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Addiction
Vhinoth Sivakumaran
Addiction is one of the largest challenges facing society today. Drugs and alcohol have obvious harmful effects to the health of the user both in the short and long term; sustained alcohol use can lead to liver cirrhosis, smoking has been estimated to cause over 80% of all lung cancer cases in the UK 149 , and heroin users are at risk of contracting HIV through the reuse and sharing of needles. 150 Addictions also come at a huge cost to society, often related to crime, cost of medical treatment, and cause time to be lost from work other social programs. 151 Addiction is estimated to cost the U.S. more than $300 billion a year due to its effect on health and productivity, 152 and the total cost to A&E units alone in the UK due to drug abuse may be up to £100 million. 153 Drug abuse has been shown to produce permanent changes to the circuitry in the brain related to the 'pleasure centre', and more knowledge about this could lead to more effective treatments for addiction. 154 Different drugs affect the nervous system in different ways, but most of their effects on the mind and behaviour are due to the drug's actions on the transmission of neurotransmitters across the synapses in our brain. The neurotransmitters are the chemicals which cross the gaps, the synapses, between the neurons in our brain to bring about a change in the next neuron, which results in the nerve impulse being transduced, or passed on. 155 Drugs can affect this communication in many different ways, such as by preventing the neurotransmitters from 149 (Lung Cancer - Risk Factors: Cancer Research UK, 2012) 150 (Why are heroin users at special risk for contracting HIV/AIDS and Hepatitis B and C?, 2005) 151 (Marvist, 2007) 152 (Nestler & Malenka, Addicted Brains: The Chemistry of Pain and Pleasure, 2004) 153 (Fleming, 2005) 154 (Nestler & Malenka, op. cit ) 155 (Wikipedia, Neurotransmission, 2012)
being synthesized or stored, or by blocking the receptors on the receiving neuron (the postsynaptic neuron). 156 Many drugs, because their chemical structures are similar to those of our natural neurotransmitters, can fit in and bind to the receptors of those neurotransmitters that they mimic, bringing about a change in the neuron. However, these changes are not exactly the same as those which would happen when our natural neurotransmitters bind to those receptors, so slightly different impulses are transmitted through the network, resulting in the change in the person's behaviour. 157 Alcohol, for example, mainly affects the brain by desensitizing the NDMA receptors of neurons, which are the receptors for the neurotransmitter glutamate. 158 Glutamate is the most abundant excitatory neurotransmitter in the nervous system 159 , and is involved in many cognitive functions, particularly learning and memory. 160 Alcohol also increases the action of the major inhibitory neurotransmitter in the nervous system, GABA. Alcohol's inhibition of glutamate and enhancement of GABA is a reason for the reduction in the pace of brain activity and the memory loss during intoxication. 161 Nicotine, on the other hand, directly mimics a neurotransmitter, acetylcholine, and binds to the acetylcholine receptors on the neurons in the nervous system. 162 All pleasurable stimuli are felt by us as pleasurable because they have all been shown to act in a very similar way on the same 'reward circuitry' in the brain, the 'pleasure
156 (Understanding Addiction) 157 (NIDA, 2010) 158 (New Scientist, 2006) 159 (Meldrum, 2000) 160 (McEntee & Crook, 1993) 161 (ARTS, 2000) 162 (Greenfield, 1997)
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