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- Herausgeber: Bentham Science Publishers
- Kategorie: Wissenschaft und neue Technologien
- Sprache: Englisch
Drug Addiction Mechanisms in the Brain explores the fascinating world of drug substances and their effects on the brain. This book provides a comprehensive overview of the ten major substances that contribute to drug addiction Information about each substance is presented in a specific chapter, shedding light on their biochemical mechanisms and physiological effects. From the stimulating effects of cocaine to the sedative properties of heroin, and the hallucinogenic experiences induced by LSD, the book takes the reader through the intricate pathways of addiction. Other substances covered in the book include alcohol, nicotine, MDMA, METH, morphine, ketamine, and fentanyl. Readers will gain an understanding about neurochemical alterations in the brain Anyone looking for interesting knowledge about the addictive nature of common drugs and their complex interplay with the brain will find this book informative.
Readership
Researchers, healthcare professionals, counsellors and general readers.
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Seitenzahl: 162
Veröffentlichungsjahr: 2024
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PREFACE
It is generally believed that drug abuse can cause severe long-lasting changes in the neural network contributing to the development of addiction. Profound states of addiction may be established in brains with repetitive usage, despite its damage to the brain. Dopamine plays a very significant role in addiction to drugs. Under normal conditions, in neural communication between neurons, the presynaptic neuron releases dopamine into the synapse. At the postsynaptic neurons, there are receptors which receive the dopamine. Usually, any left-out dopamine molecule is recycled back to the presynaptic neuron by the dopamine transporters. If any drug blocks the dopamine transporter it is unable to take the dopamine back from the synaptic cleft leading to the continuous firing of neurons. As per Drug Enforcement Administration (DEA) and the Controlled Substances Act (CSA) reports, heroin is a Schedule I drug. Heroin causes addiction to the brain like any other addictive substance. Heroine use affects not only neurotransmitters but also the hormonal systems in an irreversible way. In healthy young people, the use of MDMA can lead to cognitive decline when abused with cannabis. MDMA causes hyponatremia and hyponatremia-associated deaths. This book deals with the harmful effects of drugs on brain and cognitive functions. I wish our readers can be satisfied with many questions and feel excited to find the answer to the research questions on the etiology of neurological sequelae of drug abuse in this book.
Cocaine and its Effects on the Brain
Jayalakshmi Krishnan1Abstract
Brain’s limbic system is the target site of action of cocaine. This area of the brain is involved in pleasure and motivation. Cocaine causes the dopamine build-up in the synapses by creating a feeling of being “high”. Cocaine induces action by binding to the dopamine transporter, which transports excess dopamine back to the presynaptic neuron. The nucleus accumbens (NAc) of the limbic system is the primary target of cocaine action. Cocaine also alters gene expression in the limbic system by altering dopamine transporters or dopamine receptors. Cocaine causes auditory hallucinations, restlessness, paranoia, and psychosis. This chapter reviews the impact of cocaine on the brain.
INTRODUCTION
It is generally believed that drugs of abuse can cause severe long-lasting changes in the neural network contributing to the development of addiction. Cocaine is the most powerful reinforcing drug of abuse which can bind to serotonin transporter (SERT), dopamine transporter (DAT), and norepinephrine transporter (NET) by causing blocking of the reuptake of these neurotransmitters. Cocaine is a CNS stimulant that alters sleep and causes alertness. Withdrawal of cocaine is always accompanied by lack of motivation, increased irritability, agitation, extreme fatigue, and depression. Anxiety is one of the main symptoms of cocaine withdrawal and corticotropin releasing factor/hormone (CRF or CRH) has been involved in cocaine abstinence.
Cocaine is synthesized from the coca plant, a native of South America. It is sold as a solid rock crystal form or a fine white powder. Cocaine can be snorted, rubbed in water in the gums, and can be injected with a needle. Another method of taking cocaine is just heating up the rock crystal and directly inhale.
Profound states of addiction to cocaine may be established in brains with repetitive usage, despite its damage to the brain. Studies in animal models prove that the limbic system, basal ganglia, and ventral striatum are involved in dopaminergic neurons that cause pleasure experience [1-3]. Continuous use of
cocaine can lead to damage to the structural components of the brain, causing mental health disorders such as anxiety and depression and loss of gray matter in the brain, followed by the death of neuronal cells. Cocaine also damages breathing, the immune system, heart dysfunctions, and digestive system problems. Cocaine alters the signalling of neurotransmitters in the brain. Information processing and emotions are affected by cocaine addiction, and also the prefrontal cortex becomes sensitive to cocaine addiction. Although some of the effects of cocaine on the brain are known, many things remain unknown, especially the chronic changes associated with cocaine exposure. Cocaine exposure also alters the learning process within the striatum and prefrontal cortex according to some animal studies. Low doses of cocaine can be dangerous. A single low dose of cocaine can cause structural brain damage in Balb-c mice (o.5mg/kg) without altering the metabolism [4]. As per the European drug report, 4.3 million people between 15 and 64 years old have used cocaine (European Drug Report, 2016). Cocaine also causes myocardial infarction and psychiatric illness [5].
In vitro and in vivo experiments have shown a different kind of trend when cocaine is administered. Cocaine causes less firing in neurons in vivo, whereas deep hyperpolarization in vitro. Withdrawal of cocaine leads to the impairment of sodium currents in nucleus Accumbens neurons [6]. Not only sodium currents but calcium homeostasis is also affected by cocaine in the nucleus Accumbens neurons [7]. Calcineurin is a calmodulin-dependent serine/threonine protein phosphate whose levels were decreased in neurons due to cocaine uptake (Hu et al., 2005). Whole cell calcium levels are affected due to chronic cocaine intake and distups, synaptic plasticity, and intracellular signaling cascades with substantial changes in neurotransmitter release [8].
Cocaine in Brain
Under normal conditions, in neural communication between neurons, the presynaptic neuron releases dopamine into the synapse. In the postsynaptic neurons, there are receptors that receive this dopamine. Usually, any left-out dopamine molecule is recycled back to the presynaptic neuron by the dopamine transporters. Cocaine intake binds with the dopamine transporter and blocks the normal recycling process. This results in the build up of dopamine in the synapses, contributing to the pleasurable effects of cocaine. Cocaine is also a psychostimulant [9]. In brain, cocaine usage can create a short-term change such as alertness, feeling of pleasure, increased energy, overactive, paranoia, etc. Significant neurological adaptation can be seen in mice after cocaine exposure in terms of the release of the excitatory neurotransmitter glutamate [10]. Cocaine use is also related to stress and both co-occur at any time [11]. Stress pathway and reward pathway are different in brain, but both can overlap by connections from the ventral tegmental area. Functioning of the orbitofrontal cortex (OFC) is also reduced due to chronic cocaine exposure leading to poor decision making [12]. Ventral pallidum (VP) is connected to the nucleus Accumbens via both direct and indirect pathways. Cocaine reinforcement is mediated through Ventral pallidum (VP), which is a part of the basal ganglia. Cocaine inhibits the indirect pathway of neuronal synaptic transmission in VP [13]. By inhibiting the reuptake of 5-HT, cocaine increases extracellular concentrations of serotonin (5-hydroxytryptamine or 5-HT) in the nucleus accumbens [NAc] and ventral pallidum. Cocaine also disturbs the learning and memory pathways of brain. Long-term potentiation is affected due to cocaine administration. Transcription factor ΔFosB in longterm cocaine administration, causes NMDR activation in NAC [14]. ΔFosB concentrations are increased in reinforcing effects of cocaine.
Effects of Cocaine on Brain Cells
Cocaine releases CXCL10 from pericytes and it regulates monocyte transmigration into the CNS [15]. Cerebrovascular accidents are the most common form of cocaine abuse [16]. The neurotoxicity of cocaine addiction is also due to oxidative stress, autooxidation, and apoptosis [17, 18]. Continuous exposure to a psychostimulant drug can lead to changes in cerebral glucose metabolosim [19, 20]. Cocaine causes autophagic cytotoxicity by activating the nitric oxide GAPDh signaling cascade [21]. Mesocorticolimbic dopamine system is the main reason for cocaine seeking behaviour when activated [22]. Cocaine and methamphetamine users experience changes in the orbitofrontal cortex. OFC and medial prefrontal cortex (mPFC) in rats, when analysed for spine density, revealed a profound change [23]. Alertness, attention, and energy are elevated in cocaine users.. In hippocampal neurons and astrocytes glial fibrillary acidic protein is expressed in response to cocaine administration [24]. When BV2 microglial cells were exposed to cocaine, it altered exosome biogenesis [25].
Cocaine at the Synapse
Cocaine affects DA levels in the mesolimbic reward pathway. Cocaine binds to the dopamine transporter (DAT), hence blocking the reuptake of dopamine in the presynaptic terminal. Because of this, the extracellular dopamine level is increased by much magnitude. DAT is a protein located in the presynaptic neuron, and the functioning of DAT is essential for proper dopamine neurotransmission [26].
Cocaine can also increase all monoamine neurotransmitter levels in the brain, not only dopamine. Serotonin and norepinephrine levels are also increased by cocaine use. The reinforcing effects of cocaine are due to the dopamine levels. Cocaine also alters NMDA dependent signal transduction in straital neurons. Repeated cocaine exposure decreases NMDAR interactions with the postsynaptic density (PSD), and synaptic lipid rafts in the accumbens shell and dorsal striatum in mice [27]. Sigma-1 and Sigma-2 Receptor expression modulate the effect of cocaine on dopaminergic transmission [28]. D1 medium spiny neuron subtype operates in a subtype- and projection-specific manner to negatively regulate cocaine addiction [29]. Remodelling of the mesocorticolimbic circuitry is the main reason for drug addictive behaviour in cocaine users.
Impaired function of Ca2+-activated small-conductance calcium-dependent potassium (SK) channels increases the firing of dopamine neurons in the ventral tegmental area (VTA) dopamine (DA) neurons. A single injection of cocaine within hours induces a lot of changes in the synaptic strength of excitatory inputs in the ventral tegmental area [30, 31]. Changes in AMPAR and NMDAR subunit composition lead to long-lasting neural strength that causes addictive behavior. This drug-evoked synaptic plasticity acts as an intensive signal to promote drug seeking behaviour [32]. Calcium-Impermeable NMDARs mediate cocaine induced excitatory activity in the ventral tegmental area [33]. There is evidence that various classes of drugs of abuse can strengthen the synapse, especially the excitatory synapses on the midbrain region of DA neurons. Cocaine- and stress-induced synaptic enhancement is due to the upregulation of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor subunit GluRA [34]. Excitatory synaptic transmission within the VTA region contributes to behavioural plasticity [35]. GABA synaptic transmission is also disturbed in neurons that project into the ventral pallidum. There is no treatment for cocaine addiction currently. Cognitive behavioural therapy is the only method of treatment. Any specific change in normal synaptic neurotransmission is said to be synaptic plasticity. Molecular targets are the impending features for cocaine to induce long-term synaptic changes. Drug-evoked synaptic plasticity causes changes in the mesolimbic pathways, and thus altering the functional reward circuitry [36]. It is known that cocaine infusion in rats leads to the downregulation of or suppression of the activity of dopamine and serotonin neurons [37].
Cocaine and Genetic Changes in Brain
Epigenetic changes cause both heritable and stable changes in gene expression without much altering the DNA sequence. DNA in mouse brains is altered due to the use of cocaine in the mouse brain, especially those areas which are involved in reward systems [38]. Epigenetic changes have occurred in mouse brains after cocaine intake, followed by changes in the types of RNAs cells made through splicing. Many kinds of proteins are made due to the epigenetic changes in the mouse brain. Gene expression is enhanced upon repeated cocaine exposure leading to addictive phenotypes [39]. Even cocaine induced epigenetic changes are inherited in the germline passing to the offspring. Such studies may shed light on the epigenetic mechanisms that lead to heritable changes in cocaine addiction. Enzymatic modifications to the DNA sequence can occur due to epigenetic changes after cocaine exposure. DNA methylation is one of the modifications of DNA sequence. Cocaine-induced behavioral responses are noted in conditions when cocaine is able to do changes in DNA methylation. Acute cocaine exposure upregulates DNA methylation, DNMT3A and DNMT3B levels leading to the downregulation of gene expression in NAC [40]. Cocaine causes structural plasticity due to DNA methylation. Dendritic spine density is increased in cocaine exposure due to the upregulation of DNMT3a [41]. Histone acetylation is another example of genetic modification. Acute cocaine administration increases histone H4 acetylation on immediate early genes Fos and Fosb in NAC area [42, 43]. In the striatum, histone H3 phospho-acetylation and histone H4 acetylation increase due to acute cocaine exposure [44]. In cocaine-addicted mouse brain, aquaporins have deletions and have shown to decrease dopamine levels and glutamate levels as well in the nucleus Accumbens region [45]. GDNF (Glail cell-derived neurotrophic factor) is decreased due to the decreased level of protein kinase that is phosphoRet, causing behavioural sensitivity to cocaine [46]. Cocaine induces fetal brain retardation due to the inhibition of macromolecular synthesis [47]. Astrocytes cells express corticotropin-releasing factor (CRF) in the ventral tegmental area due to cocaine exposure [48]. JAK/STAT pathways mediates the effect of chronic administration of cocaine in dopaminergic neurons [49]. Drug (Cocaine) induced adaptations in the rat brain are caused by increased phosphorylation of ERK in VTA, thus, in turn, regulates the increase in tyrosine hydroxylase, a crucial enzyme in dopamine synthesis [49]. Decreased neurofilament levels upon exposure to cocaine are shown to be the reason for the structural alterations seen in the brains of rats [50]. Region-specific effects of cocaine are also observed in the brain. For example, in Nucleus accumbans, cocaine decreased tyrosine hydorxylase phosphorylation, and did not alter the functions of this enzyme in other brain regions such as caudoputamen, and substantia nigra [51
