What in the human brain do addictive substances like nicotine react with?

Question

What in the human brain do addictive substances like nicotine react with?

Answer 1

nicotine becomes addictive because it replaces neurotransmitter substances in the nerve synapses (the gap between two nerves which a nervous impulse is passed between) in the receptor sites. these receptor sites open up ion channels in the synapse membranes which allow charged ions e.g. Na+ to diffuse down the concentration gradient creating an action potential (a build up of electrical charge which can then be passed to the next synapse).

nicotine does not release from these receptor molecules as quickly as natual neurotransmitters and so cause increased diffusion of Na+ and more action potentials and more nervous transmission. the body therfore produces more receptor molecules to deal with the increase in neurotransmitters (in this case nicotine molecule, competing with teh natural neurotransmitters) and so when nicotine is not availible we have more receptor sites than neurotransmitters, causing a craving for nicotine.

i think this is right as it does occur in the nerve synapses of the brain.

but then you may this its just waffle..

hope it helps

Answer 2

Nicotine,  once in the brain, will work specifically on nicotinic receptors in the brain. However, there is a common "addiction" pathway in the brain that pretty much all addictive substances go through.

All drugs of abuse converge on a common limbic circuit.  As an example, nicotine stimulates nicotinic receptors at presynaptic glutamatergic (glutamate is a very common neurotransmitter) terminals and increases glutamate release. Most addictive drugs increase levels of glutamate.  This increase of glutamate will directly work on the ventral tegmental area (VTA) of the brain. The VTA will respond to this with an increase of dopamine (another neurotransmitter) release out to various parts of the brain. Dopamine is the "pleasure" neurotransmitter, and whenever anything pleasurable (or even possibly highly painful) occurs, the body naturally releases dopamine. This drives the reward seeking behavior of addiction.

One of the major areas of the brain that fuels addiction is the hippocampus. The hippocampus is the area of the brain where new memories are made. Dopamine will act on the neurons in the hippocampus, and will basically fuel the formation of memories about the use of the addictive substance.  This is why certain situations/places will cause those addicted to a substance to have the craving for it.

To add on to the previous poster's mention about ion gates - dopamine will normally decrease sodium channel currents, which will reduce excitability in neuronal firing, but at depolarized membrane potentials dopamine increases excitability.