Explanations For Nicotine Addiction : Brain Neurochemistry

Question 1

Define neurochemistry

Answer 1

Relating to chemicals in the brain that regulate biological and psychological functioning

Question 2

Explain the role of dopamine in nicotine addiction

Answer 2

• neurotransmitter acetycholine (ACh) plays key role in all nervous system activity, which means there are ACh receptors on surfaces of many neurons in the central nervous system

• one subtype of ACh receptor is called the nicotinic acetycholine (nAChR)
• these receptors are special because they can be activated by ACh or nicotine

• when nAChRs are activated by nicotine molecules, the neuron transmits dopamine
• this is immediately followed by shut down - within milliseconds the nAChRs shut down and temporarily cannot respond to any neurotransmitters

• at this time the neuron is said to be desensitised
• this leads to downregulation, a reduction in the number of active neurons because fewer of them are available

Question 3

How does the transmission of dopamine (when smoking nicotine) create a pleasurable effect

Answer 3

• nAChRs are concentrated in the ventral tegmental area (VTA) of the brain
• when these nAChRs are stimulated by nicotine, dopamine is transmitted along the mesolimbic payhway to the nucleus accumbens (NA)
• this triggers the release of more dopamine from the NA into the frontal cortex

• at the same time, dopamine is also transmitted along the mesocortical pathway to be released directly in the frontal cortex

• the mesolimbic and mesocortical pathways are part of the brain’s dopamine reward system
• nicotine powerfully activates this system and results in pleasurable effects (e.g. mild euphoria, increased alertness and reduced anxiety)
• these effects become associated with smoking through operant conditioning

Question 4

Explain withdrawal through brain neurochemistry

Answer 4

• when smoking, nAChRs are continually desensitised
• when not smoking for a prolonged period (e.g. when sleeping at night) nicotine disappears from their body
• then the nAChRs become functional again, so dopamine neurons resensitise and more become available (upregulation)

• at this time the person is experiencing symptoms of withdrawal from the lack of nicotine
• the experience of withdrawal (e.g. anxiety and agitation) can be explained in terms of nAChRs

• during resensitisation nAChRs become overstimulated by ACh (as there is no nicotine to bind with them)
• nAChRs are most sensitive at this point
• this is why smokers often describe the first cigarette of the day as the most enjoyable - it strongly reactivated the dopamine reward system