Explanation for nicotine addiction: brain neurochemistry Flashcards
neurochemistry definition
relating chemicals in the brain that regulate biological and psychological functioning
dopamine definition
neurotransmitter generally has excitatory effect and is associated with the sensation of pleasure. unusually high levels are associated with schizophrenia and unusually low levels are associated with parkinson’s disease
what did Dani and Heinemann focus on
dopamine in their desensitisation hypothesis if nicotine addiction. This begins with neurotransmitter acetylcholine
what does ACh stand for
acetylcholine
what does acetylcholine do
-plays a key role in all nervous system activity, which means there are ACh receptors in surfaces if many neurons in the central nervous system
what is nicotinic acetylcholine receptor (nAChR)
type if ACh which is activated by ACh or nicotine
what happens when nicotinic acetylcholine receptor (nAChR) are activated
neuron transmits dopamine. this is immediately followed by shutdown within milliseconds the nAChrs temporarily cannot respond to neurotransmitters
when are nicotinic acetylcholine receptor (nAChR) said to be desensitised
when the have shut down due to nicotinic acetylcholine receptor (nAChR) being activated by nicotine, transmitting dopamine
what leads to downregulation
desensitisation
what is downregulation
reduction in the number of active neurons because fewer of them are available
what are nicotinic acetylcholine receptor (nAChR) concentrated
in the ventral tegmental area
how is a pleasurable effect created when nicotine is present (mesolimbic pathway)
-when nicotinic acetylcholine receptor (nAChR) are stimulated by nicotine, dopamine is transmitted along the mesolimbic pathway into the nucleus accumbens
-this triggers the release of more dopamine from the nucleus accumbens into the frontal cortex
how is a pleasurable effect created when nicotine is present (mesocortical pathway)
-same time as the mesolimbic pathway
-dopamine is transported along the mesocortical pathway to be released directly in the frontal cortex
how is a pleasurable effect created when nicotine is present
-the mesolimbic and mesocortical pathways are part of brains dopamine reward system
-nicotine powerfully activates this system and results in pleasurable effects (such as mild euphoria, increased alertness and reduction of anxiety)
-these effects became associated with smoking through operant conditioning
what causes withdrawal
-as long as the person is smoking, the nicotinic acetylcholine receptor (nAChR) are continually desensitised
-when the person does not smoke for a long period of time, such as at night, the nicotine disappears from their body
-this cases the nicotinic acetylcholine receptor (nAChR) to become functional again, so dopamine neurons resensitise and become more readily available (upregulation)
why does someone with smoking addiction have withdrawal symptoms
form the lack of nicotine
what is the experience of withdrawal in terms of nicotinic acetylcholine receptor (nAChR)
-nicotinic acetylcholine receptor (nAChR) become overstimulated by ACh (as there is no nicotine to bind to them)
-nicotinic acetylcholine receptor (nAChR) are most sensitive at this point
-this is why most smokers describe the first cigarette if the day the day the most enjoyable –> reactivates dopamine reward system
how is withdrawal avoided by smokers
having another cigarette
what does avoiding withdrawal create
constant cycle of daytime downregulation and night time upregulation, creating long-term desensitisation of nicotinic acetylcholine receptor (nAChR)
what does continues exposure of nicotinic acetylcholine receptor (nAChR) to nicotine cause
permeant changes to brain neurochemistry as there is a decrease is number of active receptors
how is tolerance to nicotine developed
smoker has to smoke more to get same effects
strength of brain chemistry as an explanation of nicotine addiction - research support
-support from human research
-research has provided indirect support for the role of dopamine. McEvoy et al studied smoking behaviour in people with schizophrenia who were taking antipsychotic drugs Haloperidol. this drug is a dopamine antagonist. these people has a significant increase in smoking, presumably as a form of self-medication as individuals used nicotine as a means of increasing depleted dopamine levels –> supports view dopamine has a key role in neurochemistry of nicotine addiction
limitation of brian chemistry as an explanation of nicotine addiction - counterpoint to research support
-explanations that only consider the role of dopamine are limited
-dopamine system is central but research shows increasing complex interaction of several neurochemical systems. Watkins et al include neurotransmitter pathways and other systems such as endogenous opioids –> neurochemistry of nicotine addiction cannot be fully understood if looking only at dopamine
strength of brain chemistry as an explanation of nicotine addiction -real world application
-neurochemistry leads to new treatments
-Nicotine replacement therapy (NRT) helps smokers quit. this has been developed as nicotine has been identified as the addictive component in cigarettes with effects on nAChRs. NRT products such as patches and gum deliver a controlled dose of nicotine. This acts neurochemically by binding with nAChRs and mimicking effects of nicotine in cigarettes including the dopamine release. cravings are satisfied and reduces withdrawal symptoms by gradually reducing dose of nicotine over weeks –> greater understanding of neurochemistry led to an effective treatment if nicotine addiction
limitation of brian chemistry as an explanation of nicotine addiction - withdrawal symptoms
-does not fully explain withdrawal
-according to theory, withdrawal symptoms depend mainly on the amount of nicotine in the body. Gilbert suggests these factors are not strongly correlated and argues instead that withdrawal depends more on the environment and personality. for example, those scoring highly on personality dimension of neuroticism generally experience worse withdrawal symptoms than people who are emotionally stable –> withdrawal effects can be explained in other ways without reference to amounts of nicotine
evaluation of of brian chemistry as an explanation of nicotine addiction -determinism
-neurochemical explanation is biologically determinist, suggesting we become addicted to nicotine because of chemical events in the brain involving dopamine reward that are beyond our control, including withdrawal. so nicotine addiction is inevitable in someone who starts smoking
-however, nicotine addiction mat not be inevitable. some people smoke without becoming dependent and show no withdrawal symptoms when the stop (Shiffman and Paty 2006). some smokers find it easier to stop than others due to their personality, such as Gilbert’s research on neuroticism
