Kyoji Okita

Kyoji Okita
National Center of Neurology and Psychiatry · Integrative Brain Imaging Center

M.D., Ph.D.

About

38
Publications
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340
Citations

Publications

Publications (38)
Article
Full-text available
Introduction: The misuse of stimulant drugs such as methamphetamine is a global public health issue. One important neurochemical mechanism of methamphetamine use disorder may be altered dopaminergic neurotransmission. For instance, previous studies using positron emission tomography (PET) have consistently shown that striatal dopamine D2-type recep...
Article
Full-text available
Abstract Background Centiloid (CL) scaling has become a standardized quantitative measure in amyloid PET because it facilitates the direct comparison of results across institutions, even when different analytical methods or tracers are used. Standard volumes of interest must be used to calculate the CL scale after the anatomic standardization of am...
Article
Full-text available
Introduction: Altered dopaminergic neurotransmission, especially in the functioning of dopamine D2-type receptors, is considered central to the etiology of a variety of neuropsychiatric disorders. In particular, individuals with substance use disorders have been consistently observed to exhibit lower D2-type receptor availability (quantified as bin...
Article
Drug addiction is associated with a range of medical and social problems, not least the negative side effects experienced by those who take drugs. The long-term effects are particularly concerning and can be difficult to treat. Changes in the behaviour of long-term drug users can include impulsivity and irrationality, which can negatively impact on...
Preprint
Full-text available
Background Centiloid (CL) scaling has become a standardized quantitative measure in amyloid PET because it facilitates the direct comparison of results across institutions, even when different analytical methods or tracers are used. Standard volumes of interest must be used to calculate the CL scale after the anatomic standardization of amyloid PET...
Article
Full-text available
Research using rodent models has established a relationship between the steroid hormone estrogen and dopamine function, by revealing changes throughout the estrous cycle and by directly manipulating neuroendocrine signaling through ovariectomy and administration of estrogen. However, a direct link between estrogen levels and dopamine signaling had...
Article
Full-text available
Background: In clinical practice, equivocal findings are inevitable in visual interpretation of whether amyloid positron emission tomography (PET) is positive or negative. It is therefore necessary to establish a more objective quantitative evaluation method for determining the indication for disease-modifying drugs currently under development. Aim...
Article
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Objective: This study aimed to examine the alterations in gray matter networks related to tau retention in Alzheimer's disease (AD) patients and cognitively normal (CN) older individuals. Methods: Eighteen amyloid-positive AD patients and 30 age- and sex-matched amyloid-negative CN controls were enrolled. All underwent 3D T1-weighted MRI, amyloid p...
Article
Full-text available
Introduction: The molecular mechanism of neurodegeneration, including tau and neurite complexity, is an important topic in Alzheimer's disease (AD) research. Methods: We recruited 27 amyloid-positive individuals identified through 11C-Pittsburgh compound B (PiB) positron emission tomography (PET) and 31 amyloid-negative individuals with normal c...
Article
Full-text available
Aim: The objective of the current study was to identify risk factors that affect the onset of dependence and chronic psychosis due to cannabis use. Methods: We examined clinical genetic factors, psychiatric disorders prior to cannabis use, starting age of cannabis use, duration and frequency of cannabis use, types of cannabis products used, comb...
Article
Background Radioligands for the translocator protein (TSPO) 18 kDa have been used with positron emission tomography (PET) to assess neuroinflammation and microglial activation in psychiatric disorders. One study using this approach showed substantial TSPO elevation throughout the brain in chronic methamphetamine users following long-term abstinence...
Article
Full-text available
Backgrounds: Although neurofibrillary tangles (NFTs) mainly accumulate in the medial temporal lobe with human aging, only a few imaging studies have investigated correlations between NFT accumulation and gray matter (GM) volume in cognitively normal older adults. Here, we investigated the correlations between 18F-THK5351 accumulation and GM volume...
Article
Full-text available
Backgrounds: Although neurofibrillary tangles (NFTs) mainly accumulate in the medial temporal lobe with human aging, only a few imaging studies have investigated correlations between NFT accumulation and gray matter (GM) volume in cognitively normal older adults. Here, we investigated the correlations between 18 F-THK5351 accumulation and GM volume...
Article
Full-text available
Cognitive assessments and neuroimaging are routinely combined in clinical practice to diagnose dementia represented by Alzheimer's disease (AD). The Montreal Cognitive Assessment (MoCA) is reported to be more suitable than the Mini-Mental State Examination (MMSE) for screening mild cognitive impairment (MCI) and mild AD. On the other hand, attentio...
Article
Full-text available
Background Selective serotonin reuptake inhibitors are often used in alcohol use disorders. Clinical trials with selective serotonin reuptake inhibitors for alcohol use disorders, however, have yielded mixed results. The goal of this project was to assess whether a single i.v. dose of a selective serotonin reuptake inhibitor reduces craving for alc...
Article
Full-text available
Rationale Microglia are the main immune cells in the central nervous system and participate in neuroinflammation. When activated, microglia express increased levels of the translocator protein 18 kDa (TSPO), thereby making TSPO availability a marker for neuroinflammation. Using positron emission tomography (PET) scanning, our group recently demonst...
Article
Full-text available
Chronic methamphetamine use poses potentially devastating consequences for directly affected individuals and for society. Lower dopamine D2-type receptor availability has been observed in striata of methamphetamine users as compared with controls, but an analogous comparison of D1-type receptors has been conducted only on post-mortem material, with...
Article
Full-text available
Individuals with drug use disorders seek drugs over other rewarding activities, and exhibit neurochemical deficits related to dopamine, which is involved in value-based learning and decision-making. Thus, a dopaminergic disturbance may underpin drug-biased choice in addiction. Classical drug-choice assessments, which offer drug-consumption opportun...
Article
In the brain, microglia continuously scan the surrounding extracellular space, in order to respond to damage or infection by becoming activated and participating in neuroinflammation. When activated, microglia increase the expression of the translocator protein (TSPO) 18 kDa, thereby making TSPO expression a marker for neuroinflammation. We used th...
Article
Full-text available
Background Cigarette smoking induces dopamine release in the striatum, and smoking- or nicotine-induced ventral striatal dopamine release is correlated with nicotine dependence. Smokers also exhibit lower dopamine D2/3 (D2 and D3) receptor availability (BPND) in the dorsal striatum than nonsmokers. Negative correlations of striatal dopamine D2/3 BP...
Article
Women differ from men in smoking-related behaviors, among them a greater difficulty in quitting smoking. Unlike female smokers, male smokers have lower striatal dopamine D2-type receptor availability (binding potential, BPND) than nonsmokers, and exhibit greater smoking-induced striatal dopamine release. Because dopamine D2-type autoreceptors in th...
Article
Stimulant use disorders are associated with deficits in striatal dopamine receptor availability, abnormalities in mesocorticolimbic resting-state functional connectivity (RSFC) and impulsivity. In methamphetamine-dependent research participants, impulsivity is correlated negatively with striatal D2-type receptor availability, and mesocorticolimbic...
Article
Full-text available
Reassurance seeking (RS) is a common feature of health anxiety (HA). RS maintains their anxiety and results in unnecessary use of medical services. Thus, understanding HA more in depth and finding the key of treatment are still crucial. The aim of this study was to provide a detailed description of RS in HA. Semi-structured interviews were conducte...
Article
Full-text available
Background: Individuals with substance-use disorders exhibit emotional problems, including deficits in emotion recognition and processing, and this class of disorders also has been linked to deficits in dopaminergic markers in the brain. Because associations between these phenomena have not been explored, we compared a group of recently abstinent...
Article
Introduction: When microglia become activated (an integral part of neuroinflammation), cellular morphology changes and expression of translocator protein (TSPO) 18 kDa is increased. Over the past several years, [(11)C]DAA1106 has emerged as a reliable radiotracer for labeling TSPO with high affinity during positron emission tomography (PET) scanni...
Article
Full-text available
A relapse prevention program called the Information Technology Aided Relapse Prevention Programme in Schizophrenia (ITAREPS) has been developed and is reported to be highly effective. However the effectiveness was influenced by user adherence to the protocol of the program, the exact effectiveness and the role of the ITAREPS have been partially unc...
Article
Full-text available
This case study reveals the effectiveness of a cognitive behavioural therapy (CBT) intervention based on a functional model of interruption of pain and a hypothetical model of functional somatic syndromes in a case of adolescent somatoform pain disorder. Yu was a junior high school student in Japan who was diagnosed with somatoform pain disorder. H...
Article
Full-text available
This case report details the therapeutic effects of tandospirone on two patients with anorexia nervosa, one with the restricting subtype (ANR), and another with the binge-eating/purging subtype (ANBP). A 22-year-old female patient with ANR and a 23-year-old female patient with ANBP were treated successfully with the 5-HT1A partial agonist tandospir...
Article
Full-text available
Objective: The forensic mental health system in Japan changed dramatically with the enforcement of the “Act on Medical Care and Treatment for the Persons Who Had Caused Serious Cases under the Condition of Insanity” or MTS Act, in 2005. The aim of this study is to evaluate the changes in attitude and behavior of general psychiatrists, towards foren...

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