Ken Inada

Antisense knockdown of drebrin A, a dendritic spine protein, causes stronger preference, impaired pre-pulse inhibition, and an increased sensitivity to psychostimulant

Drebrin located in dendritic spines regulates their morphological changes and plays a role in the synaptic plasticity via spine function. Reduced drebrin has been found in the brain of patients with Alzheimers disease or Downs syndrome. To examine whether the down-regulation of drebrin protein levels causes deficits in higher brain function, such as memory or cognition, we performed antisense-induced knockdown of drebrin A expression in rat brain using an hemagglutinating virus of Japan (HVJ)-liposome gene transfer technique. We investigated the effects of drebrin in vivo knockdown on spatial memory in a water-maze task, sensorimotor gating in a pre-pulse-inhibition test, adaptive behaviors in an open-field test, and sensitivity to psychostimulant in an amphetamine-induced locomotor response. Rats with drebrin A in vivo knockdown displayed a stronger preference for a previous event due to perseverative behavior, impaired pre-pulse inhibition (PPI), increased locomotor activity, anxiety-like behavior, and an increased sensitivity to psychostimulant, suggesting behaviors related to schizophrenia. These findings indicated that decreased drebrin produces deficits in cognitive function but not in spatial memory, probably via hypofunction of dendritic spines.

Overexpression of Ca2+-permeable AMPA receptor promotes delayed cell death of hippocampal CA1 neurons following transient forebrain ischemia.

To examine the role of Ca(2+) entry through AMPA receptors in the pathogenesis of the ischemia-induced cell death of hippocampal neurons, we delivered cDNA of Q/R site-unedited form (GluR2Q) of AMPA receptor subunit GluR2 in the hippocampus by using an HVJ-liposome-mediated gene transfer technique. Two days prior to transient forebrain ischemia, we injected an HVJ-liposome containing cDNA of the GluR2Q-myc fusion gene into a rat unilateral hippocampus. In the absence of ischemic insult, overexpression of Ca(2+)-permeable GluR2Q did not cause any neurodegeneration in the cDNA-injected hippocampus. In ischemic rats, overexpression of Ca(2+)-permeable GluR2Q markedly promoted ischemic cell death of CA1 pyramidal neurons, while complete rescue of CA1 pyramidal neurons from ischemic damage occurred in the hippocampal hemisphere opposite the GluR2Q expression. Overexpression of the Q/R-site edited form (GluR2R) of subunit GluR2 did not affect the ischemia-induced damage of CA1 pyramidal neurons. From these results, we suggest that the Ca(2+)-permeability of AMPA receptors does not have a direct contribution to glutamate receptor-mediated neurotoxicity but has a promotive action in the evolution of ischemia-induced neurodegeneration of vulnerable neurons.

Antisense hippocampal knockdown of NMDA-NR1 by HVJ-liposome vector induces deficit of prepulse inhibition but not of spatial memory

Considerable evidence suggests that an N-methyl-D-aspartate (NMDA) receptor plays a crucial role in memory and cognitive function. To identify the role of this receptor in higher functions of the brain, we delivered antisense oligonucleotides against an NMDA-NR1 subunit (NR1) to the hippocampus in rats using the HVJ-liposome-mediated gene-transfer method. NR1 hippocampal knockdown was performed by the focal injection of the NR1 antisense-HVJ-liposome complex into the bilateral hippocampus. The blocking effect of NR1-antisense on the expression of NR1 was confirmed by Western blot analysis. Spatial memory was tested by a water maze task, and sensorimotor gating was examined by prepulse inhibition (PPI). Western blot analysis demonstrated that the NR1-antisense treatment specifically provided the down-regulation (about 30%) of NR1 protein levels in the hippocampus. The water maze task showed that the antisense treatment did not affect spatial memory, while the PPI test revealed that NR1 hippocampal knockdown caused a deficit in sensorimotor gating. We conclude that mild dysfunction of hippocampal NMDA receptor causes sensorimotor gating deficit and relatively intact in spatial memory.

Effects of intraperitoneally injected lithium, imipramine and diazepam on nitrate levels in rat amygdala

Abstract  Nitric oxide (NO) has been studied in relation to the etiologies of various neurologic and psychiatric diseases. However, little is known about whether clinically available psychotropic drugs affect the NO system in the brain. Using an in vivo brain microdialysis method, the effects of intraperitoneally administered lithium, imipramine and diazepam on levels of , a marker of in vivo NO production, were investigated in the rat amygdala. Lithium significantly reduced, while imipramine raised, levels as compared with controls. These observations suggest that lithium and imipramine induce opposite effects on NO‐related systems in the brain.

Aripiprazole and haloperidol suppress excessive dopamine release in the amygdala in response to conditioned fear stress, but show contrasting effects on basal dopamine release in methamphetamine-sensitized rats.

Although emotional dysfunction in patients with schizophrenia is thought to be associated with poorer outcomes in terms of overall quality of well-being, only a few basic studies have examined the biochemical effect of antipsychotics on emotional function. In this investigation, we examined differences in the effects of aripiprazole and haloperidol on the conditioned fear response in methamphetamine-sensitized and fear-conditioned rats in an in vivo microdialysis study. Aripiprazole is the first antipsychotic drug with an action involving partial dopamine D(2) receptor agonism, thus differing from haloperidol, a typical antipsychotic that shows selective dopamine D(2) receptor full antagonism. After exposure to a conditioned stimulus, methamphetamine-sensitized rats exhibited significantly higher dopamine release in the amygdala than unsensitized rats. We considered this hypersensitivity of dopamine release to be a biochemical marker of hypersensitivity and vulnerability to stress in psychosis. In the present study, we found that aripiprazole and haloperidol equally suppressed the marked increase in extracellular dopamine levels in fear-conditioned rats, whereas haloperidol increased and aripiprazole decreased tonic dopamine levels. In conclusion, the effect of an antipsychotic drug is likely to be involved in attenuation of the phasic increase in dopamine associated with the fear response, at least in the amygdala. In addition, the contrasting effects of haloperidol and aripiprazole on tonic dopamine levels in the amygdala are likely due to the difference in their actions (selective dopamine D(2) receptor full antagonist vs. partial agonist, respectively).

A prospective naturalistic study of antidepressant-induced jitteriness/anxiety syndrome

Objective Patients often develop neuropsychiatric symptoms such as anxiety and agitation after they have started taking an antidepressant, and this is thought to be associated with a potentially increased risk of suicide. However, the incidence of antidepressant-induced jitteriness/anxiety syndrome has not been fully investigated, and little has been reported on its predictors. The aim of this study was to survey the incidence of antidepressant-induced jitteriness/anxiety syndrome and clarify its predictors in a natural clinical setting. Materials and methods Between January 2009 and July 2012, we prospectively surveyed 301 patients who had not taken any antidepressants for 1 month before presentation, and who were prescribed antidepressants for 1 month after their initial visit. Patients were classified as developing antidepressant-induced jitteriness/anxiety syndrome if they experienced any symptoms of anxiety, agitation, panic attacks, insomnia, irritability, hostility, aggressiveness, impulsivity, akathisia, hypomania, or mania during the first month. Results Among the 301 patients, 21 (7.0%) developed antidepressant-induced jitteriness/anxiety syndrome. Major depressive disorder and a diagnosis of mood disorder in first-degree relatives of patients were significantly associated with induction of antidepressant-induced jitteriness/anxiety syndrome (odds ratio 10.2, P=0.001; odds ratio 4.65, P=0.02; respectively). However, there was no such relationship for sex, age, class of antidepressant, combined use of benzodiazepines, or diagnosis of anxiety disorder. Conclusion The findings of this study suggest that major depressive disorder and a diagnosis of mood disorder in first-degree relatives may be clinical predictors of antidepressant-induced jitteriness/anxiety syndrome.

Valproic acid inhibits excess dopamine release in response to a fear-conditioned stimulus in the basolateral complex of the amygdala of methamphetamine-sensitized rats.

Valproic acid, an established antiepileptic and antimanic drug, has recently emerged as a promising emotion-stabilizing agent for patients with psychosis. Although dopamine transmission in the amygdala plays a key role in emotional processing, there has been no direct evidence about how valproic acid acts on the dopaminergic system in the brain during emotional processing. In the present study, we tested the effect of valproic acid on a trait marker of vulnerability to emotional stress in psychosis, which is excess dopamine release in response to a fear-conditioned stimulus (CS) in the basolateral complex of the amygdala of methamphetamine-sensitized rats. Extracellular dopamine was collected from the amygdala of freely moving methamphetamine-sensitized rats by in vivo microdialysis and was measured using high-performance liquid chromatography. During microdialysis, valproic acid was intraperitoneally injected followed by CS exposure. Valproic acid treatment decreased baseline levels of dopamine and also attenuated the excess dopamine release in response to the CS in the amygdala of methamphetamine-sensitized rats. The results prove that valproic acid inhibits spontaneous dopamine release and also attenuates excess dopaminergic signaling in response to emotional stress in the amygdala. These findings suggest that the mechanisms of the emotion-stabilizing effect of valproic acid in psychosis involve modulation of dopaminergic transmission in emotional processing.

Dopamine dynamics during emotional cognitive processing: Implications of the specific actions of clozapine compared with haloperidol

Clozapine has improved efficacy relative to typical antipsychotics in schizophrenia treatment, particularly regarding emotional symptoms. However, the mechanisms underlying its therapeutic benefits remain unclear. Using a methamphetamine-sensitised rat model, we measured changes in dopamine levels in the amygdalae in response to a fear-conditioned cue, serving as a biochemical marker of emotional cognitive processing disruption in psychosis, for analysing the biochemical mechanisms associated with the clinical benefits of clozapine. We also compared how clozapine and haloperidol affected basal dopamine levels and phasic dopamine release in response to the fear-conditioned cue. Extracellular dopamine was collected from the amygdalae of freely moving rats via microdialysis and was analysed by high-performance liquid chromatography. Clozapine or haloperidol was injected during microdialysis, followed by exposure to the fear-conditioned cue. We analysed the ratio of change in dopamine levels from baseline. Haloperidol treatment increased the baseline dopamine levels in both non-sensitised and sensitised rats. Conversely, clozapine only increased the basal dopamine levels in the non-sensitised rats, but not in the sensitised rats. Although both antipsychotics attenuated phasic dopamine release in both the non-sensitised and sensitised rats, the attenuation extent was greater for clozapine than for haloperidol under both dopaminergic conditions. Our findings indicate that stabilized dopamine release in the amygdalae is a common therapeutic mechanism of antipsychotic action during emotional processing. However, the specific dopaminergic state-dependent action of clozapine on both basal dopamine levels and stress-induced dopamine release may be the underlying mechanism for its superior clinical effect on emotional cognitive processing in patients with schizophrenia.

Diazepam suppresses the stress-induced dopaminergic release in the amygdala of methamphetamine-sensitized rat

Abstract Although the benzodiazepine class of drugs has proven useful in treating anxiety symptoms, recent studies yield no consistent empirical support for their use in treating psychiatric disorders. However, animal studies using a fear conditioning paradigm have suggested that benzodiazepines facilitate fear memory extinction, dependent on treatment timing and subject conditions. However, we have no data on the effect of subject conditions. The purpose of this study was to investigate whether the effect of benzodiazepines depends on hypersensitivity to fear‐memory processing. We examined the effect of diazepam, a benzodiazepine, on the extracellular dopamine level in the left amygdala of methamphetamine‐sensitized, fear‐conditioned model rats, using microdialysis and high‐performance liquid chromatography. In this model, the dopamine level in the amygdala excessively increases in response to a fear‐conditioned stimulus; the phenomenon has been proposed as a biological marker for hypersensitivity to fear‐memory processing. Diazepam inhibited this excessive increase. The extent of the inhibitory effect was greater in the sensitized condition. Diazepam alone increased amygdalar dopamine levels under physiological conditions but not under sensitized conditions. Diazepam did not shorten freezing time in any group. These results suggest that diazepam modulates amygdala dopamine with state dependence and that amygdalar dopamine fine‐tuning accounts for part of the therapeutic effect of benzodiazepines on fear memory processing. Further investigation is required to identify patients suitable for treatment with benzodiazepines. This is the first report on the pharmacodynamic effects of benzodiazepine on the amygdalar dopamine basal level and on fear memory processing.

Escitalopram attenuates fear stress-induced increase in amygdalar dopamine following methamphetamine-induced sensitisation: Implications of fine-tuning action of selective serotonin reuptake inhibitors on emotional processing

ABSTRACT Serotonin reuptake inhibitors modulate the serotonergic pathways of the nervous system and are widely used for treating psychiatric conditions such as anxiety and depression. The dopaminergic system is related to the development of these conditions. Previous studies on methamphetamine‐sensitised rats (behavioural models of stress vulnerability) have shown increased release of dopamine in response to conditioned stress in the amygdala. This biochemical abnormality was proposed to underlie the pathophysiology of stress vulnerability. However, the effect of serotonin reuptake inhibitors on dopamine levels and its consequent impact on emotional processing is unclear. Here we examined the acute effect of escitalopram, a highly selective serotonin reuptake inhibitor, on fear‐related behaviour, baseline dopamine release and dopamine release in response to conditioned fear stress in the amygdala of model rats. Male Sprague‐Dawley rats received 2mg/kg/day, s.c. of methamphetamine for 10 days to sensitise them to the drug, and a fear conditioning paradigm was instituted to model psychological stress. Dopamine changes in the amygdala in response to systemic administration of escitalopram followed by conditioned fear stress were measured using microdialysis and high‐performance liquid chromatography. Baseline dopamine release in the amygdala was increased by escitalopram in non‐sensitised rats but not in methamphetamine‐sensitised rats. Escitalopram attenuated dopamine release in response to the fear‐conditioned stimulus in both sensitised and non‐sensitised rats. The extent of suppression in methamphetamine‐sensitised rats (−90%) was greater than that in non‐sensitised rats (−48%). These findings suggest that serotonin reuptake inhibitors indirectly stabilise the dopaminergic pathway and modulate emotional processing in the amygdala.