Positron emission tomography with fluorodeoxyglucose-F18 in an animal model of mania

Intracerebroventricular (ICV) administration of ouabain to young adult rats has been suggested to model human bipolar mania. In the human condition, mania and bipolar depression are both associated with reductions in frontal cerebral metabolism. We utilized [(18)F]-fluorodeoxyglucose [(18)FDG] positron emission tomography (PET) to visualize glucose uptake in animals receiving ICV ouabain. Animals received 5 microl of 10(-)(3) M ouabain ICV, were anesthetized with isoflurane inhalation, and administered intraperitoneally with 0.5 mCi of (18)FDG. PET data were collected over 20 min 1 hour later. Additionally, the effect of lithium was examined in animals receiving lithium in their diet for 1 week before the ICV ouabain injection. Data were analyzed with IDL Virtual Machine software. Brain glucose utilization as measured by (18)FDG uptake was significantly reduced in animals receiving ICV ouabain compared with those receiving equal volumes of artificial cerebrospinal fluid. Pretreatment with lithium normalized (18)FDG uptake. These results mirror human studies.     

Mimicking human bipolar ion dysregulation models mania in rats

Psychiatric diseases in general, and bipolar illness in particular, are difficult to model in animals since the subjective nature of the core symptoms appears to preclude objective observation of behavioral changes. An adequate animal model of a psychiatric condition must fulfill three core criteria: share pathophysiological characteristics of the human condition (face validity), have similar behavioral manifestations as the human disease (construct validity), and improve with medications that improve the symptoms seen in afflicted humans (predictive validity). The ouabain model for bipolar illness mimics a widely reproduced biologic abnormality in mania: reduced sodium pump activity. An intracerebroventricular (ICV) administration of 5microL 10(-3)M ouabain induces motoric hyperactivity preventable by lithium, carbamazepine, and haloperidol. ICV ouabain may also produce environmentally dependent hypoactivity. The model, however, has not yet been examined for other potential manic behavior in rats such as reduced need for sleep, increased sexual activity, or increased irritability. While additional characterization of the model is required, the ouabain model for bipolar illness is the only available animal model that fulfills the three criteria for an adequate animal model for bipolar illness.     

Adult-onset hypothyroidism impairs paired-pulse facilitation and long-term potentiation of the rat dorsal hippocampo-medial prefrontal cortex pathway in vivo

Thyroid hormones are critical for the maturation and function of the central nervous system. Insufficiency of thyroid hormones in the adulthood causes a wide range of cognitive dysfunctions, including deficits in learning and memory. The present study investigated whether adult-onset hypothyroidism would alter synaptic functions in the dorsal hippocampo-medial prefrontal cortex (mPFC) pathway, a neural pathway important for learning and memory. Adult hypothyroidism was induced by oral administration of 1% (g/l) antithyroid acting drug 6-n-propyl-2-thiouracil (PTU) to adult male Sprague-Dawley rats for 4 weeks. Postsynaptic potentials (PSP) were recorded in the mPFC by stimulating the dorsal hippocampal CA1 region in vivo. Basal synaptic transmission was evaluated by comparing input-output relationships. Paired-pulse facilitation and long-term potentiation were recorded to examine short- and long-term synaptic plasticity. Adult-onset hypothyroidism did not change the basal synaptic transmission, but significantly reduced paired-pulse facilitation and long-term potentiation of PSP. These inhibitions can be restored by thyroid hormone replacement. The results suggest that such alterations in synaptic plasticity of the dorsal hippocampo-mPFC pathway might contribute to understanding basic mechanisms underlying learning and memory deficits associated with adult-onset hypothyroidism.     

Effects of mood stabilizers on hippocampus and amygdala BDNF levels in an animal model of mania induced by ouabain

There is a body of evidence suggesting that BDNF is involved in bipolar disorder (BD) pathogenesis. Intracerebroventricular (ICV) injection of ouabain (OUA), a specific Na⁺/K⁺ ATPase inhibitor, induces hyperlocomotion in rats, and has been used as an animal model of mania. The present study aims to investigate the effects of the lithium (Li) and valproate (VPT) in an animal model of mania induced by ouabain. In the reversal model, animals received a single ICV injection of OUA or cerebrospinal fluid (aCSF). From the day following the ICV injection, the rats were treated for 6 days with intraperitoneal (IP) injections of saline (SAL), Li or VPT twice a day. In the maintenance treatment (prevention model), the rats received IP injections of Li, VPT, or SAL twice a day for 12 days. In the 7th day of treatment the animals received a single ICV injection of either OUA or aCSF. After the ICV injection, the treatment with the mood stabilizers continued for more 6 days. Locomotor activity was measured using the open-field test and BDNF levels were measured in rat hippocampus and amygdala by sandwich-ELISA. Li and VPT reversed OUA-related hyperactive behavior in the open-field test in both experiments. OUA decreased BDNF levels in first and second experiments in hippocampus and amygdala and Li treatment, but not VPT reversed and prevented the impairment in BDNF expression after OUA administration in these cerebral areas. Our results suggest that the present model fulfills adequate face, construct and predictive validity as an animal model of mania.     

Memantine reduces mania-like symptoms in animal models

Memantine, a selective antagonist of the N-methyl-D-aspartate receptor, is approved for the treatment of moderate to severe Alzheimer's disease. Ion dysregulation is thought to be involved in the pathophysiology of bipolar illness, suggesting that memantine may be effective in treating bipolar manic and/or depressive episodes. We utilized two preclinical models of mania that mimic pathophysiologic changes seen in bipolar illness to examine the potential efficacy of memantine in the treatment of this disorder. Locomotor hyperactivity of male Sprague-Dawley rats in an open field was induced with intracerebroventricular (ICV) administration of 10⁻³ M ouabain. Memantine (2.5, 5 or 7.5 mg/kg), lithium (6.75 mEq/kg), or vehicle were administered acutely via intraperitoneal injection immediately prior to ouabain, then chronically for 7 days (oral memantine 20, 30, and 40 mg/kg/day in water; lithium 2.4 g/kg food). In a second model of bipolar disorder, cycling between population spikes and epileptiform bursts was investigated in rat hippocampal slices treated with ouabain (3.3 μM) alone or in combination with memantine (0.5, 1.0, and 5.0 μM). Ouabain-induced hyperlocomotion was normalized with acute and chronic lithium and chronic use of memantine. Memantine delayed the onset of ouabain-induced-cycling in hippocampal slices. Memantine may have antimanic properties.     

Efficacy of olanzapine and haloperidol in an animal model of mania

PURPOSE: Intracerebroventricular (ICV) administration of ouabain, a potent sodium pump inhibitor, has been used to model mania. Antipsychotic agents have demonstrated efficacy in the management of acute mania. This study was undertaken to determine the prophylactic efficacy of olanzapine and haloperidol in the ouabain mania model. METHODS: Male Sprague-Dawley rats (4-8/group) were treated with two haloperidol decanoate intramuscular shots one week apart (21 mg/kg) or twice daily olanzapine intraperitoneal injections at low dose (1 mg/kg/day) or high dose (6 mg/kg/day) for 7 days prior to ICV administration of ouabain. Open field locomotion was quantified at baseline and after ouabain administration. RESULTS: Ouabain caused a significant increase in open field locomotion (253.7+/-SEM 55.12 vs control 53.1+/-12.13 squares traversed in 30 min in the olanzapine experiments, P<0.05; and 236.5+/-41.42 vs 129.3+/-38.23, P<0.05 in the haloperidol experiments). Olanzapine alone at low dose (102.2+/-37.7) or high dose (151.2+/-49.2) did not alter open field activity. Low dose olanzapine (176.6+/-73.27) but not high dose (307.5+/-167.32) caused a modest reduction of the ouabain effect. Haloperidol alone significantly reduced motoric activity compared to control (55.6+/-18.0, P<0.05), and prevented ouabain-induced hyperactivity (60.3+/-33.1, P<0.05). CONCLUSION: Haloperidol, but not olanzapine, demonstrated efficacy in this mania model, but methodological details may have reduced the effect of olanzapine.     

Prenatal exposure to valproic acid enhances synaptic plasticity in the medial prefrontal cortex and fear memories

The prefrontal cortex has been extensively implicated in autism to explain deficits in executive and other higher brain functions related to cognition, language, sociability and emotion. Hyper-connectivity and hyper-plasticity at the level of the neuronal microcircuit in the medial prefrontal cortex (mPFC) in the valproic acid (VPA) animal model of autism has been suggested. However, the possible alterations at the system levels are not well understood. The present study investigated the basal synaptic transmission and synaptic plasticity in the mPFC in vivo in the VPA rat model of autism. Furthermore, short-term and long-term retention of fear memories were also examined. The findings displayed that paired-pulse facilitation (PPF) and long-term potentiation (LTP), representing short- and long-term synaptic plasticity, were enhanced by the prenatal exposure to VPA. In addition, the short- and long-term fear memories were enhanced. These results suggest that enhanced synaptic plasticity in the mPFC and fear memories might be one of the mechanisms underlying some symptoms of autism.     

Effect of ouabain on sodium pump alpha-isoform expression in an animal model of mania

While the pathophysiologic mechanisms of bipolar illness are unknown, a dysregulation of electrolytes, particularly intracellular sodium (Na) and calcium (Ca), are thought to contribute to the illness. Ouabain, a potent Na pump inhibitor, administered intracerebroventricularly (ICV), has been used previously to model mania. The current study evaluates the effect of ICV ouabain on Na pump isoform expression in rat brain. Animals received 5 µl ICV of either 10^− 3 M ouabain or artificial cerebrospinal fluid (aCSF). They were then sacrificed 7 days after the ICV injection and specific brain areas were dissected and frozen until the assay (frontal cortex, hippocampus, and basal ganglia). The three isoforms of the alpha subunit of the Na pump that are expressed in the brain were quantified with immunoblot analysis with actin serving as internal control. The behavioral hyperactivity seen in rats receiving ICV ouabain is associated with an increase of expression of the glial-specific alpha2 isoform in the basal ganglia, and the neuron-specific alpha3 isoforms in the frontal cortex. These findings, in association with human post mortem studies finding that alpha2 is underexpressed in the temporal cortex of bipolar subjects, suggest that Na pump isoform expression may be of interest in the pathophysiology of mania.     

Reorganization of Circuits Underlying Cerebellar Modulation of Prefrontal Cortical Dopamine in Mouse Models of Autism Spectrum Disorder

Imaging, clinical, and pre-clinical studies have provided ample evidence for a cerebellar involvement in cognitive brain function including cognitive brain disorders, such as autism and schizophrenia. We previously reported that cerebellar activity modulates dopamine release in the mouse medial prefrontal cortex (mPFC) via two distinct pathways: (1) cerebellum to mPFC via dopaminergic projections from the ventral tegmental area (VTA) and (2) cerebellum to mPFC via glutamatergic projections from the mediodorsal and ventrolateral thalamus (ThN md and vl). The present study compared functional adaptations of cerebello-cortical circuitry following developmental cerebellar pathology in a mouse model of developmental loss of Purkinje cells (Lurcher) and a mouse model of fragile X syndrome (Fmr1 KO mice). Fixed potential amperometry was used to measure mPFC dopamine release in response to cerebellar electrical stimulation. Mutant mice of both strains showed an attenuation in cerebellar-evoked mPFC dopamine release compared to respective wildtype mice. This was accompanied by a functional reorganization of the VTA and thalamic pathways mediating cerebellar modulation of mPFC dopamine release. Inactivation of the VTA pathway by intra-VTA lidocaine or kynurenate infusions decreased dopamine release by 50 % in wildtype and 20–30 % in mutant mice of both strains. Intra-ThN vl infusions of either drug decreased dopamine release by 15 % in wildtype and 40 % in mutant mice of both strains, while dopamine release remained relatively unchanged following intra-ThN md drug infusions. These results indicate a shift in strength towards the thalamic vl projection, away from the VTA. Thus, cerebellar neuropathologies associated with autism spectrum disorders may cause a reduction in cerebellar modulation of mPFC dopamine release that is related to a reorganization of the mediating neuronal pathways.     

Differential release of dopamine in the nucleus accumbens evoked by low-versus high-frequency medial prefrontal cortex stimulation

The medial prefrontal cortex (mPFC) coordinates goal-directed behaviors, which may be mediated through mPFC regulation of dopamine release in the nucleus accumbens (NAc). Furthermore, frequency-specific oscillatory activity between the frontal cortex and downstream structures may facilitate inter-region communication. Although high-frequency (e.g., 60 Hz) mPFC stimulation is known to increase basal dopamine levels in the NAc, little is known about how phasic dopamine release is affected by mPFC stimulation. Understanding the frequency-specific control of phasic dopamine release by mPFC stimulation could elucidate mechanisms by which the mPFC modulates other regions. It could also inform optimization of deep brain stimulation for treatment of neurological disorders.

Activation of Akt signaling in rat brain by intracerebroventricular injection of ouabain: A rat model for mania

Intracerebroventricular (ICV) injection of ouabain, a specific Na–K ATPase inhibitor, induces behavioral changes in rats resembling the manic phenotypes of bipolar disorder. The binding of ouabain to the Na–K ATPase affects signal events in vitro including Akt, a possible molecular target of mood disorders. However, the effects of ouabain on Akt in the brain need further clarification. In this study, we investigated changes in the phosphorylation state of Akt in the rat brain after ICV injection of ouabain. Consistent with our previous report, the locomotor activity of rats within 30 min after ouabain ICV injection changed according to the dose with higher doses of ouabain, 0.5 and 1 mM, inducing significant hyperactivity. In addition, ouabain administration induced a dose-dependent increase in the immunoreactivity of p-Akt (Ser473) in the frontal cortex, striatum, and hippocampus after 30 min, and reached statistical significance with 1 mM of ouabain. Phosphorylation of GSK-3β (Ser9), FOXO1 (Ser256), and eNOS (Ser1177), which are downstream molecules of Akt, was also increased in a dose-dependent manner within the same brain regions. Moreover, hyperactivity was seen for 8 h after a single 1 mM injection of ouabain and increased phosphorylation of Akt (Ser473), GSK-3β (Ser9), FOXO1 (Ser256), and eNOS (Ser1177) was also observed in the cortex, striatum, and hippocampus. Thus, intrabrain injection of ouabain induces activation of Akt signaling accompanied by hyperactivity, suggesting the possible role of Akt in ouabain rat model of mania.     

Effects of short and long-term lithium treatment on serum prolactin levels in patients with bipolar affective disorder

1. In this study, the authors sought to test the hypothesis that Li (lithium) treatment can induce alterations in PRL (prolactin) secretion in euthymic bipolar patients compared to controls and that short and long-term administration can lead to prolactin changes different from each other. 2. Twenty euthymic bipolar male patients on long-term lithium carbonate treatment for more than 6 months and 15 euthymic male bipolar patients on short-term Li treatment for shorter than 6 months who met DSM-IV criteria for bipolar affective disorder were included in the study. Seventeen age-matched healthy control males were chosen among the hospital staff. The mean +/- SD duration of Li use was 68.93+/-46.31 months in the long-term lithium-treated group and 4+/-3.42 months in the short-term lithium-treated group. 3. Serum PRL values in the long-term Li-treated group were significantly lower than those of the control group, while there was no significant difference in PRL values between the short-term Li-treated group and the control group. 4. Our study documents that short-term (<6 months) Li treatment does not induce any significant changes in PRL release in bipolar patients compared to normal control subjects while long-term Li treatment (>6 months) leads to lower PRL release compared to the controls. Furthermore, PRL has wide intra-interindividual and circadian variations Li-PRL relationship seems to be very complex and probably depends on various interactions among dopamine, serotonin and PRL. Therefore, further studies are needed to confirm the data.     

Essential role of D1 but not D2 receptors in methamphetamine-induced impairment of long-term potentiation in hippocampal-prefrontal cortex pathway

Methamphetamine (MA) abuse induces deficits in cognitive performance that are related to dysfunction of the prefrontal cortex (PFC). The medial portion of the prefrontal cortex (mPFC) in rats that is crucial for cognitive function has been shown to undergo long-term potentiation (LTP) in the projections from the hippocampus. However, no study has been performed to evaluate the influence of MA on synaptic plasticity in the hippocampal-mPFC pathways. In the present experiments, we investigated the effects of repeated MA administration on hippocampal-mPFC LTP, together with MA-induced stereotyped behaviors. Repeated MA administration produced behavioral sensitization and LTP impairment in the hippocampal-mPFC pathways. The MA-induced impairment of hippocampal-mPFC LTP was prevented by the pretreatment of dopamine 1 (D1) but not dopamine 2 (D2) receptor antagonists, while D1 and D2 receptor antagonists attenuated the MA-induced stereotyped behaviors. These findings suggest that D1 receptors are crucial for the MA-induced deterioration of synaptic plasticity in the hippocampal-mPFC circuits. Impairment of LTP associated with D1 receptor dysfunction may underlie cognitive deficits in MA-dependent subjects.     

Receptor Trafficking and the Regulation of Synaptic Plasticity by SUMO

Timely and efficient information transfer at synapses is fundamental to brain function. Synapses are highly dynamic structures that exhibit long-lasting activity-dependent alterations to their structure and transmission efficiency, a phenomenon termed synaptic plasticity. These changes, which occur through alterations in presynaptic release or in the trafficking of postsynaptic receptor proteins, underpin the formation and stabilisation of neural circuits during brain development, and encode, process and store information essential for learning, memory and cognition. In recent years, it has emerged that the ubiquitin-like posttranslational modification SUMOylation is an important mediator of several aspects of neuronal and synaptic function. Through orchestrating synapse formation, presynaptic release and the trafficking of postsynaptic receptor proteins during forms of synaptic plasticity such as long-term potentiation, long-term depression and homeostatic scaling, SUMOylation is being increasingly appreciated to play a central role in neurotransmission. In this review, we outline key discoveries in this relatively new field, provide an update on recent progress regarding the targets and consequences of protein SUMOylation in synaptic function and plasticity, and highlight key outstanding questions regarding the roles of protein SUMOylation in the brain.     

Lithium normalizes elevated intracellular sodium

BACKGROUND: Both mania and bipolar depression are characterized by elevations of intracellular sodium concentrations. This observation has been purported to be central to the pathophysiology of abnormal moods in bipolar illness. Reduction of sodium influx is a proposed shared mechanism of action of effective mood stabilizers, but direct documentation of this effect for lithium has never been demonstrated. METHODS: Flame spectroscopic determinations of intracellular sodium concentration were performed in the human glioma cell line, LN292, after treatment with the sodium pump inhibitor, ouabain, and co-treatment with ouabain and lithium. RESULTS: Ouabain 0.1 microM doubles the intracellular sodium concentration after 3 days. Pretreatment with lithium 1 mM for 1 week normalizes intracellular sodium. CONCLUSION: This is the first demonstration that lithium can normalize abnormally elevated intracellular sodium levels. This may be an important mechanism of lithium action.     

Lithium prevents ouabain-induced behavioral changes

Both mania and bipolar depression have been associated with decrements in the activity of the sodium and potassium-activated adenosine triphosphatase (Na,K-ATPase) membrane pump. Although the role of this observation in the pathophysiology of bipolar illness is unclear, it has been proposed that this defect could be central to the pathogenesis of the illness. In an effort to test this hypothesis, the authors examined the efficacy of lithium pretreatment in attenuating behavioral changes secondary to acute administration of a single intracerbroventricular (icv) dose of the Na,K-ATPase-inhibiting compound, ouabain, in the Sprague-Dawley rat. Ouabain (10^?3 M) significantly decreased motor activity in automated activity monitors. Lithium pretreatment for 7 d totally prevented this effect. These preliminary data suggest that icv ouabain administration in the rat may prove to be a viable animal model for bipolar illness.     

Memantine: New prospective in bipolar disorder treatment

We review preclinical and clinical evidences strongly suggesting that memantine, an old drug currently approved for Alzheimer's dementia, is an effective treatment for acute mania and for the prevention of manic/hypomanic and depressive recurrences of manicdepressive illness. Lithium remains the first line for the treatment and prophylaxis of bipolar disorders, but currently available treatment alternatives for lithium resistant patients are of limited and/or questionable efficacy. Thus, research and development of more effective mood stabilizer drugs is a leading challenge for modern psychopharmacology. We have demonstrated that 21 d administration of imipramine causes a behavioural syndrome similar to a cycle of bipolar disorder, i.e., a mania followed by a depression, in rats. Indeed, such treatment causes a behavioural supersensitivity to dopamine D2 receptor agonists associated with an increase sexual activity and aggressivity(mania). The dopamine receptor sensitization is followed, after imipramine discontinuation, by an opposite phenomenon(dopamine receptor desensitization) and an increased immobility time(depression) in the forced swimming test of depression. Memantine blocks the development of the supersensitivity and the ensuing desensitization associated with the depressive like behavior. On the basis of these observations we have suggested the use of memantine in the treatment of mania and in the prophylaxis of bipolar disorders. To test this hypothesis we performed several naturalistic studies that showed an acute antimanic effect and a long-lasting and progressive mood-stabilizing action(at least 3 years), without clinically relevant side effects. To confirm the observations of our naturalistic trials we are now performing a randomized controlled clinical trial. Finally we described the studies reporting the efficacy of memantine in maniclike symptoms occurring in psychiatric disorders other than bipolar. Limitations: A randomized controlled clinical trial is needed to confirm our naturalistic observations.Conclusion: We believe that this review presents enough pharmacological and clinical information to consider the administration of memantine in the treatment of bipolar disorders that no respond to standard mood stabilizers.     

Involvement of TLR4 in the long-term epigenetic changes,rewarding and anxiety effects induced by intermittent ethanol treatment in adolescence

Studies in humans and experimental animals have demonstrated the vulnerability of the adolescent brain to actions of ethanol and the long-term consequences of binge drinking, including the behavioral and cognitive deficits that result from alcohol neurotoxicity, and increased risk to alcohol abuse and dependence. Although the mechanisms that participate in these effects are largely unknown, we have shown that ethanol by activating innate immune receptors, toll-like receptor 4 (TLR4), induces neuroinflammation, impairs myelin proteins and causes cognitive dysfunctions in adolescent mice. Since neuroimmune signaling is also involved in alcohol abuse, the aim of this study was to assess whether ethanol treatment in adolescence promotes the long-term synaptic and molecular events associated with alcohol abuse and addiction. Using wild-type (WT) and TLR4-deficient (TLR4-KO) adolescent mice treated intermittently with ethanol (3 g/kg) for 2 weeks, we showed that binge-like ethanol treatment in adolescent mice promotes short- and long-term alterations in synaptic plasticity and epigenetic changes in the promoter region of bdnf and fosb, which increased their expression in the mPFC of young adult animals. These molecular events were associated with long-term rewarding and anxiogenic-related behavioral effects, along with increased alcohol preference. Our results further showed the participation of neuroimmune system activation and the TLR4 signaling response since deficient mice in TLR4 (TLR4-KO) are protected against molecular and behavioral alterations of ethanol in the adolescent brain. Our results highlight a new role of the neuroimmune function and open up new avenues to develop pharmacological treatments that can normalize the immune signaling responsible for long-term effects in adolescence, including alcohol abuse and related disorders.     

Nicotine Exposure during Adolescence Leads to Short- and Long-Term Changes in Spike Timing-Dependent Plasticity in Rat Prefrontal Cortex

Adolescence is a critical period of brain development during which maturation of areas involved in cognitive functioning, such as the medial prefrontal cortex (mPFC), is still ongoing. Tobacco smoking during this age can compromise the normal course of prefrontal development and lead to cognitive impairments in later life. Recently, we reported that nicotine exposure during adolescence results in a short-term increase and lasting reduction in synaptic mGluR2 levels in the rat mPFC, causing attention deficits during adulthood. It is unknown how changed synaptic mGluR2 levels after adolescent nicotine exposure affect the ability of mPFC synapses to undergo long-term synaptic plasticity. Here, we addressed this question. To model nicotine exposure, adolescent (P34-P43) or adult (P60-P69) rats were treated with nicotine injections three times per day for 10 d. We found that, both during acute activation of nicotinic receptors in the adolescent mPFC as well as immediately following nicotine treatment during adolescence, long-term plasticity in response to timed presynaptic and postsynaptic activity (tLTP) was strongly reduced. In contrast, in the mPFC of adult rats 5 weeks after they received nicotine treatment during adolescence, but not during adulthood, tLTP was increased. Short- and long-term adaptation of mPFC synaptic plasticity after adolescent nicotine exposure could be explained by changed mGluR2 signaling. Blocking mGluR2s augmented tLTP, whereas activating mGluR2s reduced tLTP. Our findings suggest neuronal mechanisms by which exposure to nicotine during adolescence alters the rules for spike timing-dependent plasticity in prefrontal networks that may explain the observed deficits in cognitive performance in later life.