Explanation for nicotine addiction- Brain Neurochemistry Flashcards
What is neurochemistry?
Relates to chemicals in the brain that regulate bio and psych functioning
Who looks at the role of dopmaine?
Dani and Heinemann
What is Dani and Heinemann’s hypothesis called?
Desensitisation hypothesis
What is the role of nAChRs in brain neurochem?
- Acetylochline (ACh) receptors located on surface of neurons in CNS
- nAChRs (nicotonic acetylocholine receptor) are activated by ACh or nicotine
- When nAChRs are activated by nicotine molecules, the neuron transmits dopamine
- Follwed by ‘shutdown’ (nAChRs shut down and cannot respond to neurotransmitters temporarily)
- Neuron is desensitised, leading to downregulation
How does nicotine create a pleasurable effect?
- nAChRs located in ventral tegmental area (VTA) of brain
- When nAChRs are activated by nicotine, dopamine is transmitted along mesolimbic pathway to nucleus accumbens (NA), which trigger release of more dopamine from NA to frontal cortex
- Mesolimbic and mesocortical pathways are part of dopmaine reward system
- Nicotine activates dopamine reward system, resulting in pleasurable effects
- Effects become associated wioth smoking (operant)
What are some of the pleasurable effects associated with smoking?
- Mild euphoria
- Increased alertness
- Reduced anxiety
What happens in the brain when an addict withdraws?
- When someone smokes, nAChRs are continually desensitised
- When they do not smoke for prolonged period, nicotine disappears from the body, so nAChRs become functional again, so dopamine neurons resensitise and become available (upregulation)
- Experience withdrawal symptoms here
- During resensitisation, nAChRs become overstimulated by ACh
What is daytime downregulation?
- Neuron has been desensitised
- Reduced number of active neurons (fewer are available)
What is night-time upregulation?
- Neurons have resensitised
- Increased number of neurons (more available)
How is dependence triggered?
- Smokers avoid unpleasant psych and physio withdrawal states by smoking
- So there is a constant cycle of daytime downregulation and night-time upregulation, which creates long-term desensitisation of nAChRs
How is tolerance developed?
- Continuous exposure to nAChRs causes permenant changes to brain neurochem (decrease in number of receptors)
- Tolerance develops as smoker has to smoke more cigarettes for the aame effects
What is the desensitisation hypothesis?
- Nicotine stimualtes nicotinic receptors in the ventral temental area (VTA)
- Causes dopamine to be transmitted along mesolimbic and mesocortical pathways to nucleus accumbens (NA) and frontal cortex
- Dopamine is released into frontal cortex, creating rewarding effects
Strength-
I- Research support
D- McEvoy et al studied smoking behaviour in schizophrenic participants who took Haloperidol (antipsychotic drug- dopamine antagonist so blocks receptors, reducing transmission). Found significant increase in smoking (self-medication)- used nicotine to increase depleted dopmaine levels
E- Supports role of dopmaine in neurochem of niccotine addiction
Limitation-
I- Dopamine explanations are limited
D- Watkins said dopamine systems show complex interaction of several neurochem systems, that include neurotransmitter pathways (GABA/serotonin) and endogenous opiods (endorphins- natural painkiller)
E- Neurochem of nicotine addicition cannot be fully understood when looking at dopamine only
Strength-
I- Real-world application
D- Understanding neurochem led to nicotine replacement therapy (NRT). Developed after nicotine identified as addictive component in cigarettes. Patches, gum, inhalers deliver controlled dose, which binds with nAChRs and mimicks effects of nicotine- dopmaine release. Satisfies cravings, allowing reduction of withdrawal symptoms through gradual reduction of nicotine
E- Improves health, and reduces burden on NHS (economic implications)
