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  1. Loganathan K, Ho ETW
    Addict Behav, 2021 05;116:106816.
    PMID: 33453587 DOI: 10.1016/j.addbeh.2021.106816
    Over the years, various models have been proposed to explain the psychology and biology of drug addiction, built primarily around the habit and compulsion models. Recent research indicates drug addiction may be goal-directed, motivated by excessive valuation of drugs. Drug consumption may initially occur for the sake of pleasure but may transition to a means of escaping withdrawal, stress and negative emotions. In this hypothetical paper, we propose a value-based neurobiological model for drug addiction. We posit that during dependency, the value-based decision-making system in the brain is not inactive but has instead prioritized drugs as the reward of choice. In support of this model, we consider the role of valuation in choice, its influence on pleasure and punishment, and how valuation is contrasted in impulsive and compulsive behaviours. We then discuss the neurobiology of value, beginning with the dopaminergic system and its relationship with incentive salience before moving to brain-wide networks involved in valuation, control and prospection. These value-based neurobiological components are then integrated into the cycle of addiction as we consider the development of drug dependency from a valuation perspective. We conclude with a discussion of cognitive interventions utilizing value-based decision-making, highlighting not just advances in recalibrating the valuation system to focus on non-drug rewards, but also areas for improvement in refining this approach.
  2. Loganathan K, Moriya S, Parhar IS
    Zebrafish, 2018 10;15(5):473-483.
    PMID: 30102584 DOI: 10.1089/zeb.2018.1594
    Ambient light and temperature affect reproductive function by regulating kisspeptin and gonadotrophin-releasing hormone (GnRH) in vertebrates. Melatonin and melatonin receptors, as well as the two-pore domain K+ channel-related K+ (TREK) channels, are affected by light and/or temperature; therefore, these molecules could modulate kisspeptin and GnRH against ambient light and temperature. In this study, we investigated the effect of light and temperature, which affect melatonin levels in gene expression levels of TREK channels, kisspeptin, and GnRH. We first investigated the effects of different light and temperature conditions on brain melatonin concentrations by ELISA. Fish were exposed to either constant darkness, constant light, high temperature (35°C), or low temperature (20°C) for 72 h. Brain melatonin levels were significantly high under constant darkness and high temperature. We further investigated the effects of high brain melatonin levels by constant darkness and high temperature on gene expression levels of melatonin receptors (mt1, mt2, and mel1c), TREK channels (trek1b, trek2a, and trek2b), gnrh3, and kiss2 in the adult zebrafish brain by real-time polymerase chain reaction. Fish were exposed to constant darkness or elevated temperatures (35°C) for 72 h. trek2a, kiss2, and gnrh3 levels were increased under constant darkness. High temperature decreased gene expression levels of mt1, mt2, mel1c, and gnrh3 in the preoptic area, whereas other genes remained unchanged. Melatonin receptors, TREK channels, gnrh3, and kiss2 responded differently under high melatonin conditions. The melatonin receptors and the TREK channels could play roles in the regulation of reproduction by environmental cues, especially ambient light and temperature.
  3. Loganathan K, Moriya S, Parhar IS
    Zoolog Sci, 2019 04 01;36(2):167-171.
    PMID: 31120653 DOI: 10.2108/zs180111
    The two-pore domain potassium ion (K + ) channel-related K + (TREK) channel and melatonin receptors play roles in the regulation of reproduction in zebrafish. Since reproduction is regulated by diurnal rhythms, the TREK family and melatonin receptors may exhibit diurnal rhythms in expression. In this study, we aimed to investigate diurnal variations of the gene expressions of TREK family and melatonin receptors and their associations with kisspeptin and gonadotrophin-releasing hormone (GnRH). Diurnal variations of trek1b, trek2a, trek2b, mt1, mt2, mel1a, kiss2 and gnrh3 expressions were examined by real-time PCR. For reproduction-related genes, kiss2 and gnrh3 exhibited diurnal rhythms. trek2a revealed a diurnal rhythm in the TREK family. mt2 and mel1c exhibited diurnal rhythms in the melatonin receptors. Since Trek2a regulates gnrh3 expression, the diurnal rhythm of gnrh3 expression suggests to be regulated by the diurnal rhythm of trek2a expression.
  4. Loganathan K, Moriya S, Parhar IS
    Biochem Biophys Res Commun, 2018 02 12;496(3):927-933.
    PMID: 29395088 DOI: 10.1016/j.bbrc.2018.01.117
    Gonadotrophin-releasing hormone (GnRH) expression is associated with the two-pore domain potassium ion (K+) channel-related K+ (TREK) channel trek2a expression and melatonin levels. We aimed to investigate correlation of trek2a expression with gnrh3 expression, and regulatory mechanisms of trek2a expression by the melatonin receptor Mt1 and α2-adrenoceptor which are regulated by melatonin. trek2a specific siRNA, Mt1 antagonist luzindole and α2-adrenoceptor antagonist prazosin were administered into the adult zebrafish brain and gene expressions were examined by real-time PCR. trek2a specific siRNA administration significantly reduced expression levels of trek2a, gnrh3 and mt1. Luzindole administration suppressed trek2a and gnrh3 expressions. Prazosin administration reduced trek2a and gnrh3 expressions. It is suggested that Trek2a regulates gnrh3 expression under the control of Mt1 and α2-adrenoceptor.
  5. Loganathan K, Chacko JP, Saravanan BS, Vaithilingam B
    J Oral Biol Craniofac Res, 2012 Sep-Dec;2(3):210-2.
    PMID: 25737868 DOI: 10.1016/j.jobcr.2012.10.011
    Even though variety of foreign bodies has been reported in a various locations in the craniofacial region, wooden foreign bodies are uncommon. Appropriate management of wooden foreign bodies is considered essential because of their infectious complications and difficulty in radiographic localization. Even though literature is replete with articles on management of foreign bodies in the craniofacial region, specific management of wooden foreign bodies are rarely reported. The purpose of this article is to report two cases of deeply placed wooden foreign body and a protocol for managing them in the maxillofacial region.
  6. Gopal D, Telang A, Telang LA, Loganathan K, Reddy BT
    J Clin Diagn Res, 2015 May;9(5):ZD21-2.
    PMID: 26155582 DOI: 10.7860/JCDR/2015/12604.5915
    Nasopalatine duct cyst ( NPDC) is described as most common non-odontogenic developmental cyst of the jaws. Despite being common, its clinical and radiographic presentation could be varied and it can sometimes be a diagnostic challenge. This paper presents an unusual case of an infected NPDC associated with an impacted inverted mesiodens and a history of trauma that misled the clinical diagnosis.
  7. Loganathan K, Lv J, Cropley V, Ho ETW, Zalesky A
    Neuroscience, 2021 01 01;452:295-310.
    PMID: 33242540 DOI: 10.1016/j.neuroscience.2020.11.026
    The process of valuation assists in determining if an object or course of action is rewarding. Delay discounting is the observed decay of a rewards' subjective value over time. Encoding the subjective value of rewards across a spectrum has been attributed to brain regions belonging to the valuation and executive control systems. The valuation system (VS) encodes reward value over short and long delays, influencing reinforcement learning and reward representation. The executive control system (ECS) becomes more active as choice difficulty increases, integrating contextual and mnemonic information with salience signals in the modulation of decision-making. Here, we aimed to identify resting-state functional connectivity-based patterns of the VS and ECS correlated with value-setting and delay discounting (outside-scanner paradigm) in a large (n = 992) cohort of healthy young adults from the Human Connectome Project (HCP). Results suggest the VS may be involved in value-setting of small, immediate rewards while the ECS may be involved in value-setting and delay discounting for large and small rewards over a range of delays. We observed magnitude sensitive connections involving the posterior cingulate cortex, time-sensitive connections with the ventromedial and lateral prefrontal cortex while connections involving the posterior parietal cortex appeared both magnitude- and time-sensitive. The ventromedial prefrontal cortex and posterior parietal cortex could act as "comparator" regions, weighing the value of small rewards against large rewards across various delay duration to aid in decision-making.
  8. Loganathan K, Lv J, Cropley V, Zalesky A, Ho ETW
    Neurosci Res, 2021 Dec;173:114-120.
    PMID: 34214618 DOI: 10.1016/j.neures.2021.06.006
    Poly-drug consumption contributes to fatal overdose in more than half of all poly-drug users. Analyzing decision-making networks may give insight into the motivations behind poly-drug use. We correlated average functional connectivity of the valuation system (VS), executive control system (ECS) and valuation-control complex (VCC) in a large population sample (n = 992) with drug use behaviour. VS connectivity is correlated with sedative use, ECS connectivity is separately correlated with hallucinogens and opiates. Network connectivity is also correlated with drug use via two-way interactions with other substances including alcohol and tobacco. These preliminary findings can contribute to our understanding of the common combinations of substance co-use and associated neural patterns.
  9. Loganathan K, Moriya S, Sivalingam M, Ng KW, Parhar IS
    J. Chem. Neuroanat., 2017 Dec;86:92-99.
    PMID: 29074372 DOI: 10.1016/j.jchemneu.2017.10.004
    kcnk10a has been predicted in zebrafish to be a member of the two-pore domain potassium ion (K+) channel-related K+ (TREK) channel family known as a thermoreceptor. Since reproduction is affected by temperature, Kcnk10a could be involved in the regulation of reproduction. However, expression of kcnk10a in the zebrafish brain and association with reproduction has not been identified. In this study, the full length sequence and localization of kcnk10a in the brain was investigated and gene expressions of the TREK channel family were examined to investigate association with reproduction. We initially identified the full length cDNA sequence of kcnk10a using Rapid Amplification of cDNA Ends and localization in the zebrafish brain using in situ hybridization. Furthermore, we examined the gene expression differences of kcnk2b, kcnk10a and kcnk10b mRNA between genders as well as developmental stages by real-time PCR. The deduced amino acid sequence of the identified kcnk10a mRNA contains highly conserved two pore domains and four transmembrane regions and was higher similarity to zebrafish Kcnk10b than zebrafish Kcnk2a and 2b. kcnk10a mRNA was widely distributed in the brain such as the preoptic area, hypothalamus and the midbrain. kcnk10a mRNA expression exhibited significant difference between mature male and female, and increase during puberty. Kcnk10a could be involved in the regulation of reproductive function.
  10. Yussof I, Mohamed Shah N, Ab Muin NF, Abd Rahim S, Hatah E, Mohd Tahir NA, et al.
    J Cancer Educ, 2024 Aug;39(4):383-390.
    PMID: 38530598 DOI: 10.1007/s13187-024-02421-0
    Breast cancer survivors on adjuvant endocrine therapy (AET) have distinct information-seeking experience compared to those in the diagnosis and intensive treatment phase. This study aimed to understand the challenges in obtaining and seeking information among Malaysian breast cancer survivors. We conducted semi-structured, one-to-one interviews among patients using AET from two hospitals and a local cancer organization. Interviews were conducted until theme saturation was achieved (N = 25). Interviews were de-identified, transcribed verbatim, and analysed using thematic analysis. To ensure rigor, coding was conducted through regular discussions between two researchers and the findings were shared with several participants after analysis was completed. Three main themes were identified: limitations in the healthcare system, pitfalls of seeking information online, and limited information from local sources. The participants perceived that their information needs were not met by their healthcare providers and sought information on the Internet to complement their information needs. However, they were faced with risks of misinformation, information overload, and unethical promotion of health products. Those with limited English proficiency had difficulties in accessing quality information, and suggested that there should be more content created by local health advocates in local languages, with information that is tailored for local cultures. As the Internet has become an important medium of health education, healthcare providers and patients should be equipped with the skills to share and search for information online. Digital health literacy needs to be incorporated in patient education modules to create a more informed and empowered patient community.
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