-(4-nitrophenyl)-5-(2,4-disulfophenyl)-2H-tetrazolium (WST-1) colorimetric assay revealed that ammonia significantly increased the cerebral glucose metabolic rate and depressed mitochondrial function, as compared to the unloaded control in each of the brain regions examined (cerebral cortex, striatum, and cerebellum), reflecting increased glycolysis that compensates for the decrease in aerobic metabolism. Pre-treatment with (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine hydrogen maleate (MK-801), a N-methyl-D-aspartate (NMDA) receptor antagonist, significantly attenuated these changes induced by ammonia in cerebellum, but not in cerebral cortex or striatum. The addition of ammonia induced an increase in cyclic guanosine monophosphate (cGMP) levels in cerebellum, but not in cerebral cortex or striatum, reflecting the activation of the NMDA receptor-nitric oxide-cGMP pathway. These results suggested that NMDA receptor activation is responsible for the impairment of glucose metabolism induced by ammonia specifically in cerebellum.

Effect of dietary zinc deficiency on ischemic vulnerability of the brain.

Deficiency of zinc, which modulates glutamate release, might increase ischemic vulnerability of the brain. We examined effects of dietary zinc deficiency for 2 weeks on ischemic vulnerability in several brain regions using dynamic positron autoradiography technique and [18F]2-fluoro-2-deoxy-d-glucose with rat brain slices. In the normal diet group, the cerebral glucose metabolic rate (CMRglc) was not significantly different from that of the ischemia-unloaded control even after the loading of ischemia for 45 min. However, in the zinc-deficient diet group, CMRglc was significantly lower than that of the ischemia-unloaded control after loading of ischemia for 45 min. With treatment of MK-801 (NMDA receptor antagonist) from the start of ischemia loading, CMRglc was not significantly different from that of the ischemia-unloaded control. These findings, obtained for all analyzed brain regions, suggest that dietary zinc deficiency increased ischemic vulnerability in the brain, and that glutamate might contribute to this effect through activation of the NMDA receptor.

Effects of antidepressants and mood stabilizers on serum levels of adiponectin.

The effect of antidepressants and mood stabilizers on serum levels of adiponectin was investigated. Fluvoxamine (30 and 50 mg/kg/day) or lithium (40 and 60 mg/kg/day) was dissolved in distilled water and administered orally to rats every day for 4 weeks. Fluvoxamine (50 mg/kg/day) alone significantly elevated the serum level of adiponectin, but no significant difference was found between other drug-treated groups and the control group. This difference of these drugs' effectiveness on serum adiponectin might contribute to their differences of action mechanisms and therapeutic effects.

Effects of vitamin E supplementation on plasma membrane permeabilization and fluidization induced by chlorpromazine in the rat brain.

Neurotransmitter receptors play a key role in most research on antipsychotic drugs, but little is known about the effects of these drugs on the plasma membrane in the central nervous system. Therefore, we investigated whether chlorpromazine (CPZ), a typical phenothiazine antipsychotic drug, affects the plasma membrane integrity in the rat brain, and if so, whether these membrane alterations can be prevented by dietary supplementation with vitamin E, which has been shown to be an antioxidant and also a membrane-stabilizer. Leakage of [(18)F]2-fluoro-2-deoxy-D-glucose ([(18)F]FDG)-6-phosphate from rat striatal slices and decrease in 1,6-diphenyl-1,3,5-hexatriene fluorescence anisotropy were used as indexes for plasma membrane permeabilization and fluidization, respectively. CPZ induced leakage of [(18)F]FDG-6-phosphate from striatal slices, and the leakage was delayed in the vitamin E-supplemented group compared to that in the normal diet group. The decrease in plasma membrane anisotropy induced by CPZ was significantly attenuated by vitamin E supplementation. Chronic treatment with alpha-phenyl-N-tert-butyl nitrone, a free radical scavenger, had no effect on CPZ-induced plasma membrane permeabilization, and the treatment with CPZ did not induce lipid peroxidation. CPZ can reduce plasma membrane integrity in the brain, and this reduction can be prevented by vitamin E via its membrane-stabilizing properties, not via its antioxidant activity.

Effects of haloperidol and its pyridinium metabolite on plasma membrane permeability and fluidity in the rat brain.

The use of antipsychotic drugs is limited by their tendency to produce extrapyramidal movement disorders such as tardive dyskinesia and parkinsonism. In previous reports it was speculated that extrapyramidal side effects associated with the butyrophenone neuroleptic agent haloperidol (HP) could be caused in part by the neurotoxic effect of its pyridinium metabolite (HPP(+)). Although both HPP(+) and HP have been shown to induce neurotoxic effects such as loss of cell membrane integrity, no information exists about the difference in the neurotoxic potency, especially in the potency to induce plasma membrane damage, between these two agents. In the present study, we compared the potency of the interaction of HPP(+) and HP with the plasma membrane integrity in the rat brain. Membrane permeabilization (assessed as [(18)F]2-fluoro-2-deoxy-d-glucose-6-phosphate release from brain slices) and fluidization (assessed as the reduction in the plasma membrane anisotropy of 1,6-diphenyl 1,3,5-hexatriene) were induced by HPP(+) loading (at >or=100 microM and >or=10 microM, respectively), while comparable changes were induced only at a higher concentration of HP (=1 mM). These results suggest that HPP(+) has a higher potency to induce plasma membrane damage than HP, and these actions of HPP(+) may partly underlie the pathogenesis of HP-induced extrapyramidal side effects.

Biphasic mechanism of the toxicity induced by 1-methyl-4-phenylpyridinium ion (MPP+) as revealed by dynamic changes in glucose metabolism in rat brain slices.

1-Methyl-4-phenylpyridinium (MPP+) is a well-known neurotoxin which causes a clinical syndrome similar to Parkinson's disease. The classical mechanism of MPP+ toxicity involves its entry into cells through the dopamine transporter (DAT) to inhibit aerobic glucose metabolism, while recent studies suggest that an oxidative mechanism may contribute to the toxicity of MPP+. However, it has not been adequately determined what role these two mechanisms play in the development of neurotoxicity after MPP+ loading in the brain. To clarify this issue, MPP+ was added directly to fresh rat brain slices and the dynamic changes in the cerebral glucose metabolic rate (CMRglc) produced by MPP+ were serially and two-dimensionally measured using the dynamic positron autoradiography technique with [(18)F]2-fluoro-2-deoxy-D-glucose as a tracer. MPP+ dose-dependently increased CMRglc in each of the brain regions examined, reflecting enhanced glycolysis compensating for the decrease in aerobic metabolism. Treatment with DAT inhibitor GBR 12909 significantly attenuated the enhanced glycolysis induced by 10 microM MPP+ in the striatum. Treatment with free radical spin trap alpha-phenyl-N-tert-butylnitrone (PBN) significantly attenuated the enhancement of glycolysis induced by 100 microM MPP+ in all brain regions. These results suggest that the mechanism of the toxicity of MPP+ is biphasic and consists of a DAT-mediated mechanism selective for dopaminergic regions at a lower concentration of MPP+ (10 microM), and an oxidative mechanism that occurs at a higher concentration of MPP+ (100 microM) and is not restricted to dopaminergic regions.

A comparative study of the plasma membrane permeabilization and fluidization induced by antipsychotic drugs in the rat brain.

We compared the potency of the interaction of three antipsychotic drugs, i.e. chlorpromazine (CPZ), haloperidol (Hal) and sulpiride (Sul), with the plasma membrane in the rat brain. CPZ loading (> or = 100 microM) dose-dependently increased both membrane permeability (assessed as [18F]2-fluoro-2-deoxy-D-glucose-6-phosphate release from brain slices) and membrane fluidity (assessed as the reduction in the plasma membrane anisotropy of 1,6-diphenyl-1,3,5-hexatriene). On the other hand, a higher concentration of Hal (1 mM) was required to observe these effects. However, Sul failed to change membrane permeability and fluidity even at a high concentration (1 mM). These results indicated the following ranking of the potency to interact with the membrane: CPZ>Hal>Sul. The difference among antipsychotic drugs in the potency to interact with the plasma membrane as revealed in the present study may be partly responsible for the difference among the drugs in the probability of inducing extrapyramidal side-effects such as parkinsonism and tardive dyskinesia.

Effects of chlorpromazine on plasma membrane permeability and fluidity in the rat brain: a dynamic positron autoradiography and fluorescence polarization study.

Antipsychotic drugs have been widely used in psychiatry for the treatment of various mental disorders, but the underlying biochemical mechanisms of their actions still remain unclear. Although phenothiazine antipsychotic drugs have been reported to directly interact with the peripheral plasma membrane, it is not known whether these drugs actually affect plasma membrane integrity in the central nervous system. To clarify these issues, we investigated the effect of chlorpromazine (CPZ), a typical phenothiazine antipsychotic drug, on plasma membrane permeability in fresh rat brain slices using a dynamic positron autoradiography technique and [(18)F]2-fluoro-2-deoxy-D-glucose ([(18)F]FDG) as a tracer. Treatment with CPZ (> or =100 microM) resulted in the leakage of [(18)F]FDG-6-phosphate, but not [(18)F]FDG, suggesting that the [(18)F]FDG-6-phosphate efflux was not mediated by glucose transporters, but rather by plasma membrane permeabilization. The leakage of [(18)F]FDG-6-phosphate was followed by slower leakage of cytoplasmic lactate dehydrogenase, suggesting that CPZ could initially induce small membrane holes that enlarged with time. Furthermore, the addition of CPZ (> or =100 microM) caused a decrease in 1,6-diphenyl-1,3,5-hexatriene fluorescence anisotropy, which implies an increase in membrane fluidity. CPZ loading dose-dependently increased both membrane permeability and membrane fluidity, which suggested the involvement of a perturbation of membrane order in the mechanisms of membrane destabilization induced by antipsychotic drugs.

Different mechanisms of hypoxic injury on white matter and gray matter as revealed by dynamic changes in glucose metabolism in rats.

Fresh rat brain slices were incubated with [18F]2-fluoro-2-deoxy-D-glucose ([18F]FDG) in oxygenated Krebs-Ringer solution at 36 degrees C, and the fractional rate constant (=k3*) of [18F]FDG proportional to the cerebral glucose metabolic rate in white matter and gray matter was investigated with positron autoradiography. In both white matter and gray matter, the k3* value with > or = 20 min hypoxia was markedly lower than the unloaded control value, indicating irreversible hypoxic injury. Next, the neuroprotective effect against hypoxia induced by the addition of an N-methyl-D-aspartate receptor antagonist or a free radical scavenger was assessed by determining whether a decrease in the k3* value after hypoxia loading was prevented. In gray matter, both agents exhibited a neuroprotective effect against 20 min hypoxia. In white matter, however, only the free radical scavenger was effective. These results suggest a similarity in the degree of vulnerability to hypoxia between white matter and gray matter as well as a difference in the developmental mechanism of hypoxic injury, i.e. the involvement of both glutamate and free radicals in gray matter, and the more selective involvement of free radicals in white matter.

Automated kinetic analysis of FDG uptake in living rat brain slices from dynamic positron autoradiography.

Changes in regional cerebral glucose metabolism were investigated for varying levels of tissue oxygenation using a dynamic positron autoradiography technique. While incubating fresh rat brain slices with [18F]FDG in an oxygenated solution, serial images of the tissue slices were obtained over a time period of up to 300 min and archived onto over 20 phosphorous imaging plate exposures. In order to properly create time activity curves of the uptake levels, images of the individual tissue samples were automatically located, digitally extracted, and registered with the later images of the same tissue samples. After applying image processing techniques for aligning tissue sample images, time activity curves were extracted for individual substructures in the rat brain and quantitative results were reported using Patlak plots. Since the levels of oxygenation can be controlled for these experiments, [18F]FDG uptakes can be reported representing states of hypoxia, pseudoischemia, and reoxygenation. The image processing techniques developed for this application have enabled more experiments and tissue samples to be acquired and analyzed than would otherwise be possible using manual ROI techniques. The objective spatial registration of tissue samples and automated extraction of data has increased the analysis accuracy and decreased the operator error associated with the interactive handling of the image data. This supports improved kinetic modeling of FDG uptake in animal studies, and can be used for more accurate dosimetry calculations in humans.

Hypoxic tolerance induction in rat brain slices following hypoxic preconditioning due to expression of neuroprotective proteins as revealed by dynamic changes in glucose metabolism.

We prepared rat brain slices following sublethal hypoxic pretreatment (preconditioning) and untreated (control) rats, and measured the cerebral glucose metabolic rate (CMRglc) by dynamic positron autoradiography with [18F]2-fluoro-2-deoxy-D-glucose before and after originally lethal 20-min hypoxic loading. In the regions of interest such as the frontal cortex, the CMRglc before hypoxic loading did not differ between the preconditioning and control groups. The CMRglc after reoxygenation was markedly lower than that before hypoxic loading in the control group but did not significantly differ from the preloading value in the preconditioning group. Thus, hypoxic tolerance induction by preconditioning was demonstrated using the maintenance of CMRglc as a neuronal viability index. In addition, profiling of gene expression using an Atlas Rat Stress Array suggested the involvement of the expression of genes such as stress protein in hypoxic tolerance induction.

Hypoxic tolerance induction in rat brain slices following 3-nitropropionic acid pretreatment as revealed by dynamic changes in glucose metabolism.

Pretreatment with 3-nitropropionic acid (3-NPA) has been shown to induce tolerance to ischemic/hypoxic brain damage. However, regional differences in tolerance induction by 3-NPA and the degree to which impaired glucose metabolism due to 3-NPA pretreatment itself is directly involved remain unknown. To evaluate these issues using dynamic positron autoradiography with [(18)F]2-fluoro-2-deoxy-D-glucose, the cerebral glucose metabolic rate (CMRglc) was serially measured before and after hypoxia-loading in rat brain slices pretreated with 3-NPA. CMRglc before hypoxia did not significantly differ between the 3-NPA pretreatment group and control group. The 3-NPA-associated recovery of CMRglc after reoxygenation was observed in the frontal cortex, hippocampus, and cerebellum, but not in the striatum and thalamus. Thus, we demonstrated the induction of region-specific hypoxic tolerance after 3-NPA pretreatment using CMRglc maintenance as an index of neuronal viability, and it is unlikely that this induction is associated with the persistence of impaired glucose metabolism due to 3-NPA pretreatment.